Control circuit for a matrixed four channel audio reproducing system

DETAILED DESCRIPTION The present invention pertains to a control circuit for use in an audio reproducing system having a plurality of speakers driven by signals from four channels, which signals are derived from a two channel input, and which system includes logic circuitry for separating the four channels into two pairs of channels and determining which signals in the two pairs of channels are dominant and providing output signals thereof.
The control circuit includes four amplifiers, for the four channels, each of which includes a differential amplifier connected to a differential to single ended converter providing very low distortion even at relatively high currents and further providing essentially a voltage signal at the output.
Balance and volume control circuitry has four outputs connected to the differential amplifiers of the four audio amplifiers and operates as a constant current source therefor.
The balance and volume control circuitry includes a first differential amplifier having common emitters connected to ground through a transistor which carries the total current for all four audio amplifiers and has a manual volume control connected to the base thereof.
The two collectors of the differential amplifier are each connected to common emitters of a second and third pair of differential amplifiers which provide the outputs to the four audio amplifiers.
The first differential amplifier has a manual control attached thereto for controlling the relative volume between pairs of channels and the second and third differential amplifiers have manual controls attached thereto for controlling the relative volume between channels in each of the pairs of channels.
An enhancement control circuit including first and second amplifier sections coupled together so that the output voltage of one section increases as the output voltage of the other section decreases and vice versa and further constructed so that the decrease of output voltage in either section occurs substantially more rapidly than the increase of output voltage in the other section, is also connected to the differential amplifier in each of the audio amplifiers and controls the amount of audio signal applied thereto