Big Muff mods and tweaks

I recently noticed that a page I referred to a lot just disappeared from internet... It is the Big Muff mods and tweaks page that was deleted recently.

Fortunately for us, there are some "internet archives" website that keep it alive for a while. In order to keep it alive, I added it here. I also added a list of personnal mods that work quite well, and some notes about mods I already tried.
Modded Big Muff

Easy mods

Diodes mods

The Big muff contains 4 diodes (2 pairs of diodes), that clip the signal to create gain, and compress the signal. Changing these diodes can change the compression and gain of the pedal drastically:
  • Silicon diodes: these are the original diodes used in the Big Muff. Usually, they are 1n4148 type diodes, and gives the Big Muff reference tone: gainy, compressed yet crispy and tight distortion.
  • Germanium diodes: germanium diodes will cut the sound more. You will have a more gainy, more compressed saturation, but also you will loose quite a bit of output volume. No germanium diodes were used in original Big Muffs.
  • LEDs: LEDs are also diodes and can clip the signal. Red diodes clip more the signal compared to yellow, blue ones. There will be less gain, less compression and also more volume output. It gives to the Big Muff a nice "overdrive" feel, with a bit more dynamics. Note from Coda Effects: I tried it on this Big Muff variant, I really like it! It gives a lot of dynamics to the muff.
  • FET / MOSFET: if you tie together the drain and gate of FET / MOSFET transistors, they will behave like diodes. Sound is similar to silicon diodes, a bit smoother.
  • Remove the first pair of diodes, and you have got a Colorsound Supa Tonebender! The unit will be louder, with more bass, but still quite compressed. Great trick for bass players.
  • Remove the two pairs of diodes: great trick! By removing the diodes from the unit now sound if fed back. Result: more volume (LOUD!), less compression, less gain and a more open (overdrive) sound. In my Dolmen Fuzz, I removed all the diodes with the central position of the switch: massive spurry sound!
A good way to see what is your favorite combination is to use sockets for the diodes. You can also use switches to change the diodes. Here is an example with silicon diodes and LEDs :

Works really well and it gives you multiples choices. With 2 of these on-on-on switches you can choose between no diodes or 2 different diodes set for each gain stage!

Emitter mod

Each transistor's emitter of the gain stages of the Big Muff is linked to the ground by a resistor (either 100R or 390R, R12 & R16). Removing the resistors will increase the "gainy-ness" of the pedal, increasing the resistors will lower it.

Resistor mod Each of the gain stages has a limiting resistor on the start of it (R8 & R13). These are 8.2k (8k2) or 10k in different models. By diminishing these values the unit gets more gainy. (Note from Coda Effects: beware! There is a typo on the original Big Muff mods and tweaks text. Diminish it for more gain)

Creamy Dreamer

Basically the combination of the Emitter mod and the Resistor mod.

Noise gate mod

This mod will quieten the Muff while not playing, thus a noise gate. To do this, add a 100k trimpot (wired as a variable resistor) parallel to the 100k to ground of the second gain stage (R14). The trimpot can be adjusted to taste to get the max noise gate effect.

Coupling caps mod

The Muff has a lot of coupling caps (C1, 3, 4, 7, 16, 12 & 13). Coupling caps are next to the block of DC also a way to set the frequency response of the unit. 

Enlarging these caps give the unit more bass, making em smaller give the unit more treble. Experiment with em. Also the sort of caps can make a difference in noise, feeling and authenticity. Old Muffs used ceramic coupling caps; using film caps here won't give you the same sound

High roll-off mod

Notice those small ceramic caps on 3 of the transistor stages? They are used to roll of excessive highs. Normally they are 470 pF (C2, 5 & 8) but larger values roll of more highs. You can also remove em for a great result.

Clipping caps mods

Next to the diodes is also a cap placed (C6 & 9). This cap determines the frequency band the unit clips. Enlarging this cap will make it clip more low notes, make it smaller for more high end clipping.

Transistor mods

The Muff uses four transistors and the type and choice of these transistors will affect the sound greatly. The higher the gain, the more the unit will focus on the high end / treble. Some known examples:
  • The Russian Muff uses E type transistors (newer ones use BC549C's though) which has a Hfe of around 500. I used BC184's as a great replacement of these transistors.
  • The NYC Muffs usually use 2N5088's or BC550's with a Hfe of around 800.
  • The Little Big Muff uses 2N5962 with a Hfe of around 1500 - 2000.
The Russian sounds darker due to the low gain. Knowing this, we can change the sound of a muff greatly by replacing the transistors. Small tip: use sockets when changing transistors. This way the transistors are not damaged by the soldering and swapping is much much easier. Some nice ones:
  • 2N5133's: used in Triangle ones (the NOS versions tend to sound even better then newer ones) as FS36999's. Very nice sound, smooth, warm, open.One of my favs! Note from Coda Effects: I would not use these ones. They are really rare and expensive. I am not sure that they really sound better... I would try to find something similar in hfe (around 100-400).
  • BC239's: also used in a bunch of Muffs around. Slight less gain as the above named but this gives the Muff quite a nice touch.
  • 2N5087's: PNP transistors instead of the above named NPN (more usualble). To use these you need to reorient some of the caps and change the + and - of the battery (called positive ground). Although they must be identical to 2N5088's they were used in some old models and do sound different.
  • BC141's: ultra low Hfe (around 100) and not suited for anyone out there. More bass, less gain but a very different sound.
  • MPSA13's: ultra high Hfe (around 10.000). Nice touch for some more gain.
Experiment! Use four of the same transistors or try to mix. For example I like a Muff with 5133's for the clipping stages and MPSA13's for the buffer stages.

Note from Coda Effects: I also experimented with a few transistors, here is my feedback about this:
  • The first transistor is the one that will define the most of the gain of your unit. Higher hfe = more gain, but also more trebles... I tried a few ones:
    • 2n5089: high gain, but also gives a "gritty" touch to the muff that I do not really like. Also quite noisy
    • 2n5088: nice sound, gainy unit, but less noisy and agressive trebles than 2n5089. I really like it and use it often.
    • 2n2222A: low gain, gives more bass and smoother sound. Beware: polarity is reversed compared to 2n5089.
    • MPSA18: extreme gain! I would suggest to increase emitter resistor to limit gain (especially for noise issues), but you can have a nice "doomy" muff with it!
    • 2n3904/BC549C: great for a low gain Muff.
  • The two transistors of the gain stages play a bit more with compression. I usually use low hfe. 2n2222 are really nice for this use. 2n5088 can also do the job.
  • The last transistor will define the final output volume of the unit. I like to have quite a lot of output volume, so I prefer to use high hfe transistor for the last stage, like 2n5089, or MPSA18.

Feedback mod

This mod is also not for anyone. It will give the Muff a weird drone note that will interact with the notes played resulting in octaves (up and down), nintendo sounds or a huge MUSH. Can sound quite nice and interesting!!!!! The mod is done with a feedback loop: connecting two points together and letting signal flow back. I found two of these loops in my Muff (note: more can be there; try for yourself!)
  1. Connect the emitter of Q3 with the emitter of Q2 through a switch (so you can turn the loop off). The sustain will be on full when this mod is engaged.
  2. Connect the collector of Q3 with the collector of Q1 through a switch. The sustain now can be varied by the sustain knob.
Great addition: add a 1M potmeter in the loop (wired as a variable resistor) or, even better!!, a LDR (light dependent resistor). With the latter, you can control the amount of feedback with the light on stage / with your foot shading the LDR from the light. Cool!

Note from Coda effects: this is really cool, but I will suggest to use a momentary footswitch. If not, you can be quickly bored with the noisy issues that will rise from this mod. However, from times to times (beginning of a song), it is a killer mod to use!


NYC muff:
BMP ref pic 37

BMP ref pic 38

Russian muff: (Note from Coda Effects: these units are getting rarer and rarer, I would not modify it)


Tonestack mods

The Big Muff Pi is legendary due to his tone section; only one knob to select between a bass, treble or in-between setting. The overall sound of this tone knob is the loved / hated mid cut.

Some Versions:

  • Triangle version: R1=33k, C1=4n, R2=33k, C2=10n;
  • Ramshead version: R1=33k, C1=4n, R2=22k, C2=10n;
  • 1975 version: R1=39k, C1=4n, R2 = 22k, C2=10n;
  • 1977 opamp version (1): R1=5.6k, C1=100n, R2=1.2k, C2=120n;
  • 1977 opamp version (2): R1=8.2k, C1=100n, R2=1.2k, C2=120n;
  • Green Russian version: R1=20k, C1=3.9n, R2=22k, C2=10n;
  • Late model: R1=39k, C1=4n, R2=100k, C2=10n
  • Reissue version: R1=22k, C1=3.9n, R2=22k, C2=10n;
  • Little Big Muff version = reissue version.
And then some different mods:
  • Swollen Pickle: R1=33k, C1=3.3n, R2 = 22k, C2=47n;
  • Flat mids: R1=33k, C1=5.6n, R2=33k, C2=5.6n; 

Tone stack bypass mod

By bypassing the tonestack the tonestack has no influence anymore on the sound thus does not color the signal in it's own way. Great way to get a more middy tone from your Muff. As the tone stack also cuts volume you get a huge volume increase

Tone stack complete mod

One of my most fav mods. Remove the tone stack altogether from the Muff and place a three band EQ circuit in it's place. Works like a charm and gives you more control over the sound! I also once added a Boss GE-7 in this place to give total control over the sound.

Read my post about the Big Muff tonestack for more infos about how the tonestack works and what mods you can do.

Bonus mods (Coda Effects)

Here are other easy mods and tweaks that can give a nice touch to a Big Muff:

Input Resistor / Capacitor:

The input resistor (R1) and capacitor (C1) defines how much signal enters the pedal, ie the overall gain of the unit. It also forms a filter that will allow some frequencies to go in or not.

Increasing the value of the resistor will lower the gain, and lower treble content of the pedal.
Increasing the value of the capacitor will increase the amount ot bass and the overall gain of the unit.

I like to use a switch to choose between a high gain bassy setting, and a lower gain treblier setting.
A smaller value in C1 also helps reducing noise. I used this mod on this Big Muff for instance.

LPB1 before the muff circuit

Adding a LBP1 before the muff circuit can allow you to add an extra gain / bass amount to the muff. It really add some "heaviness" to the distortion. You can do it on a veroboard, with a trimmer or external gain potentiometer. I want to use the PCB I made recently to try this mod. The musket from Blackout Effectors uses this trick. With a simple 3PDT wiring, you can make it activable or not.

Germanium transistors in the distorsion stage

It can smoothen the Big Muff a bit, but remember to have a high gain last stage to recover enough volume. This is used in the Hoof fuzz from EQD. I am not super found of this mod, but you can try it out if you want! Remember to use NPN germanium transistors.

Voltage starver mod

You can emulate a dead battery, that will give a very peculiar sound to the muff: it cleans up a bit, and the circuit starts to sound "gated", and "stutters" a bit because it does not have enough power to work correctly. I would suggest to use this schematic:

 Afficher l'image d'origine
Just connect the output voltage to the voltage input of your Big Muff.

18V Muff 

Beware: I never tested it on a EHX, and I do not know if the stock pedal can handle 18V... If you have already test it, tell me. However, if you have made a clone with capacitors that can handle 18V or more, you can try to use a MAX1044 as a voltage doubler to supply your Big Muff with 18V instead of 9V!

Here it is! I hope that you liked it, good luck with experimenting!
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14 Comment

This was a great read!! I've always been curious about the 18v muff, I've been messing around with a couple of these different mods to figure out that "ideal" combination for me.

By any chance can you do a circuit analysis of the Op amp Muff?


Hello! I am currently making a 18v muff with the voltage starver knob (plus a mini voltmeter-screen to know how exactly what voltage you supply to the muff), so I will let you know what to expect. I am a bit afrait of the loss of gain, distorsions trends to not sound really good with a low gain setting


Hey Benoit,
This is awesome! Thanks so much for going in depth with this. All of the info is great and VERY useful. I'll be looking forward to more of your write ups!


Hi.. I would like to hear your opinion about my problem if you would. I am building a skreddy p19, which is pretty much a muff, but the output volume is painfully low ( the gain is fine, it's just the overall volume). I had to turn up the amp volume to 100% just to hear a faint sound. What do you think I should do to solve that?


Hi! I think for sure, you have a problem. To check where it comes from, I would suggest to use an audioprobe:
Also, maybe you can reduce the emitter resistance of the last transistor to increase the volume (R23 on this schematic : )


Hi Benoit. Loved the article. I am actually thinking of using some of this mods on my big muff. But I'd like your opinion on this, if you don't mind:
I have recently bought an old Russian Big Muff, V8, Gloss Black Back, 6 screws box. It sounds great and all, but when it's turned off, I seem to lose some high frequencies from my clean guitar sound. It sounds darker then when the pedal is out of the chain. Is it normal, or can I fix this problem? Thanks in advance.


The russian big muff are not really in True bypass, that is why you loose some high frequencies. One way to correct this would be to make it True Bypass. However, as I said in this post, Russian units are becoming quite collectible so I would keep it in its original state!


Great article!
I'm using KSP13 (MPSA13) in the first 3 transistors. BC548 in the last one for a moderate output. In the input cap I've replaced the 1uf for 1.8uf: great improvement.
What's your opinion/experience about the KSP13 without increase emitter resistors?

Sounds really good.


Hello! I'm don't really know a lot about doing mods myself. Is it possible to apply any of these or other mods to a little big muff?


Chance of audio files, so we can HEAR what the mods do?


That is a great idea. I think I will make a "full mod" Big Muff one day to show all the possibilities


I have a Russian Black Pi, wanting to install a Boss style plug so I can stop changing the batteries all the time. I saw where. It said this unit is somewhat rare..... Should I just leave it alone, or will it decrease the value if I modify it in this fashion?


adding a midrange pot is a HUGE improvement as well. take the resistor to ground off the bass pot and replace it with a 50k-100k pot. you can cut the mid, have stock bmp, or boost the mids which is a great sound that makes it really cut thru the mix.
also, i invented a different noise gate mod for this years ago i had posted on diystompboxes...
a ge diode in parallel with the one marked d4 of a stock eh big muff (diode 2 according to kit's site) will nuke a lot of the hiss and noise at the expense of a little bit of gain. there still should be PLENTY on tap.
if ya want it to sound like the original big muff pi more that i bought new in 73, go with much lower gain beta transistors. 200 hfE will get ya that creamy violin like sustain of the originals. they don't distort as much, but less noise and better sustain and the ability to interact with your guitar knobs may just be worth it to ya.
try it on a breadboard and see.