This circuit is circuit use the IC TDA1904 and IC TDA1905. See schmatic below : Technical instruction : Minimum supply voltage : 4 volts Maximum supply voltage : 20 volts Minimum currents : 40 mA Input can with : CD , Tuner , Tape , Preamp Mic , Media Player device. Maximum Power Output : 10Watts Minimum Power Output : 4 Watts Impedance Speakers : 4 Ohms