This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Wednesday, July 8, 2015

Electro Harmonix Germanium OD

The EHX Germanium OD offers 60s overdrive tones using a combination of germanium and silicon transistors (all PNP). All 3 pots control the voltage is some way. The Bias pot controls the amount of voltage that reaches the Gain control, which in turn controls the remaining voltage that gets to the germanium transistor. The Volts control acts like a sag control on the overall voltage the circuit is running at, so you can emulate a dying battery. I've laid this out for on board pots mounted from the solder-side of the board using right angle PCB mount pots.



13 comments:

  1. Love your layouts. Do you take requests..? Would be keen to see http://tagboardeffects.blogspot.co.nz/2013/02/madferret-germageddon.html

    I seem to bugger up big tagboard layouts like that haha

    ReplyDelete
    Replies
    1. Thanks! I do take requests. Use the Layout Request form on the left and if you can, include a link to the schematic.

      Delete
  2. Hi. I tried this one but doesnt work. I used bc108 because I didn't find germanium transistor. Also I don't understand the led on the schematics. I link the positive on the board and another part? Sorry my poor english. And I love this blog.

    ReplyDelete
    Replies
    1. It may not work because of the BC108s. You'll need a lower gain transistor. If you don't have access to germaniums something like the PN2369 or 2N5550 might work, but no guarantees. You would connect the LED pad to the positive (anode) side of the LED, and the negative (cathode) side to the footswitch, assuming you're using typical 3PDT bypass wiring.

      Delete
    2. Thanks for the answer. I´ll try with one of this transistors. If I don't plug the led for the tests, should it work? Also I used a B pot for the bias because don't find the C pot too.

      Delete
    3. Yes it should work. It's just for on/off indication, and not part of the audio path.

      Delete
  3. Hi and really thanks for the interesting project! the 10k resistor connected to led is for a low current one?

    ReplyDelete
    Replies
    1. Yes, though you can adjust that 10k value for whatever LEDs you have on hand.

      Delete
  4. Hi! The layout is working, I verified it! a good crunch overdrive but you can turn it to something experimental or to a very 60s fuzzy sound! cleans up nicely with guitar volume pot.

    ReplyDelete
  5. I've tried with several transistors. ac128 sounds nice to me, but HFE can really make a big difference (and transistor too obviously)

    ReplyDelete