Build Your 40W Class A Amplifier: Detailed Schematic

Description

This audio power amplifier delivers 40 Watts into 8 Ω at a Class A configuration. The output transistors remain consistently activated, facilitating a substantial current flow. However, this characteristic introduces certain drawbacks, including elevated power consumption and increased temperature generation. Conversely, it presents an optimal operating domain for the transistors, resulting in superior audio attributes and minimized distortion. The design of this final amplifier is relatively straightforward. Assembly demands a degree of expertise. In the original design, Nelson Pass utilized Darlington transistors for the output stage, manufactured by the American company Lambda. These components can be challenging to locate, though attempts may prove fruitful. It has been replaced with more commonly used versions (see listing). Proper construction should occur within a large enclosure accompanied by a robust power supply and a substantial heatsink. Further information regarding this amplifier and the theory of Class A operation can be found on N. Pass’s website. Source: The Audio Amateur 4/78

Circuit diagram

Part List

All resistors are 1% metal film