Big Muff Mods

[Chistopher]

I could have sworn I already posted this, but I can't find it any where.

I modified my NYC Big Muff recently and just wanted to report back on my findings. Firstly the NYC Muff is a pain to mod. I kinda cheated a little bit by just bending the legs of the pots back to access the top of the circuit board, but I wouldn't recommend it. Also the PCB is very delicate, so there's a very low limit on how many times you can swap out the same part. I tried several mods, but there were only a few that made a meaningful difference.

Before I get too far into things, I should mention that even a modern NYC BMP has the classic EHX behavior of not really sticking to a schematic. There were several components on mine that didn't line up with the schematics I found online.

First mod - Tone stack
BMP's have a seasaw filter for the tone control, meaning that this area will almost always be the most important mod on a pedal that uses one. It's also the source of the dreaded muff mid scoop. Stock mine had 22k resistors on both sides of the tone control, I doubled them to 39k, which made the mid scoop an octave lower and quite a bit shallower. I really like it. If you are new to this type of mod, you will want to socket both caps and both resistors on the tone control.

Second mod - Emitter Resistors
The BMP is essentially 4 cascaded transistor gain stages. A clean boost, followed by two overdrive stages, followed by the tone control, followed by one more clean boost to make up for the volume loss at the tone control. Each gain stage has an emitter resistor that is essentially a gain control for each gain stage. Lowering the value increases gain (among a few other things) and raising it lowers the gain. Stock the value was 120R for both of the overdrive stages, I increased them to 390R. This reduced the fizziness of fuzz, made it more dynamic, and also, for lack of a better word, made it sound "woodier".
For the second and third gain stages it is also worth it to experiment with the two capacitors in the feedback loop near the diodes. These effect what frequencies get boosted and distorted. I didn't touch them because I didn't feel the need to.

Other Mods
Supa mod - The Mark IV Tonebender (also known as a Supafuzz) has two significant modifications from a BMP. The first overdrive stage doesn't have any clipping diodes. Imagine if you had two overdrive pedals at moderate level and gain in series with eachother. That's how a stock Big Muff works. Now, lower the gain on the first one and jack the level way up. That's how a Supafuzz works. It gives you a harsher, edgier sound. I didn't care for it that much. The second difference is that a SupaFuzz doesn't have a makeup gain stage. This makes the circuit quieter, but Supafuzzes don't cut as much volume at the tone control as a Big Muff, so it's not as bad an idea as you'd think.
Coupling caps - Every stage in a BMP is separated by what is referred to as a coupling cap. Their main purpose is to stop DC from sneaking into your signal path, but they also can be used to cut bass out of your signal. If you want to modify a distortion pedal to work with bass, increasing the value of the coupling caps is almost always the first recommendation. My BMP came with HUGE coupling caps from the factory, so I didn't make any changes. In fact, most of the caps on my Big Muff (and most NYC's) are way bigger than other iterations of the circuit

 

[Masta' C]

It's really cool that you're into this. I admire people that can tear into circuits, dissect them, tinker, and come up with something unique and functional at the end.

 

[80's_Metal]

It's really cool that you're into this. I admire people that can tear into circuits, dissect them, tinker, and come up with something unique and functional at the end.

Same. I can barely butter toast without messing it up.

 

[wildschwein]

I have always lamented the loss of my Russian Green Big Muff whch I purchased around 1994 and played for a few years. The guitarist-singer from a band called the Drones borrowed it (years before the Drones exsisted) and I didn't see that one again. It really worked in a band context for me. The NYC Big Muff big box reissue I picked up a few years ago has never sounded great to my ears, although adding a tone bypass switch (GMR Spares) made it sound a lot better with some amps. I do like it stacked with a Tubescreamer -- that's a great lead sound but I think by itself it's too boomy or too sizzly -- no matter where I set the tone knob. The scoop is kind of cartoonish in terms of what it is doing.

I recently went about comparing the component differences on the KitRae site between the two: https://www.kitrae.net/music/music_big_muff.html

After some planning, I jumped in and changed everything that I could do (within reason) to give my NYC a voice closer to the Green Russian Muff I remember so well. It worked out for me and I am finding many more useable sounds. The tone knob is not as drastic and the fuzz texture is thicker. There's more mids to play around with. The pedal works better with different amps too.

I have highlighted the components I changed in the pics attached. The NYC and Russian schemes (adapted from Kit Rae) are both marked up to highlight the parts. I used a solder sucker and an iron set to 350C to get the old componenets off cleanly and clear the holes. I broke the DC power jack connections and one of the battery connections to the jack in the process but those were easy fixes.

The NYCs vary a little bit from unit to unit depending on the year. My NYC had a 500k audio taper volume pot which I replaced with a 100k audio taper pot I had availabe in my spares (linear is more accurate but no problems so far). The caps in the NYC were electrolytics. I used metalized polyester film as replacements. I left the diodes alone as my NYC has IN4148s in it which Kit Rae states are an "approximate modern equivalent" for the Russian items. I didn't bother with C10, C11 and C12 as the value in the NYC are close enough to match what they did in the Russian.

Sources:
https://www.kitrae.net/music/big_muff_guts.html
https://www.bigmuffpage.com/Big_Muff_Pi ... part3.html
https://www.bigmuffpage.com/Big_Muff_Pi ... part4.html
https://kitrae.net/music/How_to_disasse ... _Muff.html
https://www.coda-effects.com/2015/11/bi ... s.html?m=0
https://www.diystompboxes.com/smfforum/ ... ic=88048.0
https://crazychickenguitarpedals.com/gu ... ower-jack/
https://en.wikipedia.org/wiki/The_Drone ... lian_band)

 

[Chistopher]

I just played my first Russian (inspired) BMP the other day. Completely different animal from any of the other ones.

If you hadn't already put everything back together, I'd say it might be worth the time and effort to measure all the important parts that you aren't swapping out, as I did that with mine and found some parts were seriously different from your schematic. My R10 and R21 were both 120R for example. My C3 was a whopping 10uF

But it's a Big Muff, if you like the way it sounds, there's no reason to go back and tweak component values to make it more "historically accurate" at the risk of making it sound worse. Few BMP's line up perfectly with known schematics, so it's likely that you can 1:1 duplicate your original Russian anyway.

Good project it sounds like, glad you learned something and like how it turned out. Those are the only two things you can ask for with circuits.

 

[wildschwein]

I just played my first Russian (inspired) BMP the other day. Completely different animal from any of the other ones.

If you hadn't already put everything back together, I'd say it might be worth the time and effort to measure all the important parts that you aren't swapping out, as I did that with mine and found some parts were seriously different from your schematic. My R10 and R21 were both 120R for example. My C3 was a whopping 10uF

But it's a Big Muff, if you like the way it sounds, there's no reason to go back and tweak component values to make it more "historically accurate" at the risk of making it sound worse. Few BMP's line up perfectly with known schematics, so it's likely that you can 1:1 duplicate your original Russian anyway.

Good project it sounds like, glad you learned something and like how it turned out. Those are the only two things you can ask for with circuits.

Thanks. Yes I did find some differences here and there from the layouts I was checking with. Generally though it was all in the ballpark but I didn't measure everything. It's close enough for me now though.
On this Kit Rae page he breaks down what effect each section has and what things change the sound the most:

BIG MUFF TRANSISTORS AND OTHER COMPONENTS

In terms of general topology the NYC reissue and the Green Russians are actually already pretty close.

From a players perspective the old Green one had a looseness and funkiness that probably can't be fully replicated but this is also based on my memory of playing it 30 odd years ago -- I do have something now that I like better than the stock NYC reissue which I really didn't like much. I am more a fan of the Double Muff circuit actually. That is a cool pedal with the right amp.