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.

Friday, April 14, 2017

Spaceman Effects Gemini III Dual Fuzz Generator

This week's Fuzz Friday layout happens to be the 500th layout on the blog! So for #500 it has to be something cool, so here's a really unique fuzz from Spaceman Effects–the Gemini III Dual Fuzz Generator. As the name implies, it has 2 sides: silicon and germanium. The Blend knob pans between the 2, and each side has a 3-way gain switch. I've laid it out for board mounted pots for a 125B with top mounted jacks.

It's a good idea to experiment with the transistors, especially on the germanium side. Here's some good alternatives from digi2t who traced it over on DIYSB:

Q1: Russian MP20B (hFE: 80-85)
Q2: Russian GT404 (hFE: 120-130)
Q3: Russian GT402 (hFE: 100-115)
Q5: BC109B or 2N3700 (hFE: mid 200s)
Q7: 2N5088

Also the 1nF cap near the input apparently really needs to be a polystyrene. YMMV


  1. ac128... they need to be matched?

    1. No. See the hFE ranges listed below the layout image.

  2. Hi!

    1. Congrats on youknowwhat!
    2. What is the point of using only one transformer winding? Seems to me like a bizarre method of using transformer as a choke.

    1. 1. Thanks!
      2. I have no idea. I don't design 'em, I just lay 'em out. :D

      (But I thought that was odd too lol)

    2. 2. Oh, sorry, I know. I was just wondering if anyone (you in particular) knows what's wrong with this pedal, lol :D

    3. Look up 'pickup simulator schematic' on Google. The reason they use these audio transformers, is because (I think) they're fairly easy to find, cheapish, and generally more in spec or something?

      Also: from an AMZ article - "This circuit may be used to add a frequency response before any circuit that will benefit from an input that emulates a guitar pickup. It can add a bit of enhanced high frequency response in addition to converting the signal impedance. "

    4. Hi, Charles,

      Thanks, I see now. It's weird, but reasonable. I first thought of using an unductance with the same properties as the transformer's primary coil, but could not find one that is more compact cheaper and easily obtainable then 42tm series itself. Even more, i could not find one that has similar active impedance.
      I need more research...

  3. 308k isn't a standard resistor value. I'm guessing 309k is close enough, though.

  4. You didn't specify which side of the transformer gets hooked up but i am presuming it is the primary (10k).

    The frame mounting holes for the transformer, at least in the transfer layout, aren't even close. I just cut off the tabs, like i did for my tychobrahe octavia.

    Your to92 transistor icons are backwards for 2n2222 - round vs. flat side i mean.

    It's real hard to find B50K dual right angle pc mount pots. I ordered some from china - mouser and smallbear do not carry them. initially I'll air-wire that pot.

    You didn't specify D1 or D2 but my guess is 1n4148 / 1n914 right? I guess i could read the thread where this got traced out.

    I need to order a few more parts before i can proceed so i probably won't be testing this one for a week or so. Thanks again for another good layout.

  5. Q1: AC128 is PNP
    Q2: AC128 is PNP
    Q3: AC176 Is NPN


    Q1: Russian MP20B is PNP
    Q2: Russian GT404 is NPN
    Q3: Russian GT402 is PNP

    Is this a mistake?

  6. verified this! Used Q1 pnp mp20b hfe=100,Q2 PNP mp20b hfe=70, Q3 npn mp38a hfe=70, silicon- 2n2222a, hfe = 300-350. It sound like Bender try to friend with fuzz face, like they are competing. Sound not so huge, but interesting with different harmonics, nice for playing chords. One minus - too much details! Thanks, David!

  7. i can meditation with this fuzz all day, just flicking that swithes!! founding new sound!

  8. Today i played with Q1. So i took npn mp38a, Hfe=65 & connected it like Q4 si. I Like Sound now More than it was with pnp mp20b.
    Look at schematic here:
    I changed R16=39k, C11-47n or 33n, r22 if you want=200k.

  9. So David forgot about resistor R8 3.6kom between sw2.2 & sw2.5, but without it we have just Ge fuzz variant, so i left it as exist.