Thoughts on this pedal?

[Transistor-Transistor]

As some of you may know I've been working on this overdrive/distortion for weeks upon weeks now. I think I finally finished it unless further testing reveals somethin'.



I love the body control. It's a modded Framus mid control. Turning it clockwise flattens out the eq and turning it counterclockwise scoops the low midrange. The freq switch makes it scoop a lot, or even more.
A bunch of you helped me with the bass drive control. I didn't realize how much it would affect the overall distortion until a few weeks ago. I liked it a lot  better than the fuzz face gain control I had been using, as this one is a whole lot less muddy at low drive settings.
Let me know what you think or if theres anything questionable/wrong/unnecessary about the schematic!

Atticus M

[amptramp]

If you have built it and you like it, great!

One thing I would question about the design is that the collector of Q2 is held to within ± a germanium diode drop of the base.  There are designs that put a capacitor in series with the antiparallel diodes so the collector-to-base voltage is not as constrained.

The Big Muff uses 1 µF in series with the diodes to keep the diode activity strictly in the AC signal range.  This has the advantage of requiring more drive in the bass range of the signal to achieve clipping, so the fundamental content doesn't get clipped as much as higher frequencies, making the clipping lass muddy.

The output voltage is limited to ± one silicon voltage drop.  The diodes at the output have no capacitor to limit the high-frequency hash of diode conduction coming in suddenly at the extremes of output voltage.

It looks like a simple enough circuit to put on a prototyping board but you should leave enough space to add components for experimentation purposes.

[Transistor-Transistor]

Oh hey thanks I was actually just wondering how I could fix the high freq stuff, I decided to try it loud and I heard it and I was like ehhhehheh
I'll try the big muff thing you suggested to see how that sounds!
(I'm actually really glad you brought that up because there was a lot of muddiness too that I kinda haphazardly fixed with high pass filters which added to the other problem heh)

[Rob Strand]

I love the body control. It's a modded Framus mid control. Turning it clockwise flattens out the eq and turning it counterclockwise scoops the low midrange. The freq switch makes it scoop a lot, or even more.

Are you sure the C7, C8 values are correct?  Probably won't work like variable mid notch (like Framus) with those part values.

[Transistor-Transistor]

I love the body control. It's a modded Framus mid control. Turning it clockwise flattens out the eq and turning it counterclockwise scoops the low midrange. The freq switch makes it scoop a lot, or even more.

Are you sure the C7, C8 values are correct?  Probably won't work like variable mid notch (like Framus) with those part values.

Its very modded. It already has a set notch in this one and it scoops lows too

[Transistor-Transistor]

So theres a weird buzzy crackle underneath high notes. Does anyone know why this is? Lowpass filtering doesn't help it

[Transistor-Transistor]

Yeah I did all of amptramps suggestions and theres still this quietish crackle on the decay of high notes regardless of settings

[Rob Strand]

Yeah I did all of amptramps suggestions and theres still this quietish crackle on the decay of high notes regardless of settings

Not sure if this will fix it but when I looked at the design originally I had a beef with C3 in series with C5 connecting across the output of the buffer Q1.  It's possible this connection can cause oscillation.

You can maneuver around it without affecting the tone by moving R5.

[Transistor-Transistor]

I just tried both positions and it made it worse. I up and removed C5 and the crackle is still there so I don't think its an oscillation issue but the problem may be around that soft clipping stage?

[antonis]

Try to move NFB clipping configuration from Q2 Collector to R6/R7 junction..

[Transistor-Transistor]

Hey that worked! Thanks!

[antonis]

You're welcome..

[Transistor-Transistor]

Uh oh its back now (or has always been there faintly and I just noticed)
Its very very faint now but its still noticeable at loud volumes

[antonis]

Delete R6..
(by  shorting it..)

edit: FWIW, Q3 is badly biased..
(its Collector current is strongly dependent on particular V_BE drop..)
I'd make R16 470k and R14 2k2, adding a 10 to 22 μF cap in parallel (like C4/R8) in case of high gain retention wish..

[Transistor-Transistor]

Oh that made it sound way better! 10uf was a little too high gain for me so I switched it to 3.3uf and I think it sounds great

[Transistor-Transistor]

Its back 
This time it actually literally was nonexistent until five minutes ago. Should I assume it's something to do with the breadboard?

[Transistor-Transistor]

Actually I'm starting to think I could get a similar sound with less parts with a LM386 based circuit. What do you all think?

[aron]

I don't know what your overdrive sounds like but I don't think the LM386 would sound the same.

[antonis]

Could you plz post a schematic of your final design..??

[ElectricDruid]

Its back 
This time it actually literally was nonexistent until five minutes ago. Should I assume it's something to do with the breadboard?

Random crackling that appears and disappears without apparently having anything to do with what you just did?

Yep, sounds like breadboard gremlins to me!!

If you want to know for sure, build the circuit in a more solid format and see what happens. I honestly don't know of any other way to check.