Abstract: The device includes an audio signal circuit having two separate terminals that are connected through the photoresistor elements of two, separate, optical isolators with an audio signal input/output terminal, so that signals can be routed selectively and bidirectionally along separate signal paths to or from the input/output terminal to one or both of the two separate terminals. A separate control circuit supplies DC power selectively to the LED's which control the selective energization of the photoresistor elements of the optical isolators, the advantage being that the photoresistive devices permit selective blocking of the audio signal paths without physically opening or interrupting the paths and thus avoiding objectionable signal spikes and consequent loud popping sounds in associated loud speaker systems. The DC control circuit includes two, manually operable double pole, double throw switches for controlling the selective routing of signals between the audio signal terminals.

Abstract: The output signals of a phonograph and of an auxiliary audio signal source, such as a high impedance microphone, electric guitar, or the like, are combined before being fed to the amplifier of the phonograph, whereby the combined signals are amplified without distortion, and are fed to one or more speakers, thus audibly reproducing the phonograph recording with the auxiliary sound signal superimposed thereover. The device which combines the signals includes means for suppressing the base frequencies in the auxiliary signal, and for selectively adjusting the amplitudes of the two signal components.