This is the circuit diagram of 24 Watt class A linear audio amplifier, built and tested by Marc Klynhans from South Africa. The supply voltage can be between 34V and 46V and the quiescent current should be set to 1.7A measured through R25 (a voltage of 0.75V must be measured over R25 for a quiescent current of just under 1.7A). R23 is a trimmer and must be set to maximum resistance (10kOhm) when powering up. Then the resistance of R23 must be decreased until the the quiescent current is achieved. If the amplifier is mounted on a big enough heatsink ( 0.6K/W at most) then the amplifier is very safe from thermal runaway. Intelligence must be used when choosing power and voltage ratings of resistors and capacitors.
24W Audio Amplifier (Class A) Specifications:
- 24W Class A into 8 Ohm
- 100mHz – 100kHz flat
- 305mV input for 24W into 8 Ohm (33dB gain)
This amplifier is not reliable (I think it only gets to 12W, not 24W). I’ve done extensive testing, and it has a terrible start up. It is also very inefficient. The sound it produces is wonderful, but not worth it at all. Do not build it!