Gonkulator simple clean blend mod

Discussion in 'Effects [BG]' started by ToS, Oct 22, 2018.


  1. ToS

    ToS

    Mar 4, 2014
    Europe
    Just got a brand new DOD Gonkulator and being a bass aficionado I did not like the over-the top distortion that you cannot turn off. Then I realised that distortion is paralel to ringmodulated signal. That got me thinking, how much work is it to have it converted into a clean channel.
    There are schematics online for the old version and I think Digitech did not change it that much, at least for the distortion side.

    Anyway, if you remove the pair of diodes placed after the distorsion op-amp, you can achieve the clean blend. When I opened it up, it took bit to realise that nowadays you can get diodes paired up in single SOT-23 IC.
    mas70.gif
    To mod this, you just have to desolder and lift that side with a single leg. It's not simple as those are tiny a.f. Great thing is, if you ruin the component (but you still want the dirt to be switchable or you are not sure if you want it), they are easily replaceable with regular diodes. Heh, you might even put some asymmetric clipping or Si/Ge pair for prettier distortion grain and more headroom. Anyway, pics ahoy!

    This is the general position of the distortion segment and the diode pair:
    overview.jpg

    Closeup, marked up:
    anotated.jpg

    I used scalpel to apply lift tension to the component, while at the same time heating up the sole bottom leg. Now detached, it is hanging in the air, about 1mm from the solder point. This way, one could simply install a SPST switch and have the distortion at the ready if the situation calls for it.

    QUESTIONS, a plea for help:

    (#1) There is still quite a bit of gain on that op-amp. I am guessing someone using a bass guitar with hotter output could have the problem not completely avoid overdrive/distortion (not tested). What component would be the best to change, and to what value. I'm guessing either that 470R that goes from inverting input to ground or 10kR in series with the gain pot.

    (#2) I think there is some bass cut in place, is 50pf installed between the output and the inverting input acting as a filter. What about that 10uF electrolytic that is going to ground?

    TL;DR: Detach one leg of one component and you get a clean channel with drive and blend.
     
    Last edited: Oct 22, 2018
    oZZma, Sunset Shalom and JKos like this.
  2. BUMP!
    Did you get the gain sorted? If so, how did you go about it?


    It does make sense to reduce the gain via the 10k in series with the gain pot (labelled "BUZZ" I believe); I'll add that perhaps a reduction in that pot's value itself is in order. The 470-ohm resistor plays a part, too, as you noted; I found this helpful:
    Op Amp Gain | Explanation Calculation Equation | Electronics Notes

    Calculate what gain range is now, then calculate a reduction and try it out.


    Rod Elliott goes more in depth, here's the first part of a 3-part online article I'm still trying to wrap my brain around:
    Audio Designs With Opamps
     
  3. ToS

    ToS

    Mar 4, 2014
    Europe
    Hey, thanks for the links. They seem nice but I won't have much time now to learn the workings of opamps :( . From the schem, looks like at minimum gain (GUNK) the 10K is in series with 100K (pot). This should mean that increasing the 10K to ~200K (for starter) would bring down the gain.
    That's going to be the first experiment.
     
  4. ToS

    ToS

    Mar 4, 2014
    Europe
    Finally got around to warm up my soldering station and removed 470R. After few resistors I settled with tiny 1kR from Boss pedal.
    IMG_20190401_232808~01~01.jpg

    I now have next to no gain until 9 oclock and just enough from noon and up.
     
    Last edited: Apr 1, 2019
  5. Thanks for the update.
     
  6. ToS

    ToS

    Mar 4, 2014
    Europe
    Hey, thank you for nudging me to finish this mod.
    I just might try it with 2k after the next band practice.
     
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