Esigineerinc

NOVEMBER AUF 199 ESIGINEERINC

MA GAZ II 1 www.americanradiohistory.com I Al 1111 4 K

Cold - sputtered Master Audiodiscs recorded at 45 and 3344 rpm. The record buying public is far more fidelity - 78, conscious today than ever before - more critical of surface noise and distortion. Perhaps that's why so many more recordists are insisting on Audiodisc masters.t For they know that no pressing is any better than the master from which it is made! And they know, too, that they can always depend 'n To get the best out of your Audiodiscs, Audiodiscs for consistent, uniform quality, flawless cut them with precision sharpened surface, freedom from humidity effects, excellent cut- Audiopoints, and reproduce with perfectly matched playback Audiopoints. ting characteristics and ease of processing - whether Their low cost, together with Audio's making conventional or microgroove recordings. convenient resharpening service, makes them an important factor in recording Yes -when buying masters, it pays to ask for economy. Audiodiscs.

tThe number of Master Audiodiscs sold so far in 1949 has far exceeded the rate of sales in every other year in our history, except for the boom record year of 1946. Trade Mark

AUDIO DEVICES, INC. 444 Madison Ave., New York 22, N. Y

Gent emen: Please send me the following:

11 One 200 -foot sample reel of plastic -base Audiolape. ¡l reels paper -base Audiolape -one Two 200-foot sample of Now recordists can get a magnetic tape with the same con- with red oxide, and the other with black oxide cooling. sistent, uniform quality that has characterized Audiodiscs for the past decade. Paper -base Audiotape is now available NAME with either red or black oxide. And now plastic base Audio - also in production! Send for free samples. COMPANY tape is

ADDRESS Audiodiscs are manufactured in the U.S.A. under exclusive license from PYRAL, S. A. R. t., Paris CITY STATE Audio Devices Expert Dept.: ROCKE INTERNATIONAL 13 Rost 40th St., New York 16, N. Y

www.americanradiohistory.com A, recent intensive survey discloses that among the major television set manufacturers, more than 75% use Sylvania cathode ray tubes! This impressive showing is a tribute to the research and quality production techniques employed by Sylvania in the making of picture tubes that are unsurpassed. If you wish full information about the entire Sylvania line of television picture tubes made by the manufacturers of highest quality radio tubes and electronic equipment, write Sylvania Electric Products Inc., Dept. R 1411., 500 5th Ave., N. Y.

These leading television set manufacturers use Sylvania Television Picture Tubes Admiral Air King Andrea Ansley Automatic Bendix Crosley DeWald Emerson Fada Farnsworth Garod Hallicrafters Hoffman SYL\ NIA Magnavox Midwest Motorola National Olympic Packard -Bell Philco Pilot Raytheon -Belmont Regal Scott Sentinel Silvertone Spartan Stromberg-Carlson Tele -King Tele -tone Temple ELEURIC Trav -ler Westinghouse Zenith

CATHODE RAY TUBES; RADIO TUBES; ELECTRONIC DEVICES; FLUORESCENT LAMPS, FIXTURES, WIRING DEVICES. SIGN TUBING; LIGHT BULBS; PHOTOLAMPS

AUDIO ENGINEERING NOVEMBER, 1949 I

www.americanradiohistory.com the Words #77-ansc,ríbed 6y AMPEX after The great siows úz radío

IIP Here's why At lieu series 300 AMP 1AGNWICIIPE REGER

a I wers industry need!

Designed by engineers who had your engineering Console Model 300* 51.573.75 needs in mind! Portable Model 300 S.,594.41 Rack Mounted $1,491.75 Meter panel extra F. O. B. Factum. Sun Codas. Calif. * Original program qualify preserved Use of independent reproduction facilities allows instantaneous monitoring and makes possible the most stringent comparisons SPECIFICATIONS between recordings and originals. FREQUENCY RESPONSE: * Tape and playback noise non- existant At 15 "± 2 db. 50- 15,000 cycles Use of special record and bias circuits has eliminated tape noise.* At7.5" i 2 db. 50- 7,500 cycles Extreme care has been exercised to eliminate hum pick-up. *SIGNAL -TO -NOISE RATIO: The overall unweighted system noise * Editing made easy is 70 db. below tape saturation, With Ampex editing is almost instantaneous. Single letters have and over 60 db. below 3% total harmonic distortion at 400 cycles. been actually cut off the end of words. Scissors and scotch tape STARTING TIME: Instantaneous. are all the tool; needed. (When starting in the Normal * You can depend on Ampex Play mode of operation, the tape Read what Marx, Vice in charge is up to full speed in less than Frank President of Engineering, .1 second.) American Broadcasting Company, says: "For the past two years FLUTTER AND WOW: At 15 A.B.C. has successfully used magnetic tape for rebroadcast pur- inches per second, well under poses...A.B.C. recorded on AMPEX in Chicago ...17 hours per 0.1 %r.m.s., measuring oll flutter components from 0 to 300 cycles, day. For 2618 hours of playback time, the air time lost was less using a tone of 3000 cycles. At than 3 minutes: a truly remarkable record." 7.5 inches, under .2 %.

Manufactured by Ampex Electric Corporation, San Carlos, Calif.

DISTRIBUTED BY

BING CROSBY ENTERPRISES AUDIO & VIDEO GRAYBAR ELECTRIC CO. INC. 9028 Sunset Blvd., Hollywood 46, Calif. PRODUCTS CORPORATION 420 Lexington Ave., New York 17, N. Y. 1650 Broadway, New York, New York

2 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com Successor to RADIO Established 1917 deliveries -are now being mad

C. G. McProud, Editor D. S. Potts, Publisher the Luci Turner, Edit. Prod. Mgr. S. L. Cahn, General Manager revolutionary David Saltman, Production Manager H. N. Reizes, Adv. Mgr. E. E. Newman, Circulation Manager L. B. Devine. Asst. Circ. Mgr.

Editorial Advisory Board Representatives Howard A. Chinn Sanford It. Cowan. Mid -West Sales 342 Madison Ave.. New York 17, N. Y. John D. Colvin James C. Galloway. Pacific Coast Sales C. J. LeBel 816 W. 5th St.. Los Angeles 13, Calif. J. P. Maxfield Dale International Publications, Ltd. George M. Nixon I06 Bolsover St.. London W. 1. England 21B Technical Book & Magazine Co. Winston Welle 297 Swanston St., Melbourne. C. I. S. Young White Victoria. Australia MINIATUR

CONTENTS NOVEMBER, 1949 Vol. 33, No. I I MICROPH

EXCLUSIVE Editor's Report 6 FEATURES: Letters 8 New tonal fidelity Full volume range Musician'. Amplifier-David Sarser and Melvin C. Sprinkle I1 Omnidirectional No false bass An Instructional Broadcast Studio -Eugene F. Coric/I ..14

Simplified Preamplifier Design-Howard T. Sterling _..16

Audio Frequency Measurements -W. L. Black and H. H. Scott _.18

Audio Transformer Applications -A. I. Avis '1) Practical Aspects of Logarithmic Amplifiers -C. J. LeBel Record Revue-Edward Tatuall Canby 6 Audio Engineering Society Section Convention Program and Exhibitor. '8

New Products 43

Techni -Briefs 47

Additional l'est Records 55

Advertising Index 56

ACTUAL COVER -toSIZE Montage of the new Jensen H -510 loudspeakers. This model employs a direct radiator cone for the low frequencies and a separate high -frequency horn and driver for the high channel. As in optics, the acoustic lens with the central Talen? deserves opening and offset circumferential slots controls time delay to be SEEN as well by progressively increasing the acoustic ray path as HEARD from the center to the edge of the lens. This use of an optical lens principle produces a polar pattern that is uniform over an unusually wide angle. L LTEC LAMM ON AUDIO ENOINEei(ING title registered U. S. Pat. Off.) is published monthly at New York. N. Y.. by Radin Magasines, Inc., D. S. Potts, President. Executive and Editorial Onces at 342 Madison Avenue, New York 17. N. Y. Subscription rates-United States, U. S. Possesslons and Canada. $3.00 for 1 year. $5.00 for 2 years; elsewhere $4.00 per Year Single ropier 35e. Printed In U. S. A. All rights reserred. Entire contents copy- 161 Sixth Avenue, New York 13, N.Y. right 1949 by Radio Magazines. Inc. Entered a. Second Cl.., Matter July 29. 1948 at the Post Office. New 1161 North Vine St., Hollywood 38, Calif. York, N. Y. under the Art of Marri, 3. 1870.

AUDIO ENGINEERING NOVEMBER, 1949 3

www.americanradiohistory.com H ¡g yspace

Companion series to the outstanding "HF" balanced coil structure and /or internal, high line, Stancor's compact "WF" transformers permeability, magnetic shielding to mini- are designed for applications that demand mize hum pickup from an external field. the combination of high fidelity response Cast cases, measuring only 11/2" x IV? x 2', with economy of space. provide adequate shielding together with Superior construction including nickel an attractive finish that adds to the appear- alloy laminations results in a guaranteed ance of your apparatus. Cases are tapped response within = 2 db from 30- 20,000 for top or bottom mounting and lug termi- cycles. All units, except those carrying DC nals are provided on a permanently marked in the primary winding, employ a hum- phenolic panel.

+2 T I -T WF 26 15,000.^. T O 60,000/ +I 0 DB = 80 M W. AT 1,000 CPS 0 i r- 'J -2 DOWN I DB AT 22 k 20 50- 100 200 500 IKC 2 KC 5 KC *KC 20 KC FREQUENCY IN CYCLES PER SECOND

The dotted line indicates the performance of a competitive under identical conditions. STANCOR WF Series brand equivalent unit tested

Impedance Secondary Impedance Part Primary Response -_2 DB From Number Application In Ohms In Ohms

INPUT WF -20 Low Impedance Microphone, 50, 125/150, 200/250. 50,000 30-20.000 Pickup or Multiple Line to Single Grid 333, 500/600 WF -21 Low Impedance Microphone, Pickup 50, 200, 500 50,000 50- 20,000 or Multiple Line to Single or P.P. Grids Multiple alloy shield for extremely low hum pickup WF -22 Low Impedance Microphone, Pickup 50, 125/150, 200/250. 80,000 overall, 30- 20,000 or Multiple Line to P.P. Grids 333. 500/600 in two sections WF -24 Dynamic Microphone to Single or 30 ohms 50,000 30. 20,000 P.P. Grids in two sections

I NTERSTAGE W F-26 Single Plate to Single Grid 15,000 ohms 60,000. 2:1 turns ratio 30- 20,000 W F-28 Single Plate to P.P. Grids. Can use 15,000 ohms 80,000 overall. 30-20,000 split pri. for P.P. Plates 2.3:1 turns ratio overall MIXING

WF-30 Low Impedance Mixer. Microphone, I 50, 125/150. 200/250, I 50, 125/150, 200/250. 30. 20,000 Pickup or Multiple Line to Multiple Line 333, 500/600 333, 500/600 LOW LEVEL OUTPUT WF-34 Single Plate to Multiple Line 15.000 50, 125/150, 200/250, 30-20,000 333, 500/600 WF-36 P.P. Low Level Plates to Multiple Line 30.000 Plate to Plate 50, 125/150, 200/250, 30- 20,000 333, 500/600 WF-35 Single Plate to Multiple Line 15,000 50,125/150,200/250, 50- 20,000 Primary DC 8.0 ma 333,500/600

For complete information on the Stancor "117" series and the larger WE WELCOME COMPARISON, "HF" units, see your Stancor radio parts dealer or write for the 1949 and related components under identical test conditions, of Stancor Stancor catalog B. listing over 400 transformers for sound, radio and television. "WF" units with equivalent types of any other brand of high fidelity transformer, regardless of published claims. Frequency response curve charts sent on request. STANDARD TRANSFORMER CORPORATION ELSTON, KEDZIE a ADDISON, CHICAGO 18, ILLINOIS

4 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com Somerset Laboratories offer a new High Definition 12 watt AMPLIFIER with the SOMERSET Dynamic NOISE SUPPRESSOR - the last Link in High Fidelity Reproduction - a combination having unusual performance characteristics and giving the finest in High Fidelity Reproduction. Claims of high quality audio amplifiers based only on a showing of frequency response beyond audible limits or low distortion and noise percentages evidence engineering skill, but do not guarantee High quality Reproduction. Such an Amplifier may accentuate de- fects of the program source or distortions originating within the loudspeaker. The use of tone controls to offset these effects may degenerate performance and the High Fidelity characteristics are virtually unuseable. The'SOMERSET FEEDBACK AMPIA- FIER was designed not as a laboratory exhibit but as the controlling unit in the reproducing system. Its performance with respect to frequency response, and distortion is superb. In addition it has the ability. First -To reject unwanted portions of the input signal, Second -to subject the loudspeaker to a rigid discipline the consequence of which is Reproduction with perfect definition. These outstanding qualities are produced by the SOMERSET DYNAMIC NOISE SUPPRESSOR and a UNIQUE MULTIPLE FEEDBACK CIRCUIT whereby the Amplifier acquires a more perfect control of the movements of the loudspeaker diaphram throughout the A New 12 Watt audible range. In this CIRCUIT beam power tetrodes are used in a manner which greatly re- HIGH QUALITY AMPLIFIER duces output impedance. Extraordinarily effective loudspeaker damping and sub- Including stantial improvement in bass tone response are obtained without distortion or inter - modulation. Thus, even inexpensive loud- The SOMERSET DYNAMIC speakers become capable of high quality reproduction rarely equalled by the most costly NOISE SUPPRESSOR equipment.

LABORATORIES, INC. 3a5Te....r 1701 PALISADE AVENUE, UNION CITY, N. J.

AUDIO ENGINEEFUNG NOVEMBER, 1949 5

www.americanradiohistory.com EDITOR'S REPORT

EDITORIALS are accepted as a necessity in most was drafted as president and is active in promoting the magazines -for some obscure reason -and are usual- organization. The first few meetings were held in the ly regarded as an outlet for the ideas of the maga- Music Room of the New York Public Library. but the zine's staff. This is not always so in our case, for no one need for more space and a later closing hour made it can presume to know exactly all the needs of an indus- desirable to hold future meetings at St. John's Auditor- try, and many of the ideas presented herein are effective- ium, 224 Waverly Place, in Greenwich Village. The next ly "borrowed" from letters. Such was the case last month. meeting is scheduled for the evening of November 17th, with the original idea about furniture cabinets being and all interested in recorded music are invited to attend. gleaned from a letter by Milton J. Lichtenstein; such is the case again this month, with John van Heijenoort fur- nishing the motivation. 3amrs ii. Etattsing While some form of cabinet is necessary to house a received from friend residence radio system, and while myriads of amplifiers A letter recently and contributor H. Snyder of IUBS, San Francisco, are described for home construction and many more are Ross brought sad of many available commercially, the list of acceptable radio tuners news and a tribute which expresses the sentiment of us in words which need no improvement. is relatively small. And not all of those that are available commercially are ideally adaptable for home usage. With the death on the 30th of September this year of James B. Lansing, the industry and those who knew Among desirable features of tuners-either FM or AM and loved him have suffered an incalculable loss. -should be listed a self -contained filament supply. Suf- ficient plate current can usually be furnished by conven- Jim was more than a brilliant engineer: he was an tional amplifiers, but most of them will not provide the artist of the first order. That his field was the creation additional three to four amperes of filament current for of fine machinery in no way diminishes the stature of his of mediocrity the a modern FM or combination FM -AM tuner. art. Impatient to point that he threw aside personal gain time after time. Jim lived Another desirable feature -available on some tuners - and died in the grip of a fierce ideal. His contributions is the automatic frequency control circuit. Mistuning of to the art of re- creating sound were not confined to an FM receiver can result in considerable distortion, and the inventive genius he applied to the developments of even though correctly tuned in the first place, warm -up the `thirties' nor to the products which bore his name, drift may cause an increase in distortion. Since a control but were extended and multiplied by those whom he voltage is obtainable from the discriminator without the infected with his enthusiasms. addition of any components of importance, the extra cost On the day before his death, Jim was laying plans can usually be due only to a redesign of the oscillator for the writing and publication of a work which was circuit to include a reactance tube. These two features to have incorporated the knowledge with which he im- should be adequate to simplify residence radio installa- plemented his art. He felt keenly the responsibility of tions immeasurably. communicating this to others, and deeply regretted that the pressures of active creation which drove him so relentlessly had prevented that communication. now RECORDED MUSIC ENTHUSIASTS lost. Congratulations to the newly formed New York Society The loss of the kind gray man whose devotion to an of Recorded Music which already has some fifty members artistic and scientific ideal was matched only by the who meet bi- weekly and listen to programs arranged from depth of his own warm humanity is a bitter tragedy. their individual record collections. Peter Hugh Reed, noted critic and publisher of the American Record Guide.

6 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com MagneticMas The Arnold Engineering Company offers to the trade a complete line of Magnetic Materials

PERMANENT MAGNET MATERIALS

Cast Magnets, Alnico 1, II, Ill, 1V, Y, VI, XII, X -900

Sintered Magnets, Alnico II, IV, Y, VI, X -900, Remalloy" Vicalloy" Remalloy* (Comol)

Cunico Cunife Cast Cobalt Magnet Steel

HIGH PERMEABILITY MATERIALS

DeRamax Toroidal Cores Supermalloy ` Toroidal Cores

Powdered Molybdenum Permalloy' Toroidal Cores Permendur*

'Monulactured under licensing arrangements with WESTERN ELECTRIC COMPANY

N tbr ì nozór7 i/o ig o any o/'aese /1/1ogge í10 v THE ARNOLD ENGINEERING COMPANY

SUBSIDIARY OF ALLEGHENY LUDLUM STEEL CORPORATION 147 EAST ONTARIO STREET, CHICAGO 11, ILLINOIS

AUDIO ENGINEERING NOVEMBER, 1949 7

www.americanradiohistory.com - ZutiffteL Figures -of -Merit Sir: I have just noted Mr. Powell's suggestion for a driver figure -of -merit with interest. While there are many factors which govern the merit of tubes as adequate drivers for a given power amplifier, Mr. Powell is to be commended for suggesting the product of the grid bias and amplification factor. As Mr. Powell points out, his figure -of -merit is somewhat oversimplified and is therefore valid only when the "all- other. factors-the same" condition exists. It appears that a more reliable figure -of -merit for driver tubes might be the product of the grid bias and the transconductance rather than grid bias and amplification factor. Thus the plate resistance, which is a significant factor in a tube's ability to deliver adequate undistorted output, is also taken into consideration. This can be illustrated by considering a tube such as a 6N7 for driver duty. One section of this tube may be used separately as a driver, or the two sections may be operated in parallel. In either case, the recommended grid bias as well as the amplification factor remain unaltered, indicating no change in the merit of the combination When your disc blanks go sour in as a driver. However, the effective plate re- stock ... when older recordings no sistance of the two sections in parallel is longer make good copies... only one -half of either section alone, which results in doubling the transconductance. DON'T TAKE It LYING DOWN .. o'' The reduction in effective generator im. pedance therefore results in a larger output voltage for a given load resistance. ta Since the dimension of the grid bias- transconductance figure -of -merit is that of a current, which represents the maximum pos- VAa- sible signal current available in the plate circuit, it is necessary only to multiply this figure-of -merit by the effective load imped- I dINCS don't dcteliorate with ance offered to the tube to determine the age. Perfect recordings have been maximum possible drive available to the pow- more two made on blanks than er output stage. old. Presto discs years And stay The revised "figures-of-merit" for the tubes rec- good after recording. Many mentioned by Mr. Powell and his own "fig - ords of today are dubbed from ures-of- merit" are tabulated below for pur- Presto recordings cut years ago. poses of comparison. Tube Type E,g,,, Ima1 b;,p (volts) 27 20.5 189 76 or 6P5 19.5 186 %-6SN7 or 6J5 20.8 160 %-6N7 15.5 210 It is observed that the table indicates that the 6SN7 is somewhat superior to the 6N7. In conclusion, it appears that one must consider other factors in addition to the ones mentioned by Mr. Powell (non -linearity and hence intermodulation distortion, etc.) in choosing the most suitable tube for a driver. RECORDING CORPORATION For example, a choice based on any figure. of -merit defined so far may lead to a tube exhibiting power-output capabilities far greater than the tubes chosen for the output stage. It is believed, however, that a figure - of -merit defined as the product of grid bias PARAMUS, NEW JERSEY and transconductance may prove a more ade- Moiling Address: quate index of a tube's ability as a driver for power output audio stages since it in- P.O. Box 900, Hackensack, A. J. cludes an additional factor-the plate re- In Canada: Walter P. Downs, .td., sistance of the tube. Da nInio Sq. Bldg., Montreal William J. Kessler. Project Engineer, Engrg. á Ind. Experiment Station University of Florida, World's Largest Manufacturer of Instantaneous Sound Recording Eqúrpnsenl and Discs Gainesville, Florida.

8 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com for EVERYONE! with the NEW Genuine JENSEN WIDE -RANGE LOUDSPEAKERS

16 COMPLETELY NEW MODELS Three 15 -inch Coaxials, one 12 -inch Coaxial Eleven 5 -inch to 15 -inch Single- Radiator Models No longer is truly good listening ruled out by cost or size restrictions. Now music can come to life for everyone, for Genuine JENSEN Wide -Range Loudspeakers include small sizes as well as large ... low cost units as well as more expensive models. Not alone in frequency range but also in smooth response, wide -angle distribution, low distortion, good efficiency and power handling capacity ... in all 7 Performance Points Genuine JENSEN Wide -Range loudspeakers establish new standards of reproduction quality. So whether you choose a 5" single -unit direct- radia- tor type loudspeaker at $8.00 list, a 12" Coaxial at $33.40 list, or a 15" Coaxial with the new JENSEN Wide -Angle Acoustic Lens, you get superior performance all the way ... in every attribute that makes for enhanced listening pleasure.

C/retvWlDE -ANGLE ACOUSTIC LENS

Typical of JENSEN leadership in loudspeakers engineering is the Acoustic diverging Lens used on Model H -510 illustrated at the left. Adapting optical principles to acoustics, this lens

acts in conjunction with the h -f horn to distribute h -f radiation uniformly over a wide angle ...insures constant balance and high quality reproduction throughout the whole room.

Write now for Data Street No. 152 describing all the neu, loudspeakers in the new Genuine JENSEN Wide -Range series, and booklet, "Let Music Come to Li/e."

This trademark identifies an advanced- design loudspeaker . , . with performance to meet today's exacting requirements for faithful music reproduction ... achieved through the most modern applications of acoustics.

JENSEN MANUFACTURING COMPANY oh of the Muter Company 6633 SOUTH LARAMIE AVENUE CHICAGO 38, ILLINOIS In Canedo: Copper Wire Products, Ltd., 351 Carlow A Toronto AUDIO ENGINEERING NOVEMBER, 1949 9

www.americanradiohistory.com ANxoutEiET

To users of Western Electric Microphones, Loudspeakers and Disc Reproducing Equipment

Effective October 1, 1949, the Western Electric Company has discon- tinued the sale, servicing and maintenance of sound system products, including the following major items:

Microphones Loudspeakers 633 Type 728B 639 Type 755 757

Reproducing Equipment 109 Type Reproducer Group 9A Reproducers 9B Reproducers

To assure uninterrupted service and maintenance to owners of these products, we have entered into an agreement, effective Oct. 1, 1949, with the ALTEC LANSING CORPORATION of Hollywood, California. Under the terms of this agreement the Altec Lansing Corporation receives all necessary engineering information, as well as our inventory of the above equipments and their parts, and will make available service, maintenance, repair and replacement parts for the products listed. The Graybar Electric Company will act as distributor for the Altec Lansing Corporation, as it has for Western Electric, in serving customers' needs on these equipments, under terms of an agreement recently con- cluded between the Graybar Electric Company and the Altec Lansing Corporation. The leadership and integrity of the Altec Lansing Corporation make us completely confident that all users of the Western Electric equipments listed will continue to have available to them service of the very highest quality.

Vice President

lecí-rlc Compaixy R A WstrnI R P O N O

NOVEMBER, 194'i 10 AUDIO ENGINEERING

www.americanradiohistory.com Fig. I. The two chassis comprising the amplifier patterned after the "Williamson."

DAVID SARSER*

and

MELVIN C. SPRINKLE **

Musician's Amplifier

An adaptation of a famous English circuit which has already earned an enviable reputation for quality.

sMYLIFIER$ are something like wo- publicized in England and Australia would best meet the rigid specifications men-theremen -there are a lot of 'em. And as the absolute tops for obtaining nat- for performance. -like women -amplifiers come in ural reproduction. It was written up The resistance network in the cath- all sizes, shapes, and degrees of appeal. in Wireless World (an English publica- ode circuit of the 807 tubes contains a The readers of radio magazines have tion) for April and May, 1947. This variable resistor Pi, which is set to give seen dozens of different amplifier de- circuit has become so popular in equal current in each tube. A closed signs, and audio enthusiasts are as England that it was reprinted with circuit jack is provided in the cathode vociferous in praise of their pet circuits minor modifications in the August, circuit of each 807 to permit insertion as Kentucky colonels about their pet 1949, issue of the Wireless World. of a milliammeter when making this way of making a mint julep. Having studied the Williamson cir- adjustment, and the plate current The writers of this article -one a cuit and having read the comments on should be balanced by Pi to exact equal- professional violinist in Toscanini's its intermodulation distortion in AUDIO ity, at 50 ma per tube. NBC Symphony, owner of the famous ENGINEERING for September, 1948, we The original Williamson diagram Lamoreux Stradivarius, and a builder became interested in the possibilities of contained a series resistor to adjust the of amplifiers, the other a professional the amplifier. total plate current drain of both tubes: electronic engineer whose avocation is Strictly from the technical point of After building several of these ampli- serious music-have both made a view, the output tubes are 807's with fiers it was decided to omit this control baker's dozen of amplifiers, but have triode connection. The 807 has much and substitute a fixed resistor, since felt that most of these amplifiers in one to recommend it as an audio tube. It once it is set it is never changed. way or another never completely re- is a standard type, available every- The driver stage consists of a single created a satisfactory "studio sound." where, and though it is usually consi- 6SN7GT tube connected in push pull The writers, then, have pooled their dered to be a transmitting tube, its and resistance coupled to the 807's. resources and have come to the conclu- price makes it no more expensive than Here one of the points of superiority sion that there should be a simple. other tubes used by amplifier construct- of the 807 is evident. Most low -mu easy -to -make, and thoroughly foolproof ors. It has a fairly high plate dissipa- triodes such as the 2A3 and its six -volt circuit which gives out with that in- tion. and draws enough plate current counterpart, the 6B4(á, have a high tangible something called "presence to provide adequate audio power. It is bias of the order of 60 volts and, hence, effect." In doing so, we are going to a cathode type, rather than direct require a driver stage capable of put- duck controversies regarding beam - heated and hence the completed ampli- ting out signals whose peak values are power tubes versus triodes, transformers fier has no hum even when used with of this magnitude. As a result, resist- versus resistance coupling, and all the efficient speakers with fine bass response ance coupling to low -mu triodes is not other perennial areas of enthusiastic such as the Altec Lansing 604B. practicable unless elaborate precautions conflicts and ideologies. All we're real- The output transformer presented are taken to supply adequate driving ly after -how simple it sounds! -is to somewhat of a problem as the original voltage with low distortion, a difficult reproduce music in the home which circuit called for a transformer not task. The triode -connected 807 re- sounds the same way it does in the manufactured in this country. If it quires about 35 volts bias and thus the concert hall or broadcast studio. were specially made to Williamson's use of 6SN7 as a driver becomes prac- Recently, we heard about the "Wil- specifications the cost would be pro- tical. The first two stages are unique liamson" circuit which has been widely hibitive. A careful survey and trial on as they consist of a single 6SN7 tube various transformers available through using the first section as a voltage 548 Riverside Drive, New York 27, N. Y. jobbing channels disclosed that one amplifier which is directly coupled to 5 Melrose Are., Bergenfield, N. J. t ransformer-the Peerless S -265Q- a "eathodyne" or split load type of

AUDIO ENGINEERING NOVEMBER, 1949 I I

www.americanradiohistory.com a separate chassis to eliminate hum FOR 20 DB. FEEDBACK and also to provide a more compact WWI which simplifies installa- R2, v, construction, V, V2 5000 807 tion. It is conventional with the excep- 6SN7 C2 6SN7 high grade 600 -volt oil -filled c, e. tion that R,e Ìww? 2 are used in the filter. The .05 capacitors 25 is de- T, recommended power transformer signed for continuous operation with a N; O X X PEERLESS drain of 200 ma in the plate supply. 5-265 0 after the J, In practice it is found that a á amplifier has been on all day the transformer is just moderately warm. N J2 o' o Construction Details xx a Construction of this amplifier is sim- 5 ple. The amplifier and power supply are e both placed on a 5 x 10 x 3 chassis; there CC I. 1000 is plenty of room for parts with com- S CD plete accessibility for service should ó Reo it be required. All resistors and capaci- 22,000 ISO,IOw. tors are mounted on a terminal strip which is mounted on one side of the GROUND BUS chassis as shown in Fig. 4. This type

10,,F 1O »F 30pí of construction, long used by profes- All resistors '/2 w., 20% TO ALL x sional amplifier builders, has been much 's Conned to cnass,s HEATERS x at one point unless noted differently neglected by amateur constructors and its use is encouraged to provide neat- the amplifier section. Fig. 2. Schematic of ness as well as ease of construction and repair. inverter. Use of this type of there are two schools of thought. One phase reduce hum and undesired phase inverter permits direct coupling, group holds that the source impedance In order to coupling between stages to a minimum, as the positive voltage on the phase should be made as low as possible by a grounding bus is used. This begins inverter grid is offset by the high posi- using triode tubes, by the use of inverse in the amplifier where the B- from tive voltage on its cathode. Direct feedback, or possibly both. The other the power supply enters the chassis, coupling to the phase inverter permits group maintains that the source im- connects to the grounded side (terminal the extension of the low -frequency re- pedance should be low, but not neces- 12) of the output transformer secon- to d.c. and elimi- arily as small as possible-their claims sponse in this stage then is carried along on the which can being based upon listening tests. This dary and nates coupling networks terminal strip toward the input, pick- shift and low- frequency second group feels that a representa- cause phase ing up cathode circuits and filter ca- attenuation. It will be seen from the tive value of source impedance should 1.0 times the load im- pacitor cans as it goes. It is grounded schematic, Fig. 2, that there are only be from 0.5 to near pedance; thus on a 16-ohm tap the to the chassis at only one point four coupling capacitors in the entire a grounding source impedance would be between the input connector. Use of amplifier, two on each side of the push in amplifiers is also well known 8 and 16 ohms. This amplifier has been bus pull system. Thus the response of this a large part of the constructed so that the source impe- to professionals, and amplifier at low frequencies is remark- by amateur dance is very low and those persons who difficulties encountered ably good. to haphazard ground prefer a slightly higher value may in- constructors is due of parta is Inverse Feedback crease the feedback resistor (R -21) to connections. The layout It will be noted that inverse feedback approximately 22,000 ohms, or they may shown in Fig. 5. is used in this amplifier. Inverse feed- insert a resistor in series with the At this point it might be well to re- back has been used with beam power speaker voice coil should they prefer to view a few of the beliefs held by ama- amplifiers, but the circuit is not con- retain the effects of the high feedback teur constructors of amplifiers. Many fined to this type of amplifier. Our in this amplifier. amplifier designs which have appeared amplifier incorporates approximately 20 The power supply, Fig. 3, is built on in magazines have had their virtues db of feedback which is put around four stages and the output transformer. With this much feedback there is abso- lutely no trace of supersonic or sub - audible oscillation, a tribute to the design of the output transformer. Feedback greatly improves the linearity and response of the amplifier and reduces the sources impedance looking back into the output terminals to the unbelievably low figure of about 35 of an ohm on the 16-ohm output tap. When this amplifier is used with highly damped, high-efficiency speakers, the clarity of reproduction is more than satisfactory. In connection with source impedance, Fig. 3. Schematic of the power supply. NOVEMBER, I949 12 AUDIO ENGINEERING

www.americanradiohistory.com extolled solely on the basis of frequency measurements. The measurement of frequency response is an important +4 property of an amplifier, but it is not 12 the only property which contributes to Fig. 6. Relative GO naturalness in the reproduced sound. power output 2 Frequency response is a measure of how with respect to the gain of the amplifier changes as a frequency. 4 function of frequency. If, for example, the absolute gain is 75 db at 1,000 cps WOW and 70 db at 10,000 cps, then the ampli- Ito am moo FREQUENCY IN CYCLES PER SECOND fier is said to be down 5 db at 10,000 cps. For this reason frequency response measurements are usually made at low Performance method of testing amplifiers, especially output levels. The absolute gain of this amplifier, with regard to phase shift, and it was with about 20 db of feedback, is 70.8 found that this amplifier passed with- Power Output vs. Frequency clb. The frequency response was meas- out distortion square waves having fun- One important property of an ampli- ured by feeding in a signal at constant damental frequencies from 20 cps to fier which has long been neglected in level from an audio oscillator, the signal 5,000 cps. These signals were passed the previous literature on the subject being fed through a series resistor of through the entire amplifier and not is power output at various frequencies. 500,000 ohms which is equal to the input just one stage. This confirms the fre- Magazine articles and manufacturers' impedance of the amplifier. This is the quency - response measurements and literature will state that an amplifier customary way of measuring amplifiers showed that there is uniform time de- will put out "10 watts." Sometimes they professionally. The output was meas- lay for all frequencies between 20 and state the frequency and the degree of ured across a 16-ohm non -inductive 100,000 cps. It is entirely possible that distortion that was present when this resistor and high grade meters were the startling realism in reproduced mu- i measurement was made. The import- used which had a minimum of frequen- sic is due to the excellent phase char- ance of power output over the audible cy error. Under these conditions the acteristics of the amplifier, as a non- spectrum is so great that it cannot amplifier is flat from 20 to 80,000 cps. linear phase characteristic disturbs the be over -emphasized, and it is this fac- There is a rise of 3.4 db at 96,000 cps arrangement of harmonics in compli- and the output begins to fall at about 100,000 cps. In the revised article, Mr. C4.C5 POWER PLUG Williamson states that his amplifier zo 22 is flat from 20 to 100,000 cps, but he 20 does not state the manner in which J 18 ó 16 o the response was measured. w (4 The amplifier performs exceptionally F 12 well when tested with square waves. 3 to This test consists of feeding square 8 w 6 waves into the input and observing the w 4 INPUT PLUG A4 wave form on an oscilloscope at various 2 FOR -i1 points throughout the circuit. If the TERMINAL STRIP JACKS 2 4 7 11 METER 3 5 6 8 9 10 12 13 14 15 16 SPEAKER output waveforms have sharp corners POWER OUTPUT -WATTS OUTPUT INSERTION and no tilt on top and bottom the PLATE CURRENT (P,) fol- BALANCE ADJUST. lowing things can be said about the Fig. 7. Intermodulation distortion curve amplifier: plotted against power output. Fig. 4. Parts layout of the amplifier on I. The frequency response is flat to a 5 x 10 chassis. at least 20 times the fundamental fre- eated signals such as program material. quency of the square waves. Mr. Williamson does not state the tor which is to a large 2. There is no time delay; i.e., the degree responsi- phase shift through power characteristics of his amplifier, ble for naturalness the amplifier is of reproduction and proportional to frequency. but does say that the power output is freedom from distortion. 3. Full power There is no spurious oscillation 15 watts. As our output tubes are not output over produced by steep- wave -front a wide band of frequencies signals, exactly the same as the I{T66 valves is largely such as the usual music and speech determined by the output originally used, we cannot make accu- transformer, the most important programs. l;. com- Square wave testing is a sensitive rate comparison, but with 807 tubes ponent in an audio amplifier. .and a 400-volt plate supply will The manufacturers it de- of output trans- liver 12.2 watts to the load resistor at formers more often than POWER OUTPUT SOCKET not fail to 1,000 cps at 7 per cent intermodulation make any statement as to the power distortion. As may be seen from Fig. 6, output of amplifiers using their trans- the power begins falling off at low fre- formers at various frequencies. Regard- e POWER quencies and is approximately 0.7 db ing the transformer we used, the - manu- TRANSE. down at 40 cps and 2.1 db down at 20 facturer states that the output will T2 be cps. It is down 2.1 db from full power down no more than 3 db from midrange at 15,000 cps and down 3 db at 20,000 power at 20 cps and at 20,000 cps. cps. This power curve on the surface Audio enthusiasts who make It measure- may appear to be excessive, but tests ments of power at various frequencies der I111- 4/ / /N= (u run by the authors on several well - from 20 to chassis) -e 20,000 cps would be LINE' FUSE known makes of audio amplifiers have amazed to see CORD HOLDER the very poor power shown the power to be down as much characteristic of a favorite amplifier. Fig. 5. Parts layout for power supply. [Continued on page 53]

AUDIO ENGINEERING NOVEMBER, 1949 13

www.americanradiohistory.com An Instructions( Broadcast Studio

EUGENE F. CORIELL*

Radio studios for instructional purposes may resemble professional installations, but must have special consideration in their design to be of greatest value.

in room. WHEN BETTER MILITARY RADIO shows to the director the control are built, better military writ- Since he has to watch the director for ers, announcers and directors cues, he can hardly remain unaware of will build them. This briefly is the the meter seen at the same time out of his philosophy behind the installation of of the corner eye. an instructional broadcasting studio Director's Turret Facilities at the Armed Forces Information Another use of the VU meter in an School at Carlisle Barracks, Pennsyl- instructional set-up is on the producer's vania. Here. selected enlisted and com- or director's turret in the control room, missioned personnel of all the armed as seen in Figs. 1 and 2. This not only services are trained in the techniques of gives the student director a visual public information. One of these tech- Fig. I. Preliminary layout of director's check on each actor's volume; it also niques is radio, and the pupose of this turret. The keys control the talkback shows him very graphically that the article is to describe some of the audio microphone and monitor speaker. meter alone doesn't tell the whole story. and related features of this studio oc- Due to differences in harmonic content, One solution in addition to careful casioned by its educational character. - some voices will sound too soft or too briefing - is to use comparatively rug- loud comparison with others, even To a radio man faced with the job of in ged dynamic microphones until the stu- prop- building a broadcasting studio for in- though the VU meter is peaking dents have become somewhat accus- erly. With the meter apparently lying structional purposes, it might seem that tomed to the limitations of studio gear. any conventional studio would do if it to his face, he is impelled to do some- Another aid in acquiring microphone ra- were big enough it is true that thing about this confusing anomaly, -and technique is a VU meter out in the do with it. The studio ther than leave it to the engineer. After size has a lot to studio where the student announcer can Barracks is forty - a little practice with this set-up, the proper at Carlisle see it. The meter will give him some seven feet and for demon- student director is in a much better by twenty idea of the volume limitations of broad- strations it can seat fifty students as position to listen critically in an oper- cast equipment, not so much in terms where only observers. The control room is sixteen ational control room the of volume units or decibels as in terms VU meter is in front of the engineer. by twenty feet and seats up to twenty - of the variations of his own voice. It The reason is he has learned not five persons. that might be argued, and with some merit, to believe all he hears, volume-wise. However, size is not the only dif- that this is an artificial prop and The director's turret has another ference between instructional and oper- therefore unrealistic, since most sta- gadget not usually needed in most con- studios. facilities ational Since the are tions do not have VU meters visible trol rooms - a key that switches a primarily for student use, they should from the studio. One answer is that the fixed pad into the monitor speaker cir- be planned with student habits and meter is used only during the student's cuit. This reduces the volume enough limitations in mind. For example, stu- first few times at the microphone. An- to allow the director or student director dents will sometimes blow into an ex- other answer is that after a few ses- to comment to the student observers pensive velocity microphone to see if sions with the meter, the embryo an- seated behind him regarding the per- it's working, after which, due to a rup- nouncer rarely yells into the micro- formance of the cast. tured ribbon, it works no more. When phone any more. The director's turret also contains the script calls for a yell, the student VU meters also come in handy for the usual stop clock and the micro- generally puts his heart into the yell - the organist who is sometimes a stu- phone and associated key switch for and the yell right into the microphone. dent. It is often difficult for non -radio the familiar talkback to the studio. A careless sneeze `on mike" will some- organists to accustom themselves to the Some stations may tolerate poor speech times finish off a ribbon microphone restricted volume range the equipment quality from the talkback, with the that has somehow weathered many a can tolerate. A VU meter helps con- idea that anything is good enough for class session. That these things happen siderably in the early stages, if you what is essentially only a one -way is generally not the fault of the stu- can get the musician to look at it. One intercom. However, this is highly ques- dents, who in most cases have never way to encourage him to look at it is tionable in an instructional studio. The been under studio discipline before. to put the meter on top of the organ student announcer or actor is likely to console as shown in Fig. 3, approxi- be a little on edge in the relatively Captain, Radio Instructor, Armed Forces studio. and Information School, Carlisle Barracks, Pa. mately in the organist's line of sight strange surroundings of the

14 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com Fig. 2. Control earphones, these need not be inter- room equipment locked with the microphones and are as seen from stu- fed by a separate amplifier bridged dent observers' across the outgoing line. seats. Director's Another item of instructional studio position is at gear is the turntable equipment. Turn- right of turntables intended for student use or for tables, with re- use with students should be rugged, cording rack and and that applies to everything about disc recorders at them, including the pick -up. The light- far right. rower weight variable reluctance type with supplies, patch permanent stylus has worked out very well, although panel, and radio the replaceable -stylus models probably tuners are would be a safer in rack choice for this to left of the service. The light- weight heads have the additional advantage console. of low needle talk, which is important for instructional use, as students have not his nerves are not soothed by a gravelly Program Phones had enough experience to learn to ig- voice barking at him through the talk - Some stations provide program ear- nore the annoying noise of the needle. back speaker. Good speech quality in phones in the studio so that the show While on the subject of turntables, the talkback is a good investment for may be monitored there if desired. there is a seemingly simple improve- this type of work. These phones, which are not to be con- ment that would save considerable tused with the talkback phones men- maintenance While on the subject of the talkback, on this equipment. It has tioned earlier, are often used by the been our here is another feature that is unusual, experience that sooner or la- I sound man and the organist. This ar- ter, in spite of warning, although not original. It is customary somebody puts rangement is particularly helpful in a dictionary or to interlock the talkback with the on- other heavy object down training directors of military programs on the platter of the the -air sign switch or the outgoing - turntable - or who, due to lack of radio personnel at even leans line key to prevent accidental opera- on it. The result is often 7 their home commands, will often have n sprung platter tion while on the air or while record- productive of plain- to take part in shows they direct. Mon- tively wavering ing. However, when working with stu- music. To correct this, itoring a program with earphones is somebody usually dents, it is often desirable to maintain - somebody else - not very satisfactory, due to the dis- has to spring closer control over the cast than is the platter just the right tortion introduced by the phones them- amount possible with the usual hand signals. the other way, which is no fun. selves. However, it is possible to get the center The reason is that students tend to If shaft cannot be made a fair idea of relative volumes, the heavier, some concentrate so much on the script that enterprising manufac- effectiveness of fades, and so on. The turer might provide they forget to keep an eye on the di- some deflection program phones also allow the an- stops spaced rector in the control room. One way around the circumference of nouncer- director to know when to cue getting around this is to have the out- of the platter just under its rim. Then in east members who have speeches that when some thoughtless individual leans put of the talkback amplifier automati- follow music played on the control cally switched from the studio speaker on the table, the resulting deflection room turntables. This is important would to a pair of phones when the on -the- be limited to the small clearance since the studio speaker is automatic- above the stop. If this clearance were air sign switch is thrown. The phones ally turned off when the microphones are fed through a fixed -loss pad and within the elastic limit, no permanent are alive to prevent feedback. As there set to the platter would result. are worn by the assistant director, usu- is little chance of feedback from the [Continued on page 51] ally a student, to whom the director con give instructions while the show is on the air. This arrangement is used sparingly because, as explained to the students, the announcers and actors in operational studios must keep an eye on the director, even while reading Fig. 3. To as- their lines, without benefit of a sist student or- 1r' prompter. ganist in main- taining s The devices mentioned above are a f e volume helpful, certainly, but it soon becomes limits apparent to the instructor that no during rehear- amount of VÜ meters and other gad- sals or broad- gets will prevent occasional heavy peaks cast, a stand- from getting through to the recorder. ard VU meter The result is apt to be severe distor- is mounted on tion and, in the case of disc recorders. the organ con- the peak may cost "ghosting" in the sole directly in adjacent groove. This points up the his line of vi- need for a limiting amplifier, adjusted sion. for the usual maximum compression of 5 db. Compression in excess of this amount is, in itself, a likely cause of distortion.

AUDIO ENGINEERING NOVEMBER, 1949 15

www.americanradiohistory.com Simplified Preamplifier Design

HOWARD T. STERLING*

Unnecessary complication in phono preamplifiers may be avoided by making practical compromises in the performance requirements.

THE PREAN,PLIFIMR has been a ble in many applications, and there is bone of argument and contention some question as to whether it is neces- for so long that editors will short- sary. Actually, it is possible to equalize ly look to some other subject for mate- for all these characteristics, with a rial, but there are a number of con- maximum error of 3 db, using a single siderations which have not as yet been low -frequency turnover and the simplest thoroughly brought to light, and it is type of high-frequency shunt tone con- the intention in this paper to discuss trol. their application to the development of Figure 2 shows the response curve of a new plug -in preamplifier. the plug-in preamplifier, together with This unit is shown in Fig. 1, both the ideal equalization characteristics open and with the shield in place. It for the various turnover frequencies in measures approximately 1y x 2 inches use. It will be seen immediately that and its seated height is 3 inches. In- Fig. I. External and internal appear- the maximum deviation from these spection of the open view will show ance of plug -in phonograph pream- ideals is a little over 3 db, while actual- that particular effort has been made plifier. ly, as will be shown later, it is less than that. to assure good mechanical construc- if desired, with a significant improve- tion. This is in direct contrast to some ment in the simplicity and economy of Figure 3(A) shows the familiar high - recent plug-in preamplifier designs, the amplifier system. frequency shunt type of tone control, where tube sockets have been secured While these preamplifiers may, of and if C is chosen so that X. equals R only by their leads, and electrical con- course, be equalized for the NAB tran- at 2500 cps, the resulting character- nections left floating, rather than tied scription recording characteristic, their istics will be those of the solid lines at down, on the apparent theory that since immediate application was to be for (B) for various settings of the con- they are hidden by the shield, good playing standard records in the home. trol. The dash lines again indicate practice is unnecessary. ideal for the different types Equalization correction The plug -in feature has a number and the approxima- There has been considerable atten- of preemphasis, of advantages, including interchangea- 3 db all points. the tion is better than at bility with preamplifiers of other tion recently to equalization of pre- equal- various recording Combining the low- and high -fre- ization characteristics, and with crystal amplifier for the now in use. St. George quency characteristics now, and adjust- equalizers; independent shielding; and characteristics have performed a valuable ing the base line for reasonable sym- the fact that since it is not an integral and Drisko' in providing as exact informa- metry, the curves of Fig. 4 are obtained. part of the equipment with which it is service tion as can be obtained as to these Here the maximum error is still less to be used, it may be added when and characteristics and have gone to some than 3 db, and is actually in a desirable for each of them. direction for Victor and Columbia. The Chie! Engineer, Electronic Workshop. 351 pains to equalize Bleeker Street, New York City. Such complication is not wholly desire- most frequent complaint about the

Fig. 2 (left). Response of plug -in preamplifier compared with ideal curves for turnover characteristics now in use. Fig. 3 (right). (A) Simple high- frequency shunt tone control will give curves of B if R = XC a+ 2500 cps. (B) Characteristics of high-frequency shunt tone control for different settings, together with ideal compensation (shown in dotted lines) for pre - emphasis characteristics now in use.

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20 >° ,.e. ro I MOO . . FREQUENCY IN CYCLES PER SECOND FREQUENCY IN CYCLES PER SECOND

16 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com TBrrw. I

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w0 c0rr Ill ,. 0or . -5-- ___-- _.. ' //f' i r00c0.o ro 70.03 10000 10 00000 io 10000 FREQUENCY IN CYCLESPER SECOND FREQUENCY IN CYCLES PER SECOND

Fig. 4 (left). Composite of Figs. 2 and 3B showing approximation of ideal characteristics possible with single low- frequency turnover point and simple high- frequency tone control. Fig. 6 (right). Characteristic of Columbia I0003 -M test record. Columbia 78-rpm records is that they such as shown in Fig. 5, were consi- available by General Electric, and de- are "thin," so we have about 3 db of dered before that shown at (0)-a modi- signed particularly for low noise, hum, bass boost; the LP's have, if anything, fied Pickering circuit -was finally and microphonics. Actually, the 12ÁT7 an uncomfortable amount of bass, and decided upon. The familiar circuit of or the 12AX7 may also be used in the the 1 -db drop will not be a serious loss. (A), popularized in the G.E. preampli- preamplifier, since the feedback effec- Both types are inclined toward exces- fier, was rejected because it can be tively equalizes gain, and the only sive brilliance in the xaiddle highs overdriven easily and because it has a difference will be in the noise level. which will neatly complement the dip fairly high output impedance for use The circuit as used here will take an at 1500 cps. Victor is also likely to be where the capacitance of long shielded input signal as high as 0.8 volts without a little heavy in the bass, and the loss lines may be encountered. The circuit overload at 1000 cps, and hence will of one and a half db will be all to the of Rurwen3, shown at (B), is also easy accommodate any of the low-level mag- good. Actually these deviations are to overdrive, and it is difficult to obtain netic cartridges without adjustment. significantly less than may be expected flat high -frequency response due to the The internal impedance at high fre- from other parts of the system, and loading of the feedback network by the quencies is 2500 ohms, which is suffi- there is every reason to believe that Miller effect in the second stage. ciently low to drive a line capacitance the records themselves show an even There has been some criticism of of .005 , f without frequency discrimi- wider variation. Pickering's circuit as a result of bum nation. it is not necessary, of course, to use pickup between the healer and the It was found that some noise was the precise circuit of Fig. 3 (A). A iuibypassed first cathode of the 6SL7. being produced by current flow in the treble boost -cut circuits may be modi- but this is not a serious consideration plate resistor for the first stage. Care- fied to give with the same characteristics in the 12AY7, a tube recently made (Continued on page 44) addition to the flexibility of treble boost. With regard to the LP's, incidentally. there has been a wide divergence of B+ opinion -some saying that they are distortion and noise free. and some 8+ saying that they are very poor in these 6SC7-. respects. Experimental work with one of the better recordings (Scheherazade. o--I with Ormandy) has indicated that there is a serious amount of both noise and --6SC7-- distortion, but that it seems to occur only above about 10,000 ells. Since -A- -B- most "wide range" speaker systems roll off at about this point, it was audible B+ only on the RCA LC1A and the James DECOU PLED Lansing D1000 of the speakers checked. 12AY7, t2AT7 ós 0022 .02 In these cases a 10 -kc low -pass filter or 125x7 F--0 with a slope of about 36 db /octave. .02 critically damped, was found to he ó the solution. Statements with regard óf 00 to the fidelity of these records seem to ó he justified, incidentally, since this filter noticeably altered the quality of -C- high- frequency recorded sounds. Circuit Design Fig. 5. Preamplifier circuits: (A) Burwen; (B) General Electric; (C) Modified A number If 1 ireuit configurations, Pickering circuit used in plug -in preamplifier (see text).

AUDIO ENGINEERING NOVEMBER, 1949 17

www.americanradiohistory.com Audio Frequency Measurements

W. L. BLACK* and H. H. SCOTT **

Part II: Design, development, and maintenance all depend on the measuring procedures employed. The author discusses these methods thoroughly, and presents reasons for every step.

ANALYZER DETERMINATION 01 at the 11111110E of the equipment under harmonic distortion at the output This paper was originally pre- test with the signal removed to see if W ofAVE the equipment under test in- sented at the joint IRE -RMA actual components of the signal are volves separate measurement of the in- Meeting at Syracuse, New York, causing the indication or if it is due dividual harmonics and the calcula- on April 28, 1948, and is pre- to noise or hum generated in the equip- tion of the square root of the sum of sented in its entirety in AUDIO ment. If noise causes a reading ap- their squares. The wave analyzer is ENGINEERING by authorization of proaching the order of magnitude of connected as shown in Fig. 2 and The Institute of Radio Engi- the expected distortion readings, the Fig. 11. The percentages of the har- neers. selective method of measuring the harmonic components with respect to monics with a wave analyzer will or- the fundamental are determined by dinarily result in more accurate de- calibrating the wave analyzer by tun- termination of distortion than a non- measurements. ing to the fundamental and setting the espunse and gain How- selective method. ever, in of wave analyzer meter to 100 per cent, and then reading the case A distortion factor meter,11 when measurements will not be the other components referred to this it probably used for distortion measurements, at- possible to directly calibration. The total harmonic dis- connect to the out- tenuates the fundamental of the test the tortion in per cent is then the ratio put terminals of equipment under signal output of the equipment under of square root of the sum of the squares test without producing unbalance since test and passes the remaining signal, usual wave analyzer has one ter- of the voltages of the individual com- the which is composed of harmonica and minal this case ponents to the voltage of the funda- at ground potential. In noise. The rejection of the fundamental it will be necessary to insert an iso- mental frequency. The wave analyzer is achieved either by the use of a high - in the input leads to can be used to check the signal source lating transformer pass filter or by the use of a sharply the wave analyzer. To check that such for harmonic content. Such a check selective circuit. Comparative measure- a does not introduce ap- should be made to insure that meas- transformer ments may thus be difficult to corre- urements are being made of harmonics preciable distortion, the arrangement late, particularly if the amplitude of generated in the equipment under test for checking distortion in test equip- the remaining noise approximates that ment indicated in Fig. 11 should be as indicated in Fig. 11. of the harmonics being measured. Such For such tests on balanced equip- used. meters are sometimes so arranged that of with ment the same precautions must be The measurement distortion the frequency -selective circuits may be wave analyzer tends to be more pre- observed as outlined in the section on a disconnected for use in measuring cise than measurements with a noise noise as discussed later. Such a device 'Bell Telephone Laboratories, and distortion meter under some con- is ordinarily termed a distortion and Murray Hill, N. J. ditions, as discussed later. However, noise meter. "Herman Hosrner Scott, Inc., disadvantages the ac- 885 Putnam Aye., it has the that The harmonic and noise content at Cambridge 89, Mass. tual observations are more time con- the output of the equipment under suming and that cal- test is indicated as a percentage of culations are neces- the total value of these components sary to determine Re. with respect to the value of the entire Coi >NFACILITT CALIBRATED the total distortion .4/aa output signal. As is the case in all ADJUSTALE Mofa OUT - ADJUSTABLE AT CRUSTOR TEST AT percentages. . ENIJTOR harmonic -distortion measurements, the C D In making distor- signal source and any isolating trans- ti tion measurements, used must not introduce ap- DISTORIOM former SEAMING absolute EQUIPMENT the same preciable distortion. C ARE IMPEDANCE MATCHING NET BORES AT IN ANO OUTPUT gain as well as the A. distortion factor meter may be RE SPEC TIVE LT same relative distri- substituted for the output meter as RS R, ARE RESiSTANCLS EQUAL TO NOISE RATED SOURCE AND LOAD IMPEDANCES MEASURING bution of gains and shown in Figs. 2 and 11. It will be nec- SESPECTIVELT, OI ACILIT, ARDER TEST I WIRY NT losses in the equip- essary to preserve the desired ground- FOR GAIN ANO RESPONSE ME ASUREMENTS CONNECTIONS - FOR DISTORTION MEASUREMENTS I SINGLE ERLOI ment under test as ing condition of the circuit under test Z - FOR NOISE MEASUREMENTS were used for the and to terminate the output attenuator

INSERTION zoo R 11 ICI, 1 gain and frequency properly. This termination can be in ACILITtSNOtR uH SuAI CIRAI Dye, IOLOG,G S IE..I response measure- part or in whole the input of the dis- ments must be used tortion and noise meter. For example, TYPICAL MEASURING SYSTEM FOR AUDIO FACILITIES AS DEFINED ay Pups to insure correlation suppose that the latter has a 500 -ohm ON LUDO CONM?TEE of resulta. resistive input and the proper termina- It is also advisable tion required is 000 ohms. It will then Figure 2 to slake a cheek be necessary to add 100 ohms of aerie.

18 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com resistance, properly arranged to main- expressed in dec- tain the desired grounding relations. ibels is then the In addition to the errors caused by signal - to - noise noise as already mentioned, this method ratio. In actual- of distortion measurement may be ity there are two subject to other errors. The readings major complica- may be accentuated or reduced by phase tions in measur- relationships between different har- ing the noise, as TOTAL T OUTPUT monics LOAD Or ATTEHUATOOS C D MUST EQUAL R or between the same harmonics well as questions 5KRE NS RESISTANCE introduced IS EQUAL TO ATTEMNSWISTON N IMPEDAICL by each of several elements which arise in de- CONNECTIONS FOR MEASUNEMENI Of EQUIPMENT UNDER TEST. in the equipment CONNECTONS T FON GREC. Of SIGNAL SOURCE HANMONICS. under test. Further- fining the signal FOP ENECF OF SIGNS/ SOURCE USE HIGHEST LEVEL AT M, EFFECTED TO LE USED TEST more, when the magnitude of the har- and its measure- GERING . ISOLATMG If TRANSFORMER IS USED AT OUTPUT IT SHOULD SE monica exceeds a few per cent there ment. These corn - NCLUDED IN CHECK. UNDER THIS coNOITION SOME ATTENUATION IS DE I KTMEEN R APp OUTPUT T ANSFORMER TO MINI- it a metering error as the distortion plications are the MIZE INTERACTION KTMEEN TRANSFORMERS AND TO OITAM ACTUAL MEASUREMENT LEVEL ON OUTPUT TRANSFORMER factor meter indicates the ratio of the nature of t h e harmonics to the fundamental plus the noise and the CONNECTIONS FOR DISTORTION MEASUREMENTS harmonics rather than to the funda- characteristics of mental only. the noise meter. Figure I I The nature of the noise is impor- ties for radio broadcasting Intermodulation Measurements (not includ- tant basically even though it is meas- ing studio -transmitter loops), By substituting the Com- two signal sources ured as electric energy, in the actual mittee on Audio Facilities has agreed st the input, two signals can be si- application of the equipment under upon making noise measurements multaneously applied to the equipment test it is ultimately converted to with a device having a frequency re- under teat and, by means of an analyzer acoustical energy and as such is a dis- sponse flat within plus or minus connected at the two output, the intermod- turbance on a subjective basis to the decibels from 50 ulation to 15,000 cps and between the two signals can listener. The noise energy present in having the ballistie characteristics he measured. Different of methods of mak- audio facilities for radio broadcasting the "standard VII meter" but reading ing such measurements have been dis- is ordinarily composed mainly of two (responsive to) the rms value of a cussed in the literature 12, 13. 14. is In types. The first is random energy dis- complex wave approximating a steady general such tests require - that the max tributed substantially uniformly over state condition. The Committee imum possible peak voltage value also of the frequency spectrum and of rela- notes that measurement of pulse noise the composite signal does not exceed tively uniform amplitude. This is pri- conditions has not been included the peak test voltage which be- would be marily caused by thermal noise in re- cause of lack of definition and equip- applied to the equipment under test in sistances. Vacuum tube disturbances ment. making single- frequency harmonic such as "shot effect" may also be con- The measurements. The magnitudes results of the measurement of of sum tributing. The second is energy con- noise with and difference frequencies resulting a meter having a substan- centrated at one or more frequencies. tially flat frequency from modulation within the equipment response are or- A typical cause of such noise is opera- dinarily reasonably under test are then determined at the adequate for com- tion of equipment from an alternating - output. parative use in the field outlined herein, current power source. In addition to The particularly on like equipment. For ex- results of such intermodulation these two types ordinarily present, measurements ample. in audio facilities for radio on a system composed of peaks of relatively high amplitude but broadcasting, amplifiers and related components the noise problem fre- such of short duration may be experienced. quently simplifies as attenuators can ordinarily be cor- to that of the control Such peaks may occur at random inter- of hum from power supply when power related with measurements of single - vals or may recur at repetitive time is supplied as alternating frequency harmonic distortion on the current to intervals. the heaters of indirectly same equipment. However, in connec- heated cath- The of the nuise meter odes and as rectified tion with the interpretation of such re- characteristics and filtered alter- become nating current sults in terms of minimum standards a problem because of the pos- for the other elements. sible variations Where a and associated methods of measure- in the nature of the diversity of conditions exists, noise it may be ment the Committee on Audio Facili- energy. If all noises had the necessary to qualify the re- ties of the Transmitter same wave- shape, then any meter cap- sults of noise measurements to insure Section of RMA proper has taken the able of indicating steady state elec- interpretation ; this results position that "there is largely not sufficient data available at trical energy and having the requisite from employing flat response this measurement time based on subjective observation sensitivity could be used. However, of electrical noise, as generally time to establish recommended when noises have different frequency ultimate criterion is dis- conditions turbance for test for intermodulation measure- make -ups, either due to various mix- on an acoustical basis. For ment." tures of single-frequency and random this reason, frequency weighting in the noise or due to various mixtures of dif- meter has been generally resorted to Noise Measurements ferent single frequencies, then if the in noise tests on telephone systems and The measurement of electrical noise noise meter is to give equal readings on in acoustical measurements, to simu- in u complex audio system such as the noises which are equally disturbing to late human ears at representative complete audio facilities for an elabo- a listener, the frequency response listening levels. Examples of this are rate broadcasting studio is very simple characteristic of the noise meter is im- the Bell System program noise measure - in theory. The reference output power portant and should not be flat. Finally ing equipment and the American of the reference frequency is first de- the possible presence of random pulses Standard Sound Level Meter. 15. 16. mT termined. The signal is then removed, emphasizes the time of integration of There are incorporated in the latter the input is terminated with a resist- the meter and the ballistic properties device two frequency weightings, cor- ance equal to the rated source imped- of the indicating instrument. responding to ear characteristics for ance and the residual output level is As a temporary arrangement for 40 db and 70 db acoustical levels. Re- measured. The ratio of the twn levels measuring the noise on audio facili- [Continued on page 481

AUDIO ENGINEERING NOVEMBER, 1949 19

www.americanradiohistory.com Audio Transformer Applications

A. J. AVIS*

Impedance calculations for transformers are encountered regularly in audio work. The author clarifies relations between impedances in tapped and multi -winding coils.

AUDIO TRANSFORMERS are essential in a hot bubbling mixture of rosin and db range in 1 -db steps. The output of elements of high quality audio beeswax, praying that the latest treat- the attenuator is fed into this matching systems. The broadcast engineer, ment would not again result in a transformer, which provides various to whom quality performance is a prime horribly sticky mess that eventually output impedances while handling a consideration, uses audio transformers would seep through the entire set. power range from -GO to +35 dbm over in practically every phase of his work. Reliability was a touchy characteristic a frequency band from 20 to 20,000 cps Modern design, high quality materials, then, and not many makes of trans- and with less than 1 per cent harmonic and up -to -date manufacturing processes formers were able to take both the distortion. The fact that such trans- contribute to the superb performance climate and the protective practices to formers are produced in commercial of present day transformers. which they were subjected by the zeal- quantities at reasonable cost is a good In this connection, the writer recalls ous amateurs. example of the high standards of design some experiences with transformers in Most readers, however, living in less and manufacture in the transformer the humid climate of the Netherlands trying climates, may feel assured that industry. East Indies in the early 1930's. Trans- their investment in high quality audio The application of audio transform- formers were difficult to obtain and transformers is a safe one, without ers as a rule requires a certain amount demanded highly developed protective having to resort to any maintenance of impedance matching. In most cases, techniques to combat the onslaughts program. An investment it will be, little difficulty is encountered with of humidity, termites, fungi and many however, for good quality transformers interstage transformers, which normally other threats to the delicate life of the are not cheap, and mediocre ones are are selected to operate with a specific fragile and valuable components. not worth wasting time and money on set of tubes and therefore are not sub- Radio amateurs spent many evenings if the utmost in performance is your ject to a change in conditions. With comparing, arguing, and defending goal. care, good resistance- capacitance cou- their latest developed protective tech- pled circuits may be designed to replace niques, which they claimed were guar- Specific Uses interstage transformers, but it is not anteed to allow a tranformer to remain S,auetinnrs a transformer is needed so simple to find a substitute for input unattended for fully two months. that must operate satisfactorily over a or output transformers, which are often Regularly removing transformers from wide range of operating levels and over called upon to accomodate a wide the sets and drying them slowly in hot a wide frequency band. An example of variety of impedances. boxes was old stuff -it took more cour- such an application is the matching Microphones and pickups require a age to dip the pride of one's collection transformer used in certain audio sig- wide range of input values, and loud- nal generators equipped with an output speaker voice coils vary with speaker '312 Stowell Ave., Sunnyvale, Calif. meter and variable attenuator with 110- size, type, and manufacturer. Telephone

Fig. I. Curve showing power loss due to impedance mismatch between circuits.

20 AUDIO ENGINEERING NOVEMBER, 1949.

www.americanradiohistory.com AUDIO OSCILLATOR VACUUM TUBE RECTIFIER TYPE 400 cps VOLTMETER .VARIAC' A.C. VOLTMETER o

TURNS RATIO n - eYe2 IMPEDANCE RATIO - n'

Fig. 2 (left). Simple method of measuring turns ratio of transformers when v -t voltmeter is available. This arrangement is suitable for all types of transformers. Fig. 3 (right). Meth od of measuring turns ratio of output or speaker coupling transformers. lines and multiple- speaker installations materials which are capable of develop- mismatching is shown in Fig. 1, where complicate the picture even more and ing adequate flux densities at exceed- power loss is plotted in per cent against emphasize the importance of suitable ingly low signal levels. On the other the ratio of optimum output imped- input and output transformers. hand, a transformer designed for dy- ance Z. to actual load impedance ZL. Transformer Selection namic microphone matching purposes The following example illustrates an The selection and application of each would transmit the low signal levels application of the graph. An amplifier type require special considerations, efficiently in that service, but would be is available with 8- and 16 -ohm taps. which often are not obvious to the non- unable to handle a speaker power level and it is desired to determine which because of core saturation and limited one to use to connect a 12 -ohm voice current -carrying ability in its fine wire. coil. The 8 -ohm connection gives a 2. When a transformer is used at a ratio of Z./Za of 8/12 or 0.667 and from different impedance level than the Fig. 1 a loss of 4 per cent. The 16 -ohm rated value, the frequency response connection results in a ratio of 16/12 may be affected to a marked degree. or 1.33 and a loss of only 2.5 per cent. Consider for example an output trans- indicating the more desirable connec- former designed to match an 8000-ohm tion.* plate -to -plate load to a 500 -ohm line. and having a frequency response within 0.5 db from 30 to 15,000 cps. It is desired to use this transformer to match Zc a 5000-ohm plate -to -plate load by re- Fig. 4. Coil arrangement using two ducing the secondary load in the same 125 separate windings connected in series. proportion to about 313 ohms. 50 The inductance of the primary is professional designer. Transformers are sufficient to maintain only 0.5 db loss 500 200 z usually designed for a definite applica- at 30 cps when shunting a 8000-ohm tion, and optimum performance is ob- generator. The effect of reduced gener- 50 tained only under specified operating , ator impedance by a ratio of 8:5 is 125 conditions. The performance of a unit such that the primary inductance is when applied under different circum- e now sufficient to maintain 0.5 db loss stances may differ appreciably from at only 20 cps. On the other hand, the that which is expected. Furthermore, effect of leakage reactance, which con- Zo- 125 Ohms Zt, = 50 Ohms the frequency characteristic of input zc - ? trols the high -frequency response, and output transformers and the avail- is increased by the ratio 8:5 and the able output from the amplifier are 6. Typical input transformer con- response of the transformer will be definitely affected by incorrect imped- nections. Two I 25-ohm windings con- down 0.5 db at 10,000 cps. The reverse ance matching. A few cases are de- nected in series provide a 500 -ohm holds when the transformer is used in a scribed to illustrate some of these winding; similarly, two 50 -ohm wind- higher impedance level circuit. Similar effects. 1. A 500 -ohm to 8 -ohm voice ings in series equal a 200 -ohm winding. conditions exist in input transformers. coil matching transformer with a power 3. The effect of power loss due to handling capacity of 20 watts may In the first part of this acticle, trans- perform superbly with low losses when former applications involving known driving a heavy duty speaker. However, impedance values have been considered. when used as an input transformer to Most designers and experimenters are match an 8-ohm dynamic microphone limited in selecting suitable transform- to a 500 -ohm line, unsatisfactory oper- ers to commercially available lines, ation may result. The low -level signal which include a great many with may be inadequate to provide sufficient tapped or multiple windings. The flux excitation in the large core, since values available at the taps may not the minimum signal level depends on always provide as close a match as the grade of lamination iron used. would be desirable, and one may won - Inasmuch as operations under these (Continued on page 45) conditions have not been anticipated ('Note that this applies only when maximum in the design, no provision has been Fig. 5. Coil arrangement for single power output is the primary consideration. made to utilize special costly core tapped secondary. Ed.)

AUDIO ENGINEERING NOVEMBER, 1949 21

www.americanradiohistory.com luzcúa! awrizi n. Logarithmic Amplifiers

C. J. LeBEL*

Amplifiers having wide -range linear db scales have wide use in audio measurement work. Various design problems are discussed, together with their solutions.

MIKTHODS OF CONVERTING an audio measuring surface noise on recordings. too slow for many applications, and signal to an output voltage which An easy -to -make experimental log cir- that a speed of at least 1500 to 2000 db would be proportional to level cuit will be shown, and a scale- expan- per second should be available. The in decibels were discussed by the writer sion meter circuit will be covered. modern direct-writing oscillograph with last month.' In the following para- a logarithmic amplifier preceding it graphs some phases of the practical ap- Recording Speed should replace the level- recorder in any recordings of radio pro- plication of logarithmic circuits will Oscillograph careful analysis. The oscillograph hav- gram level and of acoustical decay in a be discussed, including their applica- ing no tapped attenuator, one can be were shown in last month's ar- tion in a high sensitivity voltmeter for room sure that any detail in the curve is not ticle. These curves present a number the result of step -by -step motion over Audio Instrument Co., 1947 Broadway, New of examples of recording speeds between a tapped attenuator, nor of erratic York 23, N. Y. 1000 and 1500 db per second, showing action of servo-system clutches. ' "New Developments in Logarithmic Ampli- high -speed level -recorder fiers," C. J. LeBel, Ammo ENGINEERING, that the old Vol. 33, No. 9, Sept. 1914, kith its limit of ó00 db per second wit. Some Practical Matters Judging from recent discussions with a number of ordinarily well -informed engineers, there is little general realization of the variation of gain of an ordinary amplifier with input level, and the need of instrument -quality amplifiers for the input and output elements of a logarithmic system. In Fig. 1 the gain variation of an ordinary single-stage amplifier has been compared with that of a section of an instrument amplifier (of equal gain) employing a large amount of negative feedback. In a complete amplifier system, the overall gain variation would be three to four times the value given for a single stage or section. It is desirable to use at least 20 db of negative feedback if a highly stable amplifier is to he produced or the accuracy of the logarithmic relation is not to be in- jured. Regardless of which logarithmic material is employed, the correct value of series resistance must be employed. The amount required depends on the material chosen and on its physical dimensions. As in so many other audio problems, the quickest method is the experimental. Figure 2 shows how an increase in series resistance increases the linearly logarithmic range by improving the linearity at the lower end of the curve. This is done at the ex- pense of sensitivity. If carried too far, the driving voltage requirement becomes prohibitive. Stray capacitance Fig. I. Gain variation with output voltage for an ordinary single stage amplifier across the series resistance also begins (A) and for an instrument amplifier of different design (B) using 20 db of to affect the frequency response. This negative feedback. Both amplifiers have same nominal gain. tends to limit the resistance to 50,000

22 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com The mechanical method has been widely used, but it has the disadvantage that L4 the pointer is drawn against the left hand stop whenever the meter is not 13 in use. The spring is under constant 12 III, ..Aill u.2/11'r'" tension, and fatigue and permanent set will result eventually. LI 1111 _5iiP!21111 it3 , jj; M21111111 The answer to this is to use electrical o I zero suppression, as shown in Fig. 6. 9 An adjustable bias current is passed through the meter, of such polarity as a .8 SERIES RESISTANCE ------.rill./ ""I to draw the pointer to the left hand stop. When the level rises above the INPUT OUTPUT bias value, the meter will indicate. The .66 dIIII method can be used with virtually any /AMMER! vacuum -tube voltmeter circuit. To line .4 up the meter scale with the log element, .2 .3 .4 .5 .6 .7.89WK 2 3 4 5 6 78910 both VTVM+f sensitivity and meter sup- -20 -10 0dbr 10 20 pression current should be adjustable. INPUT First set the desired maximum level into the log element, then adjust VTV11l Fig. 2. Effect of varying resistance in series with logarithmic resistor . sensitivity until the pointer comes to or 100,000 ohms for work up to 100 kc, scale is shifted on the meter, but the the top of the scale. Decrease the input and 10,000 or 20,000 ohms for frequen- effective logarithmic range is un- to the log element by the range of the cies above that. changed. The way to get the desired meter scale (for example, 30 db for a After the resistance has been in- result is to spread the scale by using a 0 to 30 meter scale) and adjust the creased to its maximum value. it will suppressed zero type of meter. The suppression current until the pointer often be found that the accurately loga- lower, undesired, part of the db range is on the lowest line of the scale. If the rithmic range is still not great enough. is thereby shifted off the lower part of range chosen calls for a great deal of A further extension of the linear range, the scale and suppressed. suppression, such as a 20 -db scale, then by 10 or 15 db at the lower level limit, Two methods of zero suppression are the two controls interact and two or can be achieved by adding bias, by available mechanical and electrical. three adjustments will be necessary to means of the circuit shown in the pre- - vious article. The polarity of the bias will depend on the particular material used, and must be determined by experiment. An example of the variation in linearity with bias is given in Fig. 3. It is desirable to stabilize the bias voltage, and a convenient circuit for the purpose is shown in Fig. 4. This utilizes the negative voltage -current re- lationship of an ordinary half-\10 selenium rectifier junction. For regulation, a two -stage stabilizer circuit is desirable, as shown. There are a large number of logarith-

mic materials, and the main ditfcn I between them lies in the range of accurately logarithmic effect. For the engineer who would like to do a little experimenting, the most convenient

1 material is copper oxide in the form of a meter rectifier. A circuit for using a bridge -type unit without bias is shown in Fig. 5. If the range is to be extended by using bias, half -wave copper oxide rectifiers are obtainable from some manufacturers. Two should be used in a full -wave circuit, as shown in the previous article. Since a copper oxide junction itself rectifies, the rectifiers in that circuit can be omitted. Scale Spreading

I I is often found that a 50- or 60 -db scale is too big, and that a 20- or 30 -db range would be desirable. If the sensitivity of the vacuum-tube voltmeter fed from the log element is varied, it will he found that the top limit of the db Fig. 3. Effect of varying bias of logarithmic material on low level linearity.

AUDIO ENGINEERING NOVEMBER, 1949 23

www.americanradiohistory.com I-~ 6640

60db I 2160 30 db VTVM GAIN GAIN

T T 266 1 1 500 CP.S. 10,000 C.P.S. 10db STEPS LOG HIGH PASS LOW PASS ELEMENT FILTER FILTER

Fig. 7. Disc -noise meter using methods discussed in this article.

basis, the initial meter accuracy will not be affected, but the meter will re- ceive occasional 20:1 overloads. It will not burn out, but the cumulative effect of mechanical mistreatment will eventually damage it enough to require its repair. The solution to both of these problems is to have the logarithmic action Fig. 4. Stabilizer for bias voltage. Adjust rheostat to exact bias voltage. precede the meter movement. Then the meter operates as the ear does and yet ment when different materials, such as o is from The over- different pressing stocks, were used for protected overload. 10000 load protection results from the fact Bridge Type comparison. INPUT Copper Oxide OUTPUT that the meter receives the logarithm There is a sound theoretical basis for Meter Rectifier itself. such doubt. Whereas the human ear of the current, not the current o o A 40-db overload give twice normal measures logarithmically, then inte- will grates the result, ordinary rectifier meter current, not 100 times normal. Fig. 5. Full -wave copper -oxide meter meters, such as the VII meter, do the A disc -noise meter may be put to- rectifier used as logarithmic element. reverse. They integrate the energy of gether from what has already been dis- a noise wave and then translate the cussed. It is necessary only to add integrated average logarithmically by filters to limit the frequency range to means of a VU scale. that specified in the NAB disc -noise An objection may also be raised to standard -a 500-cps high -pass section the use of a limiter or clipper for meter and a 10,000 -cps low -pass section, both protection, an objection which is pecu- of the constant-II type. Figure 7 shows liar to noise measurement -the peak such a circuit, and Fig. 8 the frequency factor of noise is at least five or ten to response. one. If clipping is to start just above There may be some question as to -scale a Fig. 6. Electrical zero suppression cir- the full meter indication, on the need for such large amounts of cuit. sine wave basis, the accuracy on noise gain. However, this design contemplates of the top half of the meter scale is measuring the noise of the quietest put both ends of the scale in simulta- destroyed. If clipping starts 25 db lacquer at the center of n 20-db meter neous alignment. Electrical zero sup- above full scale, also on a sine wave scale. pression is so convenient that it is a pity it has been so little used. The circuit design is very straight- forward, and it is only necessary to make the resistors in the suppression circuit of such value they do not that .0 disturb the linearity of the VTVM, for o they form a load across its output.

uwi 0 Disc -Noise Motor z 0 CL For years it has been customary for N well -run recording studios to measure W 10 cc the noise level of every lacquer master w and mother cut and every test pressing > 20 "614\ as a means of checking the operation of I- \ 4 oquipment and personnel. The meters J used have generally been built up from 30 a combination of standard amplifiers, a VII meter, and occasionally a limiter of some sort. Not being an instrument amplifier, the gain has generally drifted yo 20000 Ido moo 10000 with time and use. Furthermore, there FREQUENCY IN CYCLES PER SECOND has been some question as to how the results compared with the ear's judg- Fig. 8. Frequency/ response of disc -noise meter. 24 AUDIO ENGINEERING NOVEMBER, 1949

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Export: 13 East 40th St., New York 16, U.S. A. Cables: Arlab ELECTRO -VOICE, INC. BUCHANAN, MICHIGAN AUDIO ENGINEERING NOVEMBER, 1949 25

www.americanradiohistory.com flawless as Goldmark played them. Why? ee., I w, -.lot k III trade of thin Those Fuzzy ( ?) LP's department, but this month's specula- Lest you think this is an amateur argu- tions are going to have even more if's ment, read further. Of course there were S TATNALL Let us and but's than usual -for this is the account EDWARD CANBY* differences in the playing conditions. the rooms. of a decidedly unfinished bit of continuing leave aside acoustics in listening questioning. The subject is familiar -the The most vital item is that Dr. Goldmark record. The questioning involves (1) is uses his own crystal cartridge, not a mag- LP except for one nasty little thing that keeps there unwarranted distortion in some (or netic, the LP -33 (now superseded by the coming up to bother me. Ever so often, needle. many) LP's and if so, how come? (2) Is Astatic U model, with replaceable along comes an LP that does not -but de- the magnetic pickup the beat for LP play- that fits both the Astatic FL arms and the finitely does not distort, and that under into an ing, as most engineers automatically assume? old Philco player arm). It plays identical conditions. I have a half dozen is, After a year and a quarter of LP history RCA amplifier and speaker system. It or so of these at least, and results are un- the confusions over LP quality continue of course, equalized to the LP curve by failing. Put on one of them at a loud part unabated and at all levels, and this I find the man who designed that curve. He ought -the sound is clean. Slip one of the other feels most remarkable. It's OK for us non - to know. Dr. Goldmark apparently LP's on, and there is that fuzziness again. engineers to disagree, what with a million that crystals are here to stay, for lie has No one has yet been able to explain this and one amateurish mistakes liable to gum designed a series of them for LP playing one for me, but I can demonstrate it. I have, up the issue-blaming the records, for in- and has not, that I know of, done any work cnly too obviously. in some semi-public stance, for "too much bass" or "too little with magnetics. The crystals are recom- "concerts" during this summer. I had to bass" when quite clearly the trouble is mended without reservation -for professional pick and choose. Certain LP's I could play. equalization, about which few record owners as well as amateur work -or so I have Others f could not, unless with a cutoff of know anything- rather than anything wrong gathered. What's more, as begins to become 8000 or lower. in the records themselves. clear, the things seem to work. At any rate, So far so good. To double -check I cus- But when, after all this time, the engineers I have the evidence of my own ears cor- tomarily listen to as many of my doubtful disagree still, and disagree mightily, there's roborated by some crystal playing at home cases as I can on other people's equipment. something that needs clarifying somewhere that the LP's do play with a great deal less From what I have heard on various engi- along the line. And worse, when the very apparent gross distortion when the crystals neer's outfits, my impression is that many results themselves seem -as has been happen. are used than when the theoretically superior an LP. played on a GE pickup, gives on ing to me -to contradict themselves, then magnetics are employed. At this point I'm other's equipment results more or less like something has got to be done. willing to make that generalization, based mine. if anything with more unsatisfactory Let's take a few of the symptoms. Work. on a lot of hearing. sound. Magnetic variants such as Pickering ing with a GE cartridge, I have in the last I can hear some engineers snickering at and Clarkstan give similar results hut even few months consistently found that many my naivete. Let me throw in a few more more unpleasant (probably because of wider LP's from Columbia produce on my machine arguments. Yes, it would seem obvious that frequency range). I have heard it said that a varying amount of "buzziness" and dis- the distortion (assuming it's there) shows up there are "no good LP's at all" when it tortion in the highest range, particularly in on the magnetics because of their better re- comes to the really high tonal ranges. the louder parts. The first and obvious sponse in the high range; the crystals just Though I violently disagree. I have heard explanation was a bad stylus. No such thing don't get up in the distorted range. Now some demonstrations that were most unhappy -that has been eliminated long since. Buz- this is a weighty argument, but not, in my in the sound. How to explain them? zings continued. Well, then something else present opinion, quite weighty enough. The But this is far from the end. T am for- in the equipment must be wrong. Perhaps several crystal models that Columbia has re- tunate in having as a good friend the man n a matter of tracking? Don't think so, for I commended are good easily to 10,000 cps who develoned the LP in the first place. have encountered the same effects quite with a downward slope that is plenty flat Dr. Peter Goldmark. When LP -itis begins uniformly with a player that, being semi - enough to be managed. The "buzziness" to hit me badly and things just sound portable and used in many places, is bound that I complain of is high -up. but I would terrible. T go to him for consolation. And not to sit at exactly the same tilt, if any, question seriously whether it is all of it T am baffled. In Dr. Goldmark's office the for each situation. I have arbitrarily tipped above 10,000. An 8000 -cps cut-off, tuned very records which have buzzed and rattled the machine this way and that, changed the sharply at 10.000, still lets through some of for me play without a trace of audible dis- stylus weight, without materially changing it in most cases. Any such distortion should, tortion! it has happened over and over the buzzy distortion. Trouble in the ampli- everything else being equal, come through again. I have even a from his fier or elsewhere along the electrical line? taken disc on the crystals more or less as it does on player that sounded perfectly clean and Sounds as though it must be there, since the magnetics, with equivalent equalization. found when got home that it was buzzy and after all, Columbia is unwilling to admit to I It does not, to the best of my experience. seemingly overcut; nor could juggling any pronounced distortion in the LP product any Why? f do. including a large dose of roll -off in okayed by them for release. Every engineer- Yes, the good LP's (the ones I have found the highs. really clean it up. Two of the ing calculation would suggest that the trou- good. if you wish) are to my ear better seven -inchers were particularly strange in ble is with me and my equipment, not with sounding via any magnetic than with any was the records. this respect. One the Welitch recording crystal. Doubtless because, after all, no crys- of a sonrano aria from Weber's 'Freischutz." I am always willing to accede to that sort tal pickup has quite the even resnonse that a the other a violin and piano piece called of argument and assuredly would here- fine magnetic pickup can give. Naturally, al- "Tsigane" by Ravel. Both were unbearable [Continued ore page 361 279 1! . 4th St., New York 14, N. Y. as T had heard them at home. Roth were

26 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com HARVEY? MAGNECORD

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AUDIO ENGINEERING NOVEMBER, 1949 27

www.americanradiohistory.com AUDIO engineering society

Containing the Activities and Papers of the Society, and published monthly as a part of AUDIO ENGINEERING Magazine

OFFICERS Theodore Lindenberg, President Audio Engineering Society, J. D. Colvin . _ ... Executive Vice -Pres. John G. Frayne . Western Vice -Pres. Box F, Oceanside, N. Y. Normen C. Pickering Secretory Ralph A. Schlegel Treasurer CONVENTION PROGRAM

Presenting a total of twenty-two sub- differences between regular broadcasting er jects in four sessions, the First Annual Friday, October 28, 1949 motion picture sound recording techniques will be discussed as well. The information Convention of the Audio Engineering 9:30 a.m. Registration. Advance Sale of of the type of program on the placement of Society opens on Thursday, October 27, Banquet Tickets. Sixth Floor microphones has been scrutinized and example, of current practices will be den- at the Hotel New Yorker. This is a Exhibits Open greater number of audio papers than 9:30 a.m. to Noon Papers have ever been presented in any one -North Ballroom Chairman Theodore Lindenberg Employment Register calendar year heretofore by all other - Fairchild Recording Equipment Corp. Positions open and available person- societies combined. 1. "Automatic Audio Gain Con- nel may be listed here at no charge to In addition to the technical sessions, trols" J. L. Hathaway - industry, or to members of the Society. the Society will hold its annual business National Broadcasting Company For insertion in this column, brief an- meeting, the installation of officers, and The development and application of automatic audio gain controls at the National nouncements should be in the hands the first banquet. The newly created Broadcasting Company is reviewed from the simple fi'ament type compressor. of 1029 of the AES Editor before the tenth of John H. Potts Memorial Award and through the present day studio units. the month preceding the date of issue. the Society's annual award will be be- General characteristics are described. such as attack and recovery times, gain reduc- Address replies to AES Editor, Audio stowed at the banquet, together with a tion, and thump. Practical units are illustrated for various applications: for con- Engineering, 342 Madison Ave., New number of Honorary Memberships. trolling or limiting in broadcast studios. York 17, N. Y. The Audio Fair, the first exhibit ever transmitters, portable equipment, and recording system. Audio Technician. 12 yrs laboratory, devoted entirely to audio equipment, A complete description is given of the mfg, and field experience. 1st phone, compe- will be held during the three days on latest type of studio control unit incorpo- tent trouble -shooter and constructor with de- rating an adjustable control characteristic, sign background. Pleasing, the sixth floor of the hotel. a double -time constant-gain recovery circuit, effective person- and a circuit which permits transmission ality. Desire responsible position with BC of pistol shots at abnormally high peak station or equipment manufacturer. Box 101. levels in order to create realistic sound Research Thursday, October 27, 1949 effects. and Development Engineer. Plt. D., specialized in electronics, circuit de- 11:00 a.m. Registration. 2. "A New Development in Directional sign, electro- mechanical devices, acoustics, Advance Sale of Banquet Tickets - Itlicrophones" Dr. Harry F. precision -mechanics, nuclear physics equip- Sixth Floor Olson and John Preston - Radio ment. Would like to be your consultant or Exhibits open. Corporation of America Laboratories part -time adviser. Box 102. 1:30 to 2:30 p.m. Business Meeting -In- The directional microphone is a second Electrical Engineer, over 20 yrs elec- order gradient system exhibiting a uniform tronic, acoustic, dynastic audio devices, sys- stallation of Officers -Grand Ballroom and narrow directivity smooth pattern and a tems. Accomplishments in development, de- 2:30 to 5:00 p.m. Magnetic Recording response frequency characteristic over the frequency range of 50 to 15,000 cycles. The sign, manufacture, for commercial, marine, Session -Grand Ballroom directional efficiency -that is. the energy govt equipment. Exp. supervision, planning, Chairman C. J. Le Bel response to random sounds-is one -tenth. estimating. Early radio background. Resi- This order of directivity makes it possible Audio Instrument Company dence NY area. Box 103. to use a pickup distance up to 12 feet with speech in conventional studios. The use of RCA Institute graduate wishes posi- 1. Operating Problems & Experi- several of these microphones, fixed in position with audio company or recording studio. ences R H. Barnaby tion and each microphone covering a sec- Box 104. -. tion of the total action, together with a National Broadcasting Company monitoring console makes it possible to cover Communications Engineer /MIT) 22. 2. General Problem rapidly changing and larger areas of action single, with good theoretical background with smaller variations in the output level W. O. Summerlin and some experience; interested in re- than is possible with the conventional micro- search, Audio & Video Products Corp. phone and boom arrangement. development, or teaching in audio, acoustics, electric 3. circuits, and vac- Standards -Present Status 3. "Microphone Placement in uum -tube circuits. Box 111. R. M. Morris - AM & TV" H M. Gurin- Audio Engineer: Three years expe- American Broadcasting Company National Broadcasting Company rience in magnetic tape development in- 4. Improving Uniformity The factors involved with sound in bring- cluding pigment research, coating formu- E. W. Franck -Consultant ing intelligent information to the listener lation, coating techniques, pilot plant or viewer are analyzed. particularly with 5. Distortion Measurements respect to the characteristics of the equip- operation, manufacturing control equip- G. L. Dimmick- ment, studio acoustics. and pickup technique. ment and techniques. Broad background Radio Corporation of America A number of variations of microphone in all phases of film and disc recording. placement in regular broadcasts. for differ- 6. Speed Regulation Problems Box 112. ent types of programs. will be demonstrated Graduate P. Brubaker -Rangertone with an explanation of the methods em- Student of radio and tele- ployed. The differences in these technique vision desires Junior Engineering posi- 7. Duplication by Contact Printing have hen carerully studied and basic gen- tion in audio or recording industry. Age Robert Herr and eral methods are recommended. 23, The problems in television sound will also married, child Willing to travel oc- J. E, Johnston - be indicated and the methods of handling casionally. Prefer midwest or south. Box Minnesota Mining & Mfg. Corp. some of these difficulties suggested. 'The 113.

28 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com 4. "Longitudinal Noise in Audio Circuits" H. \V. Augustadt- "The Standard Bell Telephone Laboratories by which This paper discusses the general effect of the presence of longitudinal noise on a Others circuit. The difference between metal'ic cir- wnen you use cuit noise and longitudinal noise is indicated Are Judged both by definition of terms and representative circuit illustration. Test circuits for and Valued" identification of type are described and die - cussed. Representative conditions by means of which longitudinal noise is introduced into a circuit are illustrated and discussed. Practical means and other limitations for the Audax POLYPHASE the reducing disturbing effect of longitudinal HEAD noise on a circuit are described. The paper closes with an illustration of the applica- for any arm tion of the principles discussed to the design of a quiet AC -DC amplifier.

5. 'Control of Sound in the Theater" ....Professor Harold Burris- Meyer- Electronic control of sound for theatrical POLYPHASE. .. purposes was undertaken in the early Thir- ties as a continuing research project at Stevens Institute of Technology, supported Abo available complete wich "Wal arte by several organizations and individuals. When the war started, electronic sound control equipment had been completed and it use experimentally in the Metropolitan Operr: Enjoyment of today's House for two seasons. The control of soon discs (micro, 78 rpm, for all theatrical purposes was substantialb ONE single unit completed. Since the war, the project has etc.) requires a single been devoted to the development of a modu- lar system of sound control equipment which pick -up unit capable of should conform to theatrical operating prac- delivering such quality tices and provide for varying demands. I. includes basic equipment with which small performances as would tasks may he accomplished and provisions for adding standard items to other equip- be delivered by two or ment as needs increase, without revision of more separate high design or the use of tools. The design of plays AIL this system and its capabilities will he de- grade magnetic )nits, scribed. each designed expressly for a given type of 6. "Logic in Relay Switching Cir- recording. cuits" \Villiam Keister- The new AUDAX Re- Bell Telephone Laboratories your records From basic control paths for an electro- producers do just that! magnetic relay are the operate, lock -up. shunt and lock -down paths. Contacts on 'l our admiration will be switches or other relays are connected in one or more of these paths to control the actions aroused when you see of relays in automatic control circuits. These and hear POLYPHASE. relays respond to particular combinations o' control events and may "remember" certain You will know that it events in order to influence later stages performs important of the circuit action. The arrangement of SUPERBLY. .. contacts in a control path is determined by functions that no other logical analysis of the combinations of events is which must cause the relay to act. A con- 't does ... that titis cise statement of conditions for closing a the logical instrument path corresponds to a series parallel circuit configuration where the words and and or for YOU ... whether relating control events correspond respec- you play one type or tively to series and parallel connection of and at less electrical contacts representing these events several types of records. The circuit may be written in symbolic form and the configuration rearranged and sim- Wide range performance plified by elementary theorems of Boolean with any type disc; algebra. Genuine sapphire or 2:00 to 4:30 p.m. Papers -East Room than the cost diamond styli, replaceable by the user himself ; 1. "A New Coupling Circuit for Audio Needle radiation very Amplifiers" F. M. McIntosh, low; Consulting Engineer After three years of laboratory work di- Ear quality par rected towards producing a sound amplifier excellence! which would fully meet the band width. of ordinary waveform distortion. transient distortion. There's an AUDAX to and phase shift requirement for completely realistic reproduction. it was found that suit every purpose . . . such an amplifier probably cannot employ conventional push -pull circuits. (the desira- available also for bility of the push -null circuit being pre- Radio Stations. sumed to he self -evident). The core of the impending problem is the apparent impossi- magnetic pick -ups Write for Editorial bility of manufacturing a transformer hav- Reprint on ing a ratio of leakage inductance referred from one -half of the primary to the second POLYPHASE Principles half. to open circuit inductance to one -half of the primary in excess of 80,000. Leakage inductance in a push -pull transformer from one -half of the primary to the second half is primarily responsible in a Class AB or B amplifier for the production AUDAK COMPANY of a repetitive transient which occurs at i7 the instant of current switching. The new 500 Fifth Avenue New York 18 circuit described herein offers a complete solution to the problem and, in addition, possesses many other excelling features. The design of an amplifier embodying this cir- "Creators of Fine Electro -acoustical Apparatus since 1915" cuit will also be discussed.

AUDIO ENGINEERING NOVEMBER, 1949 29

www.americanradiohistory.com WHAT DOES 2. "Standards -A General Discus- THE SQUARE WAVE sion" Cyril Ainsworth- TELL ABOUT TRANSFORMER American Standards Association 3. "Audio Techniques in TV broad- PERFORMANCE? casting" S. R. Patremio- DuMont Television Network PEERLESS 20 -20 PEERLESS "20 -20"-This square wave. with its nearly vertical rise, The audio in television broadcasting is sirart corners, and flat top, tells us that the frequency response is flat similar in many respects to the audio in AM to at least 20 times the square wave fundamental frequency; that there or FM broadcasting. It deals with the pick- is no perceptible time delay or phase distortion for any of the compo- up of sound in the form of voice or music. nent frequencies; and that there is no perceptible transient distortion. both live and recorded. However, television differs slightly in the fact that the micro- TRANSFORMER "g" -This trace shows some loss of high frequency phones must be out of view of the cameras. components. as evidenced by the curvature at the upper left corner; and reveals This alone is one of the most difficult prob- it a damped oscillation whose frequency is approximately lems to cope with. N times the square wave fundamental frequency. Another problem is that the talent playa TRANSFORMER "C to the camerae and not the microphones. TRANSFORMER " -In this case, the square wave has degenerated into B a trapezoidal pattern. The sloping sides indicate loss of high frequen- This makes it necessary to follow the talent cies and phase distortion. Serious trouble will be experienced if feed- with microphone booms to keep them within back is used with this transformer. range of the microphones. In the case of an orchestra, the microphones must be con- TRANSFORMER "D" -This trace shows an exaggeration of the rounded cealed and still produce the desired balance. corners of Transformer "B". with the resonance occurring at lower Therefore, new techniques must be used. frequencies; the trace also shows an exaggeration of the sloping sides In order to fully cover the problems in of Transformer "C ". It may be expected that Transformer "D" will television broadcasting, they will be separated u combine the shortcomings of Transformers "B" and "C ". into the following categories: studio and theatre, films, teletranscriptions, field trans- TRANSFORMER "E" -This pattern reveals the behavior of a transmitter, and master control. and will be former with very little high frequency response, presumably the result TRANSFORMER C discussed separately. of excessive leakage inductance. No transient distortion is revealed. It may be expected that Transformer "E" will have poor high frequency power handling capacity. and that application of feedback around the 4. "Audio Consoles for TV" transformer will encounter very serious difficulties. R. W. Byloff- National Broadcasting Company SEE THE SQUARE WAVE DEMONSTRATION IN ROOM The problems encountered in making good sound pickups for a television stage and 25 AT THE AUDIO FAIR. SEE THE SQUARE WAVE controlling several sound channels satisfactorily have troubled sound engineers since TEST APPLIED TO PEERLESS AND FOUR LEADING the beginning of television broadcasting. TRANSFORMER D COMPETITIVE MAKES OF AUDIO TRANSFORMERS. In this talk the author will describe some of these problems, and compare them with the problems met in motion pictures, radio. and recording. Equipments now used in mo- PEERLESS ELECTRICAL tion pictures and recording for original takes and re- recording. and equipment used for PRODUCTS DIVISION ALTEC sound broadcasting and television will be described and compared. The features of a 1161 N. Vine St.. Hollywood 38, Cal. proposed audio console for television use will 161 Sixth Avenue. New York 13, N. Y. be described in detail. F'razar & Hansen Ltd.. 301 Clay St., San Francisco 11, Cal. TRANSFORMER E Exclusive Export Agent 5. "Sound Reinforcing System" A. W. Schneider- Commercial Radio -Sound Corp. Basic principles for theoretically perfect results: relation of fidelity, loudness and il- lusion to practical problems and compromises required will be discussed. Several large basic Magnecorder sound reinforcing systems, illustrating applications of various types of apparatus and compromises that have to be effected. will be described. Discussion of sound reinforcing The FM requirements for broadcast and television STUDIO studios. Tafae ?eco a 7:00 p.m. Audio Engineering Society Banquet -North Ballroom Norman C, Pickering, Toastmaster M you can CARRY in the FIELD Presentation of Awards and Honorary Memberships You want low distortion and wide Special Feature: band reproduction. The two -speed A comparison test, behind screens. of loud- Magnecorder, choice of radio and re- speakers of leading manufacturers. with identi- cording studios throughout the world, fication at close of Banquet. meets NAB standards for AM and FM. Frequency response: ± 2 db 40 cy to 15 kc. You also want October 1949 Rack-Mount Amplifier utility - Saturday, 29, N portability and adaptability in and Auxiliary Spool- use. 9:30 a.m. Registration. Sixth Floor ing Mechanism with One man can carry a complete, self- Recorder in place. contained Magnecord field unit. Exhibits Open 9:30 a.m. to 12 Noon. Audio Measure- UNIT CONSTRUCTION PAYS OFF ments Session-North Ballroom The Chairman W. L. Black - several elements designed use MO for with Bell Telephone Laboratories the Magnecorder PT6 -A Recording Mecha- 1. The General Problem nism arc available as individual units. Buy W. L. Black Telephone only those you need. Carry and use them as 3- Channel Mixer -Am -Bell Oilier and Power Sup- Laboratories you need them. Magnecorder units combine ply make single carry- 2. Intermodulation for every field and studio need. Buy Meg - ing case. I necorder. A. P. G. Peterson-General Radio the only tape recorder featuring Recorder Mechanisn unit construction. H. E. Roys -Radio Corporation in carrying case. of America Write for specifications and the name of your nearest dealer. J. K, Hilliard -Altec- Lansing N. C. Pickering- Pickering & Company

aqI N C . CHICAGO 1, ILLINOIS 3. Transient Methods

3 6 0 N O R T H M I C H I G A N A V E N M. S. Corrington U E Radio Corporation of America World's Largest and Oldest Manufacturers of Professional Magnetic Recorders. 4. Operating Problems....J, D. Colvin - American Broadcasting Company Exhibits open until 4:00 p.m.

30 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com TIiE AUI)10 FAIII A ieatlohs Umiimi1'eá ! Ilirerlorv I:xlaibi/or%

ALTEC- LANSING CORP. 625 I Peerless Electrical Products Divisioni 161 Sixth Avenue, New York 13, N. Y. Power transformers, filter chokes, input, inter - stage, output, modulation, and replacement transformers. "A transformer for every audio application." IN ATTENDANCE: H. S. Morris Dave Sonkin Mel Sprinkle Marty Wolf

AUDIO & VIDEO PRODUCTS CORP. 614 -615 1650 Broadway. New York 19, N. Y. Ampex Tane Recorders; Minnesota Mining & Mfg. "Scotch" Tape Alter -Lansing equipment. IN ATTENDANCE: Charles E. Rynd Russell O. Hudson W. O. Summerlin

AMPEX ELECTRIC CORP. 614 -615 San Carlos. California. Ampex tape recorders IN ATTENDANCE: Charles E. Rynd Russell O. Hudson W. O. Summerlin

AUDAK COMPANY, Inc. 642 500 Fifth Avenue, New York 18, N. Y. THE Electronie- acoustical anparatus. IN ATTENDANCE: POWRMIKE Maximilian Weil George V. Sullivan Alf Weberg AMPLIFIES WITHOUT AUDIO DEVELOPMENT CO. 635 VACUUM TUBES 2,433 13th Ave. Se., Minneapolis 7, Minn. Audio and power transformers, filters, ampli - fiers, jacks, and plug.. OPERATES FROM ANY IN ATTENDANCE: Walter E. Lehnert Eric R. Slayton 6 VOLT D.C. SOURCE INSTANTANEOUS OPERATION AUDIO DEVICES, Inc. 651 444 Madison Avenue, New York 22, N. Y. DEPENDABLE, FOOL - PROOF, Audiodiscs, Audiopoints. P udiotape. IN ATTENDANCE: ALSO FOR MOBILE AND INSTALLATIONS ECONOMICAL Wm. C. Speed C. J. LeBel SPECIAL Bryce Haynes Herman Karnbrodt The new UNIVERSITY POWRMIKE opens a new field for sound requiring no amplifier, completely portable, AUDIO FACILITIES CORP. 646 distribution. Low in cost, 605 Fifth Avenue, New York 20, N. Y. POWRMIKE can be used in thousands of applications where power Specialized audio and electronic apparatus. POWRMIKE has theatre sound systems, artificial beration supply or high cost rule out sound amplification. equipment. a maximum output of 1.5 watts, reproduces speech with excellent IN ATTENDANCE: operated by handy press -to -talk switch. John H. Beaumont Lewis S. Goodfriend fidelity and is instantaneously Additional speakers may be added for broader coverage and special AUDIO INSTRUMENT COMPANY switching arrangements. 637 1947 Broadway, New Ynrk 23. N. Y. POWRMIKE is the perfect answer for voice amplification in stores, Bridger, Logarithmic amplifier, logarithmic volt- rooms, auctions, outdoor markets, sight seeing meter, intermndulatlon analyzer, artificial ears. carnivals, rallies, waiting heating aid test equipment, preamplifiers for buses and boats, school group activities, police and fire department condenser microphones, disc -noise meten, custom today. built audio measuring instruments. work, etc. Get the complete story on sensational POWRMIKE, IN ATTENDANCE: PC -66 For applications requiring portability. Includes: POWRMIKE C. J. LeBel MODEL - microphone wired to loudspeaker, "Hot- Shot" type battery mounting bracket with volume control, and automobile current adopter. Inc. BALLANTINE LABORATORIES, For mobile operation and special installations. POWRMIKE 622 MODEL PC -60 - automobile cigarette lighter adapter, supplied Boonton. New Jersey. microphone, loudspeaker, and Electronic Voltmeters unwired. IN ATTENDANCE: WRITE DEPT. B FOR ILLUSTRATED CATALOG Chas. L. Gawler Walter A. Knoop 411 Harry C. Gawler Allyn W. James BURLINGAME ASSOCIATES, Ltd. Agit1;74,7 647 -648 11 Park Place, New York 7, N. Y. Manufacturers' Representatives LOUDSPEAI(ERSOINC IN ATTENDANCE: 80 SO. KENSICO AVE., WHITE PLAINS, N. Y. B. O. Burlingame Robert Asen G. C. Engel Milton Lichtenstein POWRMIKES Charles Sargeant Famous World -Wide for LOUDSPEAKERS DRIVER UNITS TWEETERS PORTABLE

AUDIO ENGINEERING NOVEMBER, 1949 3I

www.americanradiohistory.com Audio Fair Exhibitor. for the I design plug -in pick -up first the J BROCINER SOUND LABORATORIES studio quality reproduction heads permit use for the first time 647 -648 of highest quality pickups as used (Burlingame Associates. Ltd., 11 Park Place. in an New York 7, N. Y.) automatic record by many broadcasters. Klipsch system loudspeakers changer for all types of rec- IN ATTENDANCE: Victor Brociner R. O. Burlingame ords: RCA Victor 7" 45 RPM, Columbia 7" LP. BRUSH DEVELOPMENT CO. 647 -648 (Burlingame Associates, Ltd.. 11 Park Place. Columbia 10" and 12" LP New York 7, N. Y.) "Sonndmirror" magnetic tape recorders 33% RPM, Standard 78 IN ATTENDANCE: RPM 10" and 12" rec- J. H. :1lunchausen B. O. Burlingame ords played auto- -all FRANK L CAPPS & Co., Inc. 636 matically. 244 W. 49th Street, New York 19. N. Y. Recording and reproducing styli, advance balls, shaving knives. IN ATTENDANCE: Controls are marked for simple selection, ae. Isabel M. Capps Wally Rose cording to type of records to be played. Records Sill Clifford Rom Marcucci may also be played manually. Quiet jam -proof Dick Marcucci Sal Gualtieri mechanism. Webster Chicago 356-27PS supplied with special matched pair type W Pickering car tridges balanced to give only 17 grams stylus CLOUGH -BRENGLE CO. 622 1060 Broad St.. pressure on standard records and 6.7 (Gawler -Knoop Company. grains on Newark 2, N. J.) LP Microgroove records. Special Pickering car. Sweep Frequency generators. tridges have built -in precision sapphire styli for IN ATTENDANCE: standard and microgroove records. s Chas L. Gawler Walter A. Knoop MATCHED CARTRIDGES 6 CKERING Price with cartridges, all hard- 2 1 Harry C. Gawler Allyn W. Janes trace and instructions NET COOK LABORATORIES 636 Webster Chicago 356.27 PD same as above with special matched pair 139 Gordon Blvd., Floral Park, N. Y. type W Pickering cartridges with Feedback recording heads. Q -C recording equip- equipped laboratory ground dia- ment, Aodioid synthetic damping. Series 10- mond styli for years of finest reproduction with record and 20,000 -cps frequency d. stylus wear Price IN ATTENDANCE: 356-27 G.E., same as above, with pair of General Electric variable Emory Cook Joe Kuhn reluctance cartridges equipped with sapphire styli Price Aboie changers operate on 105.120 colts 60 cycles AC. THE DAVEN COMPANY 616 Dimensions: Base plate 14" x 14 ". Height above main plate 5% ", below main plate 191 Central Ave., Newark, N. J. Attenuators, rotary selector 314". Note mounting size is sanie as older models 56. 156 and 256. potentiometers, switches, precision wire -wound fixed and variable resistors, transmission measuring sets, decade resistances. volume level indicators, and all types of test and measuring equipment. ?lead SCOTT DYNAURAL CONVERTER IN ATTENDANCE: Lewis Newman E. L. Grayson Model I I IA _ A dynamic noise asp. J. P. Smith, Jr. R. J. Newman pressor which effectively eliminates annoying C. F. Scott record scratch and .omble. For use with any amplifier or radia -phono ALLEN B. DuMONT LABORA- combination. Useful frequency range is 20 to 14,000 cede. Remote dynaral control for TORIES, Inc 622 adjusting degree of suppression. High impel. (Gawler -Knoop Company, 1060 Broad St.. input and output. Convenient plug adapter Newark 4. N. J.) lits s under 6%6, 616. 6F6, 6K6 or milar octal Cathode -ray oscillographe. voltage and time based tube for power takeoff. Tubes used are calibrators. 1 -- 6SQ7 and 2 - 6SG7. Sire: 7" W s 4%" H s IN ATTENDANCE: 33/4" D. Complete with tubes. remote control, cables, instructions. etc. Chas. L. Gawler Walter A. Knoop 295° Harry C. Gawler Allen W. Janes ELECTRIC INDICATOR CO. 649 .'-eagr High Fidelity Su per het Parker Avenue. Stamford, Conn. Electric motors and generators. AM Tuner 4'hassin IN ATTENDANCE: ForerM 330 -- 1700 KilorwrIes Ralph Kricker Joseph Marcus

Fit, anyplace - measures 4 v 4 v inches! Stable Alfred Debona rait with huihn A power supplyl insures fine performance without the difficulties often e treed with Inc. Ai: -1W tuners. Adjustable output s lip lto THE ELECTRONIC WORKSHOP, to soh. for ronnertion into phono or radio input 634 of an) standard amplifier. Tubes: 613E6. 66A6. 351 St.. New York 14, N. V. 6AT6. Bleecker 711'4. For operation on 115 volts 60 cycles High fidelity audio components and systems. AC. Supplied tested and aligned with 21/2 ft. control units, and instru- shielded cable and instructions. audio amplifiers and ments for audio or special applicati,.ns. IN ATTENDANCE: 1995Net Frank Ganci Leonard Sherry Howard T. Sterling Byron St. Clair Ben Bell Jan Syrjala Alan Sobel Alice Fee

ELECTRO- VOICE, Inc. 618 Buchanan, Michigan. RAO\O CORPORAt\ON Broadcast and public address microphones: crys- Distributors of Radio & Electronic tal magnetic, and ceramic phonogra,.h cart- Equipment ridges and arms: microphone stands. trans 85 CORTIANDT ST, -NEW YORK 7e N Phone -WOrth 4 -3311 Cable- TERMRADIO formers, and accessories. IN ATTENDANCE: Jack E. Willson A. R. Kahn

32 AUDIO ENGINEERING NOVEMBER, 1949

16. www.americanradiohistory.com Audio Fair Exhibitors

FAIRCHILD RECORDING EQUIPMENT CORPORATION 653 PICKERI IflOUUES TWO 154th St. and 7th Ave., Whitestone, 1.. 1., New York. Tape recorders, synchronous disk recorders synchronous transcription turntables, transcription pickup, magnetic playback cartridges, cutter - head, equalizers, amplifiers, VU panels, mixer B1WD NEW AUDIO panels, complete unitized amplifier systems. DEI WES Complete recording installations built to specifications. IN ATTENDANCE: A NEW ... A NEW RECORD Jay H. Quinn Avery Lockner PREAMPLIFIER Leon A. Wortman C. V. Kettering COMPENSATOR Wm. Hazlett for magnetic phonograph pickups and for all makes of records.

GAWLER -KNOOP COMPANY 622 The PICKERING model 130H PREAM- 1060 Broad Street, Newark 2, N. J. Manufacturen R ives. PLIFIER ... engineered to properly IN ATTENDANCE: equalize the bass response of records Chas. L. Gawler Walter A. Knoop and transcriptions and to provide the Harry C. Gawler Allyn W. Janes necessary gain for high quality magnetic pickups represents the GENERAL ELECTRIC COMPANY 619 ... Electronics Park, Syracuse, N. Y. most advanced design ever achieved Speakers, tone arms. pirk',ps, preamplifiers. in phonograph preamplifiers it is IN ATTENDANCE: ... unique and superior in its R. S. Fenton J. W. Duffield accuracy T. J. Nicholson of equalization . . . its intermodulation and harmonic distortion is JAMES B. LANSING SOUND, Inc. extremely low, better than most pro- ) 611 -612 fessional equipment ... it will operate THE PICKERING model 132E RECORD COM- 2439 Fletcher Drive, Los Angeles 26, Cali- fornia. with any high quality amplifier having PENSATOR ... developed to provide the Loudspeakers. a high impedance input is self - flexibility required to properly equalize for IN ATTENDANCE: ... powered, operates from the 115 volt the different recording characteristics used ti C. G, Barker John S. Boyers AC line and is installed by simply by various record manufacturers . . , is a plugging in. most important addition to any record play- H. J. LEAK & CO. LTD. 650 Brunel Road, Weatway Factory Estate, Ac- ing system using magnetic cartridges and ton, London W.3, England. an amplifier having a high gain preampli- "Point One" audio frequency amplifiers: Leak dynamic pickup: Leak "550" loudspeaker system fier with 6 db per octave rise below 500 IN ATTENDANCE: cycles per second ... it permits proper H. J. Leak, Esq., M. Brit I.R.E. compensation of the amplifier system for optimum record reproduction ... it permits LIVINGSTON ELECTRONIC CORP. getting the maximum out of each individual 646 record, scratched and worn Livingston, New Jersey. ones included Phonograph pickup arms, "MB" Loudness con- ... its six positions correctly equalize for trols, Stylus pressure gages. all of the established recording IN ATTENDANCE: characteristics including microgroove C. O. Smiley John Gardner and standard TECHNICAL SPECIFICATIONS records, domestic and foreign. Because all FREQUENCY RESPONSE: Within 2 from linear MAGNECESSORIES 609 db circuit elements are used it has no 20,000 cps. Box 6960, Washington 20. D. C. 40- Compensates for 6 db per inherent distortion. Carson Tape Splicer - Visi -Meg octave loss below 500 cps. OUTPUT: IN ATTENDANCE: High impedance, 2 volts average from SWITCH POSITIONS Robert H. Carson phonograph records. (For 500 /600 ohm output at -10 dbm use Pickering 600G 1. EUROPEAN RECORDS-This group covers MAGNECORD, transformer, available as accessory equip- HMV, DECCA FFRR, TELEFUNKEN, etc., and Inc, 611 -612 ment.) DISTORTION: Not more than 0.2% 360 N. Michigan Blvd., Chicago 1, III. American pressings of European record- Tape recording equipment. intermodulation at normal output level. ings. VICTOR IN ATTENDANCE: Not more than 0.4% intermodulation at 2. 45-For all 45 RPM rec- C. G. Barker John S. Boyers 10 db over normal level. Not more than ords. 3. VICTOR 78-For 78 RPM records, 1.7% intermodulation at ; 20db over nor- 500 cycle turnover. 4. COLUMBIA -CAPITOL mal level HUM LEVEL: -56 db below J. A. MAURER, Inc. 631 maximum signal. -This position is for most domestic 1 INSTALLATl(N: Unit rec- 37 -01 31st Street, Long Island City 1, N. Y. furnished with 6 ft. approved cord which Maurer 16 -mm professional motion picture ords, including Decca, MGM, etc. 5. MICRO- cameras. Magrer 16 -mm sound -on -film recording can be connected to wall socket or ampli- system. Maurer t6 -mm film rhonograph. fier. Input socket -standard type; matching GROOVE LP -For all makes of 331/2 RPM IN ATTENDANCE: plug furnished with unit. Output-terminal microgroove recordings. 6. NOISY RECORDS L. A. Root strip. Rubber shock mounts provided. -This position permits playing Of Old, DIMENSION, TUBES AND WEIGHT: Size of preamplifier: noisy records with objectionable hiss McINTOSH ENGINEERING 81 /2 inches long. 51/2 inches deep and 41/2 inches high. Tubes: 6SJ7, removed. LABORATORY -612 611 615, 6X5 (any good, standard brand). 710 14th St., N. W., Washington 5, D. C. Amplifiers. Weight 2 lbs. 10 oz. IN ATTENDANCE: Frank McIntosh PICKERING CARTRIDGES AND AUDIO EQUIPMENT THE MIGEL DISTRIBUTING CORP. ARE AVAILABLE THROUGH LEADING JOBBERS 601 AND DIS- 118 East 25th Street. New York 10, N. Y. TRIBUTORS EVERYWHERE. The Betsey Portable Microfilmer and Reader. IN ATTENDANCE: Morton R. Shapley John Migel Ralph DeSola William Nichols Oceanside, Long Island, N. Y.

AUDIO ENGINEERING NOVEMBER, 1949 33

www.americanradiohistory.com ,tudio Fair Eóibitor% Recording and Transcription Amplifiers by THE MINNESOTA ELECTRONICS REK -O -KUT CORP. 622 (Gawler -Knoop Company, 1060 Broad St. Newark 2. N. J.) Amplifiers, filters, Noiserasers. IN ATTENDANCE: Compare Compare J. H. Munchausen

for for NEWARK ELECTRIC CO., Inc, 662 242 W. 55th St.. New York 19, N. Y. Wharfdale speakers, Du Mont scopes for audio measurements, Audledisca, Audiotape. Altec- Quality Value Lansing sound equipment, Daven attenuator pads. IN ATTENDANCE: Herman Holstein Samuel Weisbroth

PANORAMIC RADIO PRODUCTS Illustrated: R -8A in case Inc. 626 10 South Second Ave.. Mount Vernon. N. Y. Panadaptor, Panalyzor. Panoramic Sonic Ana- R -8A SPECIFICATIONS R-5A SPECIFICATIONS lyzer, Panoramic Ultrasonic Analyzer. (Powers Rek -O -Kut "Challenge," Deluxe) (Powers Rek -O -Kut "Challenger" Standard) IN ATTENDANCE: Frequency Response: !'1 db from 30 to 20,000 cycles at normal setting of equalizer con- Frequency Response: ±1 db from 50 to 15.000 Bernard Schlessel Joseph F. McClean trols. cycles at normal setting of equalizer con- Ben H. Tongue Ralph Segel Power Output: 13.5 watts at less than 3% trols total distortion. Power Output: 12 watts at less than 8% Input Channels: Four: 2 high impedance mic- total distortion. PEERLESS ELECTRICAL rophones, phono channel compensated for Input Channels: Three: high impedance mic- PRODUCTS 625 rophone. high impedance phono -up DIVISION G.E. or Pickering -up, radio. pick I pick and Altec- Lansing Corporation) Gain: Microphones: 120 db; Phono: 90 db; radio. 161 Sixth Avenue. New York 13, N. Y. Radio: 80 db. Gain: Microphone: 125 db; Phono: 76 db; Power transformers. filter chokes. input, inter - Output Impedance: 4, 8, 15 or 500 ohms. Radio: 76 db. stage. output. modulation, and replacement Hum and Noise: 64 db below 13.5 watts with Output Impedance: 4, 8. 15 or 600 ohms. transformers. "A transformer for every Radio all controls turned for maximum hum and Hum and Noise: 64 db below recording level. application." noise output. Tubes: (I) 6SJ7; (2) 6SL4: (2) 6V6GT; IN ATTENDANCE: Tubes: (2) 6SJ7; (2) 6SL7; (1) 6SC7; (2) 11 5Y3GT. H. S. Morris Dave Sonkin 6V6: (I1 5Y3. RACK MOUNT PRICE, $89.95 net Mel Sprinkle Marty Wolf RACK MOUNT PRICE, $129.95 net including tubes, on-ludo ng tubes) CASE OPTIONAL 517.95 PERMOFLUX CORPORATION 641 SFR IS AT THE äl'1)1(1 FAIR. ROOM 632. 4900 West Grand Ave., Chicago 39, Dl. Speakers. baffles. heado hones. microphones. REK -O -KUT COMPANY, INC. tape recorders and amplifiers. 38 -01 QUEENS BLVD., LONG ISLAND CITY, N. Y. IN ATTENDANCE: L. M. Heineman T. Trzyna C. C. Fisher

PICKERING AND COMPANY, Inc. 624 "Wow-Meter 309 Woods Avenue, Oceanside, N. Y. Phonograph pickups: pre-amplifiers; equalizers: amplifiers; audio equipment; solenoids: tree - formers: magnetic devices; l -M distortion measuring instruments. IN ATTENDANCE: Walter O. Stanton Norman C. Pickering

PRESTO RECORDING CORP. 623 (Mail) P.O. Box 500, Hackensack, N. .J (Plant) Paramus, New Jersey. Recording and transcription turntables, studio and portable tape recorders. recording amplifiers. IN ATTENDANCE: Thomas B. Aldrich Irving Rosenblatt Fred Jorysz John Strampfer

PRESTOSEAL MANUFACTURING CO. 647 -648 (Burlingame Associates, Ltd.. 11 Park Place New York 7, N. Y. Magnetic tape (plastic) splicers, film splicers. IN ATTENDANCE: Leonard Herzig

Newly developed direct- reading instru- The Furst Model I I 5-R "Wow- Meter" is ment simplifies measurements of wow and suitable for both laboratory and produc- PROCTOR SOUNDEX CORP. 639 133 N. Sixth St., Mt. Vernon, New York. flutter in speed of phonograph turn- tion application and eliminates complex Turntables and pickup arms; audio sound equip - tables, wire recorders, motion picture test set-ups. ment. IN ATTENDANCE: projectors and similar recording or A switch on the front of the panel reproducing mechanisms. It is the only permits selection of low frequency B. A. Proctor J. J. McCann meter in existence giving direct steady cut -off and corresponding meter damp- B. A. Proctor, Jr. Emil B. Kurkowski indication of meter pointer on scale. ing for use on slow speed turntables. M. A. Peckham

Frequency Response: 1/2 to 120 cycles or 10 to 120 cycles RACON ELECTRIC CO., Inc. 617 Inquiries Invited on our line of 52 E. 19th St.. New York 3, N. Y. Po.. "r Surn'r_ Loudspeakers for public address systems. re- entrant trumpets, driver units. pacing speakers, marins speakers, tweeters. FURST ELECTRONICS. IN ATTENDANCE: A. I. Abrahams 16 S. Jefferson St., Chicago 6, III. Edward Maged

34 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com Audio Fair L%IIillitur

RADIO CORPORATION OF AMERICA 632 -633 Camden and Harrison. New Jersey. SEND NOW FOR HELPFUL Tubes, Sound Products and Broadcast Audio Equipment as follows: Rack-Mounted Tape Re- corders, 70 -D turntable with 45 rpm modifies. Bon, LCIA speakers, and microphones. IN ATTENDANCE: W. O. Hadlock Julius Haber Harold Becker A. R. Hopkins Industrial & General Purposé C. M. Lewis E. Miller J. E Hill M. A. Trainer W. T. Babcock H. W. Rhodes A. K. Ward A. Lof H. C. Elwes H. C. Somerville R. von de Linde Kenneth Shaffer Lawrence Le Kashman Nick Carter Catalog o -20A

RANGERTONE, Inc. 621 73 Winthrop St., Newark 4, N. J. Magnetic tape recorders and magnetic recording. IN ATTENDANCE: R. H. Ranger F. Whitehouse ives S. L. Ackerman P. Brubaker Valuabl A. Colabella Data on Wide RECOGRAM RECORDERS CO. 610 Variety 11338 Burbank Blvd.. North Hollywood, Calif. of Magnagram magnetic film recorder; Centogrip Relays splicers. Carried IN ATTENDANCE: in Stock D. J. White Wm. H. Stutz for Immediate REK -O -KUT COMPANY, Inc. 652 38 -01 Queens Blvd., Long Island City 1. N. Y. Shipment Cutting units. transcription turntables, recording mechanisms, playback units, recording amplifiers. IN ATTENDANCE: George Silber Frank Scannell Sydney Simonson

SOMERSET LABORATORIES, Inc. 628 1701 Palisade Ave., Union City, New Jersey. Amplifier, dynamic noise suppressor preampli- fier. IN ATTENDANCE: Carl E. Ring James Evans John T. Loomis Besse Auerbach

SONAR RADIO CORPORATION 644 59 Myrtle Ave., Brooklyn, N. Y. Tape recorders: amateur equipment. IN ATTENDANCE: Jack Babkes Ray Morehouse Edward A. Babkes Adolph Schwartz John Yinaga Jos, Abrams This is the book for busy men! This is the book with hundreds of economical answers to STANCIL -HOFFMAN CORP. 645 1016 N. Highland Ave., Hollywood 38, Calif. quick relay needs! This is the book you'll turn to when time Stancil- Hoffman magnetic transcription B- ers and reproducers, magnetic communications means money! It's your handy guide to WL light-duty recorders, the "Minitspe" miniature magnetic recorder, the Elken automatic tape splicer. and heavy -duty stock relays for control of radio and IN ATTENDANCE: Henry J. Geist and Associates electronic devices, electrical equipment and appliances. Puts factual data and useful information at your finger-tips. STEPHENS MANUFACTURING WRITE TODAY FOR YOUR CATALOG D -20A CORPORATION 620 8538 Warner Drive, Culver City. California. Loudspeakers and Microphones. Electronic Distributor Division IN ATTENDANCE: Robert Lee Stephens Art Cerf Ward Leonard Electric Co., 53 R West Jackson Blvd., Chicago 4, U. S. A. Henry Hold Dick Mittl

SUN RADIO & ELECTRONICS CO., Inc. 640 122 Duane St., New York 4, N. Y. Distributor of sound products. WARD LEONARD IN ATTENDANCE: Samuel N. Gerard Irving Green RELAYS RESISTORS RHEOSTATS CONTROL DEVICES Sy Bosworth Joseph Greenfield Burt Zimit Al Goldberg Walt Zuckerman Lionel Phillips WHERE BASIC DESIGNS ARE RESULT- ENGINEERED FOR YOU Sanford Herman Bob Smith

AUDIO ENGINEERING NOVEMBER, 1949 35

www.americanradiohistory.com Audio Fair Exhibitors For the First Time . - - TECH LABORATORIES, Inc. 638 "ON STAGE" REALISM Bergen & Edsall Blvd. Palisades Park. N. .1. Attenuators, potentiometers, tap switches, fixed OF BOTH HIGHS pads, matching pads, gain sets, viscosity meters, resistance measuring equipment. IN ATTENDANCE: AND LOWS \f. Bjorndal A. L. Budd G. Van Baaren Speaberd 6E UNIVERSITY LOUDSPEAKERS, Inc. 643 80 S. Kensico Ave., White Plains, N. Y. BOZAK Commercial and industrial loudspeakers, driver units. tweeters and accessory equipment, Powrmike systems. New tone values, never before avail- IN ATTENDANCE: able to the critical listener, are now Seymour Blumenfeld Irving Golin distributed the Saul White Lawrence Epstein over entire area of mu- Haskell Blair sic's most useful frequency range. From robust basses to clear, non -piercing U. S. RECORDING CO. 611 -612 highs, richness is the keynote of loud- 1121 Vermont Ave., N.W., Washington 6, D.C. speakers by Bozak -the gratifying re- Consolette. IN ATTENDANCE: sult of over 10 years' skilled development. H. P. Meisinger PLUG-IN WITH RECORD REVUE [from page 26]

most every engineer uses magnetics as a matter of course for this reason. But how about the many LP's that don't come through well via the magnetic treatment? Well, they do come through via the crystal. ... be assured of "good connections." Which leads on to a bit more. It is at That's why television stations, for in- once evident to me in listening to - stance, use Cannon Electric Type K, P, WOOFER: Dr. Gold mark's office machine a and other series for cameras, micro- Model B -199 that there is decided difference in tonal balance between what he phones and transmission equipment Twelve -inch unit specially developed for is getting and what I am accustomed to as that must not fail. Shown above is a low resonance. Not only are low frequency the average sound from engineers' equip- camera at KTLA- Hollywood. tones distinctly but have the audible, they ment. The seem rich fullness of true orchestral bass. Unique highs far less pronounced Cannon Plugs are available through Bnaak cone eliminates "drumhead" charte- -so much so that at first my impression a network of radio parts dealers all over ter.atic common to many woofers. Response: was the "tone control" effect of severe roll - 40 -3500 cycles; Rating: 12 watts; 22 oz. the U. S. A. Buy them from Seattle Alnico V permanent magnet using special off, until, after a bit, I begin to hear the Radio Supply in Seattle; Cooper Sound low carbon cast pole pieces. $52.60 list. triangles and what -not that indicate the Equipment in Cincinnati; Radio Inc., presence of high highs. I am sure that most in Oklahoma City; Van Sickle Radio in engineers, reacting earwise, would be struck St. Louis; Offenbach -Reimus in San Fran- at once, as I am, by this seeming lack of cisco; and over 400 other distributors. highs. Aha! Of course you don't hear any distortion; you can kill any distortion if you roll down those highs enough, you are saying. Just a moment. Who said they were rolled off? To the best of my knowledge the CBS player and the RCA amplifier are equalized to match the LP record's curve. DUAL There is no extra roll -off. TWEETER: Then what....? Well, one conclusion I Model B -200 am forced to, in the face of this, is that most engineers are not equalizing their High tones, brought out with new degree of realism, now made acceptable to the ear by equipment to match the LP curve. Tin ears Bozak system of rubber damping. Direct ra- -we all have 'em. I begin to suspect that diated highs dispersed over wide angle. Clean. smooth response makes high frequency listen- most engineers have been listening to hi.fi ing a pleasure. No distorted, piercing tones. equipment for so long that the stuff has Response: 1500-beyond 13,000: Cones : 2 VI" crept up on 'em. Equalize dia. with aluminum alloy apex; Coverage: correctly and it 120 deg. at 10 kc., 100 deg. at 13 kc; Rating sounds dull, so quick boost up those highs 5 watts: 7 oz. Alnico V permanent magnets. and get some real hi -fi! We all know the DESK SIZE CHARTS -FREE $27.50 list. (Patents pending). notorious love of J. Q. Public for the exag- Two desk charts of Type "AN" and "K" insert shown half scale are available on gerated juke -box arrangements These speakers require only 4 mid. capacitor type of bass: hadn't we request. Address Catalog Dept. K -109 at factory, lot crossover. better look at that beam in our own little Development Company. Division eye and check up on highs? Cannon Electric our of Cannon Manufacturing Corporation. 3209 Hum- See your distributor or write If you don't agree, then you explain it. boldt St., Los Angeles 31, California. Canadian Because I have one final argument that may factory: Toronto. World Export: Frezer &Hanson. San Francisco, New York, Los Angeles. H. T. BOZAK clinch this last, and that is an ingenious 1.NO 1111 DESIGNER 8 MANUFACTURER new crystal soon to be put out by Columbia and Astatic, of which I have an early 90 Montrose Ave. Buffalo 14, N. Y. ßL.1G7G70C] 0110ß4a0ß sample. It embodies a new e slant to the

36 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com problem of equalization, for this is a "pre - equalized" crystal which has been doctored FAIRCHILD up to match in itself the curve of the Colum- WHY CHOOSE bia LP record almost exactly, and that to beyond 10,000. (It is housed in the same PERFORMANCE case as the just-available model CQ -J, now FOR TOP being used in the stew Columbia player, but Each month you read equipment spec- differs internally and will go by another ifications in the advertising pages of code name, C -AC.) your favorite magazines. Specifications often to in- Now here is a crystal pickup that is a are fine things, but difficult terpret in terms of what the equipment natural for experiment. No equalization at will do for you. For example, suppose is a all; it designed to be fed directly into we say that Fairchild Disk Recorders flat amplifier. When so fed, it gives auto- and Transcription Turntables have a matically the curve required to reproduce time accuracy of 1 part in 4.6 x l0'' the LP record. And this on the authority of at 33V3 rpm; an instantaneous speed the designer of both. deviation of .075 %; a noise level of such and such decibels below some stylus What happens when it is put to work? velocity at so many cps. Impressive? (1) The music comes out sounding like the Sure. And factual, too. But what you sound I have heard in Dr. Goldmark's office. want to know is . . . what effect do A bit "rolled off" on the high end. You may these specs have on your operations. point your own moral for that. My own What is the performance, after the specifications are paid for? Here are the conclusion, again, is that a lot of us have Turntable Drive. Recording and Play- Precision been overindulging in highs. What sounded data on Fairchild Used in all Fairchild Disk Equipment. back equipment, in facts and effects. to me on the dull side sounded to others quite natural and brilliant. (2) The records FEATURE FAIRCHILD EQUIPMENT OTHER DESIGNS that have been buzzing away merrily these many months on my magnetic again pickups Type of Drive Direct to center-gear. Rim drive -puck or pulley. come out definitely minus the buzz, or what- and ever other name the unpleasantness can be Resultant Speed Absolute synchronism for Usual accuracy-6 seconds given. This crystal, automatically equalized, Regulation use with soundonhlm and in 20 minute play period on the nose programming. (.5 % speed regulation). acts as does the original LP crystal, the Accurate within .00026 sec. Does not permit rigid syn. chronization nor on the LP-33. In some unexplained manner it onds in 20 minute play period at 331/3 rpm. nose programming. "matches" the LP record better than existing magnetics. Records that sound distorted Possible time ± .000s2 seconds ± 52 seconds (based on on the magnetic come clean on this. What error- record above) and playback have these crystals got that avoids the trou- (20 minute disk) ble which crops up in the magnetics? It is .tzs % possible that the difference is not electrical. Instantaneous less than .ojs % approximately speed deviation Keep in mind that this new crystal is equal- and Wow usually evident at ized definitely to the LP curve up to 10,000 Effect on aud- None ible signal this figure and continues on out "to 12,000." limited by Could there be some subtle mechanical Noise and Rumble Experienced users of Fair. Dynamic range child Equipment claim dy noise and rumble when factor or factors that have been overlooked namic range of 6z db. wide tolerances are permit- in the designing of the magnetic LP car- ted in machining. tridges and in the setting up arm -and- of Control of cutting Studio model: turn knob Portable and Studio mod - cartridge combinations? It is notable that pitch (lines per for conrinuoua and inaraa els: disassemble lathe mech. anism -change feed screw whereas Inch) ¡garoso pitch change from engineers using magnetic LP car- So to over soo lines per -reassemble lathe mechan. tridges invariably use the long and bulky inch. Can be varied at will ism. Or, change pulley during the recording. ratios. professional -type arms, CBS crystal LP- Portable model: Insert playing equipment just as invariably em- small gear -no disassembly required -only one feed ploys smaller and shorter arms. The de- screw for all pitches. mands of home players could not, I'd say, entirely account for this. It is already Overhead cutter Secured as integral part of Lift or swing into position. assembly turntable deck. Always in Possibility of cutter mis- obvious enough to me that there is a lot positive alignment. alignment-causing varying depth of cut and incorrect more tracking trouble - with the fancy long groove shape. arm set -ups than with the very short and light arms used for crystals. Passages that Portable model Actually a console model Sacrifices in mechanical de- portability not track in a portable case. Same sign to gain will on an expensive long arm performance on location as further exaggerate inferior (blame the record!) will track with no in the studio. performance. trouble at all on the Asiatic FL short arm. Maintenance Periodic lubrication of Lubrication, and frequent These are factors. What else? I leave that drive mechanism. Always replacement of puck and to you to suggest, since I am fast getting at peak performance -no pulleys. Continued adjust - headache for the owner and ment necessary to keep out of my depth in this area. operator. speed of turntable up to specifications. c

So there you have it -as fine an example Fairchild specializes in LIP SYNCHRONOUS recording and playback equip- of inconclusive writing as this magazine has ment for SOUND -ON -FILM, TV PRODUCTIONS, and all such installations so far sported. My conclusion is mainly requiring laboratory' standard performance. Write for full details. that there are things that need explaining, and my intention is to stir up comment and perhaps argument so that in the end they will be explained to everyone's satisfaction. I want to know what causes the unpleasant distortions I have heard from magnetic LP pickups. I want to know why a few LP's are astonishingly free from them, played on identical equipment -especially since CBS 154TH ST. AND 7TH AVE. WHITESTONE, L. I., N. T.

AUDIO ENGINEERING NOVEMBER, 1949 37

www.americanradiohistory.com is not admitting any difference between those that sound good to me and those that FEEDBACK CUTTERS don't. I want to know why the CBS- designed crystal LP cartridges do not show up this The 5 -B distortion, why the LP records seem so much less temperamental as played thus crystal - priced without a Competitively but wise. Just what has CBS got there, and why competitor in its field. can't the magnetics do the same? The 5 -B uses the full feedback cir- Comments of any sort are invited from cuit of the larger model. Interested parties, especially accounts of It is capable of tremendous output your experiences with LP's and your expla- level. nation of same, all in the interest of good, Completely stable clean fun. We all, naturally, beg the in- Maintenance free dulgence of Columbia Records, Inc., as the largest producer of the LP type of disc only $46500 net and hence automatically the butt of our inquiry. Since Complete with cutter in these matters Columbia, advocating crystal, seems to stand against many professionals who advocate magnetic, The 3 -B I suggest you experiment with the new cr stals yourself. Approved cartridges to For the highest possible quality re- date are the LP -33, now being withdrawn, gardless of price with response - and its successor the model U -J; the small through 20,000 cycles. Cross -mo- standard -mounting CQ -J, just now becoming dulation under I% all the way to available; the C -AC, to come later, all de- 20,000 cycles. For those who can't signed under CBS supervision. Other crys- afford to fool around with quality. tals may or may not give comparable results. LP records that are strikingly free of the Write or wire for detailed buzzy -style distortion -at least as I hear 'em information on magnetic cartridges -are:

Beethoven, Symphony #1 (Bruno Walter t $115000 net Rimsky- Korsakov, "Scheherezade." Enesco, Roumanian Rhapsody #L COMPLETE } Hindemith, Metamorphoses on Themes of Weber. Saint -Saens, Symphony #3, with Organ. COOK LABORATORIES 139 Gordon Blvd. Floral Pork, N. Y. Walton- Sitwell, "Facade." As for me-I'm playing my LP's on magnetics, at home. But my FM -AM New York broadcast of LP's weekly will be done ex- Model S -20 clusively via crystals. Fair test. 20 watts Schubert, "Trout" Quintet in A, opus 114 20 - 20,000 cycles Franz Rupp, piano; Stross Quartet. I% distortion Capitol EDL Loudness control 8019 (4) Individual bass and This recording, on 78 and 45 but not so treble controls far scheduled for LP. is not only one of the Variable treble cutoff most delightful of all Schubert's instrumen- for phonograph noise tal works, but it happens to be an excellent reduction test recording for the bass range, since the quintet of instruments is one of the very $99.95 net few in all classical literature (maybe it's the only one ?) that includes a string bass See them at the Audio Fair, Room 635, or ask your local dealer. or "double- bass." The instrumentation is for piano, violin, viola, cello and bass. The Model P -3 Model C -3 Control Unit bass here serves just as it does in a small Preamplifier jazz ensemble, to put body and depth into 40 db gain the music, to hit off the rhythm and the Supplied for flat re- harmony, almost drum -wise. It is beauti- sponse or phono equali- fully recorded, close -to and loud but never zation 20 db bass 8 treble controls too loud. On a table phonograph it is com- Loudness control pletely inaudible (the overtone that ordinar- Insertion $14.95 net Loss 20 db ily give us a sense of bass are here rather $14.95 net weak, and the notes are mostly too short THE ELECTRONIC WORKSHOP, Inc. for very much to register, anyway) but play these 351 Bleeker Street WA 4 -6530 New York 14. N. Y. records with an extended range outfit and presto -the double -bass practically stands right up in front of you. A very nice Subscribers to AUDIO ENGINEERING should notify our check on low- frequency resonances, since this massive instrument .AddreJ.3 Circulation Dept. at least 5 weeks in advance regarding plays its way all any change in address. The Post Office Dept. does not over the lower tonal range and with con- forward magazines sent to a wrong address unless you siderable power, at that. % pay additional postage. We can not duplicate copies Schubert has a very special piano tech- C! a Jes . . . sent to your old address. Old and new addresses MUST nique that he used when that instrument be given. was playing "ensemble" is, playing AUDIO ENGINEERING -that along with other instruments: he writes 342 Madison Ave. New York 17, N. Y. high ,ataves near the extreme top end of the

38 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com keyboard, and the sound is almost like a xylophone or marimba, a sort of bell-like melodic line. In the "Trout" Quintet this highly ornamental piano writing is set off °,e!lJt4°0/ BY TURNER particularly nicely by the fat and tubby sound of the double bass at the other frequency extreme. The title is explained by the 4th movement, a set of variations on the melody of one of Schubert's best known songs. "the Trout." O N SNE "ES Stravinsky. Concerto for Two Pianos Vronsky and Rabin, duo- pianists. Columbia MM 837 13) LP. ML 157 MODERATELY PRICED Stravinsky, Suite Italienne ('Pulcinella ") Raya Carbousova. cello; Erich Itor Kahn, piano. Concert Hall C5 (2) OQENO Two interesting Stravinsky items. The NJ\0N1/ concerto is a major work and a difficult one for two pianos alone minus orchestra. It was issued last year in a Vox recording by HIGH Appelton and Field t with "program notes" by Canby) ; now it gets its second trial, on LP as well as 78, with another team (and Columbia has done me the honor of "borrow- ing" the substance of the Vox program notes for its description. Both versions are mira- RESPONSE WIDE RANGE cles of piano teamwork, for this is an incred- ibly difficult work, written as though the two instruments were one, the players a single lour- handed superman. Both are flawless in the performance and convincingly tremendous in massive effect. But I like the Appleton -Field version better. It seems to me warmer, more musical, better phrased, and I think the music comes through in more easily digestible form, too. The advantages of LP, however, weigh on the other TURNER side. Both recordings are models of what two -piano recording can be, the Vox version MODEL 25X -25D a bit erratic but fundamentally excellent, the Columbia sharper and more "pingy" in CRYSTAL OR DYNAMIC the percussive passages, smoother in the L over -all. If you like big, dissonant, brilliant piano noises and you have a big outfit that will take all you can feed it, maybe this PRACTICAL FOR ALL SOUND APPLICATIONS concerto wouldn't be such a bad bet. Worth a try. It's potent music. If you need a microphone for studio or record- The "Pulcinella" suite is a strange and 25X CRYSTAL system, public address, or amateur 52 db below 1 volt /dyne /sq.cm. interesting hybrid. The original was for ing work, call want a Model Flat from 50 -9,000 c.p.s. orchestra (1920), music for a ballet. The communications -you Turner List price $27 50 stuff has not one but two composers, nor 25X -25D. It's an all around unit for all around performance. You'll praise its smooth, wide do I mean one composer and one arranger. 25D DYNAMIC The ballet music was written by Stravinsky range response and high output level. And head and 54 db below 1 volt dyne /sq.cm. "after" Pergolesi (the brilliant young Italian you'll like the full 90 degree tilting at high impedance in composer of the early 1700's who wrote the convenient removable cable set. Finished Flat from 50- 10,000 c.p.s. famed Stabat Mater and the operetta "La two tone umber gray with chrome plated grill 30, 200, 500 ohms-wired for bal. Serva Padrone'), by which Stravinsky means or bright chrome at slight additional cost. onced line that he wrote new and original music of his Turner Engineers went all out in designing the List price $40.00 own that incorporated actual thematic mate- 25X -25D. See it at your dealer. High impedance -wired single rial of Pergolesi and, even more, the "feel- ended List price $40 00 ing" of the older music. It may he hard to Write for Complete Microphone literature figure this one out, but I can only suggest All models in brill- chrome finish at ardltioral. per- THE TURNER COMPANY $2.50 List that, for an engineer, this is equivalent Push -to -talk sw tch, $2.5) List additional. haps to the creation of a new electronic 929 17th Street N.E. Cedar Rapids, Iowa circuit in which certain basic and character- EXPORT istic elements an older one are made IN CANADA from Canadian Marconi Co., Ltd. Ad. Auriema, Inc. use of and given due credit. Engineers of Montreal, P. O., and branche. 89 Brood St., New York 4, N. Y. course do it all the time, and so do musicians, but most musicians aren't as definite about it as Stravinsky, who has also written Licensed under U.S. patents of the American Telephone and Tida- a ballet "after" Tchaikowsky. In such cases, 1 graph Company, and Western Electric Company, Incorporated. as might be expected, one hears some of _ Crystals licensed under patents of the Brush Development Company. each composer-and if you think the mix- AUDIO ENGINEERING NOVEMBER, 1949 39

www.americanradiohistory.com ALIlO ENGINEERING

Jhe Per/ed otet

All surveys prove that AUDIO ENGINEERING is preferred over all other technical magazines read by the best informed in the audio field, the broadcast, sound and reproducing engineers. Each issue brings you outstanding articles on five or more of the following subjects:

Broadcasting Public Address

Sound on Film Industrial sound equipment and applications

Recording Acoustic treatment of studios, rooms, auditoriums, etc.

Phono Reproduction

In addition, each month, AUDIO ENGINEERING presents latest improvements in sound reproducing equipment design, test methods, and technical news from here and abroad. The Editorial Staff includes top authorities in the sound field.

AUDIO ENGINEERING, the one and only publication devoted exclusively to the SOUND FIELD, has, since its in- ception in 1947, been acclaimed by its thousands of readers as well as the entire Audio Industry for its constantly superior editorial content. The standard of excellence set for feature articles and all departments will be more than maintained for 1950. A1' 1/ 10 ENGINEERING

l'i,i,sh,i RADIO MAGAZINES_ INC. 342 MADISON AVENUE

NEW YORK 17, N. Y.

40 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com ture of Stravinsky and Tchaikowsky sounds incredible (or S- Pergolesit, just listen to it. It works! (P.S. -See last month's review of Hindemith's 'Metamorphosis on Themes of Carl Maria von Weber" -same kind of AMPERITE thing -and note the unexpected results of the mixture of Hindemith and the early Studio Microphones 19th century Weber.) Brahms, Serenade #I in D, opus II at P.A. Prices Concert Hall Society Orchestra, Swoboda. Concert Hall C4 (4) If it didn't make good reading there Ideal for BROADCASTING wouldn't be much point in reviewing this RECORDING for engineers, since it is available only to subscribers for the Limited Edition. Still, PUBLIC ADDRESS it's well for all of us to know what's going "The ultimate in microphone quality," says Evan on, if only second -hand. This recording is Rushing, sound engineer of the Hotel New Yorker. for me the answer to a fifteen years' wish. For that long I've had a single record of two Shout right into the new Amperite short movements from this rarely heard work Microphone -or stand 2 feet away - and have wished all that time, some day. reproduction is always perfect. to hear the rest of it. This is its first com- V Models The only type microphone that is not plete recording as far as I know, and why RBLG -200 ohms it isn't played more I by any climatic conditions. often cannot say, for affected RBHG -Hi -imp. it you like Brahms at all, this is bound to Guaranteed to withstand more "knock- List $42.00 please. It's a very early work, and, as such. @= type mike. a product of genius, without question. The ing around" than any other 3 rich combination here of horns, woodwinds Special Write Special Introductory Offer,'.%; and strings is orchestra -like. yet with the for fullness and nearness of a smaller group of Offer: and 4 -page illustrated folder. t. virtuoso soloists; the music is equally rich, i¡.'+.r .., 1"ti L. ?RFcrr:...'%.:. harmonically and melodically. Recording is r 70'_' ! . excellent and on good vinylite. Concert "Kontak" Mikes Hall's usual (apparent high turnover, big AMPERITE Gmpany Model SKH, list $12.00 pre -emphasis in the highs. If you ever have Inc. access to it, try the third movement or 561 BROADWAY NEW YORK 12, N. Y. Model KKH, list $18.00 the last. In Canada: Atlas Radio Corp., Ltd., 560 King St. W., Torotto Haydn, Symphony #94 ( "Surprise ") Berlin Philharmonic, Schmidt-Isserfeldt. Capitol ECL 8021 (3) LP: P 8038 - This is perhaps the most familiar of all Haydn symphonies, but there has never been a performance like this one on records. Haydn is the so- called "father of the sym- FM SIGNAL phony"-by which is meant that this benign and wonderful man, one of the simple,' and yet most profound minds in all of mu-e GENERATOR developed a type of musk for a considerable ensemble of players from earlier styles that MODEL 202 -B involved music for solo players with an occasional background framework for larger FREQUENCY RANGE groups. "Considerable," however, indicates not the huge 100 -piece symphony orchestra 54 to 216 MEGACYCLES of later days, but a group of about 30 or 40 players at the most -plenty to make a big The model 202 -B is specifically designed noise in a small hall for selected audiences. to meet the needs of television and FM Most performances of Haydn today are done engineers working in the frequency range with a much larger orchestra and in a heavy- from 54 -216 mc. Following are some of the weight style. borrowed from later music, outstanding features of this instrument: that only succeeds in making Haydn sound RF RANGES -54 -108, 108-216 mc. 0.5% ac- rute and silly. Especially on records, where curacy. Also covers 0.1 mc. to 25 mc. with accessory 203 -B Univerter. as any engineer knows the bigger an orches- VERNIER DIAL - 24:1 gear ratio with main fre- tra is, the muddier the general effect, with- quency dial. out of course the slightest gain in volume, FREQUENCY DEVIATION RANGES-0-24 kc., since volume nowadays 0 -80 kc., 0 -240 kc. is a function of Conti ly veri- AMPLITUDE MODULATION - RF VOLTAGE 0.2 volt to 0.1 micro- 50% OUTPUT - electrical "level," not of instrument power. able 0-50 %; calibrated of 30% and volt. Output impedance 26.5 ohms. points. Moreover, because of the physical charac- FM DISTORTION -Less than 2% at 75 kc deviation. MODULATING OSCILLATOR -Eight internal mod- teristics of musical instruments, a large ulating frequencies from 50 cycles to 15 kc. SPURIOUS RI. OUTPUT-All spurious RF voltages orchestra has an utterly different balance Available for FM or AM. 30 db or more below fundamental. from a small one. Strings can play together writ. for Catalog G -2 in large groups. hence your big orchestra has many more strings than your small one. DESIGNERS AND MANUFACTURER] OF But woodwinds, flutes, oboes, etc. do not THE O METER . OX CHECKER BOONTO '`RADIO FIFOUENCY MODULATED SIGNAL GENERATOR blend well and must remain pretty much BENI FREQUENCY GENERATOR solo instruments. Hence. in the larger BOONTONN-JUSA UiC/[QLCl/%( AND OTHER DIRECT READING INSTRIMENWS orchestra they are far weaker in proportion

AUDIO ENGINEERING NOVEMBER, 1949 41

www.americanradiohistory.com to the strings. Later writers, taking this into account, fix their music to match. But when Haydn (and Mozart) are played as ELINCO OFFERS written but with an over -sized orchestra, the woodwinds are lost in a huge mass of Specialliy -$ ed i.sed string tone, the balance thrown off. The larger mass of strings, too, simply cannot play the rapid, clean-cut notes originally designed for a small, close-working group of string players. The Berlin Philharmonic recording of the "Surprise" is done with a small orchestra, MOTORS and the players are almost soloists, as it should be. Nor is there any striving for "big" effects, no cuteness; the music is played accurately and seriously, and you'll FOR AUDIO find it a lot more powerful NAS in effect than NO A IaPREc1AT1pN the numerous recordings made with "mod- OF EQUIPMENT ern" orchestras. TONE,

Enesco, Roumanian Rhapsody # I It is possible to Lase. Mephisto Waltz produce amplifiers that measure up to the New York Philharmonic, Rodzinski. most rigid requirements and tolerances of a "mechanical Columbia LP: car "... amplifiers that show ML 2057 perfect laboratory measurements, BUT Here are two reissue jobs, one of which may, despite their mechanical and technical rates as the best LP of the month -the perfection fall short of providing enjoyable Roumanian Rhapsody. This (see article "listening-quality:' above) is one of those LP's that on my When you buy a phonograph amplifier you SINGLE, DUAL, & THREE - magnetic pickups comes through crystal - buy one thing ... listening quality. That clean and without a elusive characteristic SPEED HYSTERESIS buzz. As already stated, which, after all, is I am in a state of infinite confusion right any amplifier's prime reason for being. SYNCHRONOUS now as to what this indicates. But whether Newcomb amplifiers must not only measure all LP's or few sound good on your mach- up to the highest standards electrically MOTORS ine, I'm sure that this recording of a rather but in addition are subjected to critical silly show piece will delight you with a 'listening quality" tests by trained experts. top -ranking sound. Put it next to "Schehere- That is why Newcomb amplifiers provide more real listening pleasure. DUAL SPEED IN FRAME zade" on your LP shelf. The Liszt (also SIZES FROM 2.1 4" TO inexplicably) is not as clean, not as clear, 4 -3 8" DIAMETER even though it involves the same orchestra, same conductor. It's OK, but not super. RATINGS FROM I 1200 / fo 120 H. P. Britten, Young Person's Guide to the ...ET 4 YOUR OWN Orchestra EARS BE THE TAKE -UP AND REWIND Handel, Royal Fireworks Music (arr. Harty) Columbia LP: ML 4197 V V MOTORS FOR USE ON Aha! Here's that super test record that most engineers have 'long since discovered ALL TYPES OF REELS in its 78 version, complete on LP, and my insist upon hearing a Newcomb. Compare report is that it's good on LP, too. You can the listening quality of Model KXLP30 from have that famous pistol shot to your heart's the standpoint of enjoyment with AVAILABLE IN A WIDE VARIETY OF content. that of any other amplifier. Your ear will I'd say that, somehow or other, readily hear the pure natural FRAME TYPES, SIZES, AND quality and MOUNTING'. the low -turnover, heavy- bottomed character- true character of each deep bass note. istic of the English records has been pre- Now, listen to the clear, undistorted, served in the LP. (Does Columbia try to brilliant, high tones with their remarkable SEE US equalize for the known difference between freedom from surface noise made possible English and U.S. recordings ?) The highs by Newcomb 's exclusive MACac RE» KNOB: A comparison will convince you AT ROOM 649 here are fairly modest in strength as com- that Newcomb Sound is without question the pared to some domestic Columbia LP's, but FOR closest you can get to "Live Music" quality. ANNOUNCEMENT the stuff is there all right. There is some noticeable change in quality (so I detect, Newcomb Phonograph AND DEMONSTRATION at least) between beginnings and ends of Amplifiers from $59.50 OF THE the 78 rpm sides, especially when a side ends loud. Neweil elfeuelcipore sil The Handel "Fireworks" supersedes the famous album played with Harty himself IN HYSTERESIS conducting (Columbia X 51). That album still is tops musically, but this is a fair MOTORS approximation in the playing. As an LP this is fairly clean, but the loud strings are just a bit mealy. (A kind of unclarity that might, Write for Bulletin No. 49A I'd hazard a guess, he a matter of resonances in the cutting assembly, or inter - ELECTRIC INDICATOR CO. modulation of some sort; it's a sound that's very familiar on older records, as some 50 PARKER AVENUE would put it, a `Phonograph" sound as STAMFORD, CONNECTICUT distinguished from the clean sound of natu- AUDIO PRODUCTS CO. ral strings. Very slight here.) 6824 Lexington Avenue, Hollywood 38, Calif.

42 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com NEW PRODUCTS EASY and ACCURATE Way to The Polyphase Reproducer -a high - An quality magnetic unit that solves the problem of playing the various types of discs now in use -has just been an- Measure Audio Frequency Voltages

pounced by Audak Company, 500 Fifth Avenue, New York 18. It permits ten different combinations of removable styli, is easily mounted on most arms, and has excellent "ear- quality." The Polyphase provides wide -range performance at exceptionally low cost.

Ballantine Model 300 SENSITIVE ELECTRONIC VOLTMETER

Featuring a logarithmic A new tweeter, of aluminum, has been introduced by Voltage University Loud- Scale and speakers, Inc., 80 S. Kensico Ave., White Uniform Plains, N. Y. This model is designed for Decibel Scale 600-cps crossover, and may be had for either 20- or 40- watt systems. The coverage extends to 80 deg. horizontally. and makes possible the economical assembly of a two -way speaker system. Further information may be obtained from the manufacturer.

Designed for the measurement of AC Voltages from .001 Volt to 100 Volts over a frequency range of 10 to 130,000 cycles. Accuracy of readings is *2% at any point on the scale. Very stable calibration- unaffected by changes in line voltage, tubes or circuit constants. Range switching in decade steps -easy to use -only ONE scale to read. Output jack and output control provided so that Voltmeter can be used as a high -gain (70 DB) high- fidelity amplifier. Acces- sories available to extend readings up to 10,000 Volts and down to 10 microvolts. Precision Shunt Resistors convert Model 300 Volitmeter Audiotape- heretofore available only with paper base -may now he had with to very sensitive direct- reading milliammeter. Write for complete data. plastic base, thus making the line com- PRICE $200.00 plete with all types of magnetic recording tape. Two coatings are being offered, both the high- coercive black oxide and In addition to the Model 300 Voltmeter, Bat- the medium- coercive red oxide, and both BALLANTINE 1I tontine Laboratories also manufacture Battery may be had on either paper or plastic. Operated Electronic Voltmeters, R. F. Electronic New low prices on the entire line of INC. Voltmeters, Peak to Peak Elect -onic Voltmeters, Audiotape will be furnished by Audio LABORATORIES, and the following accessories -Decade Ampli- Devices, Inc., 444 M ilkon Ave., New BOONTON N. J. U. S. A. York 22, N. Y. fiers, Multipliers, Precision Shi.nt Resistors, etc. AUDIO ENGINEERING NOVEMBER, 1949 43

www.americanradiohistory.com 3 I[- CLaIIKSTaN-- O PREAMPLIFIER DESIGN

z3 [from page 171 PICKERING o 1.11 O ful selection and handling would be

,= y Fig. 7. Equalized necessary with standard resistors in this G.E. RPK-O4O , response charac- position, so special low -noise English D _j teristic of popu- resistors now being made available in Y. this country are used instead. 9 .s lar pickups. *STATIC ors u Pickup Rpon o \ led to some -3 This design has related research on the matter of pickup response and comparison, which seems ao woo to FREQUENCY IN CYCLES PER SECOND be of considerable interest. Since both the Pickering and Clarkstan cartridges .1re guaranteed to be flat within 2 db (once the roll -off resistor is removed from the Clarkston) it was considered FULL POWER -afe to assume the mean between the ALL IWO as essentially Hat response. On this basis the curve of Fig. 6 was determined for the Columbia the way 10003-M test record. This indicates a significant drop in the high frequencies with the new over the published characteristic, and this drop is confirmed by the light pat- MODEL 2 tern of the record.

The comparative curves of Fig. . AMPLIFIER were plotted for the Clarkstan, G.E. 7 1{PA NT. 171 Ss. -040, and the Pickering, as well SPECIFICATIONS: as the Astatic QT -3.T. POWER: Rated 20 watts actual RESPONSE: Flat within one db 560 Performance of the G. E. is very power measured 19.6 watts @ 15 cycles fo 100 kc. 1/2% total harmonic distortion critical with respect to loading, both INPUT: I volt level professional from 30 cycles thru 15 ke. NET resistive and capacitive. The curve of OUTPUT: 8 FEEDBACK: Over 20 db to 20 ohms Fig. 7 was run with a load of 0.5 megohm and 500 µµf. Loading of the 30 w. colorado st. order of 0.1 megohm may cause the audio pacific co. pasadena I, calif. response to be down 3 db at about 7500 cps. Where the plug-in preamp. is to be used with G. E. cartridges, the input resistor should be raised to 0.5 The DUAL -HORN Corner Reproducer a megohm. The QT -3J, although a crystal, shows relatively little distortion, and is com- 'Generally recognized by speaker critics as the STANDARD parable to the magnetic cartridges in

by which other . . speakers . . . are judged," says a this respect, although, as might be ex- leading consumer organization. pected from the curve, its transient Utilizing the corner of the room as an integral part of the acoustic system, performance is not as good. the Dual -Horn Corner Reproducer It has uses a horn for the bass tones in addition not received to one for the upper register. True fundamentals down to 30 cycles are repro- the attention it deserves, duced in their original beauty, without distortion or "boominess."

Attractive, more compact, cabinets 68 sus Improved driver units. NEW Lower Prices. E 1 30 to 15,000 CYCLES 4.7 Meg. I with negligible distortion. CRYSTAL o INPUT ó Consultation Service and Complete Custom 1' ' J Installations. 0.5 Meg. AMPLIFIER INPUT ( LOW CAPACITANCE) BROCINER ELECTRONICS LABORATORY 1546 SECOND AVENUE NEW YORK 28, N. Y. Fig. 8. Equalizer for QT3 -J cartridge to give response of Fig. 7

44 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com however, largely because few people have taken the trouble to equalize it MANUFACTURERS OF properly. Figure 8 shows the equalizer FINE ELECTRONICS 8 INDUSTRIAL EQUIP. used to obtain the curve for the QT -3J _ e CORPORATION in Fig. 7. This may be built into an octal base and substituted for the plug - in preamplifier when desired. THE ARM WITH A HAND BIOGRAPHY

I "Versatile Phonograph Preamplifier," Paul HAS SLIDE -IN W. St. George and Benjamin B. Drisko, CARTRIDGE HOLDER AUDIO ENGINEERING, March, 1949. 2 "Flexible Dual Control System," Howard T. Sterling, AUDIO ENGINEERING, Feb. 1949. 3 "Feedback Preamplifier For Magnetic Pickups," Richard S. Burewen, At two ENGINEERING, Februar. 1948.

A fine quality tone arm that features the ing weight adjustment pives positive and new "SLIDE -IN" cartridge holder. It Att. accurate balance plus proper regidle force. any cartridge. lust a quick twist of -thBqg - Meets all requirements for LP records as TRANSFORMER thumb screw and the cartridge Is seeurely well as standard speed and {reeve sizes. held in place. No need for soldering. Silver Arm made In two sizes, for records up to plated spring loaded plungers maintain posi- 12" and also up to 17 ". See your jobber or tive electrical contact. The quick act- write for Bulletin No. APPLICATIONS

Prom page 211 STEADY STATE J FREQUENCY der how to determine the impedance RECORDS

values between taps, and the imped- Clarkstan now offers ance of unequal windings in series. three new test records were which for the fiat time This would be a simple matter conform to exact spe- the actual number of turns known, but cificetions. permitting this is usually not the case. the user to wo -k in known quantities. Tie by which the reproduction of these There are two methods fine test records in- CLARK STAN RV WIDE RANGE from a volves no and impedances that are available polishing PICKUP WITH EASILY given transformer may be determined. employs the very 1t °st techniques which in- REMOVABLE STYLUS If an audio oscillator and a vacuum - sures exact duplicatb'n This Wille range variable re uctafce pickup of the original rec., tube voltmeter are available, the turns meets the requirements of dis'Arninq users ings in earn pressing- C ontlyl, te sieci. and FM specifications. Removable and In- ratio may be measured directly. Apply fications of the original recordings are terchangeable stylli available with various tip radii for all types retords. LP micro- See your 'libber or write for a known voltage from the oscillator to furnished. groove. etc. See your jobber or write ter one winding and measure the voltage Bulletin No. 1810. Bulletin No. 141D. with the high -impedance vacuum -tube voltmeter at the desired terminals, as in Fig. 2. The impedance ratio is then the square of the voltage ratio. By measuring and recording the values at various taps, a convenient set of data on that particular unit may be obtained. With output transformers, a rough check may even be made using only a multirange rectifier -type meter with 1000 -ohm- per -volt sensitivity and the CLARKSTAN EQUALIZER regular 117 -volt 60 -cps line, as shown Designed to work with the Clarkstan R\ RECORDING MICROSCOPE Pickup and other high impedance variable in Fig. 3. This method is not recom- reluctance cartridges, this low cost equal. analyzer microscope for inspecting Groove useful curves mended for input transformers because surface qualities of all types of disc re- izer includes the four most cordings and pressings. Built -In light for broadcasters and owners of fine high - of the load presented by the voltmeter. source is optimum for observing groove quality equipment. It offers playback walls. width. depth of cut. ate. furs magnification of either 20x or 40x plus equalization for all modern ords in- effi- If the impedance values are known excellent resolving power and light cluding LP microgroove. Has afoure posi- Reticle assists in making direct ciency. lion selector switch for standard curves. at several taps or of separate windings, comparison measurements. Valuable for record manufacture. Recording studios. Mounts on panel with a e diameter a simple calculation may give the de- technicians. Moderately priced at $22.50. center hole, for a neat installation. See See your jobber or write for Bulletin your jobber or write for Bulletin 1650. sired answer more quickly. A few for- NO 231B. mulas have been derived which are fairly easy to remember, and values SEE to the SEE CORPORATION are obtained without reference YOUR primary impedance. To illustrate this, YOUR 11927 W. Pico Blvd. the following simplified derivation is JOBBER CIA RKSTgN Los Angeles 34, Cal. JOBBER presented. Note that the primary im- TODAY TODAY

AUDIO ENGINEERING NOVEMBER, 1949 45

www.americanradiohistory.com pedance is used as a common factor, E. = Z. VZ./Z, Now and subsequently drops out. E. =E. +E. Assume a transformer having three = EA/Z. / 0 Z. windings, p, a, and b, corresponding Similarly = E, (VZ. +0Zu.) /Z, voltages E,, E., and Eb, and impedances From above Z., Z., and Zb, with the arrangement Eb = E,OZ. / 0Z, Z, = E.2 + Z, I E,2 shown in Fig. 4. It is desired to derive and an equation for Z. representing Z. and Substituting and solving E. = EA/Z. Z. Z. wired in series, observing "aiding" / Z.= (0Z. +VZs)2 polarities. E.2 = E,2 Z. / Z, Z. =Z. +Z, +2V Z. Zs (1) E./E, = 0Z./Z, Z. = E.2 Z, / E,2 Similar derivation for the value between taps of a winding as shown in the diagram of Fig. 5 yields the following PROCTOR formula: SOUNDEX Z. =Z. +Zn- 2VZ.Zb (2) These formulas have been of great FLOATING DISC DRIVE use to the writer and it is hoped that Multi -Speed Turntable they may serve the reader equally well. The following examples are given to 33- 1;3 -45 -78 illustrate their application: or any other speed from 1. An amplifier has to be matched to 30 -I 10 RPM. a 600-ohm load. The output transformer has a 500-ohm winding and a winding tapped at 2, 4, 6 and 8 THE MUCH TALKED ABOUT ohms. The 500 -olnn winding in SOUNDEX STUDIO ARM series with the 4 -ohm section will WITH NEW give, using formula (1) : AUDAX POLYPHASE or any other cartridge Z.= 500+4+20500x4

of your choice - = 504 + 2V2000 = 504 + 89.44 = 593.44 ohms Note stylus pressure control. The 6 -ohm section together with the 500 -ohm winding will yield: Send for Bulletin Proctor Soundex Z. =500 +6 +20500x6 Corp. = 506 + 203000 13:1 N. tills Ave., Mt. Vernon, N.Y. = 506 + 109.6 = 615.6 ohms The 4 -ohm section apparently would STATEMENT OF THE OWNERSHIP, MANAGEMENT. CIRCULATION, ETC., REQUIRED be the better choice. By THE ACT OF CONGRESS OF AUGUST 24. 1912, AS AMENDED Ifl- THE ACTS OF 2. The 20-ohm dynamic microphone MARCH 3, 1933. AND JULY 2, 1946. has to be matched to an of AUDIO ENGINEERING. published monthly at New York, N. Y., for October 1, 1949. amplifier while the input transformer has State of New York 55.: County of New York two tapped windings as shown in Before me, a Notary Public in and for the State and county aforesaid, personally ap- Fig. 6. The known values would peared Dorothy S. Potts, who, having been duly sworn according to law, deposes and says that she is the publisher of AUDIO ENGINEERING, and that the following is, to the best of her result in considerable mismatch knowledge and belief. a true statement of the ownership, management. etc., of the aforesaid and publication for the date shown in the above caption, required by the Act of August 24, 1912, the value of the unknown sec- as amended by the Ant of Marsh 3. 19n and July 2, 1946 embodied in section 637, Postal tion is investigated: Laws and Regulations, to wit: 1. That the names and addresses of the publisher, editor, managing. elitor and business manager are: Publisher: Dorothy S. Potts, 1737 York Avenue, New York 28, N. Y.; Editor: Z. = 125 + 50 - 2050 z 125 Charles G. McProud, 7 Peter Cooper Road, New York In, N. Y.: Managing Editor: None: Business Manager: Sanford L. Cahn, Westmoreland Gardens. Little Neck, N. Y. = 175 - 2V6250 2. That the owners are: Radio Magazines, Inc., 342 Madison Ave., New York 17. N. Y.; Dorothy S. Potts, 1737 York Avenue. New York 28, N. Y. = 175 158 = 17 ohms 8. That the known bondholders, mortgagees, and other security holders owning or hold- - ing 1 per cent or more of total amount of bonds, mortgages, or other securities, are: None. This match is 4. That the two paragraphs next above, giving the names of the owners. stockholders obviously closer and security holders, if any, contain not only the list of stockholders or security holders as than would be possible using only they appear upon the books of the company. but also, in eases where the stockholder or security holder appears upon the books of the company as trustee or in any other fiduciary the known values and best results relation, the name of the person or corporation for whom such trustee is acting, is given; are obtained by using both Z. also that the said two paragraphs contain statements embracing atfiant's fall knowledge awl belief as to the circumstances and conditions under which stockholders and security holders sections in parallel. who do not appear upon the books of the company as trustees, hold stock, and securities in a In capacity other than that of a bona fide owner: and this affiant has no reason to believe that closing, the writer wishes to call any other person, association, or corporation has any interest direct or indirect in the said attention to the fact that two equal stock, bonds, or other securities than as so stated by him. impedances in series will give a value (Signed) DOROTHY S. POTTS, Publisher. Sworn to and subscribed before me, this 7th day of september, 1949. four times that of the single winding (Seal). HARRY N. REIZES, Notary Public. and that one half of a winding presents State of New York. No. 24- 3249560, Qualified in Kings County, Certs filed with Kings an impedance of one -fourth of the total a N. Y. Co. Clk. Off. & Kings Co. Reg. Off. Commission expires March 30. 1961. winding.

46 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com TO INPUT OF MAIN AMPLIFIER R10 Mt c, 0.15 Meg. TechnIl- .005 v, CS V2 C5 VS 1/2 6SN7 005 Y2 6SN7 .005 6V6 T II- II- R, o rnefs 0.1 Meg. oá oO

Tweeter Amplifier ó a0 1c6 o, T01 0.1 0.25

Fig. I 0

At first consideration, the idea of 300 V. building a separate amplifier to operate a tweeter may seem like a lot of trouble to achieve results that can be attained adequately by the use of cross -over networks. However, there are several ad- For the High Fidelity Enthusiast! vantages to the use of this system that may be worth taking advantage of. The Full Range SUPER COSPIRAL One, strangely enough, is its economy. The parts that are required for this than amplifier can be purchased for less Model 102FR -Full 20 watts of power handling capacity. Seamless, ten dollars, whereas a coaxial speaker molded, curvilinear cone of advanced design with the Ily low two to fifteen times that f 45 cps. Two acoustic sections, one for reproducing low will cost from fundamental bass tones, and one for the most extended high tones. amount. The reproducing range is 30 to 14,000 cycles, flat -±5 db from 50 to Fig. 1, is straightfor- 9500 cps; utilises 4.2 lbs. of the new super powerful Alnico V orange The amplifier, streak magnet material, which is 10% more efficient thon regular to construct. The RC i ward and easy Alnico V. This new production has a more extended range and greater coupling is designed to filter frequen- electro-acoustic transfer efficiency than its famous predecessor, the 10,000 cps, and although Model P52FR TRU -SONIC Cospiral unit. The unique Silver Spiral dif YOUR COST cies below ferential diffuser, is employed with over 90° of high frequency dis. some lower harmonics are present, persion. This unit is designed for outputs of from 8 to 16 ohms nominal they are not noticeable except at a impedance. Depth behind mounting panel, 81/2 Overall diameter, $54.00 gain than would ever be 151/e Net weight, 25 lbs. much higher Order From Your Distributor necessary in operation. Practically any output transformer designed for single - will serve, the sec- ended 6V6 operation 800 -Cycle 2 -way System ondary impedance being uncritical at from the frequencies amplified. With a nylon SPECIAL} (Available only on direct order the factory) or nlulticellular tweeter it will be found that the amplifier is highly efficient. tweeter diaphragm is since the rigid PLUS FIELD SUPPLY not loaded down with unwanted lows. Another advantage of this system is AND CROSSOVER -over is at the input stage that the cross NETWORK rather than at the power output, and IF DRIVER HF DRIVER 2 x 4 HORN of cross-over few of the usual problems The 2 x 4, 8 -cell 800 -cycle cutoff horn and above, and with the STEPHENS Model FS-3 networks are present. electrodynamic High Frequency Driver Unit, Power Supply and special 800.cycle full m The subjective effect is quite inter- shown above, were originally manufactured derived V/2 section crossover network, these FM program is by STEPHENS for the Magnavox Company. A components represent the buy of a lifetime esting. When a live small excess of these items on hand is offered for the high fidelity enthusiast. amplified, a turn of five or ten at a tremendous saving! Combined with the being FOR degrees on the tweeter- amplifier gain electrodynamic Low frequency Driver shown ALL $89.50 control will give an edge and a clarity to the sound which may not have been High Frequency Driver and Horn ONLY $29.50 missed previously, but that is appreci- ( 150 ohm field, 250 ma, 16 ohm voice coil) ated when it is heard. If the main -with SO161M crossover $47.50 amplifier is then turned off, it will be GUARANTEE found that the output from the tweeter All items carry STEPHENS Serial numbers, and the Order these special units direct a marked change in timbre standard factory guarantee when purchased os a corn. from the factory by sending 50% that caused plate package. No warranty applies on the horn and deposit with you order. Balance is scarcely audible by itself. high frequency driver unless purchased with the cross- will be shippedr to you C.O.D., over unit described above, insuring proper crossover F.O.B., Los Angeles. David Hancock point and low frequency attenuation. 510 Lexington Ave. New York STEPHENS Amplifier designed by 8538 Warner Dr., Culver City, Calif. Peter Hancock, Manufacturing Corporation Federal Telephone and Radio.

AUDIO ENGINEERING NOVEMBER, 1949 47

www.americanradiohistory.com for service PROFESSIONAL with the speed AUDIO FREQUENCY DI RECTORY of sound... MEASUREMENTS

[from page 19] C. J. LEBEL AUDIO CONSULTANT sults of acoustical measurements with such a meter would of necessity require supplementary data for coordina- Sound Recording Instrumentation tion with previous results of flat re- sonse measurements of the electrical 370 RIVERSIDE DRIVE noise in amplifiers intended as compon NEW YORK 25, N. Y. cots of an electro- acoustical system. However, generally available data co- related with weighted electrical measurements made on amplifying sys- Winston Wells tems do not appear to exist in sufficient for everything in sound, electronics, volume to warrant abandonment at the Designer and Consultant present time of the existing use of flat radio and television equipment Acoustical, Electronic and Nuclear weighting for electrical noise measure - Research at DEALER LOW PRICES! meets on the audio systems under discussion. This decision is an expedient 307 East 44th St. MU 4-3487 WHAT DO YOU NEED? and is subject to review in the light of New York 17, N. Y.

The most . more adequate information which may complete stock of equipment . from the most minute port to the largest become available later. installation . ready for instant delivery As noted above, the Committee on from our THREE HUGE STORES AND Audio Facilities WAREHOUSESI has specified that the noise measuring device have the ballis- Custom -Built Equipment tic characteristics 1: of a standard VET XCLUSIVE meter but that it road the rms value of U. S. Recording Co. First Time in America! a steady complex wave. Since the standard VU meter does not read this 1121 Vermont Ave., Washington 5, D. C. See the Famous English rms value, it is of interest to inquire what discrepancies would arise if a STerlinq 3626 Vi 11.1 1 Ií LI)ALE standard VU meter (with suitable SPCAKEnS gain) were used as the noise measuring With Cloth Suspension Cone device. This meter has a characteristic i Keg, at the New York = where Consultation Design Fabrication i = numerical magnitude of instan- AU111O FA 11t taneous value of current fed Iloutss 602 to indicating instrument. Audio Facilities Corporation _ numerical magnitude of instantaneous value of input voltage. 608 Fifth Avenue r = 1.2 ± 0.2 FREE! New York 20. N. Y. K = a constant A lc POSTCARD WITH 2. YOUR NAME 8 ADDRESS For an rms device, x = With an to Dept. AE will brimg rms device, if two equal -amplitude RATES FOR you NEWARK'S great new sine -waves of frequencies, not harmoni- 1950 SOUND CATALOG cally related, are fed PROFESSIONAL CARDS supplement! to it, the output indication is 3 db greater than that for IN THIS DIRECTORY MAIL, WIRE & PHONE either sine -wave component alone. For ORDERS FILLED AT the VU meter, tests indicate that the $10 Per Month. ONCE! NEW LOW CREDIT increase in this case is about 2.1 instead Orders Are Accepted TERMS: 10% DOWN...UP TO A YEAR TO PAY of 3 db. From the above formula it is for 12 Insertions Only . only 6% carrying charge - no morel seen that the VU meter rectifier does 3 GREAT STORES! uptown otns W. 45th St. not differ greatly from a full -wave Downtown at 212 Fulton St in NEW YORK linear rectifier. Computations 323 W. on the Madison St. in the heart L-,1 CHICAGO linear rectifier indicate that on a wave HERMAN LEWIS CORDON MAIL NOW! consisting of fundamental and 50 per Registered Patent Attorney cent third harmonic would ADIO a IBOa it differ from the rms device by from to NIWeA rllrrNtt ra 1Ne. DPn+ AE -2 +0.3 db, depending on the relative Patent Investigations and Opinions NEWARK EIEC. CO., 242 W. 35th Si., t r C

rl..,., I rara: Itt:,o Ness] L ,. phase of the fundamental and har- Nome monic, and that on a wave consisting Warner Building IDO Normandy Drive iAddress of fundamental and 50 per cent high Washington 4. 1). C. Silver Spring. Md. N Ational 2497 Shepherd 2433 City Stole hartnonics the linear device would read

48 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com about 0.3 db below the runs device.8 It seems likely that on ordinary steady noises found in audio systems the difference between a VU meter reading and an rms reading would not exceed J/octinjction about 1 db. For noises of markedly peaked wave shapes, the difference for all TV Cameras would be greater; but these are not ordinarily originated in audio facilities. The Committee on Audio Facilities "BALANCED" TV TRIPOD has not specified re- the frequency Pat. r'endinq sponse of the noise measuring equipment above 15010 cps. It would seem desirable that this response cut off fre- This tripod was engineered queaeies above IS,IM)O cps, since the and designed expressly to broadcast reveivcr and listener would meet all video camera re ordinarily be insensitive to theta. It quirements. measuring instruments of differing frequency response above 151100 cps are Previous concepts of gyro used to IIICaSIII'e a twist. having com- have ponents above 15,0011 cps, different and friction type design readings will be obtained, particularly been discarded to achieve it the equipment under test has a sub- absolute balance, effortless stantial frequency response above operation, super- smooth tilt 15,000 cps. However, the difference be- and pan action, dependabil- tween the readings of a standard volume indicator and an ordinary noise ity, ruggedness & efficiency. and distortion meter, contributed by the differences between their frequency - Below: response characteristics, will usually 3 wheel portable dolly with balanced amount to only a few tenths of a db, TV Tripod mounted. though in particular cases (e.g. where the apparatus under test picks up the field from a long -wave radio- telegraph 360° pan without station) larger differences may be Complete found. ragged or jerky movement is accomplished with effortless con- Noise Measurement Using a trol. It is impossible to get any- Distortion and Noise Meter thing but perfectly smooth pan and tilt action with the II;l lee rise tic :1- 1Lotnents with "BALANCED" TV Tripod. the distortion and noise meter of the general type already described its cali- Quick -release pan handle adjust- bration is first adjusted so that it indi- ment locks into position desired cates 0 db with a test signal at a me- by operator with no "play' be- tripod dusa frequency such as 10110 cps after tween pan handle and the input level is established at the head. Tripod head mechanism h normal or operating level. The gain rustproof, completely enclosed, and control settings of the equipment never requires adjustments, under test should again be the same as cleaning or lubrication. Built -in for previous measurements. The out- spirit level. Telescoping exten- put of the equipment under test should sion pan handle. be terminated by resistance equal to the Write for further particulars rated load impedance. Noise measurement is then made by removing the input to the equipment under test and RmERA ECJUIPmEI1T C. substituting a resistor actual to the I600 FRORO'.OFY ^EW SO.( CITY rutted input source impedance across the terminals. The resistor should be non- inductive and of a type, such as a wire -wound resistor, which will not in ISSUES? itself generate appreciable noise. In NEED BACK high-impedance, low -level circuits it Only a few are available and may be necessary to shield it carefully to the supply is limited avoid hum pickup trouble. August 1948 ] March 1949 1948 issues If the noise set is substituted directly D O September 1948 May 1949 5Oc for the output ureter .1/_ of Fig. 2, the El November 1948 June 1949 noise and distortion meter will indicate December 1948 August 1949 1949 issues the number of decibels which the noise Payment should accompany order. 3 5 c is below the level indicated by .11e. To Circulation Dept., Audio Engineering, 342 Madison Ave., New York 17, N. Y. 11m obtain adequate meter deflection under :1' I i.,. err . . . ., . .4 1 r.i...,- ...... I I I :I I , I I . i. U . I i.. i.d41a .II.I'..II.

AUDIO ENGINEERING NOVEMBER, I949 49

www.americanradiohistory.com Scientific Tests Show How To some conditions, it may be necessary to connect the distortion and noise meter PRESERVE directly to the output of the equipment tinder test. The meter will then indicate the noise level in decibels below YOUR RECORDS the predetermined signal level at that Means a lot to And Get Superb Reproduction point. us The frequency -response characteristic of the distortion Living Presence DIAMOND STYLI and noise meter used may be a factor in obtaining com- maintain a polished, rounded tip which parative results particularly Lifetime minimizes wear on record grooves if a rela- Performance tively flat response of the AFTER 1000 PLAYS ON equipment STANDARD -GROOVE RECORDS under test is maintained appreciably Low Price beyond the audible frequency range as already mentioned. Library Protection Acknowledgments The authors wish to ackowledge the Lasting Patronage assistance of Mr. W. F. Byers of the Osmium 11\Sapphire Diamond General Radio Company for his help in LP should also mean a lot to AFTER ONLY 15 PLAYS ON the preparation of a preliminary draft. MICRO- GROOVE RECORDS In addition, thanks are due to those YOU because these are to be who offered constructive comments to found in a new line. this presentation in manuscript forni and to the many persons who, over the Livingston Products years, have published results of their work and thus made this compilation Transcription Arms thmlum Sapphire Diamond possible. The footnote references and The above photomicrographs (greatly enlarged) the appended bibliography are not in- Loudness Controls show the resulta of wear on stylus tips. Note the smooth, round, unchanged contours on the dia- tended to be all -inclusive but they do Stylus Pressure Gauges mond styli. Compare them with the sharp chisel indicate some of the sources of points worn on the sapphire and osmium tipa. infor- These sharp edges cut groove walls and destroy mation available which bear on the sub- response. ject matter. Livingston Electronic Corp. Scientists find that diamond is REFERENCES 90 TIMES MORE RESISTANT TO WEAR ll' / Livingston New Jersey AND 4 -10 TIMES STRONGER N. Tuttle-A Method of Measuring Di. than sapphire -the next- hardest rectly the Distortion in Audio Frequency material Amplifier Systems. J. Soc. Mot. Pict. Eng., Why subject the ree.o.is you treasure to the February 1932. Vol. 18, No. 2. ruinous grinding action of worn styli? You can 12H. H. Scott -Audible Audio Distortion. preserve your collection -and save money too - Electronics, January CAPPS* by using a 1945. diamond stylus. It would cost at least laJ. K. $100 in sapphire stylus replacements to equal Hilliard- Distortion Tests by the Ill - tennodulation the durability and efficiency of one diamond Method. Proc. IRE, Decem- 17-Groove A. N. 19a* .: stylus. ll ber 1941. Vol. 29, No. 12. G. Frayne SPECIAL OFFER SAVES YOU MONEY 14J. and R. R. Scoville -Analysis Recording stylus and Measurement of Distortion Remember that in many cases a stylus become,, in Variable worn -and causes damage -long before the de- Density Recording. J. Soc. Mot. Pict. Eng., fect is audible. It is far cheaper to replace your June 1939. present with stylus a diamond than to have to "American Standard Sound Level Meters replace or bear the loss of fine records. And you for Measurement I can now obtain a genuine diamond stylus -for of Noise and Other standard or micro-groove records-at the LOW- Sounds. American Standards Association EST PRICE EVER OFFERED! Z24.3, 1944. These are the finest styli available. 10R. S. Tucker-Measurements of Noise on The same styli are used by radio stations. Program Circuits. Bell Laboratories Rec- REPLACEMENTS CAN BE MADE ON ord, March 1936. Vol. 14, No. 7. NEARLY EVERY TYPE OF CARTRIDGE 17J. M. Barstow -A New Noise Meter. Bell Laboratories Record, For ATTENTION G. E. CARTRIDGE OWNERS: April 1937. Vol. 15, Don't throw away your old model variable No. 8. Versatility reluctance cartridge. The worn stylus can be replaced with diamond by our experts. BIBLIOGRAPHY Uniformity and K. S. Johnson - Transmission Circuits for Finest Recorded Quality Here's how to get your diamond stylus replacement, which will pay for itself over and over Telephone Communications. D. Van Nos - Just fill out the coupon below and mail it to- trand Co., 1925. Cuts either 331/3, 45 and day. We will send you a special mailer in which W. L. 78 R.P.M. you mail your cartridge or stylus assembly to Everitt-Communication Engineering. us; we will replace with a new diamond stylus McGraw -Hill Book Co.. 1932 and return to you within a few days. If not Electrical Engineers' completely satisfied after a 10 day trial, your Handbook- Electric money will be refunded. Communications and Electronics. Ed. by Please Print H. Pender and Mcllwain. John Wiley ANDREW'S RADIO COMPANY & Sons, 3rd edition 1936. 1s/a Warburton Ars., Yonkers 2, N. Y. Radio Engineers' Handbook -F. E. Terman. micro groove and coarse groove Enclosed is check money order for $14.95 for one diamond stylus replacement. McGraw -Hill Book Co. 1943. Make and modai of cartridge Stylus required for at andard groove N. B. Fowler-Measurements in Communi- 1.0 mil playback for micro -groove cations. Electrical Special radius sires on request; no extra charge; Engineering, February 1947, Vol. state size 66, pp. 135 -140. H .H. Scott 02.5 mil playback Name -The Measurement of Audio Distortion. Communications, Street April, 1946, and Engineering Handbook of National Iteg. U. S. Pat. Office City Zen... st.t=.. . Association of Broadcasters. U.S. Pat. applied for

50 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com PROFESSION, AN HONORED NAME INSTRUCTIONAL IN THE BROADCAST STUDIO the [from page 15] Getting back to existing equipment, Altec Lansing_. turntables with self- contained amplifiers are sometimes operated by the students, and it is difficult to keep the A -256A hum level down, particularly when teaching schedules conflict with maintenance schedules. It sometimes Helps amplifier_ to ground the amplifier chassis, and the same is true of tape recorder chassis and any other instructional equip- WILL MEET YOUR REQUIREMENTS ment - provided, of course, that they are not of the a.c. d.c. type To facili- FOR AUDIO POWER tate grounding, a bare copper wire is strung around the studio under the Your need for high quality audio frequency ponents insure the user of long trouble- chair rail and connected to one of the power can be handled better, with greater f ree life without deterioration in per- building water pipes. Fahnestock clips dependability and with better quality by formance characteristics. the Altec A -256A Beam Power Amplifier. are spaced every ten feet along this Rated conservatively at 65 watts,the SPECIFICATIONS wire, the of permitting grounding ap- A -256A Amplifier will deliver 75 watts CAIN: 50 DB, 500 ohm input. paratus anywhere in the studio without with less than 2% total harmonic distor- FREQUENCY RANCE: within Vx DB. the hazard of long wires trailing across tion. At 65 watts the intermodulation is 20-20,000 cycles only 2 %. Never before has there been a NOISE LEVEL: -45 dbm (.001 watt reference). the floor. In this connection, every ef- high quality amplifier which will deliver fort is made to keep the floor clear, you as many watts per dollar as you re- OUTPUT IMPEDANCE: Taps for 8 & 16 ohm loads. not only of grounding wires, but also ceive from the A -256A Amplifier. Full INPUT IMPEDANCE: 30, 250 & 500 ohms. power available within 1 db at 40 cycles 5,000 ohm bridging input. of microphone and other audio cables, and 15,000 cycles. a.c. power cables, and so on. All these The A -256A Amplifier is assembled on For technical bulletin, write circuits are carried in separate wall a relay rack of recess pan construction, making it adaptable to either rack or ALTEC LANSING CORPORATION conduit runs that girdle the studio, cabinet mounting. Sound design and the 1161 North Vine Street. Hollywood 38. California with outlets at ten -foot intervals. use of conservatively rated quality com- 161 Sixth Avenue. New York 13, New York Echo Device Another audio facility is the echo device. This arrangement, which did not originate at Carlisle Barracks, consists principally of the reverberation NEW... Improved Wiring Eliminates Leakage attachment and associated preamplifier from the studio Hammond organ. 't ne r TYPE 12ÁT 8 TYPE 12ATK (KIT! attachment is a delay -producing arrangement in which a loudspeaker driver unit is mechanically coupled to TRANSMISSION MEASURING SET a crystal pickup through long, helical springs that slow down the signal appreciably. Since this device is in parallel with the microphone circuit between Range: 111 db. in 0.2 steps. any two convenient low -level points, Frequency resp.: 0.1 db. the main or program amplifier receives from 0 to 20 kc. both the "on- time" and the delayed Accuracy: 0.1 db. portions of the signal, and the phase Impedance, load section: 4, 8, 16, 50, difference provides the echo effect. The 150, 200, 500, d degree of echo can be varied by the 600 ohms. tap switch, which is part of the rever- Impedance, transm. beration preamplifier. set.: 50, 150, 200, Then there are some electrical power 500 It 600 ohms. Reference level: 1mw. items to be considered. The first is a into 600 ohms. master switch and pilot light at the Circuit: "T ", A precision Gain Sel with specially developed door of both the studio and the control unbalanced. wiring that permits no troublesome leakage room. Students and experienced per- Attenuators: 10x10, and provides improved frequency character- - 10x1 8 5x0.2 db. istics. Available complete!), assembled, or sonnel too - sometimes leave the build- Load carr. cap.: ing without turning off all equipment. Transm. sect. 1 w. in kit form -which permits the sale of a high The master switch permits the instruc- Load section 10 w. accuracy instrument at a low price. tor to kill all a.c. power on the base- WRITE FOR DESCRIPTIVE BULLETIN board outlets as he leaves for the day. The pilot light, visible through observation windows in the door, will re- Manufacturers of Precision Electrical Resistance Instruments mind him if he forgets. PALISADES PARK, NEW JERSEY The on -the -air warning light outside

AUDIO ENGINEERING NOVEMBER, 1949 51

www.americanradiohistory.com the studio door is another power item. Save Space Originally, this was a red bulb over the door frame, but no one paid much attention to the light, nor to the as- and Weight sociated large warning sign on the door itself. A flasher button was inserted in the bulb socket to make the light with TRIAD blink, on the theory that a blinking light was more noticeable - but it didn't work out that way. Finally, a "//S''Transformers red lutniline tube was mounted verti- cally at eye level on each side of the door frame, complete with flasher, and t!:at (lid the trick. The seemingly obvious solution of a bolt on the inside of the studio door would be a safety hazard, especially since the studio door opens inward. SQUARE WAVE GENERATOR The devices described in this article Model 71. Frequency Range: Cont ln- are the result of considerable cyuly variable from 5 to 100,000 experi- cles. wave Shape: Rise time less than ence in teaching the - 0 2 tetertuerontla. Output voltage: 75. basic of announce 50, 25, 15, 10. 5 peak volts tined. ing and production in a very limited 0 -2.5 rolls continuously variable number of instructional hours. They are based on the assumptions that the MEASUREMENTS student knows nothing of the broadcasting field and that almost any device CORPORATION is legitimate as a training aid to em- BOONTON NEW JERSEY phasize and perhaps dramatize the points made by the instructor. The corollary to this latter principle is that the training gadget should not develop habits in the student which must be unlearned when he finally steps into an operational -Audio. new aitancrtcUca Wire Markers: New 12 -page illustrated Western Lithograph catalog en- Re/ifl l t NO 11: ticed "The Most Effective Wire Marker ULTRASONIC FUNDAMENTALS u, /o Ever Devised" shows latest methods of marking wire, pipe, cable, conduit, etc., By S. YOUNG WHITE Input Transformer - The rapid Increase in the use of ultrasonics during with die -cut, self -adhesive EZ Code :he last few years makes it natural that the well - markers. Western Lithograph Co., 600 E. informed sound engineer should want to learn some- Dims: lró x l, x 2f thing of the application, and potentialities of this Second St., Los Angeles 54, Calif. amazing new field. But interest in ultrasonics In Film production not confined to the 60 111111 engineer-It to of still and TV Equipment: greater Importance to the industrial engineer for he Weight: 11 02. S. O. S. Cinema Supply Corp., 002 \V. la the one who will visualize its uses in his own 52nd St., New York 19, offers an 88 -page processes. Element ary in character, ULTRASONIC FUN - catalog listing approximately 1600 items DAMENTAI.S was written originally as series of Both transformers covering 16mm and 35mm magazine articles Just for the purpose of acquainting shown above are high studio cam- the novice In this field with the enormous pouibiliti.a fidelity input transformers, frequency response eras, accessories and lenses, as well as of new tool for Industry. It serves the double purpose of introducing ultrasonics to both from 20. 20,000 recorders, projection equipment, and sound and cycles and 95db. shielding. industrial rug i nerrn. Tic: list of chapter headings Yet the Triad transformer is only one - most other items required in this work. will Indicate how It can help you. seventh as large by volume, occupies one - The catalog -entitled "Sturelab 8A" CHAPTER HEADLINES fourth the space and is one -fourth as celebrates nearly a quarter of a century Too Much Audio. Opportunities in U llrasonlas. Elements of U ltrasonir. Experimental Ultra heavy. In the production of today's high as an industry leader. tonics. Coupling U ltraeonic Energy to Lead. fidelity equipment, where space is at o premium, Radio and Television: So comprehen- U ltraaonica in Liquids. U Itralunica In Solids. Testing by U Itraaonits. High -Power U llrasonl ea. that's important. sive in content :old clear in presenta- Notes on Using H iah Power U ltrasonies. Appll- Triad transformers, tion that it is a veritable handbook, cat ions of Ultrasonies to Biology. Economics of "HS" (hermetically sealed) the Industrial Ultrasonics. built to meet JAN specifications, ore providing new catalog offered by Lafayette Radio, The applications of ultrasonics have already e new standards of performance for quality elec- 100 Sixth Ave., New York 13, lists a I ended to many Industries, and as Its possibilities are explored they will increase a hundredfold. To keep tronic equipment - yet they cost little more than number of "packaged" high -fidelity o hreaat of its growth, engineer In all fields must ordinary cosed types. radio -phonograph equipments in addition know what they may expect from ultrasonics, how It is used, how the energy is generated, and the tech- Triad builds a complete line of transformers to the entire line carried in stock in the niques of applying ultrasonic treatment to many pro- for original equipment, replacement, geophysical many Lafayette stores. Relays: Colorful New D120A ULTRASONIC FUNDAMENTALS Is not big and amateur applications. Catalog took -it doer not cover the entire field of ultrasonic. illustrates and describes various types of with hundreds of pages of dull reading But in the Write for three hours it will take you to read it, you will get relays, gives contact ratings, coil speci- a down -to -earth glimpse into the far -reaching pool - Catalog TR -49 fications. sizes, prices, and other helpful bllitles of a new art. data. Ward Leonard Electric Co., Elec- ULTRASONIC FUNDAMENTALS tronic distributor Division, 53 W. Jack- By S. YOUNG WHITE son Blvd.. Chicago, Ill. 36 pages, 40 illustrations. 81/4 s II, 16 -mm equipment: New catalog of paper cover. 51.75 post -war models provides rather detailed Book Division, Dept. A information about the major units of RADIO MAGAZINES, INC. Maurer equipment. Free copy may be 2254 sepgtlt/ede Blvd. 342 Madison Avenue obtained from J. A Maurer, Inc., 37 -01 New York 17, N. Y. Les Angeles 44, CdN: 31st St., Long Island City 1, N. Y.

52 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com RACON MUSICIAN'S AMPLIFIER

TWEETER [from page 13] Highest Music Quality as 20 db at 211 and 20,000 cps. The over- 'The Musician's Amplifier' all iutermtodulation distortion curve is presented in Fig. 7. On the surface it may appear. that 12.2 watts is rather poor output from tint 807 tubes, but it must be remem- hcr(Hl that the SO7's are triode-connected and the efficiency of triodes is much less than that of tetrodt <. Moreover, the power output compare very favorably with 2:1:; 6 MODEL that from type or -volt Clean CHU -2 equivalent triodes. The power ratings Output to $37.50 given in the tube manual for these types Us? hice 15,000 Cycles! are the power developed in a load resis- Wide Distribution Pattern! tor connected plate to plate, while our power measurement was of useful sec- Are The Amplifier you looking for the rich brilliance ondary power. Those who have built and life -like realism of concert hall mu- With Real sic? Then add this Racon tweeter to "10 watt amplifiers" using 2A3 or your present 12 or 15" cone speaker and equivalent tubes might find it very Presence Effect for the first time enjoy a seal in 10th enlightening to measure the undistorted row center instead of the dark recesses The SMA -12 an power in a resistor connected in place is all- triode, fixed - of the balcony. gain, 2- chassis power amplifier for of their speaker. We have found that Response is clean and smooth to 12,000 use with tuners or other front ends cycles, with usable output to 15,000 the power of 12 useful watts is more containing their own volume and tone cycles. High frequency horn logarith- than enough for fume volume, even controls. mically expanded as two horns for wide. when operating with a 10 db safety Designed by David Sarser, it uses uniform distribution pattern. When used factor. the classic Williamson circuit. with crossover network, will handle Complete kit is sold by Sun Radio. The amplifiers rated to 25-30 watts. Source intermodulatiuu distortion in Can be wired in less than 3 hours. impedance 4-15 ohms. Dimensions 10.3" this amplifier was checked on Altee All capacitors and resistors in the wide, 7" high, 83" deep. Lansing iutermodulation equipment, audio amplifier chassis are already Cast aluminum throughout. Cutout tem- using frequencies of 40 and 2,000 cps. mounted and wired on resistor board flush mounting. for simple installation. Chassis plate provided for easy It was found to be extremely low at Free wiring diagram and instructions to punched to accommodate all compo- powers 8 build an economical professional type up to about watts. As a matter nents. fact, IM ordinary two -section crossover network. of the distortion for SPECIFICATIONS: Listen to the Racon tweeter at your room volume powers was less than .21 Peerless transformers used exclusively nearest distributor or write for free which is entirely negligible. As pointed throughout. Catalog 1. Tubes: 2- 807's tied as triodes in push out in Armo ENGINEERING for Septem- - pull output, 2- 8SN7's, 5Ú4G rectifier. ALL BACON PRODUCTS GUARANTEED ber 1948, the power read on the IM Output: 12 watts with less than 8% inter - equipment may be converted to equiv- modulation distortion. 18 MONTHS Source impedance: alent single-frequency power, the usual 0.75 ohms. IntermodulaUon distortion less than 8% at way of rating an amplifier, by multi- 12 W output using freq. of 40 & 2000 cps. ACOUSTICAL EXCELLENCE plying the IM meter power by the fac- Frequency response: ±0.5db, 20- 80,000 cps. Absolute gain: 70.8 db. 1.47. This has been done in the tor 20db of feedback around 4 stages & the published curve and it will be noted output transformer. that the amplifier does not begin to Cathodyne phase inverter. On 2 chassis, each 5" x 10" x 3 ", each exhibit serious distortion until sine properly punched and cadmium finished. 52 East 19th Street, New York 3, N. Y. wave power of 12.5 to 13 watts is Kit comes complete with tubes, punched reached. Thus the power curve for var- chassis, prewired resistor & capacitor board, sockets and all necessary parts. ious as reproduced frequencies, in this NET PRICE $89.50 article, is for substantially distortion - Lab wired & tested, complete with curves less reproduction. the reader wishes TAPE If of tests run on that individual amplifier. SPLICER to be conservative in his amplifier per- Tests include 3 curves showing frequency formance, the power output as read response, power output and harmonic FOR MAGNETIC content. NET PRICE $119.50 be RECORDING from the curve should divided by the TAPES factor 1.47 in order to get the IM Order by mail today! meter power for a given amount of AMATEURS or PROFESSIONALS - The ('arson Tape Splicer can do your splicing in a hurry - No distortion. tricky adjustments - Tape is held in one position for sit operations. Pies a cutting edge such as When this amplifier is connected razor blade with any kind of cellulose adhesive tape to a wide range speaker and although Scotch 41 splicing tape is recommended. system fed ASO ELECTRONICS COMPANY. INC. CARSON TAPE SPLICER - postpaid - 22.00 with good program material (e.g., local, 122 -124 DUANE EET SCOTCH 41 splicing taps live FM transmission) the resulting STR 1ß- a IOW roll on dispenser - .29 New York 7, N. Y. BArdoy 7-1840 realism is so startling that it must be MAGNECESSORIES 2 BLOCKS NORTH OF CHAMBER ST heard to be appreciated. The inter - Box 6960. Washington 20. D.C. STORE HOURS: n -( Daily, 9.4 Saturday. modulation distortion is so low that

AUDIO ENGINEERING NOVEMBER, 1949 53

www.americanradiohistory.com when a full symphony orchestra is playing, the various instruments are easily Jfiyette detected. The thud of the bass drum and the tinkle of the triangle are re- R AD /O ELECTRO NEWS produced naturally at low levels, together with other sounds, even the The famous ACA -100 Amplifier - a self-balancing, squeaking of chairs and shuffling of drift -correcting, direct- coupled amplifier - the most feet. One very prominent musician, satisfying musical amplifier ever designed. Based on LAFAYETTE HI -FI early Loftin -White circuits, perfected by A. C. Shaney who is a composer, arranger and con- in 1936. and now brought to e standard of quality far above that of any corresponding amplifier. Exclusive ductor and in whose home one of these features include: SELECTOR RACK amplifiers has been installed, said: hskFall Triode Expander. "You not only can hear the difference B.a frequency-discriminating noise suppressor. between the flute and clarinet, but you ashp.11 hi and lo freq. variable equalizers. Makes It Easy To if you ore satisfied with nothing less than the best, can also separate the first and second write today for free technical literature. clarinets when they play together ". Special models for all magnetic cartridges. Controls It will be noted that the circuit diagram does not show any gain control. COO' is authors' contention that an ARE It the CHOOSE ideal amplifier should be one which can be tucked in some corner and for- gotten while gain control and equali- Laid end to end, the components we zation should be accomplished in a have for your comparison would stretch separate control unit. The equalization more than a city block. Yet we've con- and gain controls together with a pho- AMPLIFIER CORP. OF AMERICA densed them into one rack in one sound- nograph preamplifier may well be n proof room. Practically known 398 -4 Broadway New York 13, N. Y. every it is desired. component is hooked up in this special part of an FM tuner. If a gain control, Lafayette hi -fi rack. From it you make however, to incorporate your choice of tuner, amplifier, speaker, the 0.5 meg grid resistor of the input baffle, record changers, etc. Test them stage may be replaced with a 0.5 meg in any combination. Compare them left hand taper volume control. No NEED RECORDING side -by -side! In this rack you'll find the equalization (tone controls) should be A makings of your radio -phono combina- added to this amplifier, as the feed - TAPE IN HURRY? tion that lias no equal in the commer- hack loop goes from the output trans- For emergency use. we will cial market. You'll also find single units former to the first stage, and the large rush -ship (by Air if outside to improve existing sound systems or N. Y. area) up to 20 reels of feedback will negate any York stock at receivers. And everything for LESS amount from oui New equalization introduced within the feed- prices listed for such quantities. til: 11 i'ß,11 .I t 1-r'R'1 back loop. If equalization is desired it must be incorporated before the vol- AMONG THE FAMOUS ume control. There is such power avail- MAKES FEATURED able at both the bass and treble end so ARE: that when the bass and /or treble boost .11t cc- Lan sing, today for complete Bell, Bogen, I;rotcning,Cinaud- is used, the result:; are positive and free agraph, Collins, Recording Tape price Espey, Fisher, Garrard, from distortion at all comfortable levels. General Electric, Goodall. Hallicrafters, list and a Free supply of When bass boost is added the founda- Howard, Jensen, Lafayette. Meissner, Program Identification National. Pickering, tion music is solid and free from thuds. Labels. Radio Crafts- To a couple of fiddlers -one who men, Scott, fiddles all day on a Stradivarius, the AUDIO & VIDEO PRODUCTS CORP. Stephens, other who fiddles all day with ampli- Stromberg- i 650 BROAOWAY, N.Y.19,N.Y. Carlson, fiers, this amplifier is the best that we Thord arson, have yet heard. We suggest that you University, build one and judge for yourself. UTC, Web- PARTS LIST ster, and ENGINEERING SCHOOL (.I, C7 -0.25 µf. 400 v. paper. AUDIO many other 1 in Sound C2, Cg 600 Y. paper. national- -.05 µf, r. i. .I AGNETIC re- C.4, C5 -10 µf, 450 v. electrolytic. I. Va.,l,. AUDIO Frequency ly - known Siren,,- Muting RraadeSst, Mo- C6-30 µf, 500 Y. electrolytic. tion- Picture. Television s and Commercial Recording. makes. JI, J2- Closed circuit jack, Mallory A -2 Approved for Veterans tllusr be insulated from chassis). HOLLYWOOD SOUND INSTITUTE, Inc. J3 connector. Amphenol 75 -PC151 1040 -A North Kenmore, Hollywood 27, Calif. send (or .\'/i II l'FII:L (IATALO(3 -Input (R1 is mounted inside this connector). Currespantrnre course, available cable connector, Amphenol 86- Dept. AK-9 J4 -Power LAFAYETTE RADIO RCP4 (4-pin male chassis plug). New York or Chicago address PI -100 ohm, 2W. wire wound potentio- meter. FOR SALE R1, Ra, R7 -0.47 meg, / W. Audio Consultant di.po.ing of large stock of COME IN FOR A R'.- 47.000 ohms. high fidelity audio rrnlipment including amplifiers, R5-470 ohms, % W. 10 %r. speaker rrl etn s, tweet erg, woofers, obiers, teat DEMONSTRATION equipment, etc. Manufarpmed by ALTEC LANSING. R4, R5- 22.000 ohms. 10%n, (matched). BROOK, BOGEN. RCA, TtAVEN, MOSTLY NEW NEW YORK: 100 Bth Ave. & 542 E. Fordhem Rd. Rs % W. 10 EQUIPMENT. SOME USED. ALL AT FRACTION CHICAGO: 901 Wert Jackson Boulevard -390 ohms. %. OF ORIGINAL COST!! SEND STAMPED, AD- BOSTON: 110 Federal Street Rg, R10- 47,000 ohms, 2 W. 10% (matched DRESSED ENVELOPE for list. Bow 311. c/o NEWARK: 24 Central Avenue meg, W. Audio Engineering, 342 Madison Ave., New York ATLANTA: 265 Peachtree Street R11, R12 -0.1 / 17. N. Y. Rta, 14, R22, R23 -100 ohms.

54 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com R15 -250 ohms, 10 W. wire wound. Rte. 17-1000 ohms, / W. R18- 27,000 ohms. MODEL R19-22,000 ohms. R20-150 ohms, 10 W. wire wound. 100 R21 -5000 ohms, 10%. BRIDGER T1- Peerless S- 265 -Q. Using a cathode follower of advanced design, the Power Supply BRIDGER makes it possible to measure the Cs, C9-0.1 µf, 600 v. paper. charac- Cto, C11, C12-8 µf, 600 v. oil filled. teristics of high- impedance electro- Ft- Littelfuse 342001 fuse extractor post with 3AG fuse, 2 amps. nic circuits without affecting the J5 -Power cord socket, Amphenol 77Ú1P4 (4 -hole socket). performance by the addition of L1, L2-Peerless C-325 -A. 10 11, 120 ma, either the capacitance or the load- d.c. resistance 240 ohms. Tÿ- Peerless R- 560-A. 800 v. CT ing effect of the 5vat3a; 6.3vat6a. at 200 ma; measuring instruments, and without introducing hum into the circuits being measured. Power Cable 1- Female connector, Amphenol 78 -PF4. 1 -Male connector, Amphenol 86 -P\14. SPECIFICATIONS 4 -wire cable, of required length. THE Model I CO Bridger Input I m pedane.: Approximately 100 Ine.01003 in parallel anis ow( end AUDIO INSTRUMENT i All resistors are 1 -watt, 20% tolerance, un- at of three -foot cable. less otherwise specified. Output Impedance: 200 ohms, one side grounded. Voltage Ratio: Output voltage/Input voltage = 0.05, or -0.2 LINE db up to limit of undistorted output. Undistorted Output: 30 volte, when frrding a low.eaparitanee cable and typical high- impedance load. OW put /input ratio will not change over 2 per cent up to 30 volts and 10,000 L1ni a t re Preamplifiers ens, for nor up to 35 volta and 5000 cps. Undistorted output 640AA Condenser limit drops at higher frequencies, reaching 6 volta at Microphones 200 Ws. Noise: Output noise equivalent to 00 microvolt, input, when additional fed by high- impedance circuit. This low value has been achieved by using d.c. on the heater circuit of the cathode- LOGGER -VTVM and loga- follower tube. rithmic recording -meter amp- Dimensions: 5/ x 6 2 11 inches. Weight: 9 lbs. lifier with 50 -db range jiat V lJWAdi AUDIO INSTRUMENT CO. DISC -NOISE METE' In order to complete the catalog of 1947 Broadway New York 23, N. Y. test records which appeared in the Sep- tember issue, the following types are described - having been released after AUDIO the nic'in,ll list lca< prepared. ENGINEERING SUPPLIES KEYS CLARKSTAN 102M 12 -inch, 33 -1/3 rpm. Vinylite, SF. PANELS PLUGS Microgroove audio sweep -frequency rec- POWER SUPPLIES ord, similar to 1000A but for long -playing microgroove records, covering range from 70 to 10,000 cps and recorded with GAIN SETS NAB characteristic. Sweep repetition TRANSFORMERS rate, 20 per second. 2000S 12 -inch, 78.26 rpm. Vinylite, SF. EQUALIZERS Steady -state frequency record ; recorded KNOBS DIALS CV above 500 cps, constant amplitude below. Frequencies: 500 cps, 10, 9, 8, 7, 6, break, 5, 4, 3, 2, and 1 kc; 700, break, 500, 300, 200, break, 100, 70, and 50 cps, fol- VU METERS lowed by 1000 and 500 cps. 2001S/20025 12-inch, 33 -1/3 rpm. Vinylite, n p RE.0510 DF. Microgroove tai`v steady -state frequency auno DB METERS record. Frequencies : 1 kc; 10, 9, 8, 7, 6, 1reak. 5, 4, 3, 2, 1.5, and I kc; 7110, break, 500, 400, 300, 200, 150, break, 100, 70, 50, and 1000 cps. One side recorded with TRANSMISSION LINE TERMINAL BLOCKS NAB modified characteristic; other side recorded CV above 500 cps, constant amplitude below. AMPLIFIERS PATCH CORDS FILTERS 101 12-inch, 33 -1/3 rpm. Vinylite, SF. In-

termodulation test record, 1 :4 ratio, 7 kc and 100 cps recorded with NAB charac- ICnníé teristic. Clarkstan frequency records may be ob- CINEMA ENGINEERING COMPANY tained from most radio jobbers, or from 1510 WEST VERDUGO AVENUE. BURBANK, CALIFORNIA the Clarkstan Corporation, 11927 West lapon Agemr avec. nom,n, Pico Blvd., Los Angeles 34, Calif. t Ltd 701 Cloy Woe San Francisco, CN., U. S. A.

AUDIO ENGINEERING NOVEMBER, 1949 55

www.americanradiohistory.com BETTER ELECTRONIC EQUIP BENT The IMPOSSIBLE took 3 years! ADVERTISING v\vb tier performance didn't just happen STANDAREIZED nor is it just another amplifier. It is the result INDEX of many thousands of hours of painstaking research and development resulting ill a radically different, READY - complete and patented solution to the problem both electrically and mechanically. This McIntosh circuit has better than a IO to I advantage over conven- TO -USE tional circuits. Allied Radio Corp. 56 Look overer these It Is the result that counts. Altec- Lansing Corp. 3 51 performance characteristics which are fully met -- CABINETS Amperite Co., Inc. 41 Ampex Electric Corp. 2 a Amplifier Corp. of Americo 54 CHASSIS Andrew's. Radio Company 50 aa Arnold Engineering Co. 7 Audak Company 29 ALL Audio Devices, Inc. Cover 2 PANELS Audio Facilities Corp. 48 P. A. a Audio Instrument Co. 55 NEEDS Audio Pacific Co. 44 RACKS Audio & Video Products Corp. 54 Par -Metal 50W -1 McINTOSH AMPLIFIER Equipment 01 ,.I Inc. 43 I. 50 walls fry" - Ballantine Laboratories, is preferred by 20 cycles In 24 I,. Boonton Radio Corp. 41 2. 1 nb orr less inter nmlulo nun di st onion up to Service Men, loo pea Bozak, R. T. 36 Amateurs, and 3. I ^o or less hate onie distort tun at 50 walls Brociner Electronics Lab 44 on any frequency - 20 cycles to 20 k l bicycle=. Manufacturers 4. Small size mounts on 7' x I9- relay rack. because they're 5. Adequate design margin fur safely. Camera Equipment Company 49 at watts: adaptable, easy - 6. High plate efficiency 60ó 50 70't Cannon Elec. Dev. Co. 35 at 60 watt. to- assemble, eco- 7. Low power consumpl ion fill watts no signal; Capps, Frank L. & Co. 50 f output. nomical. Beautifully 100 watts at 50 walls Co. 55 Low Infernal impedance, 1 /10 nor- Cinema Engineering S. generator designed, ruggedly 't mal: eliminates distortion due to load hnped- Clarkstan Corp. 45 change and reduces "hang over" effects constructed by spe- ance Cook Laboratories 38 In load device. cialists. Famous for 9. Simplified servicing - all plug -in elements. 10. +2 db 10 cycles to 200.000 cycles. Daven Co., The Cover 3 quality and economy. 11. Negligible Impulse distortion. 12. Negligible phase shift Iless than 201 - 20 Write for Catalog. .i cycles to 35 kilocycles. Electric Indicator Co. 42 The McIntosh 15W. I Amplifier has situ I tar Electronic Workshop, Inc., The 38 lmwer output. rharacferisl ics except for maximum Electra- Voice, Inc 25 PAR is dcdieeted -METAL The McIntosh Engineering Laboratory to produce only one line THE HEST: CORPORATION - Fairchild Recording Equip. Corp. 37 PRODUCTS dealer for the McIntosh story or write to us. 32 -62 -49th ST., LONG ISLAND C TY 2. N.Y. Ask your Furst Electronics 34 McIntosh Engineering Lab., Inc. Export Dept.: Rocke International Carp. 40 Street, New Yogic 1e 910 King Street Silver Spring, Maryland Gordon, Herman Lewis __48 13 East Telephone: Juniper 7 -9200 Hartley, H. A. Co., Ltd. 56 Harvey Radio Company, Inc. 27 Hollywood Sound Institute 54 NO OF DEVALUATION Jensen Mfg. Company _9 HARTLEY- TURNER QUALITY The 215 speaker has I... .elliog steadily Lafayette Radio 54 at $60 because its per0am.,nce -cost figure LeBel, C, J. -_48 is exceptionally high. We did not need the Livingston Electronic Corp. 50 NEW help 171 of the British Chancellor to boost AWED'S our sales They by in the U.S.A. gained Magnecessories 53 honest endeavor allied to good design and the position so far as we were concerned Magnecord, Inc. 30 was O. K. McIntosh Engineering Lab. Inc. 56 CATALOG! is stay Our first instinct to let the price Measurements Corp. 52 1950 where it was, but we might bo thought of pulling a fast one if we didn't reduce. In this business we don't pull fast ones and Newark Electric Co., Inc. 48 for the moment the pride rimes down to Newcomb Audio Products 42 $40. which is virtually where it was before 196 PAGES - we had to raise it because of increased cost Par -Metal Products Corp. 56 of production. 30 Everything in But devaluation is not a wizard's trick of Peerless Elec. Products shifting unsaleable COMMOd ities, It is a Pickering & Co., Inc. 33 Radio and realization of what the £ is really worth. Presto Recording Corp. 8 The inevitable result is a rise in the cost 46 Electroni, c of living and of raw materials in Britain. Proctor Soundex Corp. This has already taken place. So our new Professional Directory 48 price is based on what the speaker costa to make, allowing a reasonable profit for our- Racon Electric Co., Inc. 53 GET RADIO'S selves. GUIDE Rek -O -Kut Company, Inc. 34 LEADING BUYING Hartley -Turner products will never he Engineers: At: available in the "bargain basement," We Service Technicians and Somerset Laboratories, Inc. 5 I.IED's 1950 Buying Guide brings you all have made our U.S. customers because we val- can offer something you can't get anywhere Standard Transformer Corp. 4 the new releases and money -saving largest stocks of else. The '215 speaker at $40 is coupled with Stephens Manufacturing Co. 47 ues - from the world's a 20',4 reduction in prices quoted in litera- test instruments, amplifiers, P A. sys- ture already sent out, and this discount Sun Radio & Electronics Co., Inc. 53 tems and equipment, tubes, parts, tools, applies until our new price list has been Sylvania Electric Products, Inc. books and accessories -ready for instant sent out (and it may cost you more then). expert shipment. Send today for your In a world of financial chaos we are stick- Tech Laboratories 51 FREE new 196 -page ALLIED Catalog. ing fast to performance that matters and the sooner you switch to Hartley- Turner the Terminal Radio Corp. 32 sooner will you realise that there is at Triad Transformer Mfg. Co. 52 least ALLIED RADIO CORP., DEPT. 17 -1 - -9 one company which will never sacrifice qual- 39 Turner Company, The 533 W. Jackson Blvd., Chicago 7, III. ity to expediency. We don't mass -produce New ALLIED Catalog. and we don't want to because we pin our United Transformer Corp. Cover 4 Send FREE faith to craftsmen's hand -made quality. U. S. Recording Co. 48 Read uó our past advertisements Name and get in touch today University Loudspeakers, Inc. 31 H. A. HARTLEY CO., Ltd. Ward Leonard Electric Co. 35 Address 152 HAMMERSMITH ROAD Wells, Winston 48 LONDON W. 6, ENGLAND Western Electric Company 10 ALLIED RADIO

56 AUDIO ENGINEERING NOVEMBER, 1949

www.americanradiohistory.com Choose .. . From Daven's Complete Line of Volume Level Indicators Daven Volume Level Indicators are designed to indicate aucio levels in broadcasting, sound recording and allied fields where visual indication of volume is desired. Extremely sensitive, they are sturdily constructed and correctly damped for precise monitoring. Preferred by Type 920 Rack motel, low -level bridging Irrding sound and electronic engineers through- type. Meter multiplie- ranges out the world, these units incorporate all the -20 VU ío+20 VU. Power sup- latest DAVEN mechanical & electrical features. ply, 100 -130 V, 60 cyue AC. with voltage regulator for nor - mol variations. Reference level: 1 my into 600 ohms- .pecial ranges on request. GENERAL SPECIFICATIONS:

Imput ImpedarceType 910 and 911- 7500 ohms. Type 915 - 7500 ohms bridging and 600 ohms terminating. Type 920- 12,500 ohms. Frequency Range Less than 0.2 db variation from 30 fo 17,000 cycles. Meter Scale -20 VU to -3 VU and O to 100%. Type A has VU reading on Type 915 upper scale. Type B has percentage reading on upper scale. Rocs model, terminating and bridging type. Meter Scale is large, clearly marked and carefully designed to minimize multiplier range "Termi- eye fatigue. nating, -6 VU to +32 Indicating Meter NAB Standard; 4 inch square, rectifier type possessing ideal VU; bridging +4 VU to +42 VU; or terr'isating, characteristics for monitoring purposes. -6 VU to +16 VU; bridg Mounting Rack models 19" long for standard relay rack: portable models 'ng, t 4 VU to t 26 VU. available in walnut 2 VU steps. Reference cabinets. level;1 my into as ohms Finish Standard, black alumilite panel. Other colors available upoe request.

Type 910 Rack model hos toms characteristics os Type 911. Available with Write to Dept. A -6 for additional information. '` jr Type 911 illuminated scale, if Partible model,bridging desired. type. Meter multiplier is a constant impedance T' The best equipment deserves network which extends the range of the instru- the finest attenuators ment in steps of 2 VU Always from +4 VU to 1-42 VU ... Specify DAVEN! or + 4 VU to - 26 VU. Reference level: Ism in- to 600 ohms.

191 CENTRAL AVENUE NEWARK 4, NEW JERSEY

www.americanradiohistory.com FILTER SPECIALIS7S PRODUCERS OF PER MALL G Y MI TOROID COILS AND FILTERS FOR 0 A DECADE =1111111,11 ' iimraiiiniìi .a 11111 IliI!III1NIiIIi11 OD

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Fillers employing SUBOUNCER toroids and SU B -C U NCER special condensers represent the optimum in performance. The TOROID FILTERS miniaturized filter band pass Titer shown weighs 6 ounces.

ISO VARICK STREET !1 NEW YORK 13. N. Y. writs for catalog PS-409 EXPORT DIVISION: 13 EASt 'Ot\ STREET. NEW YORK 16, N. Y., CARIES: 'ARIAS"