Unusual use of LM386 in drum circuit

I came across this awhile ago, but was reminded of it by a post in "my build progress " thread. Im not quite sure what effect the pot feeding pin 7 (bypass) would have on the behaviour of the amplifier, otherwise it seems it’s being used as a dc amplifier, does pin 7 vary the gain?


The gain LM386 is adjusted by a resistor/capacitor between pins 1 and 8. When left unconnected, the internal resistor sets the gain at 20. Pin 7 is for the bypass capacitor which is part of the biasing network of the amplifier.

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I know, but pin7 is not being used in the normal way, there is a resistor and pot in addition to the usual bypass capacitor. Im gonna have to breadboard this to try and figure out what is happening here.

Thanks K.ostas

In either case pin 7 has nothing to do with the gain. The datasheet is not very clear of how to use pin 7, hinting that its mostly optional, but its clear that you can use it with a capacitor to filter the supply. Perhaps more creatively, you can use it to control the current (grounding it to shut it off, or somehow regulate the flow by connecting it to the supply), in order, for instance, to drive a speaker with an external transistor stage.

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It’s likely varying the capacitance by changing the voltage at the “far” side of the capacitor. This trick is used to voltage control the resonance on some simpler filter designs like the transistor based paia voltage controller filter.