LM386 instability, Ruby amp

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skipwave

Well-known member
Joined
Jul 8, 2005
Messages
1,416
Location
Los Angeles
Well, I'm almost embarassed to post about this. I broke out my Smokey amp last week, to record some late night song ideas through an 8" speaker. It sounded fantastic, so I decided to build a better LM386 mini-amp with junkbox parts.

I built the Ruby amp, since I wanted something clean(er) to start, that I could throw another FET gain stage in front of to get some grind. I used the perfboard layout shown on the Ruby page.

The only deviation I made was to upsize the output cap to 470uF and use the RC network seen in NYDave's schem: Fist of Fury. Also, it's running on a 12VDC wallwart, which puts out 15V unloaded, through a couple of RC filter stages that drop the B+ to 11V.

Well, the thing sounds great at low volumes, but breaks into a horrible low frequency oscillation right at the level it starts to break up nicely and get fuzzy. This sounds like a car accident, just wretched.

I've tried everything I can think of, and I'm ready to conclude that the LM386 (a RatShack type) is just bad. This was supposed to be a quick little project, and now it's taking up too much time. The thing that keeps me going is that the stupid little smokey design, with just two 47uF capacitors and nothing else is loud and steady on. Argh! :? Any thoughts?
 
IIRC the smokey uses a JRC386.

I built some small amps using a NS 386 they did not sound that good when driven to clipping.

The JRC is most likely a different die and mask.

I don't think your chip is bad but the circuit is chip brand sensitve
 
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