The circuit that gave rise to this configuration was found in a magazine of the 1980s with the exchange of the main components to other modern circuit becomes feasible today. Its purpose is to switch audio signals from digital logic levels and control voltages. The transistors may be the BC245 or MPF102. Care must be taken with the shield of input cables and signal output. The source must be symmetrical 15V and equivalent to 741 operational amplifiers can be used. They can also be added more inputs for the signals.
