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I'm planning to make some mini amps out of old tins and I've been looking at kits based around the LM386 chip. I don't want to buy them from the US or China (I'm in the UK) as I'll have to wait a while and pay import duty. I've come across a UK company which do them very cheaply, £2.60 including a speaker and battery connector.

https://www.kitronik.co.uk/2154-mp3-mono-amplifier-v20.html

The problem is they don't have volume or gain controls. Would it be possible to wire in potentiometers to them to do the job, and if so, how?

I've attached their circuit diagram for reference

Any help would be gratefully received!

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The power supply of 9 volts is adequate. Unless the IC is the LM386N-3 or -4, which are rated at higher power supply and output. Likely, the one on yours is the more common LM386-N1.

The circuit you showed related to the kit has a few components that bleed off some of the source signal (guitar or MP3) to ground. Probably to filter out and "clean up" the signal before the last stage, through the 100uF cap leading to the speaker.

This is a diagram of the circuit I use. There are a number of differences from yours. Note the 220uF electrolytic cap between pin 5 and the speaker, and the 0.1uF disk cap on pin 7. These changes, along with the 10uF cap from pin 1 to 8 (the gain stage), give this amp a well rounded sound. Play your guitar lightly, and it has a nice mid range break up. Play aggressive, and it's crunchy, but not so distorted as to become annoying.

The volume control is more for looks, since a 10k volume pot reacts as either "full volume", or when turned to about 1/2, it is way too quiet. Many builders/players have volume and/or tone pots on the guitar, which allows for better control and adjustment.

As for piezos, I tried them in my earlier builds and they do have merit. But I prefer to wind my own mag pups or use inexpensive ones from recycled guitars.

That's brilliant Scott, thank you! I'll have to order up some components and give it a try. I'll crack this thing yet!
Thanks for everyone's support and advice, I finally got one made! I went with the kits I bought and put a gain pot on which gives it enough welly with a bit of crunch thrown in. Didn't bother with the volume control as it went from nothing to nearly nothing! I'll have a go at Scott's circuit next but I think the biggest problem is speaker size. I need to get bigger speakers to get decent clean volume out of this.

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