Hey guys and girls. I decided to attempt to build the ruby guitar amp (schematic found here). First I breadboarded it and tested it with one minor change to the design. I didn't have the 1K pot designated for the gain (pins 1 and 8 on the LM386) so I used a 5K instead. When I breadboarded it and tested it, it sounded great! With low gain I got a nice clean sound, with increasing distortion as gain was turned up. And it was plenty loud.

Since that test I have tried twice to reproduce the results on a pcb. In both cases however I wasn't able to get the right sound at all. I've double checked my connections and I can't figure out what is wrong. The sound is noticeably quiter (hardly audible over the guitar strings). The only time that I get a decent volume is by turning the gain all the way up, thereby shorting pin 1 to pin 8 on the LM386. However, this produces a very dirty sound.

I'd like some help figuring out what I may have messed up on to cause this problem. Its so frustrating since I had it working yesterday and now I can't figure out what I've been doing wrong... I'd like to be able to get a decent volume no matter what the gain setting, with gain adjusting how clean/dirty the signal comes out. What could I have done?

Thanks!

 

Most likely you've fried the MFP102 FET. They're easy to zap. Static electricity will kill them instantly.

 

The datasheet for the LM386 shows a 10uF capacitor between pin 1 and pin 8 for high gain and the capacitor in series with a pot for adjustable gain. The RUBY circuit does not have the capacitor.