Discrete Component AF Amplifier
2+ Watt AF Amplifier from discrete components ( No IC involved)
Building your own 2+ watt AF amplifier is not all that hard. This circuit should draw very little current when idling with no input because the output transistors are biased just at the edge of conduction by voltage drop across the two silicon diodes. Frequency response should be from near DC to well above the range of human hearing. Both Lo-Z input and Hi-Z input methods are shown. Both circuits have approximately the same amount of gain.
The NPN-PNP pair of output transistors should be fairly well matched, but you don't have to be fanatic about it. If the output transistors run a bit warm, you can remove one of the 1N4148 bias offset diodes. Using only one diode between the two output transistor base connections may cause a bit more crossover distortion but for non-critical applications you probably won't even notice it.
Feedback resistor Rx is bypassed for AC, so all that gets fed back is DC to adjust the output to 1/2 the supply voltage.
The output capacitor can be anything from 200 mfd to over 1000 mfd.