Reducing output volume of Muffin Fuzz / Big Muff Pi

[Coach_McGuirk]

This pedal is far too loud for me. I would like the volume knob to be more operable. What can I change in order to help reduce the output?

 

[Feral Feline]

You'll want to play around with R21 and R22.

Decrease R21
Increase R22


What values are in there now?




Oh, and try A100k for volume if you've used B100k.

 

[Coach_McGuirk]

R21: 12k
R22: 4.7k

Maybe I'll just stick two trim pots in there? Can I adjust one and not the other, or do they need to remain balanced?

 

[Giorfida]

This pedal is far too loud for me. I would like the volume knob to be more operable. What can I change in order to help reduce the output?
View attachment 73860

Use an a100k (audio/log taper) pot instead of the b100k (linear taper) pot for the output volume
Will give you the control you need (I run mine at unity gain or slightly below), and that’s all I need

You could tweak some of the resistor values on the last transistor stage, or replace it for a lower output transistor, but I’d personally change the pot first as that will have the most impact on volume control and least impact on the tone

 

[Coach_McGuirk]

Use an a100k (audio/log taper) pot instead of the b100k (linear taper) pot for the output volume
Will give you the control you need (I run mine at unity gain or slightly below), and that’s all I need

You could tweak some of the resistor values on the last transistor stage, or replace it for a lower output transistor, but I’d personally change the pot first as that will have the most impact on volume control and least impact on the tone

Good call. This helps a lot. Much more use from the volume knob now. Thanks.

 

[Feral Feline]

If the different pot-taper doesn't fully resolve your problem...

To give you an idea of the ranges for those two resistors, I've gone to
Kit Rae's website (stock Kit Rae refdes in parentheses):

BIGGEST
R21 (R6) — 15k
R22 (R4) — 3k3

SMALLEST
R21 (R6) — 8k2, 5k6 on Ibby's 850)
R22 (R4) — 2k2, 2k-Colossus, 1k5-Original Pickle, 1k-Ibby 850


I've read that small changes = big differences in sound.


So for R21 you could try going down to 10k or even 8k2;
and for R22 go up to... well, I wouldn't go much higher than what you've got: 4k7 — so you were building the PPCB Stomp '75 ?

 

[Coach_McGuirk]

If the different pot-taper doesn't fully resolve your problem...

To give you an idea of the ranges for those two resistors, I've gone to
Kit Rae's website (stock Kit Rae refdes in parentheses):

BIGGEST
R21 (R6) — 15k
R22 (R4) — 3k3

SMALLEST
R21 (R6) — 8k2, 5k6 on Ibby's 850)
R22 (R4) — 2k2, 2k-Colossus, 1k5-Original Pickle, 1k-Ibby 850


I've read that small changes = big differences in sound.


So for R21 you could try going down to 10k or even 8k2;
and for R22 go up to... well, I wouldn't go much higher than what you've got: 4k7 — so you were building the PPCB Stomp '75 ?

I built the David Gilmour pedal discussed in this thread.

Didn't you say I should *increase* this value though? Should I try decreasing it instead? Or just add a trim pot?

 

[Feral Feline]

I built the David Gilmour pedal discussed in this thread.

Didn't you say I should *increase* this value though? Should I try decreasing it instead? Or just add a trim pot?

Didn't you say I should *increase* this value though?

Yes, R22 in your posted schematic (Kit Rae's R4), but 4k7 is quite large for this resistor when most other Muffs are 2k2 or 3k3.

Should I try decreasing it instead?

R22? Only if you want to INCREASE gain.

Or just add a trim pot?

This is a good application for Robert's TRIMMIT! You could then dial in the amount of gain you want.
I'd use a 5k trimmer, and then you can see how lowering resistance on the emitter increases gain.


The thread Big Muff Ram's head 1973 "violet #4" vs Stomp 75 does indeed reference the Stomp '75 in the Muffin Fuzz build doc:
ie R4 @ 4k7 in that thread is Stomp '75, which is R22 in the Muffin Fuzz schematic posted in your OP of this thread.

If you decrease R22, you will increase the gain of that associated transistor.

For example; the Creamy Dreamer's first & clipping stages have NO emitter resistor for a very gainy result. To quote Kit Rae:
"I found there was no limiting resistor mod, but the emitter resistors were removed in the first three stages. ... pulling those emitter resistors makes for a very high gain Big Muff "



Also note, that the collector resistors are quite big — R13, R18 and R11 @ 15k, further intensifying the gain.


I really like this following schematic from Kit Rae's website, it explains a lot about the Muff circuit;
check out the info about R22 on Q4 (R5 & Q1 in the Muffin Fuzz schematic) and the other emitter resistors (and collector resistors):




You could further reduce overall gain of the circuit in a number of ways, but sticking with emitter manipulation for now, you could also check out:

KR / PPCB​

R22 / (R5) = 100Ω​

R21 / (R11) = 100Ω​

R10 / (R16) = 100Ω​

All of those are quite low, practically jumpered to ground, very high-gain. Increasing them to 1k each and...


Their corresponding collector values are as follows:

KR / PPCB​

R13 / (R4) = 12k​

R18 / (R10) = 12k​

R11 / (R15) = 12k​

...Decreasing all collector resistors to 10k ...

... might get you what you want without deviating too far from the inherent sound of the Stomp '75.
As mentioned before though, a little goes a long way — so maybe making those suggested changes to the emitter & collector resistors would soften the character of the circuit too much.


My recommendation would be to tune the entire circuit to what you like, and not worry about authenticity of achieving a purported Violet/Gilmour/whatever schematic's values. Tune to your gear, your fingers, your ears, the sound inside your head.

 

[Coach_McGuirk]

@Feral Feline, I might have already committed a bit to the David Gilmourishness of this one.

 

[Coach_McGuirk]

But I will certainly be building a second muff sometime soon and will definitely take your advice to let me ear guide me. What are your thoughts on the Muffin Factory? I feel like that might be too many permutations for my OCD mind.

 

[Feral Feline]

@Feral Feline, I might have already committed a bit to the David Gilmourishness of this one.

View attachment 74013

Great Jumpin Jehosaphat uhm graphic. Very graphic...

 

[Feral Feline]

But I will certainly be building a second muff sometime soon and will definitely take your advice to let me ear guide me. What are your thoughts on the Muffin Factory? I feel like that might be too many permutations for my OCD mind.

I love the Muffin Factory — so much potential; I think the Muffin Factory is great for distilling all the Muff variants you like into one pedal;
ie. I don't plan on building my Muffin Factory PCB to the "stock" build-doc values.

I'm still deep Muff-diving exploring the circuit to better learn what I like. I currently have well in excess of 50 variants I need to bread-board/build/test.
So though I have the MF-PCB, I'm not sure when I'll build it, if ever. It's one deep rabbit hole...

Mind, I recently bought a second Muffin Factory PCB, so maybe I'll build that one "stock" and then build the other one to taste(s) and then if those tastes change, I could always buy another MF-board...

Dangnabbed rabbit-hole just got deeper.

 

[Coach_McGuirk]

Sounds like you have done a good deal of leg work. Do you have any of those variants published with notes on how they sound? Or any other guidance to share beyond what you wrote above? I will probably build another Muffin Fuzz or two and then maybe tackle a Muffin Factory. It's daunting to think about the available permutations both above the enclosure and below.

At some point, I have to remind myself to pluck the strings on the guitar instead of just hunching over my pedalboard endlessly tweaking things, in this particular case David's chest berries.

 

[Feral Feline]

I haven't done any real leg-work.

It's all theoretical and my silly "what if" ideas: for example I once checked to see what all the BIGGEST values were for any given component, both for just EHX and for boutique-derivatives (which swing to extremes compared to EHX). I call it the...

RBMP — Really Big Muff Pi

I've drawn up the schematic, but haven't breadboarded it yet. It might sound horrible because everything is at the extreme and it might squeel or mush out.— who knows? I've completely disregarded any electronics theory 'cause I don't know any.
Go here http://www.muzique.com/lab/big_muff.php to calc resistor values for the basic shunt feedback transistor circuit to set the proper DC operating point. Let me know if you figure out and can understand that gobbledygoop.
I did read somewhere that
"the collector voltages do not have to be 1/2 the power supply [9v, so 4v5] ... a Si type version I built I have the collectors at 2.5V or so." — Gus

Also, huge-value clipping caps are anathema to bass-friendly Muffs; the Muffs bass-players tend to like are the Russian variants with 47nF clipping caps (and 1n in a boutique-y non EHX!). Sticking to the maxim of biggest is best for the RBMP, the clipping cap will be a whopping 10µF!
That's 10µ vs 0.047µF, or 10000nF vs 47na — So the latter Russian clipping cap is not even a half-percent of the former '76 Ram's Head!
I suspect I will not like the RBMP on bass, and it may well be too fizzy on guitar.

Nonetheless I have graphics ideas for the RBMP, but I suck at graphics... So will the RBMP ever see the light of day on a pedalboard, will it ever even make a noise from my breadboard? Time is running out, too many things to do in life. Right now I should go practice my bass, or trombone...

 

[Coach_McGuirk]

Look at what you made me do.

 

[Feral Feline]

Sorry, not sorry.

 

[jwin615]

Look at what you made me do.

The Feline made me do it won't stand up as a valid defense in court. The precedent is already set that one should never take tone advise from a bass player.(jk) You're on your own but the sacrifice you made today will not be forgotten.
Also, your graphic is hilarious.

 

[Giorfida]

But I will certainly be building a second muff sometime soon and will definitely take your advice to let me ear guide me. What are your thoughts on the Muffin Factory? I feel like that might be too many permutations for my OCD mind.

What fun is the muffin factory, when you can build multiple pedals instead! Already have a Russian/Gilmour (switchable), a Rams Head, have a Triangle queued, and likely also do a Zappa mod version someday as well! And of course, splitting out the Gilmour to its own board for my planned “Gilmour/Cornish” clone board build.