The Big Muff Pi is a timeless classic in the
fuzz-pedal world. It’s been heard on numerous
recordings and been offered by countless
boutique pedal manufacturers in one
form or another over the years. There are
several different versions of it, but for this
article we’re going to talk about the newest
Russian version (black box).
While it is a good-sounding pedal in stock
form, as DIY’ers we have to ask ourselves how
it can be improved. What are its shortcomings?
What kind of modifications would turn this
great fuzz into an amazing fuzz? Let’s look at
the circuit and break it down in layman’s terms.
The signal comes in and passes through R1 and
C1 before hitting the first stage, a basic transistor
signal boosting stage. Once the signal is
boosted, it goes through C3 and uses a potentiometer
connected as a volume pot in order
to control the gain. The signal goes through C4
and R8 before hitting the next stage, which is
boosting the signal but also clipping the signal
quite a bit via the diodes (D1 and D2) in conjunction
with C6. The signal then goes through
C7 and R13 before hitting the next stage,
which is nearly identical to the preceding stage.
After this stage, the signal goes into the tone
control, which pans between a high-cutting
section and a low-cutting section. This explains
why when you turn the tone control down the
sound is very bassy, while turning it up cuts
the bass, and it gets very bright. After leaving
the tone control, the signal goes through C12
and enters into the final signal boosting stage
before exiting through C13 and going out of
the volume control into the pedal’s output.
Modifications
A common complaint is that the stock big muff
tone control takes out too much of the mids. In
a band situation this can make the guitar tones
seem to disappear a bit. In order to bring the
mids back in, I like to change the tone stack,
so it’s more like a traditional high-cut type of
control. In addition, I like to control the bass
frequencies so they aren’t so overwhelming.
Here are the changes I would make:
• C1: 1uf
• R8: 22k
• R13: 22k
• Remove R19 completely; do not replace it
with anything.
• In place of R18, connect a 20k potentiometer
as shown in the schematic. This requires drilling
a hole and mounting the new pot. Alternatively,
you can wire in a 20k trimpot and just set the
pot to taste. This modification will allow you to
have separate bass and treble controls.
• C12: .01uf (make larger if you need more bass)
• R22: 1M
• C9: 1uf
This will make it nice, big and full—something
closer to a Queens of the Stone Age
type of tone. We can also make the gain control
more useful in lower gain applications:
simply connect a .001uf cap between lugs 2
and 3, shown as C3A on the schematic.
For a creamier, Gilmour-ish tonality, jumper
R1, and connect a .001uf cap in parallel
with R24. If you want more of a higher gain,
open-sounding distortion, make all the same
changes, except make C1 a .01uf and C12 a
1uf. For an extra bit of creaminess, replace
R12 and R16 with jumpers.
I prefer poly film or metal stack film capacitors
whenever possible. This isn’t absolutely
necessary, just a tonal preference. If you use
electrolytics, make sure you get bipolar electrolytics.
You can get any of these parts from
smallbearelec.com,
mouser.com, or
digikey.com, among other places. I do not recommend
Radio Shack-type caps, though; sometimes
the parts are so large you can have
trouble fitting them in the pedal.
If you happen to like the scooped-mid sound
of the Big Muff, but still want a separate bass
and treble, I would make the following modification
to the tonestack:
All of the changes in the previous mods still
apply, the only thing we are changing is the
tonestack, shown in blue on Schematic 3.
Some DIY’ers also like to experiment with
different types of NPN transistors, which do
indeed give a bit of a different sound. They’re
inexpensive as well, so it can be very fun.
These modifications can be done to any Big
Muff-style pedal; just cross-reference the
schematics shown here with the particular
schematic you have for your pedal. I guarantee
you’ll have a killer-sounding tonal twist on
a classic fuzz pedal.
Have fun!
Brian Wampler
Brian Wampler is an author, effects designer/builder and operates IndyGuitarist Custom Effects -
IndyGuitarist.com and
Wamplerpedals.com. His books include
How to Build Effect Pedals,
How to Modify Effect Pedals, and
Advanced DIY Effect Pedals available at
GuitarTone.net.