For an amplifier with 150 Watt in power, may be this is the cheapest one . This amplifier circuit built based on two Darlington power transistors TIP 142 and TIP 147, this circuit can deliver a blasting 150 W Rms to a 4 Ohm speaker.
TIP 147 and 142 are complementary Darlington pair transistors which can handle 5 A current and 100V, famous for their ruggedness. Here two BC 558 transistors Q5 and Q6 are wired as pre amplifier and TIP 142, TIP 147 together with TIP42 (Q1,Q2,Q3) for driving the transistors. This circuit is designed so rugged that this can be assembled even on a common board or even by pin to pin soldering. The circuit can be powered from a +/-45V 5A dual power supply. You must try this circuit. Its working great.
Notes:
- Remember TIP 142 and 147 are Darlington pairs. They are shown as coventional transistors in figure for ease. So don’t get confused. Even though each of them have 2 transistors, 2 resistors and 1 diode inside, only three pins, base emitter and collector are coming out. Rest are connected internally. So its quite OK to assume each of them as transistor for ease.
- Use a well regulated and filtered power supply.
- Connect a 10K POT in series with the input as volume control if you need. Not shown in circuit diagram.