The LM386 Low Power Amplifier
A most useful IC, easy to use as a headphone amplifier or with a speaker. It has a gain of 200 max with bass boost as shown. To adjust the overall gain insert a resistance up to 10k in
series between the 10uf and pin #8. For a minimum gain of 20 remove the 10uf cap. between pin #1 and pin #8. The .047uF cap and the 10K ohms resistor between pin #5 and pin #1 are used to boost the bass frequencies and are optional.
Two small Handy Dandy circuits to monitor your batteries fading voltage supply .