This amp provides 36W in 4ohms and 18W in 8ohms with a minimum distortion due to using ultra low noise transistors like BC550 and two power Mosfet transistors IRF530 and IRF9530 the preamp is very basic so almost no distortion will come from it given its supplied with a very stable source like an lm7812 or even a simple zener diode will do. The 680mOhm resistors are needed because resistors with this kind of values are wirewound and the 1-2uH inductance will filter any radio frequency noise that had gotten into the amp. Resistors also act as dampers when a huge capacitance drasticaly decrease as voltage gets down a forced out of capacitor charge can create nanosecond spikes of high magnitude and such resistors prevent this. Also use well stabilized power supply. An lm317 at max voltage (around 38V) with an external transistor of course should do the trick.
