Contents TH E HI-F I IDEA Hi-fi and stereo Hi-fi and live sound ..... 2 Hearing errors 2 Chapter 7 THE HI -F I CHAIN OF EV ENTS 4 Audio sources ...... 5 Amplifier/Receiver ...... • .. 5 Speaker systems/Headphones ...... 6 Chapter 2 THE TURNTAB LE 7 Motor and drive system .. 7 Turntable platter ...... 9 Pick-up system ...... 9 Phono cartridge ...... • . . . • ...... 10 Stylus ...... 12 Demands upon phono cartridges ...... 12 Tonearm ...... 13 Auto-return tonearm ...... 14 Automatic record changer ...... _ . . . . . 15 Anti-skating device ...... 15 How to read turntable specifications . . . . • ...... 16 Chapter 3 THE TUNER ...... • . . . . 18 AM and FM 18 Functio n of FM tuner ...... 19 FM MPX (stereo) ...... 2 1 Tuner controls ...... 22 How to read tuner specifications ...... 24 Chapter4 TAPE EQUIPMENT 21 Recording a nd playback process 28 Tracks ...... 28 Tape speeds ...... 29 Tape quality ...... 30 Low-noise high-output tape ...... 30 Chromium dioxide tape ...... _ ...... December, 1975 Tape deck, recorder, player? ...... _ ..... Revised Fifth Edition . 31 Dolby noise reduction system ...... _ ...... 31 ...... July, 1971 Open reel, cassette, cartridge? ...... 32 First Edition . Published in Japan Drive mechanism ...... _ . . . . 33 2 and 3 motor systems ...... • ...... 34 by PI ONEER ELECTRONIC CORPORATION Recording and playback heads ...... 34 3-head decks ...... 4-1 , 1-chome, Meguro, Meguro-ku, Tokyo 153, Japan 35 Amplifiers, equalization ...... 36 Copyright © 7972 by Pioneer Electronic Corporation Automatic stop, auto-reverse . . . • . . . 37 How to read tape deck specifications ...... 37 Chapter 5 THE AMPLIFIER ...... 39 . . . ted amplifier receiver 39 Pre-amplifier, power a mplifier • Integra • 40 Tile Hi-Fi Idea Pre-amplifier functions · · · · · · · · · · · · · · · · 41 Phono equalization · · · · · · · · · · · · · · · · · · · · · · · 42 Ever since the first grammophones began squeaking their scratchy messages into •• • 0 ••• Inputs . · · · · · · · · · · · · · · · · · · · · · · 42 • • 0 0. 0 0 the ears of a surprised world around the turn of the century, there has been an Tape monitoring · · · · · · · · · · · · · · · · · · 43 uninterrupted search for better, clearer, finer methods of recording and replaying Volume, balance, tone controls · · · · · · · · · · · · · · · ...... 45 Filters, loudness co ntour · · · · · · · · 46 sounds. Yet all the major breakthroughs were made in the last two decades - the first • • 0 • •••• Headphone jack · · · · · · · · · · · · • · · · · 46 LP records, the invention of stereophonic recording and reproduction, the beginning of Power amplifier function · · · · · · · · · · · · · · · · · · · 46 FM and FM stereo broadcasting, the development of noise-free amplifiers, the intro Criteria of quality · · · · · · · · · · · · · · · · · · · · · · . 47 duction of solid state engineering into audio equipment and, quite recently, the advent 0 • • 0 0 •• Protector circuits · · · · · · · · · · · · · · · 48 of four-channel stereo sound. Speaker terminals . · · · · · · · · · · · · · · · · · · · · 48 How to read a mplifier specifications · • · · · · · · · · · · · HI-FI AND STEREO Chapter 6 Here we mu st make a distinction between two terms LOUDSPEAKERS AND HEADPHONES 51 51 that are often confused: high fi delity and stereo. High Structure and functions · · · · · · · · · · · · · · · · · 51 Double cone and coaxial spea ker s · · · · · · · · · · · fide lity or hi-fi makes very mu ch the same demands as 52 Two-way, three-way, four-way systems ...... 53 an oath sworn in a court of law: " ..... the truth, the Directionality · · · · · · · · · · · · · · · · · · · · : : : : : : 53 whole truth, and nothing but the truth." The goal of Speaker enclosures · · · · · · · · · · · · · · · · · 54 hi-fi is to record, preserve and rep roduce sou nd, chiefl y How to choose speakers .. · · · · · · · · · · · · · · · · · · · 55 mu sic, exactly the way it was pl ayed by the performers, Crossover network, level contro ls · · · · · · · · · · · 56 without adding anything, without leaving anything out. How to read loudspeaker speci fi cations : : : : : : : : : : : 57 Headphones · · · · · · · · · · · · · · · · 58 Stereo, on the other hand, means that sound is E1ectrostatic headphones · · · · · · · · · · · · · · · · · recorded and reproduced via two channe ls in order to Chapter 7 add a directional, spatial sensation. Stereo creates th e MULTI-AMPLIFIER SYSTEMS · · · · · · · · · ~: same effect to the ear that 3-D ph otograph y offers to Reasons for multi-amplifier systems · · · · · · · · • · 59 th e eye. To continue the visual analogy: hi-fi demands Electronic crossover network · · · · · · · · · · · · · 60 sharp, clear, undistorted pictures; stereo creates an Features and drawbacks · · · · · · · · · · · · · · · · · · 61 Hints concerning multi-amplifier systems .... . •... illusion of space, width, and locations. Unfortunately, the two don't always go together. ChapterS There are stereo sets on the market wh ich do not deserve FOUR-CHANNEL STEREO ...... 63 63 the name "hi-fi" because thei r sou nd quality is inferior. four-channe l systems · · · · · · · · · · · · · · · · · · · · · · ••• 0 ••••••• 63 Conversely, there are hi-fi systems with only one channel Discrete system · · · · · · · · · · · · · · 64 Discrete four-channel tape · · · · · · · · · · · · · · · · · · · (" monoph on ic"}. 64 Discrete four-channel disc (CD-4 disc) · · · · · · • · · · · · The ideal hi -fi system has never and will never be 66 Discrete four-channel FM broadcasts · · · · · · • · · · · · · 66 built, simpl y because the demand to speak the whole Regu lar matrix system · · · · · · · · · · · · · · · : : : : : : 67 truth and nothing but the tru th cannot be realized. SQ matrix system · · · · · · · · · · · · · · · · · · Between the perform ers in the recording studio and the Chapter 9 li stener in his livin g room, there is a long and co m OF DOLLARS AND DECIBELS ...... 68 plicated chain of equip ment and transformations, tearing Chapter 70 off something from the original sound here, adding DO'S AND DON'T · · · · · · · · · · · · · · · · · · 69 something there. These unwanted fiddlings and diddlil)gs A GLOSSARY OF AUDIO TERMS · · · · · 70 can be reduced to a min imum - an d th is is wh at h i-fi PURCHASE PLAN FOR RECORDS technology is all about - but they can never be totally 89 & TAPES ... . . · · · · · · · · · · · · · · · · · · · · ·eliminated. HI-FI AND LIVE SOUND the bass-heavy bellowing of jukeboxes, the babble and On the other hand, hi-fi has things to offer that no squall of cheap transistor radios and TV sets -- the hi-fi li ve performance can match. Freedom. You, the li stener, novice hasn't had opportunity to train and hone his choose what you want to hear, when you want to hear sense of hearing. Experience shows th at, left to his own it and with whom, how many times. From this poin t resources, he wi ll usu all y choose an "impressive sound of vi ew, hi-fi isn't a substitute for live concert per ing" sys tem, mostly with exaggerated bass response and formances, it's an addition or, if you want, an poor bri ll iance. As his hearing becomes sharper, as he altern ative. gets used to the possibilities of his system and compares This brings us to another common misconception, it with his friends' hi-fi installations, he will gradually one that you find repeated in too many advertisements: ou tgrow his origina l purchase and wi ll begin to grade up. that a good hi -fi system will bring the concert hall into But since every replacement costs money, he will finally your home. It's simpl y not true, and it wou ld be bad if end up wi th a good system that has cost him much it were. First, much of the world's great music, both more than if he had bought it in the first place. We feel old and modern, wasn't composed to be pl ayed in that that ou r - and every conscien tious hi-fi salesman's - 19th century inventi on, the concert hall . Chamber advice to the hi-fi novice should be to trust a reputable music, first of all the string quartet, call s for th e manu facturer and store more than his own as yet intimacy of small rooms. Bach wrote his organ works as underdeveloped hearing. Even though, his fi rst encounter an integral part of church li turgy. Brass bands are for with hi-fi sou nd may not be pl easant at all, simply outdoors, and much modern music is composed especial because he is unaccustomed to hearing musical sounds ly for the recording studio and electronic reproduction. as they really are. But even those works which were intended for concert With these remarks we have fi nally touched upon the hall performance, such as the classical and romantic main theme of this booklet: How to choose a hi- fi sy mph onies, can't and shouldn't be played over a system, and how, as a salesman, to help a customer make li ving-room hi-fi system with concert hall volum e - the a wise choice. At Pi oneer, we want you to thin k in cannon in Tchai kovsky's 1812 overture wou ld shatter terms of Pi oneer hi-fi equipment, of course, and the the window panes. No, hi-fi isn't supposed to put the purpose of this brochure is to prov id e you with the concert hall in you r living-room; it's supposed to put tec~ni ca l knowledge essential for ma ki ng the right the music in your livi ng-room, and that it does cho1ce. In the fo ll owing paragraphs, you will find remarkabl y well. concise expla nations of the function of each component i~ a ~tereo hi -fi installation, as well as hints concerning HEARING ERRORS llsten mg rooms, com ponent match ing, an d a glossary While we're on the subject of misconceptions: there's of technical terms. We have tried to limit the technical another one that says "when choosing hi-fi equipment, explanations to the bare essentials (and even these have trust your ears rather than the manufacturer's specifica come out quite vo luminous) while avoiding over tions." Several reservations mu st be voiced against this simpl ificati ons and pure advertisi ng. You may wish to advice. The most important is that a person who buys a read on from this page to the end, or to skim, reading hi-fi system fo r th e first time in hi s life is in most cases onl y those sections that deal with things you are hazy ill-equipped to judge the quality of musical sound ~bout. E_ither way, we have tried to keep it interesting, reproducti on. Subj ected from morning to night to the mformat1ve and unbi ased. ceaseless trickle of non-hi -fi sou nds - the traffic din,
2 3 AUDIO SOURCES Chapter I At the recording studio, the sound waves em itted by the voices or instruments are caught by, in a stereo recording, two or more microphones and converted into The Hi-Fi Chabt of Ewents electrical sign als. These sign als are recorded on the so-cal led mas ter tape in th e form of magneticall y charged What happens to the sound between the recording particles. Recording engineers control the conditions studio and the listener's living-room? A brief explanation and later edit the tapes to obtain the desi red sound of the "musical flow char t" may be helpful in answering effect and to get rid of background noise, etc. What this question, in as much as it creates an awareness of results is called a "master tape" (or simply "master") the many transformations - and accompanying dif and from it are made records, tapes (in open-reel, ficulties - that the sound has to go through. cassette or cartridge formats), or broadcasts via rad io waves, and th ese "deli very sys tems" are what are Playback process avail able to you for reproduction in your hom e. Record player To be more specific, let's take th em one at a time. Fi rst, records. The signals on the master tape are con verted in to mechani cal vibrations wh ich are engraved on a rotating di sc, usually made of lac quer, in a process known as '''cutting. " From this engraved di sc (also called a "master") th e record manufacture r makes a metal mold which in turn is used to press "biscuits" of viny l which end up as the records you buy and pl ay. Mak ing pre-recorded tapes (open-reel, cassette or car tridge) from th e master tape is simpl er: th e signals from Fig. 1- 1 the master are passed from a playback head to th e Recording and Playback recording head of a tape duplicator and stored on the in a Monophonic System "dubbed" or duplicated tape in the form of magneti zed particl es of iron ox ide (see "Record ing and Play back Process" in Chapter 4). For broadcast on AM or FM waves, the master tape (or a copy of it) is pl ayed on equ ipment in the studio and transmitted; you receive it and reproduce it with the proper equipment. This brings us to the pl ay back or reproduction end of the chain, and the equipment you need to reconvert the information contained in the three delivery systems described above into sound. In a stereo system, these three di fferen t kinds of pl ay back systems are comm onl y ca lled "sound sources," although they are, of course, not the origin al sources of sound. They are: 1) turntable, cartridge and stylus (NOTE: th e nam e "record player"
5 4 is perh aps more apt, but in today's usage it usually denotes low-priced equipment withou t claim to hi-fi performance.); 2) tape deck (NOTE: the name "tape player" also can be used, but like "record player" it usually denotes someth ing less than high quali ty hi-fi perform ance.); and 3) AM, FM or FM Stereo Tuner. None of th ese sound sources by itself can produce a signal strong enough to drive a hi-fi speaker system, as is explained below. Therefore, they must be connected Speaker systems to an amp li fie r (or a receiver, which simply is an integrated preamplifier and power amplifier combined in the same cabinet with a tuner capabl e of receiving FM and also usua lly AM broadcasts).
AMPLIFIER/RECEIVER Fig. 1- 3 Hi·Fi Stereo System The signal sup pi ied by tuner, tape deck or turn tabl e is too feeb le to be converted into audible sound . There· fore, an ampl ifier is required to augment th e signals and supply them to the speaker systems. The ampl ifier also prov ides a convenient opportunity to control the volume, tone quality and other characteristics of the sound which is why it usuall y has a whole array of knobs and switches. Very comm only, amplifier and tuner are combined into one unit whi ch as mentioned above is then cal led a "receiver," a word that mu st not be confused with a regular rad io or TV receiver.
SPEAKER SYSTEMS/HEADPHONES The speaker systems (or, for private listen ing, th e headphones) are the fi nal link in th e chain of sound reproducti on. What fin all y comes ou t of the speaker systems is the acid test of the whole audio system, and they mu st be chosen with equal ly great care as all oth er components. Now, a word from our sponsors: Pioneer makes (and sell s!) all parts of a hi-fi system, from tuners, turntables and tape decks to amplifiers, receive rs, headph ones and speaker systems, in a startling variety of models to match all needs and budgets. In the following chapters, the individual components, their functions and charac teristics will be exam ined in some detail, together with ex pl anati ons of how to read and evalu ate th ei r specifi ca ti ons. 6 7 tions, inconsistencies an d wobble, and in a turn tabl e Chapter2 these wou ld cause noise, uneven ness of pitch ("wow") and rum ble. Let us exami ne what is being done by turntable designers to cou nterac t these troubles. The Turntable First, the phono motor in a hi- fi tu rntable has to meet six conditions: (a) it must revolve at a specifi ed, The turntable, and its components including tonearm, constant rotati onal speed; (b) its speed must remain cartridge, stylus, etc., is the sound source which makes constant even if the supply voltage fl uctu ates; (c) it it possible to reconvert audio information stored in disc must operate almos t withou t vibrations; (d) it must have recordings. Those that are designed well and perform power ful torque (rotati onal force) to overcome changes properly do this with maximum fidelity. On a stereo in its load and to bri ng the turntable qu ickly up to the phonograph record, the sound information is contained speci fi ed speed, (e ) it must not produce any magnetic in the microscopic grooves or rather, to be exact, in the tl ux lea kage as this would induce noi se ("hum") in th e undulations of the two walls of the groove. One (the pickup system; and (f) it mu st be ab le to operate con inner) wall bears the information for the left stereo tinuously for many hours. channel, the other (outer) wall that for the right channel. Essential ly there are three types of drive systems: The two are at an angle of 90 degrees. 1) rim drive; 2) belt drive; 3) direct drive. In the rim drive system, one or more id ler wheels transfer the 1 Arm Elevation Device power fro m the motor pu lley to the tu rntabl e platter 2 Stroboscope 3 Cartridge by way of friction of their rubber rims. Advantages arc 4 Head Shell 5 Function Lever relatively low cos t, easy speed changes an d the possibility 6 Speed Selectors to use motors of comparatively low torque. On the 7 Speed Control Knobs 8 Anti-Skating Control other hand, as the ru bber rims wear ou t, a certai n 9 Counter Weight amount of slippage is bound to occur. 10 Lateral Balancer 11 45rpm Adaptor The common belt drive system emp loys a rubbe r 12 Arm Rest or plas tic belt to convey the motor power to the turn 13 Tone Arm table. Speed changes are made by guid ing the be lt around either of two motor pull ey secti ons with dif fe rent diameters. The belt prevents motor vibrations from reaching the turntabl e, thus reduc ing noise and rumble. In precision engi neered hi-fi turntables, the belt is often made of polyu rethane because of its resistance to heat, hum id ity and oil an d its low elas ticity. DRIVE SYSTEM Recently, a third drive system - direct drive - has The tas k of the turntable drive system seems simp le appeared on the market, receiving much atten tion and at first glance: to do nothing but rotate the disc at a winning many customers despite the relatively higher specified, constant speed. But at closer in spection we see cos t attached to turntables wh ich use it. Bas icall y, the difficu lties hidden behind those innocent looking the term "direct drive" explai ns the system: a brush less Fig. 2-2 words " nothing but," "specified" and "constant." Any DC motor is used to drive the platter direc tl y, with no Belt Drive System mechanical system with moving parts generates vibra· connecting rim idl ers or belts. This is achieved by
Model PL-71
8 9 centering the drive shaft of the pl atter in the center of PICK-UP SYSTEM the motor itself; the motor rotates at very slow speeds Most efforts in the design of hi -fi record playing (33-1 /3 or 45 rp m) th us eliminating th e need for speed equipment have been concentrated on the pick-up ~·~~~~ reduction mechani sms. The motor is controlled by system, i.e. tonearms and phono cartridges. an electronic servo mechani sm to maintain speed accuracy. Head shell Tonearm Balance weight TURNTABLE MOTORS IIJIIJa b c d For rim drive and bel t drive sys tems, onl y two types "'- Cartridge a: Left signal only Stylus Arm rest b: Right signal only of AC motors can be used: th e induction motor and th e c: Left and right signal of synchronous motor. Of th ese, the induction motor is Fig. 2- 4 Pick-Up System any phase d: Left and right signal of being used mainly for low priced turntables because its Th e difficulties are caused by the great number of _ same phase speed is li ab le to flu ctu ate with load var iations. This often co nfli cting - factors th at have to be taken into Fig. 2- 3 DIRECT DRIVE SYSTEM leaves the sy nch ronous motor. Its speed is locked to the consideration. The theory of phono pick-up systems The Groove of Stereo AC line frequency and therefore very constant even if alone cou ld fi ll a boo k. Disc and Stylus the power voltage fluctu ates. A special - and ra th er Movement expensive - va ri ety is th e hysteresis sy nchronou s motor PHONO CARTRIDGE whose features inclu de freedom from vibrations an d The cartridge, mou nted in a shell at th e tip of the noi se-free operation. Most top class turn tables are tonearm, has the task of tracking the record grooves equ ipped with hysteresis motors alth ough other des igns and transform ing mechanical vibrati ons into an electric (servo-controlled DC an d AC motors, etc.) have been signal. As th e stylu s ("needl e") res ts in the rotating tri ed with good results. record groove, it is defl ected laterall y and vertically in Dampers Elements As all of these motors run at higher· rpm's th an th e accordance with th e undulations in the groove walls. Stylus Cantilever 33-1/3 and 45 rpm required for turning th e record, they Thi s function already expl ain s one of the greatest Flg.2- S problem s: th e stylus must fo ll ow ("track") the com must be coupl ed to the turn table by means of speed Sc~ematlc VIew of redu ction mechan isms such as the rim drive or belt pl icated meanderings of the groove in stantly and without a Ceramic Cartridge drive systems explained above. loosing contact with the wa lls or jumping out of th e groove. To be able to do this, the mass of th e sty lu s and TURNTABLE PLATTER all moving parts must be kept as li ttl e as possible The turntable platter must be large enough to ac ·because the greater th e moving mass, the higher its com modate 12-inch LP's, but there's anoth er reason inertia, i.e. resistance to qu ick changes in move ment. for mak ing it as large and heavy as the motor torque will Other conditions for good track ing are: a sufficient perm it. A large, heavy pl atter, once in motion, serves downward force call ed "tracking force" must be applied as a fl ywheel an d keeps th e speed cons tant by its own to the stylus to keep it in the groove - which, if too iner tia. Turntab le platters are made of pressed steel great, wi ll cause sty lu s and records to wear out more pl ate or di e-cast aluminum all oys. The latter is preferable qu ickly than necessary, however; and the stylu s assembly for hi gh quality systems because of its better electrical mu st have enough freedom of movement, technicall y Fig. 2-6 properties (anti-magnetism) and greater machining preci called "compliance" or sometim es "trackability ." Schematic VIew of sion. To work as an efficient flywheel, th e turntable The mechani cal vibrations pi cked up by the stylu s a Moving Magnet pl atter must be balanced just like an automobile whee l. are converted into an electri cal signal by any of a Cartridge
10 11 number of systems. Let us briefly ex plain their func th ey promise excellent resul ts. One is the se m i c onductor .------~----. tions and weigh th eir merits and demerits. cartridge in wh ich mechanical forces created by stylus Ceramic cartridges utilize the so-called "piezo-electric vibration work up on a silicon semiconductor, changing effect. " Movements of the cantilever (which is fi xed to its elec trical resistance in correspondence with stylu s the stylus) appl y varying forces - twi sts and pressu res - movement. The oth er type is called "photo-elec tric." on a special crystall ic material wh ich generates an Light from a tiny bu lb in th e cartridge fall s upon a electrical vo ltage in accord ance with the stylus move photo transistor whi ch converts it into an electric ment. The rigi d armatures requ ired to exert thi s twisting voltage. By mov in g a slotted mas k in the path of th e Fig. 2- 10 Photo-Electric force natu rally inc rease the mov ing mass, and the light beam, the light intensity can be varied in ac Cartridge cerami c elements are sometimes affected by heat an d cordance with stylus vibrations. moisture. Although comm onl y used in low priced Fig. 2- 7 STYLUS Schematic record players, they do not fu lfi ll th e di sc rim inating VIew of a Moving deman ds of real hi-fi. Th e stylu s in a hi-fi cartridge is made either of Coli Cartridge Mov ing magne t (MM) cartrid ges have a tiny perma sapph ire or diamond. Diamond is pre ferable because of nen t magnet attached to the cantil ever which, by movi ng its longer service life which averages 400 to 800 hours of Coils fr eely between an assembly of coil s, induces a voltage operation. Its durabil ity depends large ly on the tracking in th ese coil s. Mov ing magnet cartridges are the mos t force, i. e. the weight with which the stylus is pushed comm only used hi-fi cartridges, offer in g the benefits of aga in st the wall s of the record groove. The tip of th e small mov ing mass and relatively high output voltage, i.e. stylu s is machined to ex treme precision. It can be effi ciency. radial, with a tir radius of about 0.5 mil (1 mi l = 1/1000 The reverse principle is applied in mov ing coil (MC) inch) fo r a stereo cartridge, or ell iptical, wi th its greater ca rtridges. Here, the magnet is fi xed and th e coils- one wid th across the record groove. Elliptical stylus usuall y for each chann el - move in the magnetic fi eld, thereby deliver better response to high audio frequencies, i.e. receiving an induction voltage. The moving mass of MC they track hi gh notes better. cartridges is even smaller than that of MM types, but Parabo li c Stylu s and their output voltage is so low th at the amplifier mu st For mono LPs I mil (0.026mm) have special inputs of very hi gh sensitivity. Shibata Sty lu s Mono/stereo 0. 7 mil (0.017mm) Newly-designed stylus tips hav ing In addition to low mov ing mass, MM an d MC Stereo 0.5 mil (0.012mm) " line con tact " with the disc grooves. cartridges offer very good fre quency response and Stylus tip radius Especially distinguishe d by frequen- channel separation, factors whi ch explain their great Stylus tip cy response and separation cha rac- popularity in hi- fi appli ca tions. 1 te rist ics, thus perfect for C D-4 Indu ced Magnet (IM) cartridges have fi xed magnet Fig. 2- 11 Various Stylus Tips d iscrete four-channe l d isc rep rodu c- and coil assemb lies. Two ti ny iron plates move in the ""--~------J tion . ~ magnetic field, causing variations in the magnetic flu x DEMANDS UPON PHONO CA RTRIDGES Snlcon element and, th ereby, in the coils' indu cti on voltage. Let us sum up once more the demands made upon Stylus All the cartridge systems described above generate an a hi-fi cartridge. It must trac k the record groove with Fig. 2- 9 electrical signal directly from th e mechani cal vi brations. precision, fo ll owing even abrupt movements such as Schematic View of There are, however, two types of cartridges which sudden trumpet blasts with ease. This abil ity is usually a Semiconductor requ ire an outside voltage su pply. This is the chief Cartridge expressed mathematically as "comp liance." The cartridge ....______. reason why they are not bei ng used widely, although should trac k th e record even at low force, because too
12 13 much pressure between stylus and groove causes disc adjusted by fi rst balancing the arm horizontally, then ....------. and stylus to wea r out quickly. Because of th e ex tremely applyin g the des ired force by moving the balance ~a~~~\ tiny area of contact between stylu s and groove walls, weight (or a sub-weight) further toward th e arm pivot ~ seemingly fantastic pressures occur - at a track ing fo rce ("static balance" ). On some arms tracking force is . Spring / Jd, of a few grams the pressure is several thousand applied by the force of a spring {"dynamic balance"). Fig. 2- 14 atmospheres, in other words thousands of t imes higher On most high qu ality turn tab les, the tonearms are Dynamic Balance th an the air pressure in an automobile ti re. equipped with several auxi li ary controls to improve their The cartridge must separate the two stereo channels perfo rmance and ease of operation. ~Only tracking force applied clearly and at all au di ble frequencies. And it must de liver It requi res a certain dexterity to set th e stylu s down an output voltage large enough for the stereo amplifier on a record and to lift it off again, and coun tless records to work with. and cartrid ges have been da maged by careless handling. Fig. 2- lS Most hi -fi tonearms are therefore provid ed wi th a lifter or .._s_ta_t_lc_B_al_a_n_ce_____ ..J TONEARM cueing dev ice, mostly a hydrauli call y damped piston A cartridge can only de liver its full performance if whi ch gently fl oats the tonearm down on the ini tial it is mounted on a tonearm of eq uall y hi gh quality. record grooves and li fts it up again at the end. The tonearm's main function is to hold the cartridge in ANTI-SKATING DEVICE its path wh ile it travels across the record, an d to apply th e necessary tracking force whi le compensating fo r One other device must be men ti oned here - the anti other, un wanted forces. skating device prov ided on many high quality tonearms, Mos t high quali ty tonearms are made of light metal also called sidethrust compensator or ins ide force alloy because of its light weight, stabil ity, and easy canceler. To understand its function, we must realize mach ining. By thei r shape, arms can be grouped into th at a tricky combination of forces ac t upon stylus and three types: straight (or 1-shaped) types, j-types, and tonearm as they track th e record. Among these, the mos t $-types. In every case, th e shell -car tridge assembly is at disturbing is a force which tries to pull the tonearm an angle (o:) to the arm ax is, the line connecting stylus inward, toward the center of the disc, th ereby pushi ng tip to arm pivo t. This angle is called offset angle, and th e sty lu s aga inst the in ner wa ll of the record groove or, Anti-Skating Control in extreme cases, causing th e stylus to jump out of th e .._____ (M_ o_d_ei_P_L_·_S_1_A_)...... ___ ...... _ __...... __-....~ its purpose is to minimize th e arm's track ing error. (Tracking error is the angle that th e cartridge ax is groove. To assure perfect trackin g of both groove walls deviates fr om the record tangential at any given point (both stereo channels!), th is fo rce mu st be compensated. on the record. The smaller the trackin g error, the better.) Usuall y, a li ttle weight affi xed to a string applies a On some economy type equipment, the shell cannot be corresponding cou nte rforce on the tonearm. As the removed from the tonearm ("in tegrated arm"). Most skating force varies with the sty lus tracking force, the modern tonearms, however, have standardized plu g- in anti-skating device shoul d also be re-adjusted each time the tracking force is changed. co nnecti ons fo r the cartridge-shell assem bl y, so th at all cartridges fo llowing these standards can be freely AUTO-RETURN TONEARM interchanged. One step further advanced towards automation is the Since diffe rent cartridges require diffe rent tracking "auto-return" tonearm - at th e end of the record it forces, th e tonearm should have a movabl e balance li fts off and returns to its rest position au tomaticall y.' we ight on its rear end, preferably with a graduated scale ...... ,;;;...;.;~..;.;;;.;s..______. of tracking fo rces. The tracking force can then be
14 15 up-and-down effec t in th e pl ayback sou nd. Flutter is a high-speed quive r, especiall y noticeable in long-held notes. Both M C caused by defi ciencies in the drive 'system of the turntable and arc ex pressed as a percentage in the specifica tions. The small er the figure, the better. Max imu m al lowabl e wow/fl utter percentage for high fidelity pe rform ance from a turntable is arou nd 0.1 5% (WRM S). b) Signal-to- Noise Rati o (S/N) This is a measure of the amount of low-pi tched " rum bl e" a turntabl e produ ces in r·e lation to the des ired signal. The larger th e S/N figure, the better. Hi -fi perform ance requires th e fi gu re to be 45dB or above. Speed selector Cartridge c) Turn tabl e Platter Weight is importan t here. The moment of inertia is Model PL-55X related to smooth rotati on, and weigh t, in turn, is The logical extension of this is the fully automatic related to inerti a. In belt-drive turntables the recom turntable. A singl e fun cti on lever controls the entire mended weight is between 3 lb. 5 oz. and 5 lb. 8 oz. For operation. In positi on start, the tonearm moves over the direct-drive models the weight should be abou t 2 lb. 3 oz. initial record grooves, the platter begins to revolve, the tonearm floats down, th e record is played, and at th e Hu'" to llt•ad l'm·ta·idnt• Sa•t•t·il il'alimtK end the tonearm li fts off and returns to its rest. There a) Frequency Response are usuall y two other controls: a speed selector, and a The lowes t and th e highest audi o frequ encies to whi ch record size selector which adju sts the tonearm drop a cartridge will respond are used to indicate the point for th e three common record diameters (12, 10, cartridge's frequency response range. The wider the Model PL- 55X and 17 inches). range th e better. Also, there should be no peaks or cl ips within the range. Hi-fi cartridges shou ld have a range of AUTOMATIC RECORD CHANGERS at least 20 llz to 16,0001 1z ±3d B. For discre te 4-channcl Pi oneer feels that at th e present stage of turntable reproduction, th e ca rtridge is requ ired to have an upper technology it is not possibl e to manufacture an auto frequency response limit of at leas t 45,000Hz. matic record changer that will reli ably and continuously b) Ch annel Separa tion live up to hi-fi requirements. The abil ity of a cartridge to separa te the tw o cha nnels of a stereo record. The fi gure is expressed in decibels, How to Read Turntable S&JerUiratlons and should be above 20dB at l,OOOHz. When comparing and evalu ating tu rntables on the c) Outpu t Vo ltage strength of th eir catalog specifi cations (you should li sten The voltage generated by the cartridge at a certain to them, too, before buying), the fol lowing technical stylus-to-groove velocity and at a 1 ,OOO Hz signal input. items deserve the greatest attention: Th is voltage may differ according to th e cartridge a) Wow & Flutter sys tem, but should be greater than the sensitivity (in Wow is a slowly cycling speed inconsistency causing an microvo lts, expressed " mV") of the amplifier's ph ono
16 17 inputs. Generally speaking, about 2.5mV is recom mended. Chapter:) d) Load Impedance The amplifier's input impedance as seen from the cartridge. For MM and IM cartridges the standard value The Tuner is about 47,000 to 50,000 ohms (47 to 50k0hms), Next to the turntable, the tuner is the most common which is what most amplifier phono inputs are designed sound source in hi-fi installations. In many cases, tuner to receive. MC cartridges have low impedance (2 to 20 and stereo amplifier are combined into one unit, a ohms), and the amplifier must have special MC or so-called "receiver"; in these instances, the tuner section "ceram ic" phono inpu ts. If no such inputs arc prov ided, of the receiver should fulfill the demands outlined the user will need a step-up transformer or booster below. am pli fier between the MC cartrid ge and th e amp lifier. c) Com pl iance AM AND FM A measure of the stylus' ab ili ty to foll ow sudd en and We are concerned with the two basic methods of vio lent changes in the undu lations of the record groove. radio broadcasting here, AM and FM. In both, a signal Com pliance is expressed as th e amount of deflection (the music, etc.) is carried from the transmitter through (in centimeters) that a force of 1 dyne upon the stylus th e air to your tuner in the form of electroni c impulses will cause. The larger the figure, the better. The via a carrier wave. Model TX-9500 recommended figure depends on the tracking force, but AM stands for Amplitude Modu lation, that is, the 6 should be at least 8 x 10 em /dyne. carrie r wave is modu lated by a fl uctuating signal so that ,..------, f) Tracki ng Force its instantaneous amplitude varies in sympathy wit h t h e Carrier ampl;tudt modulated bV audio signal. The required downward force that wi ll make a cartridge signal. The frequency of the carrier remai ns uniform. stay in the record groove and track it. Di rectly related FM stands for Frequency Modulation. Here the to compli ance: th e larger th e compliance, the sma ll er carrier's instantaneous frequency is varied by an amount the requ ired tracking force. As a li ght track ing force proportional to the instantaneous am plitude of the will save wear an d tear on the record and the stylu s, modu lating wave (th e signal). In th is case the amplitud e the small er the figure, the better. It shou ld never exceed remains un iform. (See Fig. 3- 1. ) FM_~~AmplitudeU~I::m 4 gra ms. Most hi -fi-tuners are AM/FM models wh ich means . . ...L that they rece ive AM broadcasts as well as FM and FM Catrlor frequoncv modulotod bv oudlo signal. stereo programs. A few exclusive FM models ex ist, but ...._Fi..-g,_. _3_- _l_ A_M_ a_n_d_F_M__ ~ since there is hardly any difference in cost, the AM/FM tu ner with its grea ter fl exibility has advan tages. AM reception in the 535 - 1605 kHz radio band has been around since th e earliest days of the "wireless". Although there are built-in limitations which delegate AM to the realm of lo-fi, it won't hu rt to have it availab le for news, sports programs, etc. When choos ing a hi- fi tuner, its FM -and FM stereo - performance is of in comparably greater importance.
19 18 A good FM tuner will deliver th e same degree of hi -fi wanted stations. In modern tuner designs, cross sound purity as a turntable or tape deck - in many modu lation resistance has been improved considerably cases its sound will be superi or simply because FM by the use of fi eld effect transistors (FET's) because stations use top-grade professional reprod uction equip of their higher linearity. Si nce cross-modulation depends mcnt outside the range of the hi-fi amateur. Add to th is largely on the strength of these unwanted sign als, it can the fact that the FM radio waves don't cost th e listener be further reduced by correct, precise orientation of th e a cent and that FM mu sic programs can be tape antenna towards th e wanted stati on. recorded with out difficu lty, and you will understand As th e RF stage employs an oscill ator circu it, it fll SELECTIVITY why for many budget-m inded hi -fi fans the FM tuner must be designed in such a way that th e oscill ator has become th e chi ef source of sound. frequency does not " leak" from th e tuner, causing interference in nearby TV sets, radios, etc. !8 a=E~R!E,,~s=SE=ES Tuning meter Stereo indicator The RF stage delivers an intermediate frequency ~ t-t-++-t-tm-t 1 oo,f-++fii~H-+-IH-j signal of 10.7 MHz, whi ch is th en amplified and again f? H-+t--t--i~H-t-++lltH-t-H-1 se lec ted in th e IF (Intermediate Frequency) stage. Th e ~ H--t-t+-i-llt-k-';;;;t--t-+HIH--t-+-H--1 bf 'BOdB'ti-H--t-t-t--1 problem is to amp lify only the desired, sharply defined ~ t!l ~~E~~~7a0 3irJfBf1~ sec tion of the band th at contains the wanted sound ~ 60 ~ 1 '60d inform ati on. This is done by a series of fi lters of very .. r-...... ,t--t-~+,-t_-Htt-H '~tt-.....++_-t.--1.,. .--I.. H. precise electrical dimensi ons, preferably cerami c filters. ~ ~:-;.:.~.;;;to---i JLfMi: ..l .. ,,l,!,.,. Th ese are a major fac tor in determining an FM tuner's ""'""""::.., t; !~ l:±fl1T 'CISI.IItOI>GI'lALllVIL selectivity. ~ IJ'I ' 20<18 I The limiting circui t, also part of the IF stage, fu lfill s - 600 - 400 200 0 200 400 600 J:~QtJLF:.ttD_ ------_j one of the most important functions - it suppresses the FREQUENCY DIFFERENCE IN KHz Fig. 3-2 Block Diagram of FM Stereo Tuner Mono/stereo switch atmospheri c noise. This is one of the special features of Fig. 3-3 FM broadcasting and ex plains the high sou nd quality Selectivity FUNCTION OF AM FM TUNER attainable. The limi ter begins to work only when a sign al Characteristic The demands made upon a hi-fi tun er will become of sufficient strength is present, and its function is ._C_u_r_v_e....;(!...,;T_X_·-.9_500__,_) ___ _ clear if we exam ine its fun ction s step by step. Th e FM antenna supplies th e radi o signal (FM occupies th e 88 - 108 MHz band) to the tuner's input, i.e. th e RF (Radio Frequency) ampl ifier stage. There, th e signal is amp li fied Lif'ter Noise is cut. and, more importantly, separated fr om those of other Noise I A ~~ FM stations and from random noise signals. This outlines I ~ n I th e fi rst two tasks of an FM hi-fi tuner: sensitivity, i.e. ~ th e ability to pick up weak signals; and selecti vity, which
is its ab ility to "slice out" only th e desired station while ~ v l j 1 1 suppressing ad jacen t signals and noise. Anoth er item S1gnal still noisy at A mp l'f1 1cat1on' ! RF stage output. B ~ Noise is cut. found in tuner specificati ons and determined at th e • in IF stage. Limiting effect tuner's RF stage is cross-modu lation resistance which Fig. 3- 4 Limiting Effect describes a tuner's ability to prevent th e desired signal from being influenced ("modulated") by strong un-
20 2 1 therefore closely related to the tuner's sensitivity an d stereo broadcast has only about half the reach of a antenna sign al strength. monophonic program transmitted with the same power. The muting circuit, usuall y switchable with a control This makes it easy to understand why a good FM on the tuner's front panel, has a simil ar purpose - it outdoor antenna is needed in most cases to assure good cancels the noise encountered on unu sed FM channels, stereo reception. that irritating hiss that you hear between stations. The muting control can be either a simple on/off switch or, TUNER CONTROLS on expensive models, a continuously adjustable control. The quality and usefulness of an FM tuner are As the muting switch cancels out weak stations along determined not on ly by the precision of the circuits, with the noise, it must be turned off or turned down but its operating convenience is equal ly important. when such a weak sign al is to be received . Let us take a bri ef look at the controls, dials and After passing through the IF stage, th e signal is switches fou nd on upper grade AM/FM hi-fi tu ners. demodulated, i.e. the audio signal is extracted from it. The operation mode is determined by a function This signal is stil l too weak, however, to drive the selector which usuall y has three positions: AM, FM loudspeakers; it must first be augmented in the MONO, and FM AUTO. In FM MONO position, all FM am plifier. programs are received monophonicall y, i.e. the MPX demodulator is deactivated. In FM AUTO mode, the FM MULTIPLEX (MPX) FOR STEREO tuner automaticall y switches to FM stereo reception The greatest attraction of today 's FM tuners lies in when tuned to an FM MPX broadcast. th e possibility of stereophonic reception. (Of course, this is possible only in areas where FM stereo stations are operating. ) When broadcasting a stereophonic (MPX} program, the station transmits a sub·carrier wave along L + R side the main carrier and removed from it by 38kHz, ~~~====~====~~~· ; 1 Signal Meter Fig. 3- 5 and a pilot frequency of half the sub-carrier i.e. 19kHz. II: 2 Tuning Meter Carrier of FM MPX FM Stereo Indicator A pilot detector circuit in the tuner detects the presence Power Sw itch Stereo ____. of this pilot signal and activates the so-called FM MPX 'I; ~ Headphone j ack Headphone Ou tput Level Con trol demodulator circu it. AM & FM Ou tput Level Controls Let us call the sound information for the left channel Fu nction Switch w=~~~~~~~~~~~l 9~ Pu lse Noise Swi tch L, that for th e right channel R. In a stereophonic FM 10 MPX Noise Filter broadcast, th e main carrier contains the sum of both 11 FM Mu ting Level Switch Tuning Knob ------.... signals, i.e. L+ R. An FM tuner with out a mu ltip lex l r------r------~ 123 AM Ferrite Antenna Main carrier demodulator will receive only this signal and deliver 14 AM Antenna Terminal Pilot L - R 15 Ground Terminal signal monophonic sou nd. The sub-carrier transports a dif 16 FM Antenna Terminals (300.n) ferent signal, L- R. In the FM MPX demodulator, 17 FM Antenna Terminal (15.n) 18 FM Multipath Terminals these two L+ R and L- R signals are added and sub 19 Fixed Outpu t Term inals tracted to re-gain the signal for each chan nel: 20 Variable Output Terminals 0 15kHz 19kHz 38kHz (L +R) + (L- R) = 2L ...... left channel sound Fig. 3- 6 (L +R) - (L- R) = 2R ...... right channel sound Spectrum of FM Stereo For reasons too complicated to explain here an FM
22 23 re-adjustments should be entrusted to qualified service SIGNAL TUN ING Tuning is dcne by turni ng a large knob and watching one or two meters as well as the station dial. The engineers only. signal strength meter deflects to the right when the Other controls found on tuners include output level station is turned in - tre grea ter its deflection, the controls, sometimes separate for AM and FM, wh ich ~~ stronger the received signal. (It is also help fu l in finding regul ate the tuner's output voltage in order to match its sound volume with that of other source equ ipment
24 25 familiarity with electronic circuits is requ ired to find reject the fal se im age give you sound with "ghosts" one's way through al l the ratios, rejections, res ponses, (as in tv). This is caused by interac ti on of the oscillator and factors. Neverth eless, the fo llowing brief explana freq uency and the RF frequency. Im age rejection is the tions should be sufficient guidance. tuner's abil ity to suppress this frequency. Bigger values a) Scnsitivity arc better; they pay off as less probl ems in areas with Th e minimum antenna signal which the tun er can many FM stations broadcasting. convert into a satisfactory sound signal. Expressed in f) Spurious Response or Rejection 11V (m ic rovolts = 1/1 ,000,000 of a volt) and defin ed An FM tuner's bad habit of creati ng unwanted, meaning by the Institute of High Fidelity Manufacturers (IH F) less " li e" sign als which it then (a) emits through the as the signal strength at which the tu ner will suppress antenna, causi ng interference in th e neighbor's TV se t or noise by 30d B. Sensiti vity ratings of 3J1V are qu ite radio, and (b) picks up itse lf, affecting its own reception respectable, values below 2J1V arc ou tstanding. because this sci f-gc ncratcd lie signal can in terfere with b) Signal-to-Noise Ratio (S/N) the true wanted station signal. Expressed in decibels, Th e ratio, expressed in dec ibels, between a 400Hz higher value s arc preferable. fu lly- modul ated signal and the noise component. The g) AM Suppress ion rating 60dB, for example, means that the signal is 1,000 AM in this context has nothing to do with AM broad times stronger than the noise. Here, the higher the valu e, casting; AM here means the (amp litude modulated) the better; for hi-fi FM it shou ld be at least SOd B. Some noise signals emanating from fl uorescent lamps, motors, Pio neer tuners offer a superb signal-to-noise ratio as high automobile ignitions, etc. whi ch, unl ess suppressed, as 7 Sd B. cause that notorious irritating crackle during FM recep c) Capture Ratio tion. AM suppression is expressed in decibels, higher Assume that two stations are broadcasting on the same valu es are better, 40dB is about minimum. frequency. "Capture rati o" descri bes a tuner's ab il ity to h) FM Stereo Separation suppress the weaker of the two wh ile receiving on ly the The FM MPX demodulator's abi lity to separate the left stronger. Also related to the tuner's su ppress ion of and right chann el signals of FM stereo broadcasts. For random noise. Exp ressed in decibels, smal ler values arc stereo effect, channel se paration in the medi um audio better. A rating of 4.5d B is usua lly sufficient. fre quency range (400 - 1 ,OOO Hz) is most im portant. A d) Sclcctivi ty good tuner should have 40dB separati on in this range or This is simi lar to capture ratio, but instead of dealing 30d B between 40Hz and 8kHz or 25d B over the total wi th signals of di ffercnt strengths on the same freq uency, 20Hz - 15k Hz range. it deals with signals wh ich arc broadcast on fr equencies i) Output Level very close to the one you arc trying to select. The tuner's This is usually in the 0.7V range, and is adjustable on ability to slice away the adjacent signals and se lect out high quali ty tu ners. You arc in terested in the output the one you want is expressed also in decibels, the level of a tuner because it mu st match the input require higher the better. A selectivity of SOdB is usually ments of you r amp li fier or receiver. In most Pioneer su fficicn l. stereo tuners, two kinds of ou tput terminals (fixed and c) Image Rejection variable) arc prov id ed. Thu s, you can, for example, usc " Image " means a tuner's undesirable reception of the th e fixed term inals to connect the tuner to a tape deck same signal at two or more points on the dial, of wh ich for off-the-air recording, while using the variab le only one is the true station signal. Tuners wh ich can't terminals to connect with oth er equipment.
26 27 retain this magnetism. Chapter Magnetized particles 4 RECORDING AND PLAYBACK PROCESS The recording process is, briefly, as follows. Electric Tape Equipment signals supplied by a sound source are amplified and th en applied to the coil of a small electro-magnet called Turntable and tuner are "passive" sound sources a "recording head." This causes a magnetic field, they can only reproduce commerciaffy recorded or alternating in accordance with the sound's rh ythm and broadcast sound. Tape equipment, with the exception intensity, in and arou nd a tiny gap between the two Emulsion of so-caffed tape players, lets the listener participate poles of the magnet. As the recording tape travels past Fig. 4- 1 Schematic View of "actively" in the selection and even creation of music the recording head, its iron oxide particles are magnet Recorded Tape programs. This great advantage, together with the ized by the altern ating magnetic field. The tape thus operational ease and relatively low price of modern tape stores th e sound information in the form of magn eti sm. equipmen t, may explain the tremendous tape recorder To retrieve this informati on, the reverse process is boom that has been sweeping the world. used. The tape, transported past the so-called pl ayback head - another small electro-magnet with a similar THE TAPE structure as the recordi ng head - induces a small, According to the tape form at, tape equipm en t can be alternating current in the magnet's coi l. As this current grouped into open-reel, cassette an d cartridge. The contains the sa me sound in formation as the original recording tape itself is basically the same for all three signal - provided that the tape travels at the same speed types, and so are the essential functions of the machines. at recording and pl ayback - it can be amplifi ed and Magnetic record ing tape consists of a thin polyester used to drive a speaker system. or ace tate film (usually about 15 to 35 microns thick, TRACKS or as expressed in mils, 0.60 to 1.40 mils thick). This fi lm, called backing (consisting of the base and emul Th e fi rst tape recorders, bu ilt during and after World sion), is covered with a layer of fi ne, crystal lic iron ox id e War II , used up the ful l tape width for a si ngle passage. Model RT-1020L particles imbedded in an adhesive. These iron ox id e Later, as tape recorder comp onents, recording tape and particles can be magnetized in a magnetic field and will techniques became more refin ed, the tape width was I Pause Switc split into two and then four "tracks." This provides 2 Power Switch greater tape economy and, moreover, the possib ility to 3 Reel Size Switch 4 Tape Speed Selector store two (or more) chan nels on the tape. Most modern 5 MIC Recording Level Control 6 Line Record ing Level Control open reel stereo tape recorders for amateur use are Current 7 Recording Indicators 4-track models, whereas in cartridge recorders and 8 Level Meters 9 MIC Input jacks players the same tape width (1/4 inch) is divided into I 0 REC Bias Sw itch eight tracks. II REC EQ Switch 12 Phones Jack 4-track stereo 13 Output Level Control Tracks 14 Meters Switch 1 & 4 I 5 Monitor Switches (L, R) Tracks 16 Play Switch '§j r>.~:·l >-·r;~T Magnetic flux 3 & 2 17 REC Switches (L, R) Fig. 4- 3 18 Function Buttons Tape Shield 19 Tension Arm Structure of 20 Ta e Counter Fig. 4- 2 Track Locations in Tape Heads Tape Head
28 29 TAPE SPEEDS recording time. The tabl e (P.30) shows recordi ng times r------. Another tend ency in tape recorder design has brough t (per track and per return trip) for common types of about slower and slower tape speeds. Although profes- ree l tapes at 7-1/2 ips recording speed. Remember th at sional studio machines transport the tape at least the 3-3/4 ips speed provides twice the recording time, 7-1/2 or usually 15 or more inches per second (ips), and1 -7/8 ipsfourtimesas much. most home·use tape decks offer a choice between 7-1/2 and 3-3/4 ips, and sometim es 1-7/8 ips. Cartridge player1 TAPE QU~LITY always ru n at 3-3/4 ips whi le cassette tape is transported The quali ty of the recording tape is equall y as at 1-3/4 ips. This explains the comparatively long important as that of the equipm ent itself. Poor qual ity 30 31 DOLBY SYSTEM advantages, however, the tape recorder mu st have < Dolby system is a unique noise special provision, an adju stable or switchable "biaPPEN REEL, CASSETTE, CARTRIDGE? reduction system, which elec current." The choice between open ree l, cassette an d cartridge tronically eliminates the irritating (An audio frequ ency sign al is never recorded orhas become very mu ch a question of personal prefer noise (tape hiss, circuit noise, magnetic tape as it is: the tape develops its optimurrences. Until only a few years ago, no status-conscious etc.) without sacrificing the characteristics only after it has been "primed " with ;"eli te" hi-fi fan would go near a cassette recorde r, original tonal quality. Mode l CT- F71 71 rather high frequency bias cu rrent. This bias currentbranding them as kid stuff for amateu rs. The latest (F ront-access Cassette Deck) usually applied through the recording head together wittgeneration of casse tte decks have made many a "reel the audio signal, is different fo r ord inary tape and fo1snob" eat his words because they deliver, despite thei r low noise, hi gh output tape.) slow tape speed and narrow track width, quite respecta- Noise Before we talk about the factors that determine thtble sound in ad dition to their great snap-i n, pop-out Level qu ality of tape equipment, let's take a brief look at th1convenie nce. This was made possibl e by th e development many, sometimes confusing, types bei ng marketed. w1of new precision drive sys tems, ultra narrow gap heads have already made a distinction between reel, cartridg and; las t but not least, better recording tape. Cassette 1 Model CT - F6161 and cassette equipment. Each group is further dividecdec ks can be recommended ch iefly to hi-fi fans who (Front-access Cassette Deck) into "tape dec k," "tape recorders" and "tape players." prefer to get their mu sic the easy, uncomplicated way Noise , and who don't mind that cassette tape cannot easily be Level ..,. .f\,. .,...... ,,., TAPE DECK, RECORDER, PLAYER? edi ted, i.e.cutand spliced . RECORDING PROCESS A tape deck, the most com mon and sensible variet) Cartridge equ ipment for hi-fi install ations owes much for use in hi-fi in stallati ons, consists of the tape transporlof its popu larity to its almost fully automated ease of ovu hrlt~'tM:--- and the required recording and playback pre-amplifien operation and to the wide-spread use of automobile but no power ampli fiers or loudspeakers. A tape dec~s te r eo players which use the same tape cartridges. Most Noise can record through microphones or from a tuner o1cartridges are recorded with eight tracks. Since one track Level amplifier, and pl ayback is also possible via an ex ternalcorresponds to one stereo channel, fou r stereo programs @ amplifier and speaker system. (or two 4-channel programs) are contained on one PLAYBACK PROCESS A tape recorder is, in addition, equ ipped with it1cartridge. The tape is wound in an end less loop, travel ing DOLBY SYSTEM own power amplifier and loudspeaker(s). It can be usedarou nd and around. At one point, a metal sw itching foil (graphs) as a self-contained unit for record in g and playback. lnis attached which, when trave li ng past the head, activates 32 33 serious hi-fi enthusiast, and it is th e open-reel stere so that each can go about its tas k with max imum Car.trldge Rae! dec k that wi ll be examined in the fo llow ing paragraph! efficiency. '~----~----,, --~ although the principles appl y to cassette and car tridg ' \ equipment as well . \ I I DRIVE MECHANISM I ...... ··""','. I The mechani cal part of a tape dec k has to move th 1 Flywhaal tape past the heads at constant, specified speeds. This i .....\ ••••• • Capstan done by a rotating capstan against which the tape i Pinch roller pressed by a pinch roll er. In the des ign of thi 4/8f pol e capstan drive motor mechan ism special attention mu st be paid to avoid tap slippage. Th e mechani sm mu st perform two other fun( Fig. 4- 9 Fig. 4-7 tion s: rapid forward winding and rew inding of the tapt Two-Motor Drive Mechanism Endless Loop Type Tape All three tasks can of course be carried out by a sin gl Pinch roller Cartridge motor and a system of belts, pulleys and idlers - Fit Three-Motor Drive Mechanism 4- 8 shows such a drive system. RECORDING AND PLAYBACK HEADS A tape deck needs at least two heads - an erase head which cleans th e tape of previous recordings and noise, and a combined recording/play back head. The im portance of the head gap has already been mentioned. Other points of interest incl ude the heads' surface polish - the tape must travel ove r it with as little friction as possible - and its dimensional accuracy and adju stm en t. {The trac k locations on the tape are of course deter Model RT-1050 min ed by an intern ati onal standard so that a tape ( 15ips, Half-track Deck ) recorded on one machine can be pl ayed back on any .. other provided th ey use the same 2-trac k or 4-track .-:.- ~~-.:.. :: : __ , ... Fig. 4- 8 system.) - One-Motor Drive Mechanism THREE-HEAD DECKS ~~~!i~j{J{J,ii TWO AND THREE MOTOR SYSTEMS Hi-fi enthusiasts who wi sh to make their own record Where highest precision and rapid winding speed ings are well advised to bear th e extra ex pense of buying are requ ired and cost is the minor consideration, separat a 3-head tape dec k, i.e. one with separate recording and motors can be used to drive the capstan and both reel pl ayback heads (p lus erase head). No t only can each Model MA-62 or three separate motors fo r the capstan and each reel head be designed especiall y for its own purpose, but (Microphone Mixing Amplifier) Such top cl ass tape transports are often contro lled vi 3-head systems offer the only really accurate recording electronic relays and pu sh -buttons and embody tensio1 control possibi lity: tape monitoring. It works li ke thi s: regulators and other devices to protect th e tape fron as the tape travels pas t th e recording head, it is " im excessive forces. In two and three motor transports, th pregnated" with th e audio signal. This same, original capstan and reel motors are of radi call y different desigr audi o signal whi ch comes from the sound source ca n 34 35 can work with them ("pl ay back equ al izer, play back pre-ampl ifi er" circuits). (Technically speaking, an au di o signal of flat fre quency response, when recorded and played back via Input Mic o-..--o... _ tape, would drop off in its very low an d very hi gh line portions. To compensate for this, the low and high Frequency (Hz) Outputo.----+;...;.::..:.::..;~------1 parts of the frequency response curve mu st be ra ised. This is done accord ing to an intern ationall y agreed-upon Fig. 4-14 NAB Equalization Curve 4- 11 Two-Head Mechanism method, the so-called NAB equal ization curve. The high portion is boosted in the recording equalizer, the low portion in the pl ayback equ alizer so that th e tape deck's outpu ts again supply a signal with fl at response.) -Recording head RECORDING LEVELS As recording tape has only a lim ited capacity for Level meter storing magneti sm, the recording level - th e strength of the signal applied to the tape head - must be controlled. This is done with a control knob and usually two VU or level meters (one per channel). Excessive recording Fig. 4-12 Three-Head Mechanism level causes di stortions, whi le an insu ffici ent level results in noisy, hissi ng tapes. si multaneously be monitored through speaker systems The need to appl y a high-frequ ency bias to the tape (via the amplifier) or headphones. Then, as the tape while recording has been menti oned; this frequency, travels on past the playback head, the just-recorded som ewhere in the 30- 1OOkHz range, is gene ra ted by the sou nd can agai n be pi cked up and monitored. Three-head "bias oscill ator." tape decks are equi pped with a switch to switch back and forth betwee n source monitoring and tape monitoring. AUTOMATIC STOP, AUTO-REVERSE Thus, the operator can compare the source sound instantly with the recorded sound and make necessary To make the tape deck as convenien t to operate as re-adjustments. Because of th e distance from recording possible, a number of auxiliary devices have been de to pl ayback head which the tape has to travel, there is signed. Very com mon is an automatic stop mechanism of course a short tim e lag between source and tape that halts the reels when the tape runs out. Among monitor sound. the several possibl e meth ods, the most common one employs a lever which, normally held upward by the AMPLIFIERS, EQUALIZATION tape, drops forward and activates a stop switch when Although tape decks don't need power am plifi ers, the tape runs out. EH : Erasing heed they do need electron ic circuits th at transform the To ge t rid of the necessity to remove, turn over and PH : Playback head signal to be recorded into a shape acceptable by the re-thread th e tape after each run, various au tom a tic RH: Recording heed RPH : Recording;playback heed tape ("recording am plifier, recording equalizer" circu its) reverse systems have been devised. One, the sensing-foil EH : Erasing heed Fig. 4-13 Tape Monitoring an d others th at augment and again transform th e signals method, is th e most popu lar. The user affi xes short Fig. 4-15 picked up by the playback head so that the amplifier pieces of metallic foil near either end of the tape. Tape Auto-Reverse Function 36 37 gu ide and tension arm (two parts of the tape path! another. Expressed in decibels. The higher the value, the serve as contact points for a relay. When the meta better. Channel-to-channel crosstalk should be at least sensing foil reaches these parts it closes an electri1 30dB, track- to-track crosstalk of a 4-track mach ine circuit, activating the reverse relay which, in turn, mak~ should be above 55dB. th e tape travel back in the other direction. The length oi e) Ch annel Separation tape betwee n the two sensing fo il s thus trave ls bacl Another word for channel-to-chann el crosstalk (above). and forth infinitely. At each reversing point, tape head! f) Max imum Reel Di ameter and tracks are switched accordingly. As illustrated in tht 'The largest reel size that the tape deck will accept. drawing, an au to reverse tape deck needs two erase head Most open reel decks accept up to 7" diameter reel s; an d two double-action recording/playback heads. All Pioneer decks accept th e profess ional-sized 10-1/2" reels. How to Read Tape IJecl• Specifications a) Wow & Flutter Inconsistencies in the tape speed whi ch can cause pitd variations and qui verin g sou nd. Expressed as pe rcen tagc1 with differen t val ues for each tape speed. Look for th lowest values. 0.25% is about th e permissible maximum b) Signal-to-Noise Ra ti o Denotes the tape deck's freedom from sci f.create. noise. Expressed in decibels, hi gher valu es are bettct 45dB is about minimum. Pionee r decks arc 55dB o better. c) Frequency Response The lowest and highest aud io frequ enc ies th at the tap deck wi ll record and reproduce. Should be as fl at a possible and cover at leas t 50 · 13,0001-fz at 7·1 /2 ipso 50· 1 O,OOOHz at 3-3/4 ips. Excel· Parameter lent Good Fair Un Signal to Noise Rati o 54- 56 50- 53 45- 50 dl 30- 50- 50- H 7-1/2 16,000 13,000 10,000 50- Frequency 3·3/4 50- 50- H response 12,000 10,000 8,000 SO- 50- 50- 1·7/8 8,000 7,000 5,000 H d) Crosstalk The amount of signal that leaks (i) from one stereo chan nel in to the other and (ii) fr om one tape track int 38 39 cabl e connections. Chapter5 On the other hand, the pu rchaser of a separate tuner plus pre-amplifier plus power ampli fier sys tem may ga in a little bit in perform ance and may obtain a more The Amplifier individuall y "selected" kind of sound, but he definitel y As the audio signals supplied by the turntable, tuner gains in flex ibility; he can replace individual units as technology progresses and new model s appear on the Stereo Receiver or tape deck are much too weal? t o be converted into (Model SX-1 0 10) market; he can easil y add an electroni c crossover net audible sound directly, they must first be raised to a higher level. This is done by the amplifier which thereby work and one or two more power amplifiers to upgrade his sys tem into a multi-amplifier install ation (see page becomes the heart of every hi-fi installation. Before we 59); he can move on to a four-channel sys tem (page63 ) examine the fundamentals, functions and features of without sacrifi cing any of his present equipm ent; and hi-fi amplifiers, we must first clarify a few distinctions he gets, last but not leas t, the pride of owning hi s own in terminology. Stereo tuner custom-assembl ed persona lized system. (Model TX-9 1 00) PRE-AMPLIFIER, POWER AMPLIFIER, The serious audio enthusias t, when deciding on the ...... , .... 0 INTEGRATED AMPLIFIER, RECEIVER purchase of a receiver or integrated amplifier, shou ld, • : oo e oo ....•o o: An amplifier system in a hi-fi instal lati on consists of however, in sist on one feature (found on most Pioneer Receiver two parts: the pre-amplifier which includes all the models): th e possibili ty to use the pre-amplifier and controls for regul ating tone, volume and channel power ampl ifier stages separately. This is done by mov balance; and th e power amplifier which, as its name ing a rear-panel switch (in th e case of Pioneer amp lifiers) implies, suppl ies a sufficiently powerful signal to drive or by removing jumper cabl es or plugs, and permi ts th e Stereo Integrated A mplifier (Model SA-9100) th e loudspeakers. Manufacturers provide the audio system to be enlarged into a multi-amplifier configura en thu siast with a multiple choice: he can pu rchase tion at a later date. separate pre-amplifier and power ampli fier un its, he can Th e foll ow ing expl anations deal with pre-ampli fier select a combinati on of both which is co mmonly called and power amplifier functions, in that order, but th ey "in teg rated amplifier," "control amplifier" or just simply apply to integrated amplifiers and receive rs, to o; onl y "amplifier," or he can opt for a receiver, i. e. a combina· the remarks about connections and matching of com ti on of tuner, pre- and power amplifier. ponents may be di srega rded. Since units bui lt to ve ry high performance standards can be found in each group, the qu esti on is not so PREAMPLIFIER FUNCTIONS mu ch one of sound quali ty but rather a question of To the hi-fi novice, th e need fo r and functions of th e fl exibility versus economy and convenience. pre-amp li fi er are usuall y more di fficult to und erstand It stand s to reason that a combination of two or three than those of the power amplifier wh ich after all func tions in one unit shoul d be more economical th an cl earl y produces power. The pre-a mplifi ~r can b ~ separate sets - just think of the cost of chassis and thought of as sort of super switchboard - it selects the enclosures and power suppl y uni ts (i. e. th e transformer sound source to be pl ayed, it determines th e mode of rectifier assembly in each unit which supplies th e sound (4-channel, stereo or monophonic), it influences Fig. 5-1 the sound color with its tone controls, it regul ates th e needed operatin g current to the circu its). Wh at's more, Stereo Preamplifier Classification of an integrated ampli fi er or receiver saves space and vo lum e and channel balance, and it brings the signals Amplifiers eliminates the need for - sometimes troublesome - up to a voltage level which the power ampli fier can then 40 41 work with. INPUTS The different sound sources are connected to the Because the ph ono inputs have to be equali zed, they preamplifier inputs: the turntabl e to the phono inputs, are called "non-linear" inpu ts as opposed to "linear the tuner to the tuner inpu ts, the tape deck to the tape inpu ts" such as those for tape, tu ner, microphone or (or sometimes "monitor") inputs, .and an aux iliary auxiliary signals. Some high grade amp li fiers provide two source such as a cassette tape deck to th e aux inputs. or even th ree pai rs of ph ono in puts, permitting two or Some ampli fi ers also have microph one inputs. more turntables or cartridges to be connected simu l PHONO EQUALIZATION taneously for easy comparison. Also, the input se nsitivity Model DM- 30 Let us observe th e phono signal on its way through and impedance of the phono inpu ts is sometimes switch the pre-amplifi er. First, it enters a circuit called an able to accommodate cartridges of differen t char equalize r amp. To understand its function, we must be acteristics. In this context, anoth er val ue often foun d aware of a peculi arity of phonograph records. Wh en the in pre-amplifier specifications is of im portance: max i mas ter disc is cu t, th e high sound ranges are over mum input vol tage of the phono in puts. Th is describes Electret condenser type emphasi zed ("boosted") while the bass range is some· the highest signal level that the amplifier can accept microphone what suppressed. This mu st be done in ord er to obtain a through the phono in pu ts withou t ove rl oad ing, i.e. reco rd groove with sufficient modu lations in the high distorting. It should be at least 10 times higher than th e range for the needl e to "feel" and, on the other hand, output level of th e pickup cartridge. without excessively wild bass undu lations (because these Tape deck and tuner conn ections usually do not pose would requ ire a wider groove). Technically, cu tting of a much difficulty because the electrical characteris tics disc is not " fl at" but foll ows a frequency response curve are pretty much standardized. With microphones, how as shown in Fig. 5- 2, called the RIAA curve (es tabli shed ever, it is important to choose the righ t ty pe. Pioneer by the Record Industry Association of America). There· microphones of course are matched to Pioneer amp li fiers, but mikes of other brands must correspond in th eir 11< fore, the aud io signal delivered by the pickup cartridge would result in equall y disfigured sound if it were passed impedance to the amp 's mic input im pedance, within a Frequency (Hz) tolerance of about ±20 percen t. Fig. S- 2 on as it is. The RIAA curve must be "equ alized" first RJAA Equalization to obtain natural sound - and this is the function of TAPE MONITORING Curve the equ alize r amp. Switching between the different connected sound sources is usuall y done with a program se lector, mostly a rotary knob with five or more posi tions. Tape sound, however, is switched on an d off with a so-call ed tape ~ monitor sw itch with two posi tions: "source" and "play" ~~----- (or "tape"). For tap e playback, this switch is set in a: position " pl ay," for all other program sources it must be in position "source." When making a recording on a ,_ '· ,_ '· ,__ tape deck with in dependent record ing and playbac k Recording --Equalization in amplifier-Resultant flat response heads (a 3-head deck), this switch provides two ways of monitoring th e reco rding qu ali ty. In position "source" Fig. S- 3 Equalizing the origina l before-tape sound is heard from the loud ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ speake~; in position ''play," howeveG the already 42 43 reco rded after-tape sound is reproduced. By switchi ng with these kn obs and will usually wind up with a setting iT WIN TONE CONTROL back and forth between th ese positions, th e source of heavy, boomy bass accentuati on. The more advanced SYSTEM sound can be eas ily compared with the taped sound hi·fi listener, however, will use the tone co ntrols sparing ifhis system is unique with Pioneer. and readjustments made if required. It features spec ial SUB controls in ly and near th e neutral level, except for tes t purposes. addition to the more conventional VOLUME, BALANCE, TONE CONTROLS The true purpose of th e bass and trebl e con trois on a BASS and TREBLE controls. The hi-fi amplifier lies indeed not in th e dictatori al power SUB controls permit you to boos The volume and balance controls of the stereo pre or cut the frequency in both the amplifier are more or less self-ex pl anatory. Note, how pl ay of the novice, but in the ability to compensa te ow and high ranges without ever th at th e balance co ntrol, wh en turned to the right, fo r certain weaknesses in the program material , the affecting the midrange sound. doe; not increase the right channel volume but actually listening room and, to some degree, th e speaker systems. Practical applications of this sys· With good, new LP records or tapes pl ayed on good tem are as ind icated in the follow redu ces the left channel vo lume. Al so, volume and mg diagram: balance controls do not affect th e signal supplied to the equipment in a normal family living room, however, tape deck for recording. ex treme tone control settings are almos t never required. How do tone controls - and th eir cousins, the high and low filters and th e loudness switch provided on most ampli fie rs - work ? In its simplest, bargain basement fo rm - as found on portabl e radios etc. - a tone control is simply a combinati on of a capacitor with a res istance, and it cuts off the high parts of th e sound spectrum. More suitable to hi·fi applications is the passive CR (capacitors· resistors) type which boosts or reduces frequencies 17 I above and below a " turnover" point in a way as 1 Speakers Switch illustrated in Fig. 5- 4. For even more precise, ac tive 2 Protection Pilot Lamp control, nega ti ve fe edback techniques (NFB) have to be 3 Bass Controls 4 Treble Controls introdu ced whict- require rath er elaborate circuits with 5 Level Set Control 6 Volume Control transistors, etc. The obtainable frequency response 7 Function Selectors characteri stics are illustrated in Fig. 5- 5. 8 Power Switch, Pilot Lamp 9 Headphone jack On some amplifiers, the tone controls work on th e 10 Muting Sw itch left and right stereo chann el simultaneously, which is 11 Low Filter Switch 12 Tone Defeat Switch quite sufficient for most home applications; on oth ers, 13 High Filter Switch there are separate knobs (usually concentric double Frequency Response 14 Loudness Switch 15 Balance Control knobs) for controlling th e left and right channel 16 Tape Monitor Switch separatel y whi ch is useful in difficult listening room 17 Tape Duplicate Switch conditions. 18 Mode Switch 1t is usuall y not difficult to tell th e hi-fi greenhorn FILTERS, LOUDNESS CONTOUR from the old pro - just watch him operate the tone Low and high fi lters (also referred to as rumble or controls of hi s amplifier. The beginner will show grea t 50Hz 100Hz lOKHZ 20KHz bass filters and noise or scratch filters, respec tively) Frequency Response deligh t in his abili ty to turn up th e bass and suppressing have fun cti ons as shown in Fig. 5- 6. The bass filter is the trebl e or vice versa, he will play around endl essly designed to cut off (or, more precisely, to attenu ate by 44 45 so many decibels) th e sound spectrum below a certain an extent. That is why headphones, which req uire very point, usuall y somewhere be tween 100 and 50Hz. This little power, can be connected to a headphone jack has the effect of cancel ing out very low hum and rum ble usual ly provided on pre-amplifiers. generated by turntables. The high filter, on th e other hand, attenu ates frequencies above 8,000 or 1 O,OOOHz, POWER AMPLIFIER FUNCTION as the case may be, to eliminate scratching and hissing From the pre-amplifier, the signal enters the power noise fr om records, tapes, FM, etc. It is bad practice, (or main) amplifier. There, its power is raised several however, to use these filters indi sc riminately because hundred times to a val ue which can drive {and, if used together with the noise they also cancel part of the fully, even destroy) the speaker systems. desi rable mu sical spectrum. Use th em onl y when Much concentrated effort has gone into the develop necessary. ment of better and better hi-fi power amplifiers. Even The loudness switch on an amplifier must not be the vacuum tube types of years ago- on ly very few are STEREO POWER AMPLIFIER co nfused with th e volume control. A more accurate now on the amateur hi-fi market - produced some description of its function is found in the name excellent results. To th is day, hi-fi enthusiasts brought " physiologi call y correct loudness contour compensa up in that age swear by the vacuum tube amp Iifi er and tion." This name already hints at a deficiency of the in terms of sound quality it does possess a ce,rtain hum an sense of hearing. Indeed, measurements demon mellow charm. Its bad habits - vacuum tube am plifiers strate clearly th at the human hearing apparatus is, even guzzle electrici ty, create tropical heat waves in their at its healthy best, a far fr om perfect hi-fi devi ce. One of vicinity and break down or bu rn out at all too frequent .------. its short-comings is that it is rather insensi tive to in tervals - made it easy for so lid state designs to take extremel y low and very high tones when th e overall over in a flurry. Today, the transistor power amp has vo lume is so ft. The loudness sw itch, a special kind of emerged as the almost undisputed victor. tone control, overcomes this hum an error by boosting CRITERIA OF QUALITY th ese extreme sound ranges at low volume settings. It Solid state power am plifiers of the latest generation should therefore be turned off at high listening volum es. are true marvels in audio engineering, with tremendous power reserves, a remarkabl e absence of distortions and very high reli ability. Des ign engi neers have overcome the OCL CIRCUIT many inh erent problems one by one by making use of improved components such as silicon· transistors, by developing new circuits such as quasi-complementary and pure complementary output stages, by getting rid of coupling transformers and capacitors. Conventionally, capacitors were used to coupl e the individual stages of a power ampl ifier, and to couple BACK VIEW QF INTEGRATeD AMPLIFIER ISA-9100) the output stage to the loudspeakers. Direct cou pling techniques are posing a new chall enge to circuit designers. They promise better results not only because HEADPHONE JACK they avoid phase shifts betwee n the stages but also, and In addition to the functions described above, th e more im portantl y, because th ey use so-called balanced pre-amplifier does of course amplify the signal level to power supplies - i.e. power supply circuits provid ing L--=---.....:....:..=...:.:.~;.:.;...... :::.l!..J 46 47 matched pos1t1ve an d nega ti ve power corresponding to th e (+) and (- ) sections of the sound signal. Such direct How lo llead i\mplifier H)Jerifiralions coupl ed and OCL ("output-capacitor-less") circuits are a) Continuous Power Output - The FTC Rule already bein g used in most top grade Pioneer ampli fiers. Pi onee r has and wi ll con tinue to comply with the new The purchaser of a stereo power amplifier often ru ling (effective November, 1974) es tablished by the chooses a unit mainly on the strength of its output Federal Trade Comm ission (FTC) of the United States power rating. But as practicall y all modern amplifiers as regards the listings and claims fo r the power output provide more than a sufficient power reserve, he wou ld specifications for am plifie rs (includ in g am plifiers in be well advi sed to consid er other factors in his choice, corporated in receivers). Thus, all Pioneer specification such as di storti on figures, power bandwidth, etc. which sheets, advertisemen ts, sales promotion materials and will be explained in the paragraph dealing with amplifier other printed matter which list power ou tput specifica specifications. These give a tru er picture of the sound tions do so in the Un ited States by statin g the detail s of to be expected than the power rating. the actual continuous power output for all channel s, al l channels driven, in terms of minimum RMS (Root Mean PROTECTOR CIRCUITS Square) watts. The listings also give the exact conditions The expensive output stage of a transistor amplifier un der which th e rating is taken, with the load im pedance can be easil y damaged by a short circu it in the spea ker {in ohms), and the amount of total harmonic di stortion leads. To prevent this, designers have invented a va riety {in percen tagc) given clearly. of protector circui ts and com binations thereof which This information appears in the fo llow ing form (w ith shut down the output stage at the first sign of trouble. slight variations as rcq u ired): "continuous power output These can be sim ple heat fuses or, more elaborately, of 60 watts* per channel {for example), min . RMS at8 circu its wh ich detect a drop in output load impedance ohms, all channels driven, 20 to 20,000 Hertz with no (in other words, a short circuit). A few top quali ty more than 0.1 % total harmonic distortion." amp li fiers have protector circuits which detect the The asterisk in the listi ng is a reference to the footnote, presence of DC current at th e output stage. As DC also carried in all Pi oneer printed matter li sting specifica current cou ld also lead to loudspeaker damage, these tions, which reads "*Measured pursuant to Federal advanced protectors safeguard not on ly the amp Iifi er Trade Commission's Trade Regulation rule on Power itse lf but also the connected speaker systems. Ou tput Claims of Amplifiers." b) Music Power (Dynamic Power) SPEAKER TERMINALS Often encountered in advertisements. Of dubious va lu e Although one pair of speaker systems is usuall y because measured under conditions othe r th an norma l quite sufficient for a home stereo installations, som.e usc. Usually given as the su m of both stereo channels, ----.,-----,.------, amplifiers includ ing most Pioneer models have provi unfor tunately often without distortion figures. judge sions for connecting two or even three pairs of spea ker an amplifier's power ch ie fl y by its continuous power systems which can then be driven separately or in pairs. rating (above)! The music power ra ting does, however, One obvious use is to place a second pair of speaker provide some in formation abou t the power avai lable systems in another room. This feature also permits temporarily from the amplifier when reproducing volume STEREO DISPLAY direct comparisons of different speaker systems by Model SD-11 00 pea ks in the music. Good ampl ifiers have mu sic power connecting two or three pairs to the amplifier and For measu ring and sco p ing various ratings not very much removed from their con tinuous !J!l!~~~!:..:l±.:...d switching back and forth. kinds of characteristics of your power figures . equipment. 49 c) Frequency Response 8 oh m = 80. The lowest and highes t audio frequencies th at th e 0.1 ohm amplifier will reprodu ce from input signals supplied to Damping factor is a measu re of an am plifier's abi lity to its AUX input and at 1 watt output power. To be damp, i.e. control unwanted res idual speaker movements mea ningful , the frequ ency response rating mu st be caused by forces other th an the aud io signal. Higher accomp anied by a ± dB fi gure whi ch indicates by how values arc better, but anything over 20 is not reall y very mu ch the response varies from the standard level (OdB meaningfu l. at 1kHz) over the given frequency range. Sma ller decibels g) Input Leve l, Inpu t Impedance valu es are better - th e sa me amp may have a frequ ency Inpu t level : the minimum level of the input signal response of 20 - 18,000Hz ± 1 dB or 18 - 25,000Hz supplied to the power amplifier from whi ch it will ±3d B. Exampl e of an outstanding amplifier rating: deliver its full outpu t power. Shoul d be around 0.1 V- Frequency ...... 15 - 40,000Hz ± 1dB 1 V must be close to the pre-ampl ifier's ou tpu t level. response (through AUX inputs) (O r~ l y important if separate pre- and power amps are d) Power Bandwidth used. ) ..------., An important value th at puts output power and Input impedance : The power amplifier's load impedance Power output (W) frequency response in a relation. Power bandwidth as seen from the pre-amplifie r output. Shoul d be at 2 rJNrJN signifies the audio fr equ ency ra nge (in Hz) over whi ch least 50 k-ohms when usin g a modern transis torized the amplifi er will deliver at least half of its rated outpu t pre-am pli fie r. 1 power withou t exceeding its rated harmonic distortion. \J~ For example, if th e continu ous output power of an ~~""""'.::o--:---..--_,...... L.._ amp is listed as 20W per chann el at 1% harmonic distor- 30,000 tion, then a power bandwidth rating of 20 - 30,000Hz .FI'fqUI I\CY (Hz) means that th e amp will deliver 10 watts at 20Hz and '"~~:r-J!dwl dth at 30,000Hz without di storting more th an 1%. ------" e) Signal-to- Noise Ratio The ratio between (wanted) signal and (unwanted) noi se delivered by the ampl ifi er at maxim um volume setting and with its treble and bass tone controls set at flat pos iti on. Th e higher the valu e, the less hum and noise there is. Signal -to-noise rati os should be listed individual ly for each input; for in stance: PHONO (MAG) 65dB, AUX 70dB. A 65dB ra ting means that onl y 1/2000 of the signal will be noise, 7 5d B means 1/6000. f) Damping Factor Mathemati cally, the qu otient of the load impedance (i.e. spea ker vo ice coil impedance) and the amp li fi er's internal res istance. For example, if speaker im pedance is 8 ohms and th e amplifier's internal resistance is 0. 1 ohm, th e damping fa ctor is 51 frequency at which it " likes" to vibrate more than at chapter& others an d in the vicinity of whi ch it wou ld therefore over-emphasize the sound. One major task of designers, therefore, is to el im inate this resonance or at least to StJeaker S}'slents and Headphones bring it under con trol or lower it beyond the lowest au dible sound frequency. This is done by means of Speal?er systems in a hi-fi system are somehow like the last pages of a novel. The plot gradually thickens, speciall y se lected cone paper and cone designs. the parts of the puzzle fall into place, and from them DOUBLE CONE AND COAXIAL SPEAKERS emerges the solution and the revelation of the writer's On the other hand, a speaker can reprod uce only a intents. But, as in some stories, speal?er systems are not limited sou nd ra nge - large-diameter speakers are best always a happy end, sometimes leaving questions un at delivering the low sound spectrum, small ones are answered, wishes unfulfilled. most sui table fo r the high range. Th ough most portable Speaker systems are as sim pl e in theory as th ey are an d economy class audio equipment has only one full complex in fact. Let's look at their structure and func range loudspeaker, various ways have been conceived to tions first. And by the way, the use of the term "speaker divide th e sound spectrum into two or three ranges and system" is more techni call y correct than the terms feed each portion to a cone of th e proper dimensions. "lou dspeaker" or "speaker," because as you wil l see a One method is illustrated in the photo, the double cone speaker system is made up of several ind ivid ual parts - speaker which does not really have two cones but a cone speaker units, crossover networks, etc. - whi ch toge th er made of two different kinds of paper for the low and Fig. 6- 1 Cut View of Cone function as a system. One "speaker system" is needed high ranges. The next logical step is the coaxial speaker Type Speaker for each channel in a stereo install ation; thus a 2-channel shown in Fig. 6- 2, which has a larger, outer pape r cone stereo set-up has a "pair" of "speaker sys tems" while a for the low ran ge and a smaller horn speaker for th e 4-channel se t-up has two "pair" or a total of four medium and high spectrum. (Designs with th ree coaxial speaker systems. ly arranged low, medi um and high range speakers are SPEAKER SYSTEMS call ed tri-axial.} In the coaxial speaker, th ere is some STRUCTURE AND FUNCTIONS ti mes a crossover network wh ich di vides the signal into The signal from the power amplifier passes through the suitable portions, and level controls {attenuators} Double cone speaker a coil (cal led the "voice coil "} wh ich is suspended for each range. between the poles and around the center pole of a large, powerful permanent magnet. The interaction between TWO-WAY, THREE-WAY, this permanent magnetic fi eld and the alternating FOUR-WAY SYSTEMS magnetic fi eld generated around the coil by the signal By logical extension of this principle, we arrive makes th e coil vibrate in rhythm with the signal. A at speaker systems with two, th ree or even four separate cone-shaped membrane attached to the coil passes speakers mou nted in one encl osure. According to the these vibrations on to the surrou nding air, creating sound number of sections into which the aud io spectrum is waves. A cross section of such a speaker unit is shown divid ed, such systems are call ed 2-way, 3-way or 4-way. in Fig. 6-1. The number of speaker un its in such a box is not always The speaker cone, being a mechanicall y vibrating the same as the number of ways, because the high range mass, has a resonance point, that is a certain sound "tweeters" and mid-range speakers are sometimes 52 53 doubled , so th at we ge t 3- way 4-speaker or 3-way ma tched, the size, shape and wei ght of th e speaker 5-s pea ker sys tems. enclosure, an d the listen ing room. In such sys tems, each speaker unit can be des igned to re produce, as ideally as possible, its apportioned sound SPEAKER ENCLOSURES range. The low-range "woofer" is usually of large Enclosures can be roughly divided into two types: diameter (7-1 /2, 10 or 12 in ch} and consid erable weight closed boxes and bass reflex types . A closed box is because of its big, heavy magnet. The mid-range spea ker, hermeti cally sealed at the bac k so that sou nd emanating ~~~t-:;; about four inches or so in diameter, reproduces th e from the rear of the speakers is absorbed in the box ...______. sound range fr om approximately 500 to 2,000 or (whi ch is usually lined or stuffed with sound absorbent 3,000Hz. The top two or three octaves - up to about glass wool or plastic foam}. Only the sound from the 20,000Hz in excellent hi-fi spea kers - are the domain face of th e spea kers is radiated into th e room. Closed of th e tweeter, either a small paper cone speaker or, boxes usually excel in sound clarity and subtleness, but in creasin gly, a dome-type with a dome-shaped membrane they require rather volum inous dimensions to obtain or a horn type with a metal horn instead of a cone. satisfactory bass response. A modern variety of the (Horns are more efficient in cou pling th e sound vibra closed box is the air suspension type, often used as tions to th e air, li ke the bell of a trumpet.) A re latively compact bookshel f speaker systems, in wh ich the woofer ,.------=--..., new design is the multi-cellul ar horn used for mid -range is mou nted in a soft ba ffl e suspension so that it can and tweeter applications which is partitioned into a perform longer piston movements for better bass dozen or more ce ll s. The purpose of this is to diffuse response. the sound more evenly throughout the room. The bass reflex type, on the othe r hand, boosts the Coaxial spea ker bass sou nd by channeling part of the rear sound back to Dl RECTIONALITY the front th rough a duct or port (see Fig. 6- 7.). In Fig. 6- S This may require some ex pl anati on. Speakers have other wo rds, it behaves as if two woofers were instal led. Dome Type Speaker the sometimes desirable, sometimes unwanted character The key to successful designs of this type lies in the a.;;..;..;.;.;..;....;..:.:.....;..:...______. istic of radi atin g th ei r sou nd in a certain, cl early defined phase inversion which the box must perform, because angle which becomes narrower and narrower as the otherwise th e sou nd from the speaker and from the duct sound frequ ency becomes higher, so that twee ters show wou ld be out of phase and might cancel each oth er ou t. ~----:===-~~~~1 a ra ther strong directionali ty. As this would affe ct the Bass refl ex boxes are bei ng used widely because of their sou nd diffusion in the listen ing room and limit the smal ler volume in comparison to closed boxes, bu t their usabl e listeni ng positions, speaker designers have come drawback is that the bass range sometimes sou nd s a up with various methods of overcoming thi s deficiency. little boomy. One of th ese is the multi -cellu lar horn design, others HOW TO CHOOSE SPEAKERS in clude th e above-mentioned dome tweeter or a small The choice of speaker systems thus becomes rather Sound absorbent reflector called "diffuser" mou nted before the tweeter. tricky because specifications can say very little about the material Wh at complicates matters for the au di o amateur is character of the actual sound. The id eal speaker system, Fig. 6-6 Infin ite Baffle that the speaker enclosure wi th five speakers does not Enclosure Plate \ Driver unit of course, wou ld reproduce th e entire sound range Voice coli always sound better than the one with four - a number without arbi trarily add ing or su btractin g anything, bu t Fig. 6- 3 of other factors enter into the pi cture, including th e such a system has never an d can never be designed - Horn Type Speaker quality of each speaker unit and the way th ey are all speakers have some ind ividu al habi ts and id io- 54 55 sy ncracies whi ch are called "coloration " or "trans res ponse in each sound range. How these difficu lties can parency" or other such abstract words. When purchasing be mastered wil l be explained in th e chapter about spea ker sys tems, the specifi ca tions should be used to mu lti-ampli fi er stereo systems. determine the general size, type and power range, but The level control is a simple attenu ator which permits the final choice mu st be made ei ther after comparative the medium or high sound ranges to be suppressed or listening tests. Res tated, the effect of a speaker system boosted to an extent - a helpfu l way of matching the on human hearing is wh at has been called a "psycho speaker response to the charac teristics of the listening acoustical phenomenon." Th at is, the actual, phys ical room. Sound absorbent effect of a vibrating speaker on the air is translated to material Crossover network Level control the li stener's brain through a combination of the actions Fig. 6-7 ,.:\ .... . I , Bass Reflex Enclosure of hi s ear drum, etc., and his psychological reaction to + I : : : L------..1 th e physical perceptions he receives. This mea ns that Power 1 amplifier the "sound" of a given speaker system may be diffe rent I]::J Tweeter ly interpreted by different people. And what it means to the prospective buyer is that he should determine for him se lf wh at he is hearing. Ideally, a speaker system should be judged by the listener only when it is operat Fig. 6- 8 Wiring In a in g from his own amplifier in his own listening room. Crossover Network When th is is inconvenient, the bu yer should make every and Level Control effort to tes t the speaker system with equipment and in an environment which most closely match those he How In llead loudSJJenl•ers ti(Jecillcalitms wi ll be using. Also, keep in mind that a reall y good a} Input Im pedance spe aker system should be able to satisfactorily reproduce The load impedance of the speaker system as seen from Re: SPECIAL ENCLOSURE any kind of mu sic; there is no such thing as a "rock the am plifier ou tput. 4, 8 and 16 ohms arc the inter (Back loaded horn enclosure) music speaker system" or a "classical-music speaker nationally standardized values for speakers to be driven system." by transistor amplifie rs. Not cr it ical. CROSSOVER NETWORK, LEVEL CONTROLS b) Maxim um Power Hand ling Ability Auxili ary parts in a speaker system include th e cross Also called "maximum in put power." The power (in over network and, sometimes, one or more level wa tts} that the speaker system can handle continuously controls. The crossover network is an electronic circuit without fear of damage. Some tim es, a higher limit value which splits up th e sound spectrum into the required is also given which describes the maximu m input power number of ways - low and mid/high range in a 2-way of short transien ts and peaks. Power handling abi lity sys tem, low, mid and high in a 3-way. It consists of a docs not need to equal or exceed the amp! i fie r's ou tpu t combination of coil s and capacitors, often equipped with power unless the amplifier is to be operated at top ferrite coil cores which permit better damping and more volume - wh ich al most never happens in home applica compact des ign . Th e borde r frequencies between one tions. range and another are call ed "crossover point." Unfor c) F rcqucncy Response tunately, they are fi xed an d unflexible in such a cross The width of the sound spectrum (i n Hz} that the over networ k, and they do not always deliver equal speaker wi ll reproduce. Tak ing l ,OOOHz as the reference 56 57 level, th e lower and upper lim its arc the points at wh ich the loudspeaker wi ll still deliver 1/3 of the sou nd Chapter7 pressure level (= - 1Od B). Look for wider frequency response ra ti ngs. 60 · 15,000Hz is quite sufficient. Multi-Amplifier Systems HEADPHONES A good pair of stereo headphones is a very worth· In the chapter dealing with speaker systems we while, small investment for the seri ous li stener. Head came across the terms 2-way, 3-way or 4-way, meaning phones serve two main purposes: they permit late-night that the audible sound range is divided into two, three listeni ng in com plete privacy and at fu ll volume levels; or four portions. This division is usually made by a Model SE-700 and they are indispensable for monitorin g tape record dividing network in the speaker systems, i.e. between (High-Poly mer Headphones) in gs. Practically all modern stereo amplifiers, tape decks the power amplifier and the speal?er units, but it is of and even some tuners are equipped with standardized course possible - and advantageous, as we will see - headphone jack. In some instances, the headphone to do this at an earlier stage. The reasons are easy to volu me can be adjusted with a special control, inde· understand. pend ently from the master vo lume setting. Al so, most REASONS FOR MULTI-AMPLIFIER amp li fiers are so designed that th e loudspea kers are SYSTEMS au tomati call y cut off when the headphones are plugged Model SE-L40 1 in, or, have switches for tu rning off connected speaker Assume that two pure sou nd signals of 1OOHz and (Light-weight 1,OOOH z pass through a power am plifier. At the amp systems while leaving th e headph one circuit "live." Headphones) outpu t, we will obtain not on ly the original two signals, It must be no ted th at li sten ing through headphones but also a number of other freq uencies: 1,1OOHz, 900Hz, creates a fundamentall y different sensation from listen ing via speaker sys tems. As the sound enters directly etc. These undesirable admixtures - sums and dif into th e ear, it acqui res mu ch stronge r "presence." ferences of th e original fre qu encies - are caused by a A monophonic program heard through headphones wi ll bad habi t of all amplifiers called "intermodu lation dis appear as if the sound sou rce were located ri ght in the tor tion." Th is can of course be reduced by good amplifier design, but it can never be totally el iminated (S ealed Headphones) center of the sku ll. Stereophonic programs seem to be spread out in "interior space" - an ex peri ence that can and can be rather irritating to the listener. be startling at first. The atten tive reader wi ll also remember that a few Good headphones should be light and comfortable minor problems remained unsolved in regard to the to wear wi thout causing perspiration around th e ears. passive dividing networks in speaker systems - dividi ng They should also have a wid e frequ ency response - th e is not always even and accurate, DC resis tance can bass range is very critical - and should sound trans degrade dam ping, and such passive systems are fixed, parent, not stuffy. Pi oneer offers a wide selecti on of not flexib le. Wouldn't it be nice to get rid of these stereo headphones including some models with built-in unw iel dy networks al together? Model SE-0404 Also, wou ldn't it be lovely to be able to control (4-channel headphones) vo lume and tone con trols. the intensity of each sou nd range - bass, med iu m and high - individually and to obtain tailor-made sound for every record, tape or li stening room? 58 59 ELECTRONIC CROSSOVER NETWORK These are the main ideas behi nd mu lti-amplifier systems. The signal obtained from the pre-amplifier outpu t is div ided into two, three or even four ranges in a so-called "electroni c crossover network" {sometimes call ed "channel divider" or " di vid ing preampli fier"). tv1odel SF- 850 (El ectronic Tuner Integrated amplifier From there, each partial ra nge enters its own special Crossover Network) power amplifier, is raised to the required power leve l, ==--o: ------0 •000• 0 0 ------1 Speakers ·: oo·oo- oo: 0 0 ••••• 0 and then enters directly in to one or more speaker units of the proper type. As each amplifier handl es only a small portion of the frequency spectrum, th at irksome intermodulation di stortion can be easil y tamed. No passive dividing Fig. 7- 1 Conventional System network is needed in th e speaker system. And, bes t of all, crossover frequencies can be switched at will and each sound range can be controlled with accu racy. FEATURES AND DRAWBACKS If this sounds too good to be true, let us reveal the one great drawback: money. Two, three, or even four power am plifiers are needed, and the electronic crossover network isn't exactly cheap, ei ther. Therefore, mu lti ampl ifier systems see m to be doomed to rema in the privilege of well -heeled enthusiasts or those with extremely understanding wives. To the selected few, however, a multi-ampli fier install ation can reall y bring Fig. 7- 2 2-Way Multi-Amplifier System a degree of deli cacy and realism in sound that deserves the name "highest fidelity." {Fortunately, most Pioneer integrated amplifi ers and receivers permit their pre and power stages to be used separa tely so th at a multi-ampli fier sys tem can be built by adding only one or two more power amps and the electronic crossover network. The speaker systems must of course be equipped with separate input terminals for low, medium and hi gh range.) Fig. 7- 3 3-Way Multi-Amplifier System 60 61 HINTS CONCERNING MULTI-AMPLIFIER SYSTEMS chapterS Wiring and adjustments in such a system become rather comp licated so th at a few hints may be usefu l. Choice of add itional power ampl ifiers: it is of course Four-Channel Sound ideal to use the same types for each range, but if The development of 4-channel comes close to solving differe nt ampl ifiers are combined, the one with the the biggest problem inherent in conventional 2-channel highest power rating should be used fo r th e bass stereo, that is the fact that all sounds- both direct and spectrum. This is because, statisticall y, most energy in indirect, and of different phases - are heard from the music is found in the low freque ncy range. two speaker systems placed in front of the listener. Power handling ab ility of speaker systems: if no To improve this, 4-channel employs four speakers, separate power ratings are given by the speaker manu usually two in front and two in the rear of the listener facturer for the tweeter(s), mid-range speaker and as illustrated. woofer, note that th e rating for each segment in a 3-way The two major advantages of 4-channel are: (7) Th e system becomes approxi mately 1/9 (not 1 /3) of the listener can enjoy in his own home a musical environ total. Never, never turn up the vo lume control fully ment often comparable to a concert hall, since the two or you may overload th e speaker units and burn out rear speaker systems reproduce the natural sounds of deli ca te , expensive-to-replace voice coil s. the concert hGII - mainly the indirect sounds. And (2}, Protection of tweeters against bass pulses: strong, a new world of sound, one heretofore inconceivable, sudden bass pul ses may occur when the power amplifiers is created. Wh at one hears is music that has been com are turned on and off, and these could damage the posed, arranged and recorded with the effects of tweeters. As a protecti on, a ca pacitor of approximately 4-channel in mind, i.e., two orchestras in position, 6 - 12pF shou ld be inserted (in series) between high one in front, another in the rear to enable switching range amplifier and tweeter. back and forth between the two; surrounding the listener Setting of crossover frequency controls: start with with music; or enjoying the movement ofsound. the settings recommend ed by the speaker manufacturer or, lack ing these, start with 200Hz for low/medium and FOUR-CHANNEL SYSTEMS 2,000Hz for medium/hi gh. Then play your favorite tape There are today a number of different forms and or record and slowly ad just the controls in either types of 4-channel program sou rces. Bu t general ly direction until the sound becomes most satisfying. speaking, th ey can be cl assified into the fol lowing three (Leave tone con trols flat.) categories. (Discrete, Regul ar matrix, SQ) Finally, let us reveal one of the great joys of owning (I) DISCRETE SYSTEM a multi-amplifier system: th e advanced amateur or Th is system is the most authen tic in term s of sound semi-professional can do away with ready-made speaker quality, and also the most ex pensive, since it not on ly systems and can in stead buy individual loudspeaker req ui res 4-chann el equipment, but also 4-channel tape units and have th ese installed in custom-made encl osures. recordings. When the sou nd s are reproduced, four This provides a new dimension of freedom in sound independen t playback amplifiers are used, so that engi neering one's home. optimum 4-channel effects are achieved. This system is often referred to as the 4-4-4 system. Conceivable 62 63 program sou rces for discrete 4-channel include open 2 Discrete Four-Channel Disc (CD-4 Disc) reel, 8-track cartridge, or cassette tapes, or disc record The CD-4 disc record is a unique 4-channel discrete ings and FM broadcasts. Today open reel, 8-track record that has compatibility with mono or stereo cartridge tapes and discs are al ready on the market. records. In the CD-4 disc, four independent signals are 1 Discrete Four-Channel Tape recorded by usi ng special modulation techniques. This The illustrati on below shows the functions in discrete disc mai ntains the conventional 45°/45° record groove, 4-channel open reel tapes and 8-track cartridge tapes. but on the inner groove wall the left channel sum signals They provide the best tonal quality reproduction, as (channel 1 + channel 2) are engraved, while on the outer well as the most distinct separation of sou nds, since wall the right channel sum signals (chann el 3 + channel ind ependent signals can be recorded on each track, so 4) are engraved. Additionally, important sign al com that the pl ayback effects prov id e th e same ri ch and ponents for the rear channels are transmitted by the abundant sounds of the concert hall fo r classical or inaudible subcarrier, the center of which ex ists at popular music. Additionally with this system, other 30KH z. These signal components consist of the dif unusual effects are possible, such as sw itching back and ferential signals (channel 1 - channel 2) of the le ft forth between sounds of two orchestras or the move channel s, as well as the differential signals (channel 3 - ment of a sound field at very high speeds. channel 4) of the right channels. These sign als are frequency modulated and are then added to the walls of the record groove in addition to the above-mentioned sum signal s. When we matrix these signals and the differential signals, four independent signals are ob tained. Since this disc is the modul ation type, a CD-4 demodulator unit is required for exclusive pl ay bac k in addition to a high-quality stereo turntable and phono cartridge. Fig. 8- 2 Four-Channel Tape System Conventional 2-channel Stereo 4-channal Stereo ) i f ~ ~ )~l~~~gg OPEN-REEL 4 TRACK TAPE CARTRIDE 8 TRACK TAPE (1 3 5 71 2 4 6 81 'lllllll~ 13.11g::: Il j ]' : : : l (4, 8) ~ ~ {{ch.l+ch.2)t{ch.l -ch.2)}•ch. l track 2·channel Stereo 8 track 4-channel Stereo ~{{ch . ltch . 2)-{ch . l -ch . 2)} •ch.2 ~{{ch . 3+ch .4)t{ch.3-ch .4)} •ch . 3 Fig. 8- 3 Open-Reel and Cartridge Four-Channel Tape ~ ({ch.3+ch.4)- (ch.3- ch.4)} •ch.4 Fi . 8-4 The Principle of Discrete Four-Channel Disc (Ill) SQ MATRIX SYSTEM The one matrix 4-channel system that has no com patibi li ty with any of the others is called the SQ system. Its encoding/decoding process is dramatically differen t, and thus a special SQ decoder is requ ired in order to reproduce its program sources. Therefore, regu lar matrix and SQ decoding circu its are req uired for true matrix Fig. 8-S Four·Channel Disc (CD·4 DISC) System 4-channel versatil ity. 3 Discrete Four-Channel FM Broadcasts The FM discrete system uses multiplex modulation techniques as well as conventional stereo FM broadcasts techniques, and also employs the wide carri er bandwidth. At present, various ki nd s of systems have already been annou nced, including th e "Dorren" system. The future of FM discrete broadcasts is bright, but government regu lati ons regarding this system are still pend ing in the United States and other cou ntries. (II) REGULAR MATRIX SYSTEM Four signals recorded in the form of 4-channel are fed through a special 'encoder' and converted into two channel sign als. In the play bac k process, th ey are fed Model OX-949 Model QX-747 Model OX-646 through a "decoder" to recreate the original 4-channel (4-channel receiver) (4-channel receiver) (4-channel receiver) sound fie ld . This system is called "matrix", or "4-2-4" system, and, when used, does not require a special tape deck or turntable as is the case of discrete. All th e matrix systems avai lable today (except the SQ matrix) can be classified into this "regu lar matrix" group. All basicall y are compatible with each other. Model OA-800A Model QC-800A Model QM-800A (4-channel integrated (4-channel preamplifier) (4-channel power amplifier) amplifier) Model OL-600A (4-channel rear amplifier) 6 Chapterg chapter tO Of Dollars and Decibels Dos and Don'ts A few words of pecuniary advice to the hi-fi novice Do read the operating in structions supp lied with each unit. Keep referring to the may be warranted here because an audio system re in struction manual when setting up you r hi -fi system, and keep the manual handy presents a maj or investment and should be purchased for future reference. with wisdom and care. As a convoy of ships can onl y Do read and compare the speci fi cations. These contai n valuable figures for matching travel as fast as its slowest vesse l, so a hi-fi system will your components co rrectly. Mos t items are ex pl ained in this guidebook. only be as good as its weakest link - th e catchword is Do fill out and mail the warranty cards, if required, to obtain full warranty "balance." It makes little sense to pair off a superb protection. am plifier with a meek speaker system, or equip a top Do ex periment with different speaker positions. No cover-all ru les can be given, turntable with a so-so pi ckup. but often a min or change in the speaker position can bring about a major To help avoid such pitfalls, we have drawn up the improvemen t in sound. fo ll owing illustrations which give approximate per Do treat your phonograph records with utmost care. Always put them back in their centages of th e total avai labl e budget to be spent on each jackets immediately after playing. Store th em either in upright positi on or com ponent of a hi-fi sys tem. Absolute amounts cou ld horizontall y in stacks of not more th an 10. not be quoted because prices differ greatly from country Do store tapes in th eir boxes and away fr om motors, TV se ts or other electrical to country, manufacturer to manufacturer, but these appliances. percentages should prove about ri ght in prac ti call y all Do fo llow the manufacturer's instructions in regard to proper maintenance of all cases. units - cleaning, lu brication, fu ses, etc. Don't install any hi-fi comp onent in a dusty, hot, moist or wobbly place. Do avoid direct sunlight. Don't accidentally drop th e stylus on the turntable or record when making adjustments of the trac kin g force etc. Cartridges are eas il y damaged. Don't obstruct th e movement of a turntable or tape reel by hand. Don't ground th e sys tem at two or more poin ts. Grou nd connection should be made onl y from th e ampli fier. Don 't run th e system at fu ll bl as t for extended periods. This may dam age th e speakers and th e nerves of your neighbors. Hi-fi is not synonym ous with loud ness. Don 't call a service man immediately when you think your sys tem isn't fun ctioning properly. Refer back to the in structions. Very often there is no defect at all , onl y an operating error. Don 't open or oth erwise tam per with a hi -fi unit. This can be dangerou s and can inva lidate your warranty. Contact qualified service personnel for repairs. 68 69 J\ Glossary of J\udio Ternts Antenna: Assembly of metal bars, wires or loops for picking up radio waves. Dimensions depend large ly on the wavelengths to be received. Antenn a Directi onality: Th e characteristic of certai n antenna confi gurations, includ ing most FM and TV antennas, to receive radiowaves reaching it within AC: Alternating current. An electric current with periodicall y changing polarity. certai n defined angl es more strongly th an those com ing fro m other directions. In popular parl ance, often used as synonym for electrical house (or mains) current. Antenna Gain : An indirect measure for an. antenna's output level, i.e. the Acoustic Feedback: Unwanted acoustic interaction between output and input strength of th e sign al supplied by the antenna when compared to a standard of an au di o sys tem, usua ll y between speaker system and microphone or turntabl e antenna and at a certain frequency. Expressed in decibels (dB). cartridge. Can lead to "howl." Anti-Skating Device: Mechani sm exerting a small outward force on a tonearm Acoustics: The science of sound . Al so, th e acoustical character of hall s and to compensate the inward th ru st caused by groove/stylus friction and tonea rm rooms. geometry. Active Filter: See filter. Antistati c Fluid: A fl uid (or sp ray) used to prevent phonograph records from becoming electricall y charged, as an electrical charge wo uld attract dust. Aerial: Sy nonym for antenna in British English. Audibility Threshold: Th e minimum sound intensity that the average human AF (Audio Frequency): Frequency within the range of human hearin g - ea r can hear. Approxim ately 0.0002 mi crobar at a frequency of l ,OOOHz. app rox im ately 20 - 20,000Hz. Automatic Level Control: A circuit which au tomaticall y keeps the level of a AFC (Automatic Frequency Control): An AFC circu it of an FM tuner corrects sign al within a certain range. Examples: automatic gain control in AM radios, ALC for an inaccuracy in tuning by locking in the station being tuned. in portable tape recorders. AM (Amp li tude Modul ation) : Modulation accomplished by varyi ng the ampli- Automatic Record Changer: Record pl ayer which can change from disc to disc tude (in tensity) of the carrier. automatically. Amplifi cati on: In crease in signal magnitude. Aux (Auxiliary) Input: Inpu t on amplifi er, etc. Accepts ex tra signa l source such as casse tte tape player, etc. Amplifi er: Unit providing amplification of sign al, from low to higher voltage or current (pre-amplifier) or power (power or main amplifier). Baffle: The board on whi ch one or several speaker units are mounted. Separates the radiations from the front and back of the speaker. AM Suppress ion : Characteri sti c of an FM tuner to suppress changes of amp li tude in received signals, thereby improving the signa l-to-noise ratio by rejecting noise Balance Control: Potentiometer used to adjust volum e difference of left and an d interference. right stereo channels. Anechoic Chamber (Room) : A speciall y designed room, used for testing micro· Bandpass Filter: A circuit which will pass signals above (high bandpass) or phones and speakers, rendered acousticall y "dead" by sound absorbing material. below (l ow bandpass) a certain frequency wh il e attenu ating others. 70 71 Bass: Low audio frequency range, below approximately 200Hz. Channel Separation: Degree to which left and right channel signals are separated in a stereo pickup, FM stereo tuner, amplifier, etc. Bass Reflex: Speaker system enclosure with an outlet permitting sound fr om th e rear of the speaker cone to be radiated to th e front. Characteristi c: Refers to a characteristi c curve which conveys in formation abou t an amplifier or other item. Beat: A pul sation caused by interaction of two waves of different frequencies. Chrome Tape: A newly developed tape using the chromium dioxide particl es, Bi as: In tape recordi ng, a high frequ ency signal ap plied to th e tape to optimize and offers excellent frequency response and wide dynamic range. its frequency response. Also, the side-thrust on a tonearm. Coaxial Cable : A cable consisti ng of an in ner conductor and an outer sc reen. Bias Compensator: See anti-skating device. Used as antenna leads and for interconnecting aud io un its. Bi-Radial Stylus: See ell iptical stylu s. Coax ial Speaker: A loudspeaker consisting of a bass cone with a concentrically mounted tweeter. Block Diagram : A schematic diagram illustratin g the mai n circuit blocks and signal flow in an electroni c device. Compatibl e: (a) FM MPX signal receivable as mono by a radio or tuner; (b) Stereo disc playable with a mono pi ckup. Capacitor: A device which can store an electric charge. Perm eable to AC, (c) Stereo pickup suitable for play ing mono records, too. impermeable to DC. Comp li ance: The flex ibili ty of phono cartridge. Th e un it of compliance is Capstan: Drive spindle in a tape deck. The tape is pressed against the capstan 10- 6 em/dyne. by a pi nch roller. Component System: An au dio sys tem consisting of separate units: turntable, Capture Ratio: An FM tuner's abi li ty to re ject unwanted FM stations and inter- tuner, am pl ifier, speakers, etc. fere nce occurring on the same frequency as the desired station . Condenser Microphone: A microphone utili zing the changes in capacitance Cardioid Microphone: A microphone with a directional characteristic that caused in a condenser if one of its plates - th e microphone membrane - vibrates resembles the shape of a kidney. in rh ythm with sou nd waves. Same pr in ciple can be applied to a condenser type ph ono cartridge. Carrier: Main radio signal from a transmitter. Can be modul ated in di fferent ways (AM, FM) to convey sound or picture inform ation. Control Amplifier: A preamp li fier and amplifier combi ned in one unit. Cartridge: (a) phono pickup; (b) endless loop tape in a packaged, standardized Cost-Performance Ratio: A way of evaluating a unit's ove r-all performance by container. grad ing its characteristics with poin ts, and divid in g the sum of accrued points by the cost. Naturally high ly individual isti c. Casse tte: Preloaded contain er with tape and spools for use on cassette tape recorder. Counter Weight: Weight fitted at rear end of tonearm behin d the pivot to counter the weight of the arm/head assembly and to permit adjustment of the Center Channel: An output terminal found on some stereo amplifiers which tracking force. supplies a mon oph onic mixed L+R signal. 72 73 Crossover Frequency: In loudspeaker systems and mu lti-amplifier audio instal Demodu lator: In an FM stereo tuner, the ci rcu it that ex trac ts the left and right lations, the borderline frequencies between low/med ium range and med ium/high channel signals from a broadcast signal original ly modulated by the FM multiplex range spea kers or amp lifiers. system. In a discrete 4-channel system, a demodulator is that unit which derives four signals from a CD-4 record. Crosstalk: Leak of right channel signal into left channel, and vi ce versa. Expressed as level of unwanted signal in relation to wanted signal channel, Derived Center Channel: See center channel. measured in decibels (dB). Differential Amp lifier: A type of ampl ifie r consisting of two transistors in wh ich Cutting: The process of engraving undu lati ng grooves in a rotating, wax-coated the di ffere nti al signal of th e transistors' input signals is amplified. Because of th eir or lacqu er disc. An important step in th e manufacture of phonograph records. excellent thermal characteristics, differential amplifiers are used in the first-stage of OCL power amplifiers, FM limiter stage, etc. Cutting Angle: See vertical angle. DIN (Deutsche lndustrie Normen): German Industrial Standards. In aud io, the Cutting Stylus: Stylus used for cutting of ph onograph record s. Germ an standard of plugs, sockets, etc. DIN is used as a standard in many European cou ntries. Cut-Off Frequency : The point at which frequ ency response is effectively limited, often determined as the point at wh ich level is reduced by 3d B. Di spersion: Distribution of sound from a speaker through a room. Damping : Redu ction of resonant effects by use of resistance or its mechan ical Distortion: Output signals not present in the origin al input. See harmon ic and acoustic equivalents. distor tion, interm odulation distortion. Damping Factor: Ratio of speaker or speaker system impedance to amplifier's Dolby System: A unique noise reduction system, which electronically eliminates intern al impedance. Denotes amplifier's ability to damp unwanted, residual speaker the irritating noise (tape hiss, circui t noise, etc.) with out sacrifici ng th e original movement. tonal quality. dB (Dec ibel): A logarithmic unit used to ex press th e ratio between two power, Drift: Tendency of a tuner to move away from optimum adjustment as its voltage or current levels. components warm up. power 1 Compensated by AFC. Mathematica lly: 20 log 10 : :~: : ~ or lO iog1o power2 Drop-Out: In tape recording and playback, the "holes" in the sound caused by Decoder: In 4-channel , a circuit or circuit complex whi ch translates matrix thin or bare spots on the tape. encoded signals arri ving in the form of two se parate sign als into four signals to be amp lified and passed on to the speaker systems. Dual Cone: Speaker consisting of separate bass and treble cones mounted concentrically an d driven by the same coil. See also Coaxial. Mechanical 2-way DE -E mphasis: Attenuation of high sound frequencies in an FM tuner, to speaker. counteract the boosting of these frequ encies ("pre-emphas is") done at the FM station. Dynamic Mass : The effective mass of the movi ng parts of a pickup cartridge. This is not simply the sum of the masses of each component, but rather the Demodu lation : The process of "extracting" from a modul ated high or inter- equi valent mass that determines the mechan ics of its behavior. medi ate frequency wave th e origin al audio signal which it was mod ulated with. 74 75 Dy namic Range : In program material, the range of signal amplitudes fr om highest to lowest; the range (in dB) which a device will handle. Filter: A circuit which attenuate signal s above, below, or at a particular frequency. Efficiency: Ratio of output to input power in a transducer. In speaker systems, th e percen tage of electrical input avail able as acoustic output. Flutter: Quick waver of pitch caused by speed flu ctu ations in the movement of tape or discs. Heard as a so rt of quiver. Electrostatic Speake r: A loudspeaker utilizing the princi pl e of a membrane vibrating in a strong electric field. Flywheel: A disc of large mass which, when rotating, has the tendency to maintai n its rotational velocity. This effect is utilized in tape equipm ent and Elliptical Stylus: A pi ckup stylus shaped so th at its width across the groove is turntables to maintain constant speed. greater than the width of its sides. Claimed to have better high frequency charac ter istics than round styli. FM (Frequency Modulation) : Type of mod ul ation of radio waves in which th e frequency, not the amplitude of the carrier is modulated by the audio signal. Enclosure: Th e cabin et whi ch houses one or more speaker units. Has great FM broadcas ting achieves higher sound qu ali ty. influence on bass response of speaker. Four-Ch annel: A new ly developed au di o technique using four (instead of two) Equalization : Correction for fr equ ency non-linearity of recordings. Phonograph channels for sound reproduction. records are cut with low frequ encies attenuated and high frequen cies boosted. Equa lization compensates for this, producing a fl at frequency characteristi c. Frequency Response: Th e frequency range which a unit will reproduce or respond to. Equalizer Amp li fier: In a pre-amplifier, the circuit which amplifies and "flattens" th e phono input sign al. Needed because phonograph records are not cut Front End: Section of a tuner that selec ts the wanted stati on from th e radio with fl at frequ ency response but accord ing to a standard "equali za tion" curve. band and converts the RF (Radio Frequency) sign al to IF (Intermediate Fre qu ency). Feedback: Signal from output of amplifier or electronic network applied to input in anti-phase (hence negative feedback) to redu ce distorti on and noise, and to Function Selector: In an amplifier or receiver, the switch or knob which selects fl atten or oth erwi se shape fr equ ency response. Also, unwanted acousti c feedback. the different program sou rces such as ph ono, FM, AM, AUX, etc. Ferrite Core Antenna: An antenna, used chiefly for AM reception, consistin g Gain: Degree of signal amplification achi eved in an amplifier circuit. Expressed of wire windings around a core of ferrite. Advantages are: compact size, good in decibels (dB). Opposite: negative gain or loss. sensitivity and high directi onality. Gap: Vertical slit in a tape-head. In the gap, a magnetic field occurs during FET (F ield Effec t Transistor): Special kind of transistor consisting of metal recording, and a magnetic signal is induced during replay. ox ides. Amplifies voltage, not current. Used in audio equipment because of its good linearity and stable impedance. Ghos t: In TV, the appea rance of a secondary picture slightly to th e ri ght of the main pi cture. Sim ilarly, ghost can be used to mean multipath FM reception. Also Fi eld Strength : The intensity of an electrical or magneti c fi eld . the "images" of the true station fr equency that an FM tuner purports to receive. ' Field Strength Meter: See signal strength meter. Harmonic Distortion: The sum of all signals in an output which are multiples of the inpu t sign al frequencies ("harmonics"). The ir intensities are expressed as a percentage of the total output intensity. 76 77 Head: a) the erase, recording and play back heads in tape equipment; (b) the oscill ator and intermediate frequ encies. shell-cartrid ge assembl y of or attached to a tonearm . IM Distortion: {see Distortion) Signals in output caused by interaction of two or Headphones: Small transducers, usuall y mounted in pairs on a bracket to fi t over more input signals, but not harmoni call y related to them. Expressed as a percentage the head and designed to make intim ate contact with th e ears. of total sign al intensity. IM distorti on is known to cause li stener fatigue. Head Shell : The part of a tonearm whi ch carries the cartrid ge. Head shells in Impedance: Res istance to th e fl ow of altern ating current. Measured in ohm s. top-class equipment are usuall y detachable. It may va ry with the frequency of the applied alternating current. Heat Si nk : A dev ice used to remove heat from electro nic comp onents such as Induced Magnet Cartridge: A pi ckup cartridge in which both magnet and coils tubes, transistors, etc. are fi xed. The moving part is a tiny iron sheet. Hertz (H z): Uni t of frequency, equal to one cycle per second. Infinite Baffle: Type of spea ker mounting wi thout an air path between front and rear of spea ker cone. Horn: Speaker unit usin g a trumpet-bell shaped, fl aring funn el to couple its sound vibrati ons to the surrounding air. Integrated Amp li fier: Unit combining a pream plifier and power amplifier. Also called pre-main amplifier. Hum: Unwanted low frequ ency tone. Usuall y caused by 50Hz or 60H zAC and its harmoni cs. In terference: Un wanted in flu ences upon desired signal by extraneous signals, for exampl e from electri cal appliances, motors, automobiles as well as fr om un Hysteresis Motor: A motor used in hi gh quality turntabl es. Characterized by desirable signals generated within the audio equipment. very constant speed regardl ess of power voltage flu ctuations. LED: Light Emitting Di ode. IC (Integrated Circuit): Solid circuit bl ock containing th e functi ons of numerous transistors, di odes, resistors, capacitors, etc. Limiter: Circuits in an FM tuner that reject unwanted amplitude vari ations caused by atmospheric or ignition noise, producing an FM signal of constant IF (Intermedi ate Frequency): The frequ ency whi ch resul ts in a tuner when th e amplitude. incoming signal from the antenna is mi xed with the osc illator fr eq uency. Linearity: {a) Amplitud e linearity, di stortion of whi ch produces harmoni c 1F Transformer: Co mponent in tu ner or radi o receiver used to couple or feed di storti on and intermodulati on; IF signal between successive amplify ing transistors or tubes. Windi ngs us uall y (b) Frequency lin earity referr ing to the straightness of a frequency tuned with capacitors to resonate at th e fi xed IF fre qu ency. response curve. IH F (Institute of High Fidelity): In sti tute founded by American manufacturers Line Output: Output terminal of a preamplifier, tape deck, etc., providing a of audi o equipment, devoted to the imp rove ment of audio technology, stand ardiza signal for monitorin g, tape recording or supplying to a power amplifier. ti on of tes t and measuring meth ods, etc. " IH F" in au di o specificati ons means that valu es we re obtained in measurements accordi ng to IHF stand ards. Loudness Control (Contour): A circuit which counteracts the reduced sensitivity of the ear to very low and high notes at low volume levels. Image Rejection: The ability of a tun er to reject an RF signal which appea rs to be received, bu t which is actu ally a sum or difference frequency of the tuner's Low Filter: A filter circuit designed to remove low frequency noises (rumble, 78 79 hum, etc.) from the program. Network: In au dio, a frequency divid ing network in a speaker system, or an electroni c crossover network in a multi-amplifier install ation. Magnetic Cartridge: A phono cartridge which derives its electri cal output signal from change effected in a magnetic circuit by me ans of some mechani cal device Noise: Unwanted signal consisting of a mixture of random electrical agitations. such as a moving coil, moving magnet. Also, the sum of all unwanted sign als such as hu m, hiss, rumble, interference, distortion, etc. Main Amplifier (Power Amp lifier): Ampl ifier unit whi ch produ ces the output power required for driving speakers. Omn i- Directional: Equ al sensitivity or output in all direc tions. Said of an tennas, microphones and speaker systems. Monaural : One-eared. Sometimes erroneously use d to mean monophonic. Osci lla tor: An electronic circuit which generates an alternating current, e.g. the Mon itoring: Li stening to a program to judge or control the sou nd quality. oscill ator in a tu ner produces the freq uency used to mi x wi th incoming radio signals. Monophonic: Recording, transmiss ion and reproduction of sound via a single channel. Output Impedance: Impedance at output terminals of a device as "seen" by the load. MOS FET: An FET utilizing MOS (M etal Oxid e Semiconductor) element. Output Stage: Fi nal stage of a power amplifier which supplies power to Moving Coil (M C) Cartridge: Magnetic ph ono cartrid ge in which the coil s move a loudspeaker. and th e magnet is fixed. Output Transformer: Transformer in tube power amplifier to coupl e output Moving Magnet (MM) Cartridge: Magnetic phono cartridge in whi ch the magnet tubes to loudspeaker. moves and th e coils are fixed. Overtone: A tone accompanying the fund amental in a mus ical note. May or Mu ltiplex: Transmission of two or more channels on a signal carrier so that may not be harmonic. can be independ ently recovered by the receiver. In FM stereo: transmission of L+R (sum) signal and L- R (difference) signal on main carrier and subcarrier, respective Phasing: Connections between power am plifi er and speakers in a stereo system ly. must be made in such a way that signals representing a central sound sou rce cause the speakers to move equ i-d irectionally, i.e. in phase. Multipath Reception: Arrival of FM or TV signal vi a several path s of different length, due to obstructions, reflecting objects, etc. Phase Shift: As a signal passes through a tuner, amp Ii fie r, etc., some frequencies may lag beh ind others. In a tuner, th is phase shift can, in extreme cases, cause loss Multipl ex Demodu lator: See demodulator. of channel separation of FM stereo broadcasts. Phase shi ft in an amp li fier resu lts in blurring of stereo spa ti al localization and, in serious cases, can cause unstable Music Power: The maximum power ava il able temporari ly from a power amplifier performance and distortions. ampli fie r. Also cal led "dynamic-power." Polarity: Positive and nega ti ve te rminals of a battery or power suppl y, or the NAB: (Nati onal Association of Broadcas ters). north and south poles of a magnet. Sometimes refers to phasing of cartridges and Most widely used standard of tape recording techniques. loudspeakers. 80 81 Power Amplifier: See main amplifier. RMS (Root Mean Squ are): Abbreviation for Root Mean Square; the effective amplitude of an AC voltage waveform (RMS); equ al to the DC current or voltage Power Bandwidth: The frequency range over which a power amplifier will that in any given load wou ld produce th e same power dissipation. produce at least half of its rated output power (according to IH F standard). Ro ll -Off: The frequency at which an equalizer, tone control or filter begins Power Handling Abili ty: Max imum amount of power that can be safely fed to attenuate. into a spea ker system. Rumbl e: Low frequen cy noise resultin g from vibrations in platter and motor Preamplifier: A circuit unit wh ich takes a small signal, e.g. from a tuner or of a turntable and from record warp. turntable, and amplifies it sufficiently to be fed into the power amplifier for further amplification. Selectivity : The ability of a tuner to receive only the desired station wh il e rej ecting stations which are not requ ired. Measured in dec ibel s (dB). Quietening: Term som etimes used in stead of " muting" in FM tuners. Sensiti vity: The input signal level required by a tuner, amplifier, etc., to be.a ble Quieting: See lim iter. to produce a stated output. The lower the necessary input, the high er the sensitivity. Rated Output Power: The maximum power that an amplifier will deliver continuously without exceeding its specified distortion rating. Also called con Separation: See channel separation. tinuous power output or RMS power output. Signal-to-Noise Ratio: Ratio of desired signal voltage to unwanted noise and Ratio Detector: Circuit in an FM tuner for extracting audio signals from hum voltage. Expressed in decibels (dB). modulated radio or intermedi ate frequency sign als. Solid -State: Circuits using semi-conductors, e.g. transistors and integrated Resistor: Circuit device which offers resistance to the flow of electric current. circuits (ICs). Resistors may be made from wire, metall ic fi lm, carbon and other materials. Speaker System: Enclosure containing two or more speakers and a crossover Resonance: The tendency of a mechanical or electrical device to resonate at a network. Speaker box. particul ar frequency. Stereophonic : Recording transmission and reproduction of sound via two or Response: See frequency response. more independent channels. Reverberation: Reflection of sound from walls or ceilin gs. Echo. Can be created Stylus: A fine ly machin ed piece of sapphire or diamond . The part of a ph ono artificially by electronic or mechan ical dev ices to imi tate the effect of large hall s. pickup that traces the record groove. RF (Radio Frequency): The frequency of a radio carri er wave. AM (MW) covers Synchronous Motor: Type of AC electric motor in which rotor speed is related 535 - 1605kHz, FM occupies 88- 1 08MHz. directly to freq uency of power supply. RIAA (Record Ind ustry Assoc iation of Am erica): Usuall y refers to the disc Tape Dec k: Tape equipment comprisin g compl ete tape transport system, with recording and replay frequency response curves establi shed as standards by this motors, drive pu ll eys, linkage etc., as well as pre-amp li fiers for recording and play association. back, but no power amplifier or speakers. 82 83 THD (Total Harm onic Distortion}: See Distortion. the speaker cone back an d forth in accordance with the frequency and intensity of th e si gnal. Time-Constant: Product of capacitance and res istance in a circuit of resistors and capacitors (R/C circuit); ex pressed in mi croseconds (J.Ls) to specify response Weighted: Appl ied to a noise-level figu re or wow and flutte r, etc., which takes curve shapes such R/C circu its achi eve. account of the human ear's sensitivity characteristics. Tone Control: Control ci rcu its used to vary th e proportion of bass and treble Woofer : A speaker designed to reprodu ce the low part of the sound spectrum, in the sound. e.g. organ, bass, etc. Trackabi lity: Ability of ph ono cartridge to track record grooves of high Wow: Slow variation of pitch caused by speed fluctuation in tape or record amplitude and velocity. Also, see compliance. movement. Tracking Error: Deviation of ce nter-line of phono cartridge from tange ntial of WRMS: Weighted Root Mean Square. record at point of stylus contact. Caused by tonearm geometry. Transdu cer: Device for converting energy from one form to another; e.g. a speaker converts from electrical to acoustic, a tape head converts from magnetic to electrical. Transient: Abrupt change of state; sudden change in signal amp li tude as caused by percuss ion instruments, "attack" of plucked strings, etc. Transient Response: The abili ty of an amplifier, phono cartridge or speaker to foll ow sudden changes in the level of a sound. Tuner: The part of a receiver, or a separate unit, whi ch receives rad io broadcasts and co nverts them into audio frequency signals. Tuner-Amp lifier: Unit combining the functions of a tuner, preamp li fi er and power amplifier. Also cal led "Receiver. " Turnover: The frequ ency at which a response curve changes its shape or slope or at which an audio system undergoes change in operati on mode. Tweeter: A speaker des igned to reproduce th e high part of the sound spectrum. Vent: Opening or port in a bass reflex speaker system enclosure. Voice Coi l: A coil of wire attached to a spea ker cone. When placed in the field of a magnet, th e coi l responds to th e alternating signal from the amp li fie r, movin g 84 85 DECIBE L CHA RT 100000 10000 .;;-· 0 «:-'~~ ~,o 1000 q} .Q o.:i- ~'I> ... ~'\.\ « ~\e a:"' \c-> 100 '!o."-'l>~e ~0 20 10 5 2 1 0 4 10 20 30 40 50 60 70 80 Decibels (dB) Decibels Decibels V oltage or Power Rat io (dB! (dB ) Current Ratio 0 1 0 1 1 1.26 1 1.12 2 1.58 2 1.26 3 2.00 3 1.41 4 2.51 4 1.59 5 3.16 5 1.78 6 3.98 6 1.99 7 5.0 1 7 2.24 8 6.31 8 2.51 9 7.94 9 2.8 2 10 10 10 3.16 20 100 20 10 30 1,000 30 31.6 40 10,000 40 100 50 100,000 50 316 60 1,000 ,000 60 1,000 70 10 ,000,000 70 3,160 80 100,000,000 80 10,000 90 1,000,000,000 90 31,600 100 10,000,000,000 100 100,000 86 Ferrlte core qu ali ty, especiall y in the high sou nd range, because must [)Ot break or stretch easily, its edges must not curl, ~~~r~!r~~~uJe of a tape recorder's upper frequency response lim it il and its base must retain its strength and fl exibility for .______, a~Sh''"""'ield case•' directly and mathematically related to the tape speed many years. Al so, th e emulsion must not separate fr om Fig. 4- 4 and the gap width of its recording and playback heads. the base or wear off because this fouls the heads and Permalloy Shields The higher the tape speed, and the narrower the head tape path and causes "drop-aut." i.e. holes in sound. A~alnst High gap, th e better th e high-range frequ ency response. Most As the tape co ~st ant l y rubs against the recordi ng and Frequencies hi- fi fans with open-reel tape decks therefore prefer th e playba~k heads, 1ts surface should be as smooth and even highes t ava ilable speed for recordings th ey consideJ as poss1ble to assu re long head service life. In addition, important. Recent advances in the technol ogy of record- there are numerous requiremen ts regarding the tape's ing heads have made it possible to manufac ture ul tra- electrical characteristics - its dynamic range, frequency narrow head gaps so that excell ent frequency response response and freedom from noise. up to t~e limi ts of th e audible sound range can now LOW-NOISE HIGH-OUTPUT TAPE be obtamed even at the slow er t ape spee d s (F errite In recen t years, a new variety of recording tape has Chromlum Dioxi