Simple Class-A power amp that uses complementary pair of IRFP240 and IRFP9240 MOSFET transistors. The intention of this project was to build simple, but high quality amplifier. The aim was reached by integrating the whole input driver in one IC and adding high power transistor output stage.
As you can see on the schematic the amplifier has very simple structure. At the input there is high quality and relative high power TI IC OPA552. It drives a complementary pair od MOSFET transistors IRFP240 and IRFP9240. The gain of the whole circut is set to 40x. The TL431 is to set the operation point of output transistors. The idle current is set to 80mA, so the amplifier works in A class for it’s first few watts. The more current the longer it stays in A class, but the more power to be dissipated. With 80mA and these heatsinks it still goes very hot after long playing.