Big Muff Pi mods and tweaks (v 2.0)

 

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The Big Muff was one of the first pedals I ever bought. Drawn to it by the legend, the name, the number of users and the tone. I never tried it out in the store, it had to be loved! When I first plugged it in (into a crappy SS amp) I was disimpressed; was this the legendary Muff? Did everyone love THIS pedal??? Luckily she grew on me, I learned to control her and to get those nice tones from it. Now, I could not live without one Muff.....

Over the years, many many versions were made (great read) but the basic circuit stayed in the pedal producing the very known sound. The Muff is basically a four transistor fuzz pedal with 2 gainstages (with diodes in a feedback loop), an in and output buffer and a tone section containing the combination of a high pass and low pass filter. The big disadvantage of this tone design is the loss of mids. I will use the next schematic as a referrence point in this document

Stock Schematic from General Guitar Gadgets

Over the years I learned what makes a Muff tick, and yes, I still am learning. Here I grouped some known mods to make this fuzz sound even better! I grouped em in EASY MODS, TONE MODS and VERSION MODS.

EASY MODS

Diode mods: The Muff contains 4 diodes, 2 pairs, in a known orientation that clipping and compression occur. Changing these diodes result in the change of the overal sound. Some examples:

Small addition: as the unit uses a pair of diodes you can experiment with different diodes per pair to get more complex sounds, nice touches or just "YOUR" sound! Any diode will work here, properly orientated.

Emitter mod: The 2 gain stages of the Muff are tied to the groud by emitter resistors (R12 & R16). These are 390 ohms in Russian models and 100 ohms in NYC models (exact value can differ between models). Jumpering these resistors (replace resistors with a wire) will increase "gainy-ness" of the unit, enlarging em will reduce the "gainy-ness" of the unit. A potmeter can be used to control this value although I noticed I usually used only one setting.

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 enlarging these values the unit gets more gainy.

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 mod: 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 mod: 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 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:

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.

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!

 

Reference pics:

NYC

Russian

 

Tone Stack 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.

original from DIYstompboxes

Some versions ( view the frequency response here ):

And then some different mods:

Small note: these differences in models won't produce a very different sound but will only complete the total picture of the Muff! For a more difference in sound try the above easy mods!

Mid control mod: This mod is beloved by both guitar players as by bassplayers to regain the mids in the sound, mids that are so needed to be heard in the mix. With the next control you can dial in anything from a (huge) mid cut to a mid boost. Note that by boosting the mids you'll lose the Muff's character; still, it is a very nice addition!

This mod was designed by Jack Orman from AMZFX / Muzique.com. Great site with a lot of information!

Small note 2: the pictures in the Frequency Response page were made with the Freeware program Duncan Amp tools Tone Stack calculator, dowloadable here. I can recommend anybody tempering with the tonestack to check this out for a direct view of what the tone stack does to the sound. And hey, it is free!

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 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.

 

Version mods:

Over the years the models of the Big Muff changed. Here I will post some schematics of the different models so you can alter the values on your Big Muff and transform it into a different version. Here goes:

I tried to give a lot of mods here; for questions, just mail me! You have another mod? Please mail me so I can add it!