Stereo 4 Amplifier

This is my present stereo amplifier, designed and built in 2000. This project is unique in that I built two - one for use in my stereo, and another for use with my Korg keyboard.

I've been steadily improving the design of this amplifier for 25 years. The circuit topology is fully complementary, differential, cascode, bipolar transistor. It is direct-coupled from input to output except for one capacitor and a DC servo. It contains two power supplies: one unregulated supply for the output stage and a second regulated supply for all other stages. I think this amplifier can hold its own when compared against commercial high-end audiophile amplifiers.

The design outputs 80 watts per channel into 8 ohms and 160 watts per channel into 4 ohms. The amplifier contains roughly 500 discrete components. The semiconductor complement includes 94 bipolar transistors, 168 diodes, 2 JFETs, and 2 integrated circuits.