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Il\G/ L L/ E2 I AUDIO March 4, 1969 I.. w. BORG 3,431,357 TONE CONTROL Filed Aug. 9, 1965 I-C-CINTROL CIRCUIT “I I4 F|G_ 1 |I/25 . I " I II@ ` I ` I5 \-_: I; I 23 2| I I) Il\g/ l l/ E2 I AUDIO . ` _ ._ I2 I 24 I AMPLIFIER L_... ...____A d è? ë Eam S ì E I* t ‘J \ 52 / FIG 2 E ö E ‘1;’ ä DIS 8 / // \?\ âI-UJZ ë 33 Q. Q D a U -I cr LI- O O > I I I 2o 1K 20K f­> ë I E E E »Lf E g E 3551/ FIG. 3 O o O /f 35 I­~ 9E -J f-ß’/ / <1 (_) O \ Zä Q5ö â‘CE \>37 \ O l­­ O à â „I ää U g LL. Y O I­~ ‘| I' I' 2o 1K 20K f* INVENTOR LESTER w. BORG QMQWMEQQMWWBY ` A'IVTYS, I United States Patent O» 3,431,357 Tice Patented Mar. 4, 1969 l 2 3,431,357 system incorporating a control circuit in accordance with TONE CONTROL the invention; and Lester W. Borg, Arlington Heights, Ill., assignor to Mo torola, Inc., Franklin Park, Iii., a corporation of FIGS. 2 and 3 are graphs illustrating the characteristics Illinois of the control circuit of FIG. 1. Filed Aug. 9, 1965, Ser. No. 478,166 The invention comprises a control circuit for con~ U.S. Cl. 179-1 3 Claims trolling signals applied to an audio signal amplifier from Int. Cl. H04n1 1/00; H03h 5 / 00 a source of audio signals having a bass response which drops with increasing load and vice versa. Such a source might be a ceramic phonograph pickup cartridge or a ABSTRACT OF THE DISCLOSURE 10 ceramic microphone. The control circuit includes a vol ume control comprised of a resistor connected across the A tone control for a ceramic cartridge is provided by source and having a variable tap connected to the ampli increasing the load on the ceramic cartridge to decrease ñer to vary the strength of signals applied thereto. The the b_ass response while at the same time the impedance control circuit further includes a tone control comprising of a path between the ceramic cartridge and an audio a variable resistance portion and a fixed resistance por amplifier for treble signals is decreased to increase the tion series connected across the source. The variable re treble response. In a like manner decreasing the load sistance portion cooperates with the fixed resistance por on the cartridge to increase the bass response also acts tion to provide variation in bass response `by varying the to increase the impedance of the treble signal path be load on the effective series capacitance of the source. The tween the ceramic cartridge and the audio amplifier. 20 tone control further comprises a capacitance portion con necting the junction between the variable resistance por tion and the fixed resistance portion to the amplifier. The Ceramic phonograph pickup cartridges and ceramic variable resistance portion and the capacitance portion microphones are often used as the signal source in audio form a path for treble signals and operate to decrease reproduction systems. It is possible to provide a bass tone 25 the impedance of the control circuit to treble signals when control in a system using such devices by taking advan the bass response of the control circuit is decreased by tage of the fact that ceramic signal sources, such as ce increased load, and vice versa. ramic phonograph cartridges and ceramic microphones, Referring now to FIG. l, the invention is shown used exhibit a variation in bass response in accordance with the in an audio reproduction system having a ceramic phono load which is placed thereon. This is because of the high 30 graph cartridge pickup 11 which produces an electrical internal capacitance of such sources and results in a de output due to the vibration of the stylus 12 caused by crease in bass response with increased loading, and vice variations in the grooves on the phonograph record 13. versa. Such a tone control may consist merely of a vari The electrical signals produced in pickup 11 are coupled able resistor connected across the source to vary the load by a control circuit 14 to an audio amplifier 15. A trans ing thereof. 35 former 16 couples the output of the ampliñed signals pro A problem is presented by such systems, however, duced by amplifier 15 to the voice Acoil 17 of speaker 18. when it is desired to achieve treble tone control as well Speaker 18 then reproduces such signals as sound. Con as bass tone control. A variable resistor and a capacitor trol circuit 14 includes a volume control comprised of connected across the source will provide variation in the 40 a resistor `21 connected across the source of signals 11. treble response of the cir-cuit by providing a variable im The volume control has a variable tap 22 which may be pedance shunt path for treble signals. Such a treble tone moved up and down along the resistor 21 to vary the control, however, also varies the loading on the source strength of signals applied to the amplifier 15. and consequently, as the impedance of the treble circuit As is known in the art, certain devices, such as ceramic is decreased to decrease the treble response, there is a 45 pickup 11 or a ceramic microphone, exhibit a variation simultaneous increase of load on the source and an un in bass response with a variation in load placed thereupon. desirable decrease in .the bass response with the treble This is attributable to the fact that such devices have response. considerable elfective internal series capacitance and, ac~ It is an object of this invention to provide an im cordingly, their internal impedance will vary with fre proved control circuit for an audio reproduction system. 50 quency. It is possible to take advantage of this fact by Another object of the invention is to provide a tone providing a tone control which varies the load on the control for an audio reproduction system utilizing a ce source 11. This will provide for a variation in the bass ramic signal source wherein bass response may be de response of the system. To this end, a variable resistor creased as treble response is increased, and vice versa. 23 and a fixed resistor 24 are series connected across the Still another object of the invention is to provide a tone 55 source 11. As the variable tap or resistor 23 is moved up control of the foregoing characteristics utilizing a single Wards, reducing the value of the resistor, the load is in variable resistor. creased and the bass response of the system decreases A feature of the invention is the provision of a tone since more of the bass frequencies will appear across control having a variable resistance portion and a fixed the series capacitance of pickup 11 represented as capac resistance portion connected across a source of audio sig 60 itance 11a. nals with the junction of the two resistance portions being The particular characteristics of the source 11 present connected to the audio amplifier through a capacitor. a problem when it is desired to also provide variation in Another feature of the invention is the provision of a treble response. This is because a conventional treble control circuit having a volume control comprising a control might comprise a capacitor and a variable resistor resistor connected across the source with a variable tap 65 connected in series with each other across the source to connected to the amplitier, and further having a tone provide a variable impedance shunt for the treble signals. control comprising a variable resistor and a ñxed resistor Variation in impedance of such a treble tone control cir connected across the source with a capacitor connecting the junction between the two last named resistors to the cuit also varies the load on source 11. Accordingly, if audio amplifier. the impedance of the treble tone control circuit were de~ In the drawing: 70 creased to decrease the treble response, the load on source FIG. 1 is a schematic diagram of an audio reproduction 11 would increase accordingly, decreasing bass response as well. This is an undesirable effect. 3,431,357 3 4 A capacitor 25 is connected from the junction between varying the load on the source, said tone control further variable resistor 23 and resistor 24 to the amplifier 15. «comprising a capacitor connecting the junction between said variable resistance portion and said fixed resistance As a result, the variable resistor 23 will provide variation portion to said amplifier input, said variable resistance in treble response as well as bass response. This is be portion and said capacitance portion forming a Apath for cause, as the resistance of variable resistor 23 is decreased treble signals and operating to decrease the impedance of to increase the load on the souce 11 and reduce the bass said control circuit to treble signals as the bass response response, the treble response of the control circuit 14 will be increased by virtue of the high frequency shunting thereof is decreased by increased load on the source and path of capacitor 25. Thus, variable resistor 23 cooperates further operating to increase the impedance of said con with capacitor 25 to vary the impedance of the control trol circuit to treble signals as the bass response thereof circuit 14 to treble signals with variation in bass response. is increased by decreased load on the source.
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