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Mini-Muff Distortion
Build on AMZ Multi-Fuzz pcb

The Big Muff may be a classic distortion design, but it is often too much of a good thing. The cascaded gain stages with the dual diode clipping will remove most of the dynamic range from the sound. This aspect of the design can make the pedal less useful for many styles of music and, though I tried the Muff in my live rig many times, it always ended up off the board. This article is about trimming down the basic design to give back some of the dynamics, enhance transparency and make the pedal a more useful and versatile distortion.

The basic Mini-Muff schematic above uses PNP transistors as were found in my original 1976 EH3003 box. The parts numbering on the schematic may seem a bit odd as there are quite a few numbers missing, but that is because the schematic is numbered in reference to the Multi-Fuzz pcb, on which this design can be constructed. Parts not listed are not used and their space on the pcb is left empty.

The main idea of this modified BMP is to remove one of the gain stages in the middle, along with its diode clipping network. This will reduce overall gain but restore dynamics in the process, and allow more control over the distorted sound.

How does it sound? Not at all like the classic Big Muff. It is more of an overdrive, with much less distortion on tap. The response is mostly flat and not mid-range heavy like the TS boxes. It adds a low gain crunch to the guitar sound that has earned it a place on my pedalboard.

The BMP has used a variety of resistor and capacitor values over the years, and the transistors have been a subject of much debate. The parts list below will give you a sampling of common values for the components, but they may be tweaked to taste.

Parts List
R1 - 1M C1 - 10 uF
R2 - 47k C3 - 0.1 uF
R3 - 120 C4 - 1.0 uF
R4 - 470k C5 - 470 pF
R6 - 10k C7 - 3900 pF
R7 - 10k C9 - 0.01 uF
R8 - 100k C10 - 1.0 uF
R9 - 470k C13 - 1.0 uF
R10 - 150 C14 - 47.0 uF
R11 - 10k C15 - 0.1 uF
R13 - 39k D1 - 1N914 or 1N4148
R15 - 22k D2 - 1N914 or 1N4148
R16 - 470k R23 - 100k audio taper
R17 - 100k R24 - 100k linear taper
R20 - 3.3k R25 - 100k audio taper
R21 - 15k    
Q1,Q2,Q3 PNP silicon transistor
(2N5087, 2N3906 or similar)
Jumpers* R12, R18, R19, C6, L1
All resistors are 1/4w and capacitors are in uF unless marked otherwise.

Click here for a printable version of the parts list.

The Mini-Muff may be constructed using common methods such as perfboard or stripboard, but it may also be made using the ready-to-solder AMZ Multi-Fuzz pc board. Complete instructions on how to modify the board for this project are emailed to everyone that buys the pcb.


NOTES

*On the Multi-Fuzz pc board, be sure to install jumpers for R12, R18, R19, and C6. There will be several parts placements on the pcb that are not used, such as C11, C12 and R22, and those spots on the board are left empty.

It should be noted that this circuit is designed for PNP transistors and requires a positive ground power supply. Battery power is adequate since the current draw is low, but if an external power adapter is used, then an isolated output is needed. A dedicated negative voltage supply, such as that found on the AMZ Power Supply can also be used.

Also, the AMZ Voltage Doubler can convert +9v to -9v for powering this circuit and it has been extensively tested and found to be an ideal solution.

It is possible to convert this circuit to an NPN negative ground circuit by using 2N5088 transistors and reversing the polarity of all of the electrolytic capacitors - those are 1uF and higher values in the parts list. The pedal can then be powered with a standard center-negative 9v wall adapter or power supply.


A single Multi-Fuzz pc board is $12.00 US plus shipping. I prefer Paypal payments.
Order Multi-Fuzz pcb
Place your order
on the AMZ catalog page.


MODIFICATIONS

A link to page with modifications and upgrades is mailed to all purchasers of the Multi-Fuzz pcb.


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