Good evening guys, I plan to modify a newer Big Muff that I have. I have acquired a few Muff versions (EHX Double Anniversary Muff and EQD Hizumitas) that I much prefer so I figure that the NYC is going to become a fun modding project.

The only issue is I'm not sure what direction to take it. I'm definitely going to tweak the tone stack so it doesn't disappear as much in a band setting. Other than that, I'm not 100% sure what the "rules" are for a BMP. I've read this page, but that's the only real solid material I can find on the subject.

What components are the key players in why different iterations sound different? How much of a difference do the clipping diodes make relative to other pedals?

Is it best to match the gain stages or is it fine to have one different from the other? Do they play equal parts in the sonic signature of the pedal?

What are the common NYC mods? What mods have you tried and what have you found to be a success?

Any insight I can get would be appreciated.

Interesting, I see that removing the diodes in the first gain stage turn the pedal into something not unlike a Supa Tonebender. I'm assuming this makes the BMP clean up better?

Try to tweak Q2 & Q3 Base 10k series resistors..

You can even try to replace them with a dual gang pot and delete Sustain pot..

P.S.
Sustain pot controls the amount of signal going to 1^st clipping stage where series resistors control the gain of each clipping stage so technically they have different results.. 

Quote from: Christoper on January 13, 2025, 10:48:30 PMInteresting, I see that removing the diodes in the first gain stage turn the pedal into something not unlike a Supa Tonebender. I'm assuming this makes the BMP clean up better?

Not really.  Remember the gain in each stage is fixed, and the "Sustain" control simply attenuates what goes from the input stage to the 2nd stage.  In the absence of the diodes and feedback cap in the Q2 stage, the signal level is unconstrained, even though the gain is not changed.  In my own builds, I find that "declipping" that stage, such that it pushes the next stage harder, yields a slightly more "ragged" and harsh tone.  Not unuseful, but not as immediately pleasing as the dual clipping stage arrangement.

Scanning through the many different issues, one notes the following:

1) Some have identical gains in the Q2 and Q3 stages, while some have unequal gains, with the collector resistance higher for Q3 than Q2.

2) The feedback cap values for Q2 and Q3 vary somewhat, although given their small value (generally between 470pf and 560pf) and the wide tolerances of little ceramic discs like that, I see no point in playing with them.

3) In contrast, the caps in series with each diode pair do vary widely in value; anywhere between 47nf and 1uf.  With only a few exceptions, in most instances the same value is used for both clipping stages.

4) The location and width of the "scoop" in the tonestack does change from issue to issue.  Sometimes the treble filter rolls off a little higher or lower, and sometimes the bass filter rolls off a little higher or lower.  It is a little hard to peg down when the tone control is close to the middle, but one notices any changes to the stack most when the tone knob is closer to 7:00 or 5:00.  I use a 3-way DPDT toggle to nudge the treble rolloff down, the bass rolloff up, or leave it stock.  For my money changes to the tonestack yield the most predictable sonic variation.

Did you know that the Big Muff has been voted "Most Worms" by readers of Guitar Pedals Monthly Magazine for 23 years in a row?

I'll try to answer more usefully late. No time now to even remotely do the topic justice.

So, here we go. There are literally twice as many ways to mod a Big Muff than there are gerbils in the known universe and many of them are moderately pointless, so I will stick to the few mods that I personally like best. YMMV, as the oldtimers say. I will use the component naming scheme that Kit Rae uses on The Big Muff Page.

1. As Mark has mentioned and you seem to be aware already anyway, putting some mids back in the tone stack gives the biggest bang for the buck. Replacing R5 with a variable resistance pot plus smaller resistor is the easiest way to get a variable mid control. Jack calls it "presence":
http://www.muzique.com/lab/tone3.htm

2. C6 and C7 control, which frequencies are being clipped. Lower values for these let more unclipped bass through. Great for heavy bottom. Try 100n, 47n and 22n.

3. C5 and C13 cut bass going into the clipping stages. Reduce for tighter, more distortio-like sound, increase for woolier fuzz. Try 10n, 100n, and 1u for a start.

4. R10 and R21 influence the gain of the clipping stages. The NYC reissue is on the high gain side, so you can increase these to 220 or 330 or 470 for a more controlled sound with less noise. Or use the "magic" Green Russian value of 390 for extra mojo points.

5. Clipping diodes: I would try 2x Si, 2x red LED, and no diodes. Experiment with all nine possible combinations of these three for the two stages and see what you like. Common favorites are LEDs or nothing in the first and Si in the second clipping stage (rougher, more dynamic sound) or Si in the first and LEDs in the second for a substantial volume boost (unnecessary in my oppinion but people seem to like it).

HTH,
Andy

Edit: I forgot to mention: Don't bother swapping the transistors. There is no real sound effect to be had by doing that that could not more easily anf more predictably be had by changing a few resistors. The only legitimate reason to swap transistors, in my oppinion, would be to reduce noise but the NYC has 2N5088s, if I remember correctly, which are about as quiet as possible for this circuit.

Quote from: antonis on January 14, 2025, 05:22:00 AMTry to tweak Q2 & Q3 Base 10k series resistors..

You can even try to replace them with a dual gang pot and delete Sustain pot..

P.S.
Sustain pot controls the amount of signal going to 1^st clipping stage where series resistors control the gain of each clipping stage so technically they have different results..

This is very intriguing. Can you elaborate? Would these be R18 and R11?

Seems like we might need a series resistance? If the gain is Rc / Re what happens when Rc is less than Re? Does this affect the bias?

Quote from: soggybag on January 15, 2025, 01:44:57 PM

Quote from: antonis on January 14, 2025, 05:22:00 AMTry to tweak Q2 & Q3 Base 10k series resistors..

You can even try to replace them with a dual gang pot and delete Sustain pot..

P.S.
Sustain pot controls the amount of signal going to 1^st clipping stage where series resistors control the gain of each clipping stage so technically they have different results..

This is very intriguing. Can you elaborate? Would these be R18 and R11?

Seems like we might need a series resistance? If the gain is Rc / Re what happens when Rc is less than Re? Does this affect the bias?

R19 and R12. These eat up input voltage by forming a voltage divider with the input resistances of the transistors, thus decreasing overall gain of the circuit. By making these two variable, you can use them as a gain control.

Andy

Quote from: Fancy Lime on January 15, 2025, 12:23:43 PMSo, here we go. There are literally twice as many ways to mod a Big Muff than there are gerbils in the known universe and many of them are moderately pointless, so I will stick to the few mods that I personally like best. YMMV, as the oldtimers say. I will use the component naming scheme that Kit Rae uses on The Big Muff Page.

1. As Mark has mentioned and you seem to be aware already anyway, putting some mids back in the tone stack gives the biggest bang for the buck. Replacing R5 with a variable resistance pot plus smaller resistor is the easiest way to get a variable mid control. Jack calls it "presence":
http://www.muzique.com/lab/tone3.htm

2. C6 and C7 control, which frequencies are being clipped. Lower values for these let more unclipped bass through. Great for heavy bottom. Try 100n, 47n and 22n.

3. C5 and C13 cut bass going into the clipping stages. Reduce for tighter, more distortio-like sound, increase for woolier fuzz. Try 10n, 100n, and 1u for a start.

4. R10 and R21 influence the gain of the clipping stages. The NYC reissue is on the high gain side, so you can increase these to 220 or 330 or 470 for a more controlled sound with less noise. Or use the "magic" Green Russian value of 390 for extra mojo points.

5. Clipping diodes: I would try 2x Si, 2x red LED, and no diodes. Experiment with all nine possible combinations of these three for the two stages and see what you like. Common favorites are LEDs or nothing in the first and Si in the second clipping stage (rougher, more dynamic sound) or Si in the first and LEDs in the second for a substantial volume boost (unnecessary in my oppinion but people seem to like it).

HTH,
Andy

Edit: I forgot to mention: Don't bother swapping the transistors. There is no real sound effect to be had by doing that that could not more easily anf more predictably be had by changing a few resistors. The only legitimate reason to swap transistors, in my oppinion, would be to reduce noise but the NYC has 2N5088s, if I remember correctly, which are about as quiet as possible for this circuit.

That's very helpful, you seem to know quite a bit about this circuit. I think I'll start off fiddling with the tone stack (Probably going to keep it scooped, but not as much) and swapping the first set of diodes for red LEDs.

I've also been doing a bit of looking into the "whicker" mod that comes from the factory on the bmp tonewhicker, where you bypass the feedback loop capacitors to make the sound raspier, especially on low gain settings. I may look into that as well

For how much you know about BMP circuits, I just know you have a favorite set of mods for it. Provided they aren't proprietary, would you care to share them?

Raising the rolloff frequency of the bass side of the tonestack will reduce the amount of midscoop.  BUt at the same time, when the tone control is set to 7:00 the result is more "vocal" sounding than dull and woolly, because more lower mids are included.  Conversely, when the rolloff of the treble side is made lower, and the tone control is set to max treble, it's not as nasal or insect-like, but a little fuller sounding.  That's why I like to use an on-off-on DPDT to change the bass cap, the treble cap, or neither.

Many of the consequences of fiddling with the diodes can be set aside, by simply playing with the gain of this or that stage.  After all, the degree to which the signal is clipped by the diodes is a function of how much that stage is amplifying the signal (i.e., the gain).

Several "classic" '60s fuzzes, like the Fuzz-Rite, Orpheum, and Shin-Ei FY-2 use an approach where there are two cascaded transistor gain stages.  The first drives the second hard.  In such cases, the "Fuzz" or distortion control basically pans between the output of the first stage and the 2nd.  I'm going to open up my BMP and see if there is any value to installing such a "pan" control.  Essentially, it would feed the tone stack, and adjust how much comes from the output of the Q2 stage OR the Q3 stage.  The Q2 and Q3 stages remain in series.  I'll fiddle with it and report back; hopefully tomorrow.

Well, preliminary report is that it works.  I wired up a 100k linear pot with one outside lug going to the collector of Q2 and the other outside lug going to the collector of Q3.  The wiper of the pot went through a cap into a small test amplifier.  As expected turning the blend pot to mostly Q2 gets a very mild overdriven sound, not that dissimilar to a Muff Fuzz, while rotating the blend pot the other way gets the standard searing tone of a BMP.  Note that this tentative testing arrangement didn't go through the tonestack or gain recovery stage (Q4).  What's interesting is that in the centre blend position, the signal level drops substantially and becomes buzzy rather than fuzzy.  I had initially thought that the two stages were inverting, hence cancelling out the low end that lay in common when mixed 50/50.  But since I'm taking the collector output, that shouldn't, in theory, be the case.

Whatever the case, what I need to do now is give it a serious thoughtful listen.  If taking the output from Q2 isn't much different than simply turning the Sustain way down and taking the signal from Q3, then this experiment only adds another pot, but no greater variety of tones.  Certainly worth doing in order to hear what Q2 does to Q3, but may not add very much utility beyond that.

I did a similar sort of experiment about 20 years ago with a little op-amp-based distortion I called the Roseyray.  A smooth-sounding "hard clip" overdrive with treble rolloff pushed a second op-amp stage with LEDs in the feedback loop and a scoop filter on its output.  Because the first stage already provided gain, not much additional gain was required in the second stage to get very intense sounds.  The "Tone" control I used panned between the two outputs, just like the Big Muff experiment I just did.  Because the first stage normally had much of the treble rolled off, rotating the Tone pot (actually panning between the two outputs) yielded very different tones along different points of rotation.  Not sure if my BMP blend control is quite as effective, but the Roseyray yielded a very wide assortment of tones, from warm grunt to searing metal.

Bottom line: when there are cascaded gain stages, it can be a useful strategy to take the output from different points along the way in the circuit.

Quote from: Christoper on January 15, 2025, 03:42:04 PM

Quote from: Fancy Lime on January 15, 2025, 12:23:43 PMSo, here we go. There are literally twice as many ways to mod a Big Muff than there are gerbils in the known universe and many of them are moderately pointless, so I will stick to the few mods that I personally like best. YMMV, as the oldtimers say. I will use the component naming scheme that Kit Rae uses on The Big Muff Page.

1. As Mark has mentioned and you seem to be aware already anyway, putting some mids back in the tone stack gives the biggest bang for the buck. Replacing R5 with a variable resistance pot plus smaller resistor is the easiest way to get a variable mid control. Jack calls it "presence":
http://www.muzique.com/lab/tone3.htm

2. C6 and C7 control, which frequencies are being clipped. Lower values for these let more unclipped bass through. Great for heavy bottom. Try 100n, 47n and 22n.

3. C5 and C13 cut bass going into the clipping stages. Reduce for tighter, more distortio-like sound, increase for woolier fuzz. Try 10n, 100n, and 1u for a start.

4. R10 and R21 influence the gain of the clipping stages. The NYC reissue is on the high gain side, so you can increase these to 220 or 330 or 470 for a more controlled sound with less noise. Or use the "magic" Green Russian value of 390 for extra mojo points.

5. Clipping diodes: I would try 2x Si, 2x red LED, and no diodes. Experiment with all nine possible combinations of these three for the two stages and see what you like. Common favorites are LEDs or nothing in the first and Si in the second clipping stage (rougher, more dynamic sound) or Si in the first and LEDs in the second for a substantial volume boost (unnecessary in my oppinion but people seem to like it).

HTH,
Andy

Edit: I forgot to mention: Don't bother swapping the transistors. There is no real sound effect to be had by doing that that could not more easily anf more predictably be had by changing a few resistors. The only legitimate reason to swap transistors, in my oppinion, would be to reduce noise but the NYC has 2N5088s, if I remember correctly, which are about as quiet as possible for this circuit.

That's very helpful, you seem to know quite a bit about this circuit. I think I'll start off fiddling with the tone stack (Probably going to keep it scooped, but not as much) and swapping the first set of diodes for red LEDs.

I've also been doing a bit of looking into the "whicker" mod that comes from the factory on the bmp tonewhicker, where you bypass the feedback loop capacitors to make the sound raspier, especially on low gain settings. I may look into that as well

For how much you know about BMP circuits, I just know you have a favorite set of mods for it. Provided they aren't proprietary, would you care to share them?

I don't do "proprietary" as a matter of principle. However, I must disappoint you, I do not have a set of mods. I have never modded or even build an actual Big Muff. I only experimented extensively with the circuit on the breadboard. The rest is just understanding how a transistor amplifier works.

I personally find the "tone wicker" mod (removing C11 and/or C12) underwhelming. It just adds nasty fizzle, most of which is too high to be reproduced by a guitar speaker but can cause noise problems. You may fare better by reducing the value of these two caps for much the same sonic effect without the problems. But don't expect a dramatic change in sound.

Another easy thing to try, which will increase the brightness and grittyness on low gain settings is to put a bright cap across the Sustain pot. It goes from threr the pot connects to C4 to where the pot connects to C5. Maybe start with 1n and adjust up (more efdect) or down (less effect). This cap increases the gain of high frequencies on low Sustain settings. Popular trick in amplifiers but for some reason, I have never seen it in a Muff. You can make it switchable for more flexibility.

Quote from: Fancy Lime on January 15, 2025, 02:20:43 PM

Quote from: soggybag on January 15, 2025, 01:44:57 PM

Quote from: antonis on January 14, 2025, 05:22:00 AMTry to tweak Q2 & Q3 Base 10k series resistors..

You can even try to replace them with a dual gang pot and delete Sustain pot..

P.S.
Sustain pot controls the amount of signal going to 1^st clipping stage where series resistors control the gain of each clipping stage so technically they have different results..

This is very intriguing. Can you elaborate? Would these be R18 and R11?

Seems like we might need a series resistance? If the gain is Rc / Re what happens when Rc is less than Re? Does this affect the bias?

R19 and R12. These eat up input voltage by forming a voltage divider with the input resistances of the transistors, thus decreasing overall gain of the circuit. By making these two variable, you can use them as a gain control.

Andy

If you allow me some corrections..

R_C/R_E is considered the Gain of open-loop configuration (A_OL)..
(no 470k feedback resistor..)
In such a case, R19 & R12 series resistors act as Andy described (signal amplitude attenuation at clipping stages Bases-inputs)

Here we deal with closed-loop gain (A_CL), which is calculated by A_CL = A_OL / (1 + β*A_OL), where β = Series resistor / Feedback resistor..

So, both Base series and Emitter resistors contribute to particular stage calculation..
(the more the high A_OL the closer to 1/β the A_CL..)

P.S. (to my dear fellow Andy) 
Technically speaking, input amplitude doesn't affect stage's gain..
(it does, of course, affect output amplitude/distortion..)

Dear Antonis!

You are of course right, as always, the input amplitude doesn't affect the stages gain. That's why I did not write that but wrote that it affects the "overall gain of the circuit" instead. And I maintain that that is correct. The overall gain of the circuit is the end result of all the positive and negative gains of all things that happen between input and output.

While we are nitpicking, the gain calculations should probably not ignore the output impedance of the preceding stage... Just kidding, this is not relevant to the OPs questions.

Quote from: Fancy Lime on January 16, 2025, 01:16:32 AM

Quote from: Christoper on January 15, 2025, 03:42:04 PM

Quote from: Fancy Lime on January 15, 2025, 12:23:43 PMSo, here we go. There are literally twice as many ways to mod a Big Muff than there are gerbils in the known universe and many of them are moderately pointless, so I will stick to the few mods that I personally like best. YMMV, as the oldtimers say. I will use the component naming scheme that Kit Rae uses on The Big Muff Page.

1. As Mark has mentioned and you seem to be aware already anyway, putting some mids back in the tone stack gives the biggest bang for the buck. Replacing R5 with a variable resistance pot plus smaller resistor is the easiest way to get a variable mid control. Jack calls it "presence":
http://www.muzique.com/lab/tone3.htm

2. C6 and C7 control, which frequencies are being clipped. Lower values for these let more unclipped bass through. Great for heavy bottom. Try 100n, 47n and 22n.

3. C5 and C13 cut bass going into the clipping stages. Reduce for tighter, more distortio-like sound, increase for woolier fuzz. Try 10n, 100n, and 1u for a start.

4. R10 and R21 influence the gain of the clipping stages. The NYC reissue is on the high gain side, so you can increase these to 220 or 330 or 470 for a more controlled sound with less noise. Or use the "magic" Green Russian value of 390 for extra mojo points.

5. Clipping diodes: I would try 2x Si, 2x red LED, and no diodes. Experiment with all nine possible combinations of these three for the two stages and see what you like. Common favorites are LEDs or nothing in the first and Si in the second clipping stage (rougher, more dynamic sound) or Si in the first and LEDs in the second for a substantial volume boost (unnecessary in my oppinion but people seem to like it).

HTH,
Andy

Edit: I forgot to mention: Don't bother swapping the transistors. There is no real sound effect to be had by doing that that could not more easily anf more predictably be had by changing a few resistors. The only legitimate reason to swap transistors, in my oppinion, would be to reduce noise but the NYC has 2N5088s, if I remember correctly, which are about as quiet as possible for this circuit.

That's very helpful, you seem to know quite a bit about this circuit. I think I'll start off fiddling with the tone stack (Probably going to keep it scooped, but not as much) and swapping the first set of diodes for red LEDs.

I've also been doing a bit of looking into the "whicker" mod that comes from the factory on the bmp tonewhicker, where you bypass the feedback loop capacitors to make the sound raspier, especially on low gain settings. I may look into that as well

For how much you know about BMP circuits, I just know you have a favorite set of mods for it. Provided they aren't proprietary, would you care to share them?

I don't do "proprietary" as a matter of principle. However, I must disappoint you, I do not have a set of mods. I have never modded or even build an actual Big Muff. I only experimented extensively with the circuit on the breadboard. The rest is just understanding how a transistor amplifier works.

I personally find the "tone wicker" mod (removing C11 and/or C12) underwhelming. It just adds nasty fizzle, most of which is too high to be reproduced by a guitar speaker but can cause noise problems. You may fare better by reducing the value of these two caps for much the same sonic effect without the problems. But don't expect a dramatic change in sound.

Another easy thing to try, which will increase the brightness and grittyness on low gain settings is to put a bright cap across the Sustain pot. It goes from threr the pot connects to C4 to where the pot connects to C5. Maybe start with 1n and adjust up (more efdect) or down (less effect). This cap increases the gain of high frequencies on low Sustain settings. Popular trick in amplifiers but for some reason, I have never seen it in a Muff. You can make it switchable for more flexibility.

Yeah, I'm a big fan of keeping knowledge free. I'll definitely try the bright cap idea, I find the low gain settings on a BMP to be entirely useless.

I think for this first round of mods I'll tweak the tone control to add a little bit of mids back in and then see how a bright cap changes things

One more thing I forgot to mention: My biggest gripe with the BMP Tone Control is that the mid notch and the crossover are at too high a frequency (around 1 kHz). The reason why I, and I assume others too, like the sound of the IC Big Muff better than other Muffs in a band context is that the notch sits a bit deeper. This retains the region around 1k better, which is where a lot of the "audibility through the general band noise" sits, while still giving a muffish mid scoop. The easy way to move the crossover and notch down, is to simultaneously increase either both caps or moth resistors of the tone control. Double the value for one octave, which is what I find most useful. Adjust to taste.


And here are some useful older threads and Jacks musings on the tone control:
https://www.diystompboxes.com/smfforum/index.php?topic=88048.0

https://www.diystompboxes.com/smfforum/index.php?topic=78111.0

http://www.muzique.com/lab/tone3.htm

HTH,
Andy

The location and width of the midscoop has often changed between issues.  After a friend brought over his Russian Muff, I found the tonestack on that appealed to me. I won't go into ALL the variations over the year, but here are two examples.

The Russian Muff sets the rolloff of the treble side at 1860hz and the rolloff of the bass side at 795hz.  So a little over an octave,resulting in not much scoop when you consider the 6db/oct rolloffs of the two filters.

The PNP Triangle muff has its treble section rolling off at 1020hz, and the bass side rolling off at 408hz.  So, not only located lower, but the scoop is also wider.

Quote from: Mark Hammer on January 20, 2025, 01:01:09 PMThe location and width of the midscoop has often changed between issues.  After a friend brought over his Russian Muff, I found the tonestack on that appealed to me. I won't go into ALL the variations over the year, but here are two examples.

The Russian Muff sets the rolloff of the treble side at 1860hz and the rolloff of the bass side at 795hz.  So a little over an octave,resulting in not much scoop when you consider the 6db/oct rolloffs of the two filters.

The PNP Triangle muff has its treble section rolling off at 1020hz, and the bass side rolling off at 408hz.  So, not only located lower, but the scoop is also wider.

True, there are many significantly  different variants. Especially the old ones are all over the place. It is also worth noting that the deepest point of the notch wanders higher if you turn the tone control to the bass side (which is either clockwise or counterclockwise, depending on the variant because why wouldn't it be) and lower as you turn it to the treble side. This is, to me, one of the best things about the BMP tone control. Makes a lot of sonic sense to my ears.

Quote from: Fancy Lime on January 20, 2025, 08:49:50 AMOne more thing I forgot to mention: My biggest gripe with the BMP Tone Control is that the mid notch and the crossover are at too high a frequency (around 1 kHz). The reason why I, and I assume others too, like the sound of the IC Big Muff better than other Muffs in a band context is that the notch sits a bit deeper. This retains the region around 1k better, which is where a lot of the "audibility through the general band noise" sits, while still giving a muffish mid scoop. The easy way to move the crossover and notch down, is to simultaneously increase either both caps or moth resistors of the tone control. Double the value for one octave, which is what I find most useful. Adjust to taste.


And here are some useful older threads and Jacks musings on the tone control:
https://www.diystompboxes.com/smfforum/index.php?topic=88048.0

https://www.diystompboxes.com/smfforum/index.php?topic=78111.0

http://www.muzique.com/lab/tone3.htm

HTH,
Andy

Good to hear, seeing as doubling both my tonestack resistors to 39k was the first step in my plan.

I plan to socket the clipping diodes sections, but that led me to think about all circuit theory question. I know assymetrical diodes doesn't make too much a difference in hard clipping circuits, but how does it affect soft clipping circuits? For a specific example I plan on using both sides of a 2N7000 MOSFET for 0.7v clipping on one side and 2.0v clipping on the other

Also what's the opinion on the Swollen Pickle's deep and narrow mid scoop at roughly 600 Hz?