There are no super simple general purpose npn amps. What signal do you
need to amplify ? Do you need voltage or current gain ? If you want
current gain a simple complementary push-pull emitter follower is all you
need. One NPN one PNP and an output cap. Also has zero quiescent current.
You also need to make sure the audio does not collapse your mcu supply.
The push-pull can be powered from the unreg rail.

If you need anything more than that use a chip. LM386, TBA820, TBA705x
etc. It is not worth your while spending time on such a circuit. The
subject has been beaten to death N^N times and if you really want to you
can read about it in any electronic circuits book (f.ex. Sedra&Smith
Microelectronic Circuits).

Peter

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