[sdiy] distortion pedal for a modular system

stepan kayukov stepan.kayukov at gmail.com
Wed May 2 10:27:34 CEST 2018


Hello everyone,

Thank you for the lively thread.

I have tried placing the FET in series with the capacitor. R7 connects to
the source - and C1 is connected to the drain (and then ground.)

This tames the circuit a great deal, but the bleed is still very much
there.

As for placing a capacitor between the collector of R2 and the first op
amp... I realize I drew it wrong in Eagle. This is the "basic" fuzz circuit
that I built, before sending to op amps:
http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacepnpschematic.gif

So, the output from the transistor does pass through a 0.01uF capacitor
before going to the op amp.

Still, the problem continues. It sounds like many people have had similar
experiences bringing distortion into a modular setup. Can it be done? I am
hesitant to build a separate power supply just to power distortion modules.





On Tue, May 1, 2018 at 6:03 PM, Tom Wiltshire <tom at electricdruid.net> wrote:

> I was interested to read your experiences with that module, Quincas, since
> I had a hand in the design. I did some of the voltage-controlled elements,
> including the tone control. Later on it got an extra gain stage stuck on
> the front (to use up a spare op-amp, IIRC!) and that probably does make it
> noisy. To be fair, the original pedals aren’t exactly quiet either.
>
> Tom
>
> ==================
>        Electric Druid
> Synth & Stompbox DIY
> ==================
>
> On 1 May 2018, at 17:52, Quincas Moreira <quincas at gmail.com> wrote:
>
> The Frequency Central Meth Amp module I build recently is basically a Big
> Muff adapted to modular, and it is prone to the same bleed through
> problem.  I found that it is worse on some PSUs than others. In My Arturia
> Rackbrute it is silent, in my LM317/337 based linear supply it picks up all
> of my VCOs a lot.  My solution was to give it's very own small PSU, a
> little meanwell DC DC converter. However,  I suspect that sub regulating
> the 12v to 9v solves two problems:  It adapts the design without any
> component value changes, AND isolates the circuit somewhat from the main
> PSU. I have yet to try this myself but I think it's worth a try.
>
> On Tue, May 1, 2018 at 8:59 AM, Walker Shurlds <walkershurlds at gmail.com>
> wrote:
>
>> On May 1, 2018 1:28 AM, stepan kayukov <stepan.kayukov at gmail.com> wrote:
>>
>> Hi Walker,
>>
>> Thank you for the advice. It definitely sounds different than it would on
>> a guitar, but I still like it. The real problem arises from hearing things
>> at the output of the distortion, even when nothing is at the input.
>>
>> The R7/C1 distortion and the way the JFET is coupled created a kind of
>> gating effect that I was fond of, but if you think it might be the reason
>> for the overall bleeding, I should try it the more conventional way.
>>
>> Both of your suggestions are very helpful. I will try them immediately.
>> Since I am new to this list, I do not know if I should post afterwards.
>> Should I give an update?
>>
>>
>> Yes, please update us! I think even if you leave C1 and Q3 as they are,
>> but add some small resistance in that branch between C1 and R7 it could
>> reduce the gain just enough to reduce the noise. Another thing you could
>> try is increasing R8. There should be a value high enough that Q1 gets
>> biased all the way off—this changes the sound pretty drastically (sounds
>> kind of 8-bit) but makes it completely silent when there’s no input.
>>
>> On May 1, 2018, 8:35 AM -0500, Joe Frey <frey at radioles.com>, wrote:
>>
>> The best distortion pedal(and I have built several) I ever built is the
>> harmonic percolator. You can get the PCB layout and build info if you
>> search pepper spray distortion. Be advised that one of the transistors
>> connections are listed backwards. I used components for the original
>> version, not the Steve Albini version. JoeF.
>>
>>
>> I made one of the Tim Escobedo all-silicon version (but added the diodes
>> back in switchable) and it sounds pretty great with synth. This would be a
>> pretty good candidate for a module since the "harmonics" knob is just an
>> attenuator.
>>
>>
>>
>>
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>>
>
>
> --
> Quincas Moreira
> Test Pilot at VBrazil Modular
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