A simple discrete one-watt amplifier

Here is schema for proto @message #290.
 

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Here is last three trannies working version. No need for Q3 emitter resistor, but current must be measured, those BD139 don't like big current. Here it is around 330mA through whole amp. R7 can be adjusted or here resistor + trim.pot in series is a good choice also. Sounds good enough.
IMG_20250327_153123~2.jpg
 
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Some help, original JLH articles here :

https://sound-au.com/tcaas/index-1.htm

And PLH article by Nelson Pass :

https://www.passdiy.com/gallery/amplifiers/the-plh-amplifier

And something from this forum :


All these are big help to work with these small amps 🙂 Needs time to read all these ...
 
Some measurements using 8ohm resistor as load.

First 50kHz square (timediv 5uS, voltsdiv 0.5V)

IMG_20250327_171356~2.jpg


And 1kHz sine @2.5Vrms (voltsdiv 1V)

IMG_20250327_171635~2.jpg


This can give say only half-watt with smaller distortion (not measured) and around 0.8W with big distortion one-Watt shows big distortion, but with low power this works well, some more current is really good idea.