20W + 20W of stereo amplifier consists of two complete, independent 20-watt RMS amplifier in bridge. The input source is brought into the shunt voltage amplifier, it is by R1,
R2 and P1 thereof. Resistor R1 between the signal source and the ground provide a load resistance. Resistor R2 and potentiometer P1 binding signal. Signal through the same capacitor C1 and IC1 internal amplifier (+) input (pin 1) combined, where the signal is increased a lot. Capacitors C2 and other (B) of the internal amplifier IC1 (+) input to ground.