Audio selection circuit.

Using 4051 multiplexer to route one of eight audio channels to an amplifier circuit. Channel selection is controlled by a 555 latching switch circuit, a transistor logic inverter and two D-flip flops to provide three binary digits (A, B, C). A DC supply is fed back from the common out to the selected input to illuminate an LED to indicate the current channel selection. DC is blocked either side by capacitors. Op amp from audio input for each channel to indicate where audio is active by means of a further LED (only one implemented in this trial run).