This Amplifier is 12 watts and to operate this is use source of dual symmetric ± 12 volt. The 741 provides the required gain while the speaker unit driven by complementary Darlingtons T1, T2 and T3, T4.
Input signal to the Darlington comes from the feed current 741. Since R6 is connected to earth, positive or negative current signal is also going through R4 or R5. The voltage drop across this resistance serves as the input signal to the transistor pairs. A common dc negative feedback from the collector junction with T2 and T4 stabilize the DC circuit and the junction point is maintained at zero volts. So, there is no coupling capacitor needed for the speaker.
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