10 Watt Audio Amplifier using Op-Amp and Power Transistors

This audio amplifier circuit combines an operational amplifier with a complementary power transistor stage to drive an 8-ohm, 10-watt speaker from a dual-rail power supply. The signal first enters the LF351 operational amplifier, which is configured on an 8-pin IC base to provide the primary voltage gain. Resistors such as the 4.7k, 200R, 32k, and 47k units, along with the 0.82uF and 10pF capacitors, establish the proper biasing, feedback loops, and frequency compensation for stable analog operation. Because an operational amplifier alone cannot supply the high output current required by a speaker, its voltage-amplified output drives a push-pull output stage consisting of complementary TIP122 (NPN) and TIP127 (PNP) Darlington power transistors. These transistors provide the necessary current gain to effortlessly push and pull alternating current through the 8-ohm speaker load. The entire discrete circuit is assembled onto Vero board using a soldering iron, solder wire, and hook-up wires, with the power transistors securely mounted to an aluminium heat sink to safely dissipate thermal energy generated during high-amplitude audio reproduction.