A40 Class A Audio Power Amplifier Boards (pair)
The A40 power amplifier is a 40 Watts per channel, Class A audio power amplifier design by Nelson Pass. Despite being around for more than 40 years, it has a steady following, with some people saying this is still one of the best sounding BJT audio power amplifiers around, especially upgraded to the newer transistors currently available.
The PCB implements the front end for one channel. Two boards are required for a stereo amplifier. The output stage (4x power Darlinton transistors and 4x 0.68ohm emitter resistors) needs to be assembled off board. The board closely follows the published design with two exceptions: it is double sided and allows different pinouts for Q11, the JFET used as a current source.