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.

Tuesday, March 10, 2015

D*A*M GB-83 GreaseBox

This is the silicon version of the GB-80. The darlington pair of transistors in the GB-80 aren't needed as silicon transistors have enough gain, and the rest of the circuit has just been tweaked for the silicon transistors. One problem people seemed to have cloning this circuit over on FSB was biasing the transistors properly. The 260k resistor from the base of Q1 to ground could either be socketed and experimented with to get the right value, or replaced with a 500k trim pot to dial in the right sound. The transistors in the originals are BC series, but socket and experiment. Anything in the 300 hfe range should work for Q1 and 400 hfe for Q2.



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5 comments:

  1. IvMSeptember 4, 2017 at 10:02 AM

    I would love to say that you can tag it as "verified".
    But..there's an annoying whistle all the time that I can't debug.

    I've tried a lot of NPN's (hfe's from ~200 to ~800), tweaking with a trimpot the 260k resistor from E of Q1 to ground, and nothing.

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    Replies
    1. IvMSeptember 4, 2017 at 10:15 AM

      I found the schematics on FS forum
      I think you missed a 4n7 cap from base to ground, and another of 220p from base to collector. Both on Q1.

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  2. ManicStrat2112May 10, 2021 at 12:32 AM

    Bad oscillation starting at just under 3/4 full volume when the sustain is at max. Sounds fine at unity volume, although it starts getting really thin and tinny when you turn down your guitar volume. It works, but there is definitely something out of whack. After looking at the schematic I concur with the previous comment...I think a couple caps got missed on q1.

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  3. ManicStrat2112May 31, 2021 at 5:33 PM

    Any chance that you might update the layout with the missing caps? Thanks for all your hard work on making these layouts btw!!!

    P.s. what program is it that you are using to draw up these layouts?

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  4. JDTFebruary 26, 2022 at 8:25 PM

    There is space above Q1 and the 8.2k resistor to put the 220pf cap mentioned in previous comments. This cap stops the whistle/whine.

    You might be able to sneak in the 4n7 cap from Q1 base to ground between the 22nF and 10uF caps. My caps were too big to do this without some repositioning. The 4n7 cap smooths the highs, which is probably good since this fuzz has no tone control.

    Another option on this site is Nocentelli's Greaser Fuzz, which is a tweaked GB-83 with a tone control and an alternate gain control. I tried both gain controls and the one in the Greaser Fuzz sounds clearer as you turn it down. I also preferred Greaser's 100k Q1 biasing resistor instead of the 260k here.

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