The 15+15 Watt Class-A Power Amplifier

This project is quite old (probably dated late 1980s) and has been created before it was common to use a CAD system for schematics and PCB design. Think of abrasion symbols on foil followed by ultra violet light exposure followed by etching and drilling of photo-sensitive-PCB blanks. The foils were lost and only the pencil drawings have survived.

If you want to build this design and want to achieve the outstanding results this circuit is capable of it is absolutely necessary to carefully select the differential transistor pairs in the voltage amplification stages and the pairs used for the output stages. You should not try to substitute any of the transistors used even if some of them now are probably out of production but not out of stock.


  • True1 Class-A operation 15 Watt @ 8 Ohm per channel
  • Regulated +/-35Volt power supply for voltage amplification stages
  • Regulated +/- 20 Volt power supply for the output stages
  • Protection against short circuits and presence of DC
  • Protection circuit without relay in the signal path
  • Based on a design by Akihiko Kaneda

Download schematics as PDF files:

1 What does true Class-A operation mean? The formula to calculate maximum Class-A output power in a common SEPP power amplifier is depending on load impedance and bias current:

MaxPowerA = (BiasCurrent * 2 / SQRT (2)) ^ 2 * LoadImpedance

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