[sdiy] distortion pedal for a modular system

[stepan kayukov]

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?



On Mon, Apr 30, 2018 at 8:35 PM, Walker Shurlds <walkershurlds at gmail.com>
wrote:

> Hey Stepan,
> Pretty cool idea!
> One thing: (supposedly) part of the fuzz face sound is that due to the
> circuit’s low input impedance and the relatively high output impedance of
> guitar pickups, the distortion has a kind of “sagging” sound. This will not
> happen when you use either a guitar with active pickups, or the output of
> most synth modules. This might be part of your noise issues.
>
> The part with the JFET looks wrong to me, but I’m not certain. Shouldn’t
> the capacitor be in series with the JFET’s source, rather than across the
> source and drain? The goal here is for DC current through R7 to stabilize
> Q2, but to let a variable amount of AC current though, so that the amount
> of degeneration applied to the signal varies. As it is right now, the DC
> current varies but the AC gain is always on max. I haven’t ever used JFETs
> in a fuzz that way, personally, but I’m sure someone else will chime in.
>
> I would suggest biasing IC1A to ground and coupling the output from Q2,
> rather than having IC1A buffer the voltage from Q2’s collector *before*
> it’s coupled onto IC1B.
>
> HTH,
> Walker
>
> On Apr 30, 2018, 6:53 PM -0500, stepan kayukov <stepan.kayukov at gmail.com>,
> wrote:
>
> hello -
>
> i am new to "synths", i have mainly built guitar pedals in the past. i am
> currently learning EAGLE, so please excuse my drawing.
>
> my goal is to bring a distortion pedal design into a +/- 12v system.
> i executed the attached design, but it is extremely noisy and i hear a
> great deal of bleedthrough, even though i have added many bypass
> capacitors.
> it is a "fuzz face" pedal going to a buffer, then going to a coupled
> inverting amplifier.  the input signal enters the collector of the first
> transistor after being put through a resistor divider, from 12v to 2v, and
> then passes through another coupling capacitor.
> i also attempted to use a JFET around R7/C1, as a means of getting "CV"
> for the distortion control.  this could be improved also probably.
>
> https://ibb.co/jSnXOn
>
> can anyone help me understand how to isolate this circuit from the rest of
> my synths?
>
> thank you,
> stepan
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org
> http://synth-diy.org/mailman/listinfo/synth-diy
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20180501/38997869/attachment.htm>