> Do any of you know of any simple amp circuits that
> use only NPN transistors (plus caps, resistors, etc.,
> of course)? I need something really basic - distortion,
> fidelity, etc. don't really matter.


You say 'amplify my mcu's output.
What is the drive signal?
What voltage swing open circuit?

Use an IC amp !!!!, but
E&OE, typed on fly

If you want a REALLY basic low power amplifier try this.

1.    If it is a full rail rail swing voltage but with high impedance, so no
power.

1 x npn
1 x speaker

Base to signal source
Collector to Vdd
Emitter to ground.

This has DC through speaker which is not nice :-)

2.    As above but add a 100uF or higher electrolytic and a resistor - say
100r to start

Base to signal source
Collector to Vdd
Emitter to resistor to ground.
Speaker bottom side to ground
Speaker top side to capacitor negative terminal
Capacitor positive terminal to emitter

Vary 100r to see what difference it makes.

3. Small signal excursion.

1 x npn
2 x 100 uF ecap
3 x R, 100r, 680r, 1k, 3k9

emitter to 100r
100r other end to ground
collector to 680r
680r other end to Vdd
100 uF a to signal source
100 uF a other side to base
100 uF b emitter to ground
3k9 base to vdd
1k base to ground

Play with values.



        RM

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads