GB579256A - Tone control arrangements for audio frequency electric wave amplifiers - Google Patents

Abstract

579,256. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). April 25, 1944, No. 7663. [Class 40 (v)] In an amplifier, a tone control circuit is associated with a negative feedback circuit, so that there is a cut-off in the higher audio frequencies when the adjustable element of the tone control is moved in one direction and a rising gain in the higher frequencies when moved in the opposite direction. When the potentiometer slider SL of the tone-control circuit is in its upper position and condenser C1 connected to ground, the attenuation introduced into the forward amplifying path by the tone control increases as the signal frequencies increase. By introducing R4, C2 and the lower part of R3, an attenuation is introduced into the feedback path of valve V1 which also increases as the frequency increases. With the slider in the top position, the rate of increase of attenuation in the forward amplifying path is a maximum and the rate of increase of attenuation in the feedback path is a minimum so that the gain will decrease with frequency, thus causing a cut-off in the higher frequencies. As the slider is moved downwards, these rates of increase of attenuation change in opposite directions, so, that when the slider is at the lower end of R3 the rate of increase of attenuation in the forward amplifying path is a minimum and the rate of increase in the feedback path is a maximum, resulting in an increase of effective gain with frequency. At some intermediate point the gain is substantially uniform.