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big muff

NEW!!! Mid Control Mark 2

My original modded Big Muff in the second half of this article got "damaged" during a DC socket mod attempt. It's still repairable, but I had another unmodded black Russian Muff lying around, so I thought I'd mod that with a basic mid control mod instead.

I was a little dubious about attacking this one, since it actually sounded quite nice stock. Much better than my other black Russian. But what the hey, it's a reversible mod, right?

So, virtually the same mod as before, except the mid control pot this time was 25k logarithmic. And bingo, this gave me the smooth taper I wanted.

Note here the new blue rectangular capacitor, and the two wires to the right of it, which replace a resistor on the board and run to the mid control.

Here's the mid control pot on the top left. Note the same two wires from the previous photo.

I wasn't terribly pleased with the diode mod I tried originally so I didn't bother with that one again.

Here's the sexy finished product:

Mid Control, Diode Selection Switch

The Sovtek black Russian Big Muff. I must be the only person in the world who doesn't get along very well with this pedal. The mid-scoop is a bit too extreme and the highs are a bit too nasty for my taste. I love the Gilmour sound, but it has long been difficult for me to imagine how he gets it out of a pedal like this. Of course, his mid-boosting EQ which usually follows is the key.

What I really wanted was to be able to use this pedal without having to hang another dedicated pedal after it, be it an EQ or a Tube Driver set to low gain. So when I discovered how to tame the mid-scoop, I gave the Muff another go.

There were two especially helpful sources on the net. I found the original schematics here on the PisoTones site:
http://www.pisotones.com/BigMuffPi/psst/BMP_versions.htm

And mod suggestions from the Technophobia site (including the mid control):
http://www.student.ru.nl/r.kerkhof/Taas/Mods/Big%20Muff.htm

It's quite possible these mods originated from Jack Orman's Lab Notebook:
http://www.muzique.com/lab/tone3.htm

The first thing I did was replace the pots. The sustain control on my pedal in particular was a bit of a dud. The wiring inside the pedal was pretty flimsy, and wires did come loose from the circuit board during the course of surgery. The old pots are still pictured:

The next thing was to install the mid control. The actual component values I used are displayed in the tone stack schematic below. Be sure to compare this with the original schematic.

You can see the yellow rectangular MKT capacitor (C1) I substituted in below. The resistor to the right was also replaced afterwards with R2 and the 20k pot.

So that was about enough right there. The pedal immediately became more useful, and the mid control does indeed range from an extreme mid cut to a subtle boost. I used a 20k linear taper pot, but it's only really effective for about the first quarter turn. Next time I'm in there I think I'll try a log taper pot. I mounted the pot on the face of the pedal (see photo at the top of this article - there wasn't quite enough room for another chicken-head knob).

The other thing I wanted to do was replace one of the clipping diodes in each transistor stage with a pair of germanium diodes in series. I was hoping this would give me, well, more of a germanium sound, a bit like a Fuzz Face, or perhaps a Cornish G2?

The stock silicon diodes had a voltage drop of about 0.6v, while the germanium pairs were 0.5v. The question was whether I should replace the same diode in each transistor stage, or alternate ones. I wanted to retain an overall semblance of symmetrical clipping, and since the Muff uses inverting common emitter stages, I essentially replaced the same diode in both stages. That's my story and I'm sticking with it.

Not convinced it was all going to sound great however, I decided to install a DPDT switch for stock silicon vs the new germanium diodes. You can see my nasty piece of work below.

Good thing too. The germanium setting has about half the sustain of the stock silicon setting, and also has a very slight octave thing going on. Not bad at all and nice to have, but I'm not sure I'll use it much.

But the mid control has completely transformed this pedal, as you'd expect, while retaining a setting for traditional Muff tones.

On the still-to-do list, if I can be bothered, will be...

• experimenting with a log taper pot for the mid control
• replacing the stock pcb-mounted jacks with higher quality ones
• modifying for true-bypass with a 3PDT footswitch

 

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