The add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/connected to the output at any one time.
When power supply is turned ‘on’, channel A (AR and AL) is selected. If no audio is present in channel A, the circuit waits for some time and then selects the next channel (channel B). This search operation continues until it detects audio signal in one of the channels.