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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 (https://www.kitrae.net/music/big_muff_guts.html) 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.. :icon_wink:

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.

(https://i.postimg.cc/fkmTZRwF/open-can-of-worms-AC6-J6-A-946593216.jpg) (https://postimg.cc/fkmTZRwF)

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.. :icon_wink:

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.. :icon_wink:

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.. :icon_wink:

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.. :icon_wink:

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..) :icon_wink:

P.S. (to my dear fellow Andy)  :icon_lol:
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. :icon_lol: 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?

Seriously, you will have your hands full with simply using a 3-position SPDT on-off-on toggle to change the cap value in each of the bass and treble sections of the tonestack.  Dickering around with all the other options will waste your time and energy, compared to a quick and easy change to the functioning of the tonestack.  It will be like installing a 7-band EQ into the pedal.

So I suppose with a 3 way switch it would be putting a cap in parallel with the tonestack caps that are already there? So in the up position it would for example double the value of the treble cap, and in the down position it would double the value of the bass cap?

Quote from: Mark Hammer on January 21, 2025, 08:54:51 AMSeriously, you will have your hands full with simply using a 3-position SPDT on-off-on toggle to change the cap value in each of the bass and treble sections of the tonestack.  Dickering around with all the other options will waste your time and energy, compared to a quick and easy change to the functioning of the tonestack.  It will be like installing a 7-band EQ into the pedal.

Mark, you are right, of course, about the efficiency and veratility of modding the tone control. But after years on this and other forums, I am not entirely convinced that efficient allocation of time is of the utmost concern to people modding Big Muffs. ;)

Cheers,
Andy

P.s.: That may sound a bit mean spirited but it is not meant like that. What I mean is, its fun to fiddle with all the little bits of a complex circuit and can be quite educational. But yeah, just getting the tone control right to your liking is super effective. I first got into building pedals because I could not find a good sounding fuzz for bass. The black russian Muff was one of many pedals I tried and if that hadn't had the mid scoop, I would have just bought that, been happy and never would have learned how any of this actually works or how to build it. So, in hindsight I'm kind of glad that I didn't like the stock tone controls.

One of the big bugaboos of modding pedals/circuits is that it becomes difficult to compare modded-vs-unmodded.  That, in turn, makes it tricky to know if the time and energy invested added value.

We know how the tonestack works, and a toggle that easily adds or subtracts capacitance makes instant comparison straightforward, and more importantly, possible.  Futzing around with diodes will necessarily require adjustment of the Sustain and Volume controls to be able to hear changes to the sonic qualities, without being thrown off by volume changes resulting from differences in forward voltage.

If it's merely an academic experiment, then have at it.  If it's something one wants to actually USE, that is a horse of a different colour.  And, as ever, I remind you of what Mike Matthews said: that during the '70s and into the '80s, one could take any 4 consecutively-made Big Muffs off the assembly line, and they would all sound different from each other.  There are things worth chasing, and things not worth chasing.

True. And I suspect that the "getting lost in the weeds" that happens when many things can be changed in a circuit with or without much effect and no clear idea of what is or isn't ultimately responsible for the different sound compared to the original is one of the things that make the Big Muff so alluring and mysterious.

But more practically: Mark, you advocate switching the caps. Why the caps and not the resistors? Whenever I have to switch frequencies of an RC filter, I usually switch the resistor, not the cap. Resistors are smaller and cheaper and more importantly can be switched without popping. Yes, you can avoid the pop of cap switching with an additional resustor and caps aren't exactly prohibitively expansive, but still. The downside of switching resistors is obviously the interaction with the surrounding impedances, which, depending on the situation, may audibly change the volume and "precieved tone setting". Is that your reason for preferring to switch caps? In a Muff this is certainly a relevant concern although it has never bothered me personally in a BMP tone control.

Yes, my reasoning is that level won't be affected quite as much by playing with cap values.  Popping will be a risk, but I reason it is unlikely a person would switch caps mid-song on stage.

Symmetrical clipping favours odd harmonics whereas asymmetrical clipping tends to favour even harmonics.  The odd harmonic sound tends to make everything sound like a clarinet at the extremes whereas even harmonics tend to be more pleasant.  Of course, this is very dependent on the input signal, which may be bunched up with large peaks for a small duration and larger low-level areas.  In general, I would recommend asymmetrical clipping since it makes a more obvious and "musical" change to the sound, but that's just me.

I concurr with Ron about the characteristics of (a)symmetrical clipping. However, in the Big Muff you have the diodes AC coupled, which makes all clipping after the first few cycles symmetrical, no matter what diode combination you use. Unless the diodes and the cap are super leaky. Caveat: symmetrical with respect to the area under the positive and negative halfwaves. If you manage to get the shapes of the two halfwaves to have different shapes, there will be an asymmetrical component. However, getting this to the point where it makes an audible difference is rarely worth the hassle.

You can easily make the Opamp Big Muff to clip asymmetrically because here the diodes are DC coupled.

The degree of symmetry is highly dependent on the signal amplitude.  Remember that the diodes have a fixed forward voltage.  So their action will be contingent on signal level, relative to forward voltage.  So, for example, a 2+1 "asymmetrical" diode arrangement could produce some clipping for one half cycle and none for the other, more clipping for one half-cycle than the other, or full "square-itude" for both with one half cycle being twice the amplitude of the other; all of which is contingent on signal amplitude.  As such, the timbral impact of asymmetry is rather elusive.  The amplitude impact, on the other hand, is not.  The output of a fixed gain stage, with the identical input signal will be louder/hotter with 2+1 diodes than with 1+1, but then it will also be hotter with 2+2.

This is why I wave the flag for changes to the tonestack.  You get the changes in timbre/tone you aim for, regardless of symmetry of gain settings.  We want sonic surprises, to be sure, but we also desire certainty in settings and replicable sounds...maybe even more than surprises.  We'll let the note choices be the surprise.

Mark, I think Andy dealed with very assymetrical Collector bias.. :icon_wink:
(e.g. higher than 8.4V for 600mV diodes forward voltage drop..)

edit: Sorry, I was thinking you replied to Andy's proposal for assymetrical clipping.. :icon_redface:

Quote from: antonis on January 22, 2025, 04:36:51 PMMark, I think Andy dealed with very assymetrical Collector bias.. :icon_wink:
(e.g. higher than 8.4V for 600mV diodes forward voltage drop..)

edit: Sorry, I was thinking you replied to Andy's proposal for assymetrical clipping.. :icon_redface:

No, I was considering the "default case", meaning I assumed that only the diodes clip while the transistor delivers a perfect sine signal. But it is true, if you drive the transistor into asymmetrical clipping, you can introduce asymmetry even with the clipping arrangement of the Big Muff.

If you are looking for really strongly asymmetrical clipping as a mod to a Big Muff, you can also bridge the diode coupling cap. This turns that stage into a bazz fuzz (of sorts). It may work better to switch out the whole clipping diode arrangement, including capacitor for a single LED, if you are doing it to botth stages. Then of course, it gets more symmetrical again (although not really symmetrical) because the stages are inverting.

This is a lot of great information.

I think I'm going to put a hold on my Big Muff modding journey for now and when the BMP circuit tickles my fancy again I'll just breadboard it.

The changes I've made so far:

-Converted tonestack to what coincidentally ended up being the Hizumitas tonestack (39k both, 3n3 and 10nF)

-Replaced the 1uF coupling caps with 0.47uF. Still a very bassy muff for sure, but I'm not looking to overlap my other BMPs, so that's fine.

-Replaced 100R q2 and q3 emitter resistors with 1k trim pots. Have them set to roughly 250R each right now

I'd love to try out more with this circuit, but I like the sound of it now and the circuit board is kinda fragile on the NYC. I've changed 8 components and two of them are basically point-to-point because the pads got messed up. When I breadboard it I'm going to try more crazy things.

Also, not strictly related, but does anyone know why they changed from 100ish to 390R for the emitter resistors for the Russian Muffs? It seems like they made this change for reasons other than parts availability. Probably lost to history

Keep in mind that the gain of a transistor is not inherent to it, but is set by the components around it.  Yes, the hfe plays a role, but so does the biasing.  One can only assume that, in tandem with the diodes and other feedback components, someone thought the gain-setting of the particular transistors they used for that issue sounded "best" with that emitter resistance.

Quote from: Christoper on January 23, 2025, 09:49:03 AM-Replaced 100R q2 and q3 emitter resistors with 1k trim pots.

Q2 & Q3 stages (as well as Q4 input stage) bias and gain should be considered a bit complicated.. :icon_wink:
Emitter resistor sets Collector current which sets Collector voltage (for a given Collector resistor value) which sets Base voltage (via C-B/B-GND resistors divider) which sets Emitter voltage which sets Collector current (da capo) :icon_biggrin: ..
(a nice feedback closed-loop)

Also, Emitter resistor sets open-loop gain which is involved in closed-loop gain, improves linearity (added on intrinsic Emitter resistor), contributes to input impedance (h_FE X R_E) and, last but not least, contributes to bias stability, via negative feedback action (h_FE or V_BE variations)..
Of course, the above actions are contradictory (e.g. open-loop gain and input impedance) so there isn't a trim-pot "unique" hot spot..

P.S.
I'd suggest to breadboard a single clipping stage and tweak only one item at a time.. :icon_wink:
(although it should be more convenient and easy to understand circuit's operation and not change items randomly..)

+1 to what Antonis said. Transistor bias is a bit of a mess. The problem is that all the things that increase bias stability simultaneously decrease gain. So if you want to build a high-gain pedal with a finite number of stages, there will be compromises (some better than others). The emitter resistor is probably the easiest way to tweak the tradeoff between bias stability against hfe variations and gain. Generally, the higher hfe of the transistor, the lower the "allowed" emitter resistor value can be before things get unpredictable. For stages like the ones in the Big Muff, where the transistor properties (gain, bandwidt...) do not really directly impact the sound very much, I think it is best to always use the highest gain low noise transistors you can easily get. Usually 2N5088 or BC550C or SC1815BL are good candidates, depending on which third of the planet you live in. There are better option but they are usually much more expensive and harder to get.

Funny that Antonis should mention it, but I do have a single Muff stage on the breadboard at the moment because of this here thread. These things are a lot of fun. Lots of good overdrive and low gain fuzzy tones, depending on tuning. Makes a wicket awesome bass fuzz, too. However, one stage alone does not give very much indication of how it will sou d in a "full Big Muff" context. There is a lot of interaction going on between stages an tons more gain. But it is a very good starting point for figuring out what does what before tackling the big cahuna.

Quote from: antonis on January 24, 2025, 05:55:21 AM

Quote from: Christoper on January 23, 2025, 09:49:03 AM-Replaced 100R q2 and q3 emitter resistors with 1k trim pots.

Q2 & Q3 stages (as well as Q4 input stage) bias and gain should be considered a bit complicated.. :icon_wink:
Emitter resistor sets Collector current which sets Collector voltage (for a given Collector resistor value) which sets Base voltage (via C-B/B-GND resistors divider) which sets Emitter voltage which sets Collector current (da capo) :icon_biggrin: ..
(a nice feedback closed-loop)

Also, Emitter resistor sets open-loop gain which is involved in closed-loop gain, improves linearity (added on intrinsic Emitter resistor), contributes to input impedance (h_FE X R_E) and, last but not least, contributes to bias stability, via negative feedback action (h_FE or V_BE variations)..
Of course, the above actions are contradictory (e.g. open-loop gain and input impedance) so there isn't a trim-pot "unique" hot spot..

P.S.
I'd suggest to breadboard a single clipping stage and tweak only one item at a time.. :icon_wink:
(although it should be more convenient and easy to understand circuit's operation and not change items randomly..)

I'm picking up what you're putting down. I guess I just assumed it wasn't going to be as interactive as it was when I tweaked it because it wasn't touching too much on the schematic.

I appreciate how the two schools of thought for modding/building BMPs are "highly thought out circuit theory" and "guess and check" and it can be hard to tell which is which.

Theory is good.. Practice is better.. Both together are best.. :icon_wink:

e.g. Changing a cap in tonestack could result into desirable outcome..
So for another tonestack of the same configuration (but of different items values) you will know "which" cap you have to change but not cap's proper value..

Quote from: Christoper on January 24, 2025, 10:23:52 PMI appreciate how the two schools of thought for modding/building BMPs are "highly thought out circuit theory" and "guess and check" and it can be hard to tell which is which.

That is true for the Big Muff but is also more generally characteristic of design processes of complex interactive systems. When, as is the case for the Big Muff, the values of several components all influence the same design goal (e.g. gain, frequency response, input impedance...) and at the same time each or some of these component values influence several design goals at once, there is usually more than one "unique solution". That is, there is more than one total set of values that will give you the desired set of design goals (assuming you chose design goals that are attainable in the first place). In these cases, you often have to just kind of guesstimate part of the circuit and then apply rigorous theory to fill in the gaps. You may then find that you have to modify some of your initial guesses. And when you hit a point where one theoretical solution is no better or worse than another, you have to feel your way forward again.

Of course all this only brings you nearer your imagined goal, what you thought would sound good before you ever heard it. So in the end, even with all the theory done right, you still have to listen to it and tune the circuit by ear under real-world conditions.

Therefore, many people skip any theoretical considerations and just take a design, in this case a Big Muff version, that they like fairly well and start fiddling with a few of the usual suspects until they like what they hear.

I would argue that neither of these ways is superior to the other. Different people prefer different approaches. For a transistor based circuits, the theoretical approach is generally more challenging than for opamp circuits, which are more predictable and suffer less from parts tolerances. As a general tendency, I would say that most people on this forum here lean more towards theoretical rigor. The "@#$% around and find out" crowd congregates more on the subreddit r/diypedals, it seems.

"Circuit bending" (i.e., messing around with a circuit to see "what if I...") is a noble tradition.  One certainly doesn't wish to waste time on things that are likely to be unproductive, but sometimes you do get lucky.

As Daft Punk once said "We're up all night, trying to get lucky".

Out of curiosity, the diode arrangement in the BMP looks, sort of, like the diodes in the Tuber Screamer but, people always talk about it is hard rather than soft clipping. Why is this?

It's unfair for a single BJT CE amp to be compared with an op-amp.. :icon_wink: 

Quote from: soggybag on January 25, 2025, 11:36:54 PMOut of curiosity, the diode arrangement in the BMP looks, sort of, like the diodes in the Tuber Screamer but, people always talk about it is hard rather than soft clipping. Why is this?

Online forums tend to propagate improper use of terms such as these. If you have two silicon diodes with a threshold voltage of 0.7v in a hard clipping arrangement, any signal above 0.7v in either direction gets clipped to exactly 0.7v with soft clipping, 0.7v is just the threshold at which clipping starts. Any signal above 0.7v gets drastically reduced. The maximum output on a hard clipping 0.7v section will never reach beyond 2 * 0.7 =1.4v, but with soft clipping it can.

Someone else can probably explain this better than me. I'm good at learning and knowing things, not 100% at explaining.

So here's a whacky thing I forgot to mention for anyone interested, the clipping caps on the NYC are HUGE. 1uF and 2u2. Despite what you'd think, I find these values work quite nicely with bass.

I think I will install a blend control for versatility though.

Quote from: soggybag on January 25, 2025, 11:36:54 PMthe diode arrangement in the BMP looks, sort of, like the diodes in the Tuber Screamer but, people always talk about it is hard rather than soft clipping.

It's not all about the diodes. What is the source impedance? A weak (hi-Z) source will clip more than a fat source.

Quote from: Christoper on January 26, 2025, 02:29:02 PMSo here's a whacky thing I forgot to mention for anyone interested, the clipping caps on the NYC are HUGE. 1uF and 2u2. Despite what you'd think, I find these values work quite nicely with bass.

I think I will install a blend control for versatility though.

Large clipping caps are fine for bass. They just clip the low notes more, which can sound a bit mushy on bass. And it makes the lows less dynamic. Neither of which is necessarily a bad thing, just different. The smaller caps make the sound more bassy by clipping the bass less, which is what appeals to many bass players. But you can make up for this difference with the tone control.

http://www.kitrae.net/music/Big_Muff_Mods_and_Tweaks_Page.html (http://www.kitrae.net/music/Big_Muff_Mods_and_Tweaks_Page.html)

https://www.coda-effects.com/2015/11/big-muff-mods-and-tweaks.html?m=0 (https://www.coda-effects.com/2015/11/big-muff-mods-and-tweaks.html?m=0)

https://www.premierguitar.com/gear/electro-harmonix-russian-big-muff-pi-pedal-mods (https://www.premierguitar.com/gear/electro-harmonix-russian-big-muff-pi-pedal-mods)