24 Watt Class A Amplifier

A 24 Watt Class A Amplifier made from discrete semiconductors, built and tested by Marc Klynhans from South Africa.

Here are the specifications:
24W Class A into 8 Ohm
100mHz - 100kHz flat
305mV input for 24W into 8 Ohm (33dB gain)
THD is very low, although I have not been able to measure it properly

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.

I have been using this amplifier with a pair of Celestion F20's and the sound is unbelievable!