Volume and tone control for multi-channel audio systems

Claim 2

A gain control circuit for use in a multi-channel audio signal translating system including in combination, audio output circuit means, differential amplifier means connected in each channel and having an output terminal connected to each of said audio output circuit means and further including a control terminal, a current control device connected to each of said differential amplifier means, audio signal input circuit means connected to each of said current control devices for providing an audio signal path from said input circuit means through said current control device to said differential amplifier means, direct current supply means, a single volume control including variable voltage means connected between the control terminals of each of said differential amplifier means and said direct current supply means, said variable voltage means providing a selectable direct current bias voltage to the control terminal of each of said differential amplifier means for controlling the current conduction therethrough to vary the amplitude of the audio signal simultaneously in each channel.

Claim 3

The gain control circuit of claim 1 wherein said current control device comprises a transistor having the base electrode connected to said audio signal input circuit means and its collector-emitter electrodes connected in series between said differential amplifier means and a reference potential.

Claim 4

The gain control circuit of claim 2 including said differential amplifier means comprising a pair of transistors having their emitters connected together and one transistor having its collector connected to said direct current supply means and the other transistor having its collector connected to said audio output circuit means of the respective channel; a cross-coupling resistance connected between the base electrodes of said transistors forming the differential amplifier in each channel; said current control device being a transistor of the same conductivity type as the transistors forming the differential amplifier, and connected in series therewith to provide a DC current path for the transistors in the differential amplifier, said current control transistor having the base electrode thereof arranged for receiving the signal to be translated through the gain control circuit such that the signal is delivered to the transistors of the differential amplifier with said one transistor conducting a portion of the signal to said direct current supply means in accordance with its state of conduction and said other transistor conducting the remaining portion of the signal to said audio output circuit means depending upon its state of conduction; and a tone control circuit connected to the base electrode of said current control transistor, said tone control circuit including a capacitor connected in series with the load electrodes of a transistor.

Claim 5

The gain control circuit of claim 1 further including tone control means coupled to said audio signal input circuit means of each of said current control devices; said tone control means including a potentiometer connected to said direct current supply meAns for varying the bias applied thereto to change the tone of the audio signal, and resistance means coupling said volume and tone control means together to vary the conduction of each of said differential amplifier means connected to said volume control means responsively to variations in said tone control means.