Ruby Guitar Amp gain issues

Discussion in 'The Projects Forum' started by specialedster, Dec 23, 2009.

  1. specialedster

    Thread Starter New Member

    Dec 21, 2009
    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?

  2. SgtWookie


    Jul 17, 2007
    Most likely you've fried the MFP102 FET. They're easy to zap. Static electricity will kill them instantly.
  3. Audioguru

    New Member

    Dec 20, 2007
    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.