Tr1 and Tr2 transistors functions as direct coupled voltage amplifiers. R6 resistor, D1 and D2 diodes determine the standby current of complement driver stage (Tr3/Tr4) and output stage (Tr5/Tr6). C3, C5, C6 and R3 help keeping stability. Amplifier’s input sensitivity is 400mA at 4 ohm load and 12V supply and 600mV at 8 ohm load and 17V supply.
Gain can be increased by decreasing R4 value but it is not recommended because of increasing distortion.
Speaker’s ground must be connected directly to the ground of supply stage and must be kept away from the circuit.
Separate supply connections must be applied to the supply connection points.