Having a little problem with a Little Gem Mk II

[smoguzbenjamin]

Hey guys

breadboarded the LG2 today for use in the summer hols (going to a guitar-less France for 4 weeks ), got a 4ohm speaker here and I've used that in parallel with an 8ohm on a 10W amp with no trouble. I'm using 386N-1s and if I do anything with pins 1 & 8 the distortion gets nasty (so they're open) and when I play a little louder the distortion buzzes and sounds like crap. It's either the LM386s hitting their thresholds or the speaker not being able to cope. I've got two theories:

1) The 386s are overloading, or
2) I'm passing too much current through my speaker

any ideas as to what's happening? 'Cause I have no clue :?

[B Tremblay]

How are you powering the circuit?

[smoguzbenjamin]

I'm powering it with a 9v battery and I've also tried a 12v (but measures like 15v with no load) wallwart. The difference between the two is not much, the wart has a little more headroom but that's all. I'm confuzzled :|

[B Tremblay]

Are you grounding the unused inputs of each 386?

You can try adding a 100n cap between pin 7 and ground of both chips.

[smoguzbenjamin]

That might be it - I've left pin 7 open, but the  unused inputs are grounded. What does pin 7 do, anyway?

[smoguzbenjamin]

There, it sounds good now! Thanks Brian for your help I put two .33uF caps on pin 7 of both chips, which also helped a bit but not quite. Then in a random guess I shorted pin 7 of the LM386 I had a hunch was giving most trouble to ground.

It works great now! :mrgreen: Nice squishy overdrive, but it still has all the dynamics of your guitar. The way I have it set up, with a .47uF input cap it sounds great, nice and dark and dare I say it: warm. I might need to add another cap in parallel for a "bright" switch or something. I'll see...

But I'm very happy, it sounds great! Now to tweak it to perfection :mrgreen: Thanks ROG for another great little circuit! I'll be on my vacation in France with nothing but my guitar and my little gem... It rules!

EDIT: Holy sh*t! :shock: this little beast ate a fresh 9.5v battery right down to 6.9v (the circuit quit at this point) within 45 minutes! :shock: The battery is rechargeable thank god. I've got a 12v 200mA unregulated wallwart that I could regulate properly down to 12v... will that supply enough current though?

[B Tremblay]

Glad you got it working!

The adapter you mentioned will be fine.

[smoguzbenjamin]

Thanks Brian