It is a 12W amplifier circuit based 741 Op-Amp used for general corporate purposes which is require that medium power. 12 watt amplifier operates on the power supply source symmetric +/- 12VDC. 741 IC is used as pre-amp and driver to push the final transistors that uses a component T1, T2, T3 and T4.
The input part of the final transistors are arranged in darlington with the feedback current from 741 Op-Amp IC. Since this is an amplifier that is arranged symmetrically, on the part of the input signal to the driver, there are two different phases, namely the positive and negative currents, flowing through R4 and R5 resistors.
R6 resistor will balance the feedback DC signal that the collector junction point T2 and T4 can be maintained in a state of 0 Volt. So in this section is not required output coupling capacitors as in most amplifier circuit.
Amplifier system that does not use the output coupling capacitors is also called the OCL (output capacitor Less). The work principle of the 741 Op-amp used in this amplifier is no different as it does an instrumentation amplifier or a differential amplifier is symmetrical. R1, C1 and R3 (RC Networks) serves to balance the impedance between the input source with op-amp.
Some of the advantages of the use of the differential amplifier in amplifier circuit, That is low offset voltage, high CMRR (Common Mode Rejection Ratio), high input impedance, adjustable gain and can be customized whatever you want.
Although this amplifier circuit classified of low-power series, but at the final transistor cam gets very hot while works. To prevent overheating issue, you must add a heatsink on the T2 and T4 transistor.