Modding an EHX Muff Overdrive

[jgenet99]

I'm not a big fan of posting on social media sites, so I apologize in advance if this seems unremarkable to everyone. I've come across requests before on modding these generally unremarkable pedals, and the only mods I've seen so far have been fairly unremarkable (putting a pot on the side JHS style to control input (there's isn't all that much gain to begin with!)) I've had this pedal for about a year, and I've been largely unimpressed with it. In particular it can't handle following a buffer, and I just couldn't justify adding any impedance to the signal chain. I had been kicking around the idea of modding it, but my assumption was that it would be tiny, surface printed components... I was totally wrong!

The pedal:



This is from the nano series, there are definitely different versions (I've seen red and green), but no idea how much it varies on the board. Many posts claim that it is positive ground...my pedal is most certainly not! No idea if there is any truth about others.

The circuit:




This isn't an exact match, I assume it's the original, but it's close (the only obvious difference I know of is the larger emitter resister on q2). The story goes that this is an early EHX release, sometime after the Foxey Lady and the LPB-1, but before the Big Muff. This is supposed to be a proto-Big Muff, but the topology is more similar to a fuzz face (adding clipping diodes, but of course not to the feedback loop, a la the Big Muff).

As I mentioned before, I was surprised to open it up and find that the components were standard through-hole, easy to solder and remove, and that there was ample room to add components. You can easily add switches, and probably even a potentiometer if so inclined.







So my first thought was to add a capacitor from emitter to ground on Q2 to increase gain. This definitely works, in retrospect a little too well. It's probably worth throwing in a resistor to keep down noise and gain. I like working the volume knob on the guitar, so my plan was to just control the gain that way. I've included sound clips before and after adding the 22uF capacitor to ground.

My next step was to add mods that I personally like on gain circuits... I added a 220pF capacitor from the base to collector on Q1 to darken the tone, and then a 3.3n capacitor from the outbound signal to ground to darken the overall tone. I realize a lot of people will find these mods ridiculous, but the point is the sky is really the limit with this pedal, it's very mod-able.



I'm going to post sound clips of before, after adding the gain capacitor, and finally with the tone mods. It added a significant amount of noise, which I think is all just the huge gain boost, although I suppose it's possible I'm not using a very high quality capacitor, although I haven't really had problems with them before. I'm using a clean solid state Fender amp to really emphasize the difference. If anything is misleading about the sound clips, it's that I feel that the 'before' clip sounds much better than it really did...it sounds pretty crunchy in the clip, but to my ears it's just sort of muddy and blah. I may go back and add a resistor on the emitter capacitor to kill some noise and control it a bit, but I really like it, so we will see!

[idy]

also maybe change character by changing clippers. LEDs or MOSFETS or....

[jgenet99]

Here's a quick video I threw together with soundclips...

[jgenet99]

I thought about removing a diode or adding one more in series to make it asymmetrical. I'm not a huge fan of diode clipping and thought about removing them altogether and just letting the transistors overdrive, but I'm pretty happy with where it ended up...for now.

[Mark Hammer]

The Muff Fuzz/Overdrive is manifestly a Fuzz Face, with a fixed/nonvariable gain setting, and a pair of diodes to yield some clipping.  When the gain of the circuit is increased, the diodes become rather redundant.  You'll get serious distortion without them.  What they DO add, however, is a clamp/lid on the output.

I modded mine to have variable gain, and inserted an SWTC tone control just ahead of the volume knob.  Plenty of sizzle.  Plenty of output.

[j_flanders]

Honestly, it actually does sound that good.
Whenever I mod a pedal or amp I so want to believe I improved it.
But 9 out of 10 times eventually I have to admit the original designer already tweaked it for the best tone and reluctantly I revert it to stock.

To me this is a Fuzz Face variant. And as such it's also the way I use it.
Unlike a lot of other pedals, this circuit was (imo) never intended to be used with guitar volume on 10, vol/gain on the pedal on 10 and into a clean amp.
It's all about the interaction between guitar, pedal and amp, and finding the right settings on all three to hit a sweet spot:
-pedal needs to be first in line, having the low input impedance loading down your pickups
-single coils
-guitar volume around 7 or 8 (on my guitar)
-pedal volume around 3 o' clock (boosting the amp)
-amp on the verge of breakup. (can sound harsh into a clean amp)

Turn guitar to 6 or 7 for sparkly cleans. (the cleanup of this pedal is incredible)
Turn guitar to 8 or 9 for overdriven tones (the pedal being a kind of dirty boost into a slightly dirty amp)
Turn guitar to 10 for full out fuzz.

90% of the time I'm using it with guitar around 7 or 8 but that's me mostly strumming chords. But those single notes in the first part of your video sounded great when maxed out.

What I would really like to see is a mod to make this pedal sound like a cranked Marshall instead of a cranked 50's little tweedish Fender amp and still keep the incredible cleanup with the guitar volume.

Or how about this for a mod: duplicate the circuit and run them in series, cascaded...

I think Mark has done some mods to this pedal (or was it Gus?). Edit: Mark it was.

Anyway, thanks for posting, mod on and enjoy.

[Mark Hammer]

It's been a decade, so I had forgotten what I did.  The gist is to parallel a variable resistance and electrolytic cap to ground from the emitter.  The circuit misbehaves when that resistance is TOO low, so I inserted 220R to be the absolute minimum resistance.

[PRR]

> I just couldn't justify adding any impedance to the signal chain

This circuit "needs" impedance in front.

The original "cheaped out" by relying on the the guitar's impedance.

There is no shame in putting a $0.20 resistor or $2 coil in front. There's no "loss of signal" because the fuzz has gobs of gain, and the rest of your chain probably has more gain on tap.

[jgenet99]

I added a 150 ohm resistor between the electrolytic and the emitter, and it did the trick! the noise has appreciably diminished, and the gain is still very intense but really smooth. It actually has the long, smooth sustain that people associate with the big muff, but still retains some of the fierceness and rawness of a fuzz face.

The original pedal has some shortcomings in my opinion. I do think the rolled back clean tone sounds great, but the pedal doesn't modulate at all, it's just immediately clean, and I've noticed it makes scratchy noises when you adjust the volume. If I liked the tone of the pedal, I would probably put a larger electrolytic on it, and something like a 2k resistor... just a little more gain, so that you get the clean tone on about 5 or 6, and different levels on up. Right now I think it sounds like the original level of gain when my guitar is on 6 or so, just a little brighter from the volume being down, which I much prefer.

When I say that I don't want to add any more capacitance, what I mean is that I want a buffer as early in my chain as I can...I do like the tone of a fuzz face, but I like the option of having the sparkle. If a pedal isn't giving me that much of a benefit, I don't want to extend the signal chain before the buffer with it. I know that true bypass isn't suppose to affect the signal, but I notice a difference over just a few pedals. But this one is definitely going in the signal chain for me!