The Big Muff Pi tone circuit is a useful addition to your tone stack arsenal as either a hobbyist or professional builder. It provides a simple, low parts count framework that can be tweaked quite simply to fit the project you’re working on.
The standard BMP tone circuit (with the knob set at noon) has a hefty, wide cut to the midrange. Rolling the knob clockwise cuts lows and boosts highs, and rolling counter-clockwise cuts highs and boosts lows. Although the midrange dip does move around a little it can be seen as a nice sort of pivot point which the rest of the EQ curve moves around.
An important thing to note is that this circuit is entirely passive. Passive circuits of this nature can cause trouble as the output level will never quite be the same as the input level. You could try using after a booster or build a buffer into the circuit before the output stage.
Here is a graph showing the range of the standard BMP. (The graph is based on a 10k input; circuits react differently depending on the input they are ‘seeing.’)
I made this graph using the awesome Duncan Amps Tone Stack Calculator programme – http://www.duncanamps.com/tsc/
Green – Knob in the straight up position
Orange – Knob in the full counter-clockwise position
Yellow – Knob in the full clockwise position
Click on the image for higher resolution.
As you can see the level of boost available is fairly significant and the BMP tone control can work excellently in the chain as a slight upper-end enhancer / ‘sparkler’ on clean tones.
The BMP tone circuit is a very simple build requiring only five parts:
22k resistor
39k resistor
.004uF capacitor
.01uF capacitor
100k linear potentiometer
Here is the schematic (drawn in DIY Layout Creator).
Click on the image for higher resolution.
So there you have it: a fun, simple little circuit that can be used in a variety of situations. You can build this onto vero or any other circuit board material, or more likely you will just want to build it onto a pot as seen on Beavis Audio (http://www.beavisaudio.com/techpages/BigMuffToneControl/). Have fun and post your results in the forum!
