[sdiy] distortion pedal for a modular system

Tom Wiltshire tom at electricdruid.net
Wed May 2 12:51:41 CEST 2018


It wouldn’t necessarily have to be a full separate power supply. How about just putting separate regulators on the distortion module so it takes the +/-12V Eurorack power and runs at +/-9V (or as Quincas suggested, just +9V on its own, or -9V for the fuzz face!). That gives the module a degree of separation from other things without needing a whole extra power supply.

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 2 May 2018, at 09:27, stepan kayukov <stepan.kayukov at gmail.com> wrote:
> 
> 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 <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 <mailto: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 <mailto: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 <mailto:walkershurlds at gmail.com>> wrote:
>>> On May 1, 2018 1:28 AM, stepan kayukov <stepan.kayukov at gmail.com <mailto: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 <mailto: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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