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..
(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..

Quote from: antonis on January 22, 2025, 04:36:51 PMMark, I think Andy dealed with very assymetrical Collector bias..
(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..

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..
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) ..
(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..
(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..
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) ..
(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..
(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..

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".