GB1079893A - Improvements in controlling the gain or attenuation of electrical circuits - Google Patents

Abstract

1,079,893. Volume control; transistor circuits. G. & E. BRADLEY Ltd. Feb. 7, 1966 [Feb. 8 1965], No. 5386/65. Headings H4R and H3T' In a gain control circuit, Fig. 2 (not shown), which uses a number of variable impedance elements (D1 to D4) to control the gain of an amplifier, the control circuit for the variable impedance elements, e.g. varactor diodes, thermistors or transistors, comprises, Fig. 3, a number of transistors VT1 to VT4 each associated with one of the elements D1 to D4 and arranged so that as the control voltage input increases from zero the current through the collector circuit of VT4 and hence variable element D4 increases until collector current saturation occurs further increase in the control voltage then causes transistor VT3, which previously has been drawing very little current, to conduct and increase the current through D3 until the collector current of VT3 reaches saturation when VT2 conducts followed, when VT2 is saturated, by VT1. The arrangement provides a wide range of control. The resistors R21, R31-R32, and R41-R43, may be provided to compensate the drop in collector current which occurs in a transistor when the other transistors start to conduct, thereby increasing the voltage drop from the emitter to the negative supply line via R5.