big muff tone stack mods

[Frances Rhodes]

hi everyone

i've been willing to build a univox superfuzz (the one with an internal trimmer to tune the octave effect) but i was thinking of adding a propper tone pot, a bit like the big muff tone stack.
i fooled around with the duncan tone stack calculator to find values that would give me the 1000Hz scoop like in the original superfuzz but now i need to find other values to also get a flat response.
so my questions are, since right now i don't need a continuous variation like in jack orman's mod, what values should i change?
should i rather change resistor values or capacitor values to get either the flat response or the mid scoop when i pull the tone switch?
should i keep the values in a certain range? or doesn't it make any difference at all?

here is a set of values i found with a 100k tone pot and a stock 50k volume pot
R1=R2=8,2k
C1=3n9
C2=100n
i can't remember if i changed the impedance of the generator, so i believe it was set to 1k

thanks in advance
best regards

frances

[Mark Hammer]

One of the simplest tone-control mods you can do on the Superfuzz is the one used by the ZVex Octane, a clone of which can be found in the Madbean Poindexter http://www.madbeanpedals.com/projects/Poindexter/docs/Poindexter.pdf

The 100nf cap to ground has a 10k pot inserted between the cap and ground (although 5k is probably useful enough).  Inserting resistance between that cap and ground "lifts" the midscoop, to provide a throatier sound.

Another a^pproach you might like, that requires adding a toggle, is illustrated in the Aefea Drive - http://www.diystompboxes.com/smfforum/index.php?topic=107216.0

This uses the same sort of midscoop filter, except that the location of the scoop can be moved around with the pot.  A lot of tonal variation possible with just a 3-position toggle and one pot.

[Frances Rhodes]

thanks, that looks interesting!
but at first i was thinking of something more like a bass-treble tone pot, probably something similar to the LAL-46 (since, with a name such as the "sooper fuzz" it must be a variation of the superfuzz circuit...) hence the BMP tone stack with the flat mids switch.
but maybe the Zvex octane mod could be done on the BMP tone stack to flatten the mid scoop, maybe that's something to breadboard!!

[EBK]

Perhaps, you would be interested in looking at the Large Beaver on this page (safe for work, I swear!): http://www.bigmuffpage.com/Big_Muff_Pi_versions_schematics_part4.html

Keep in mind it is purely passive, so "mid boost" is more of a "don't touch the mids". 

[Mark Hammer]

The challenge with the BMP tone control is finding a set of values that yields enough mids that when you set Tone to 7:00 it is thick but not too muffled, and bright but not annoyingly reedy when you set Tone to 5:00.

Certainly it makes sense to start with the stock values from whatever issue floats your boat.  But keep in mind that, as an octave-doubling fuzz, the rolloffs that work well for a non-octave-doubling fuzz like the BMP might not work quite as well for something with more strident mids.

Another avenue to consider is something like what was used in the Roland Double Beat AD-50.  The original went beyond the two tone presets that the Superfuzz used to a 3-position rotary switch.  I thought I'd spice it up a bit and worked out 6 different tonal presets, including one that added some crossover distortion.  I can't vouch for it, but the component values were worked out to provide roughly equal volumes.  https://www.guitarscanada.com/index.php?threads/roland-double-beat.53902/

Sometimes it's better to have variable control, and sometimes the replicability of presets can be comforting.  Note that there is no requirement that one be confined to 6.  As Jimi said: "Just float your little mind around".

[Frances Rhodes]

Erik, thanks for the advice!
i had been going through these 4 pages for a while when i tried to find silly ideas to mod my big muff v9 but somehow never looked at the tone sections that much.
from what i can see, there is always 2 sets (or more) of capacitors to have 2 (or more) tone curves except when the need is to have a frequency sweep (like in the amz tone control, which is what i chose for my big muff)

Mark, thanks again for all the advice and information!
i think i'll try to bread board different tone sections and see what works best to my ear.
what i don't want with this build is a pedal with too many knobs so i'm looking for a tone section with a switch to toggle between a mid scoop or a "flat" response like in the original circuit plus a 1-knob EQ, but with all that was said, i feel like i could need to move that scooped frequency around and also i may want to be able to lift it on-the-go...

i think i'll build a "stock" version of the superfuzz but without the tone stack and make a bunch of tone daughter-boards and try to mix everything up

[duck_arse]

Frances, I'm not sure if I'm understanding your original intent, but perhaps you could try connecting a 50k pot between the two resistor divider "flat" output and the 1nF//10k notch output, take the wiper to the balance pot hot. from what I can see, that would/might make the fairly close to stock notch at one end, and flat at the other end.

maybe.

[Electron Tornado]

Frances, if you're looking for flat mids in the BPM this article might be helpful:

http://guitarkitbuilder.com/big-muff-pi-mod-more-mid-range-tone/

[pinkjimiphoton]

to me, the best mod for a big muff pi is to add a physical midrange control.
take out the stock 22k resistor going to ground, and replace it with a 2-7-3.3k resistor to the input of a 50k-100k (i use 100) linear pot.
then you can scoop it even more than stock and sweep to a pretty substantial midrange boost. i built my own version of my original rams head and didn't bother with schematics for cap values so much... went with what i still heard in my head and it sustains cleanish like the original one i had back in god knows whatever year it was. i found it best with .47 caps... very creamy thick saturation that sustains even with the sustain pot maybe 9 or 10 o'clock.
also lifted the snubber cap on the last stage. kinda like using a permanent tone wicker. each stage changes the tone slightly.
also lowered the value of the series resistor with the input...
makes the muff a little bit more responsive to guitar knob changes, you can dial in a "cleanish" setting right on the edge of breakup that's fairly dynamic that way as well.
anyway, those were what i did to it (also of course added some GE diodes along with si including my "d4" mod with a paralleled 1n34a for a noise reducer... try it it works great to take the ocean of hiss out substantially....no idea why it works but it does.... and adding the midrange cut/boost really brought it to life in a good way and makes the stock tone control values work better.

i mean, you could also split the circuit into treble mid and bass controls and it would be sick.

i know ya want flat mids, but adding that one pot can let you dial it in to wherever it sounds good in pretty much any situation.

[Frances Rhodes]

Frances, I'm not sure if I'm understanding your original intent, but perhaps you could try connecting a 50k pot between the two resistor divider "flat" output and the 1nF//10k notch output, take the wiper to the balance pot hot. from what I can see, that would/might make the fairly close to stock notch at one end, and flat at the other end.

maybe.

hi

sorry if this is all confusing, i'm not a native english speaker so it's not always very easy to explain myself.
what i first had in mind was to replace the tone section in the superfuzz by a big muff style tone stack with a pot.
i tried to use the duncan tone stack calculator to find a set of values that could match the original 1kHz scoop (i found several different values, one set is mentionned above) and i thought of several "problems".
one of them was, since that filter section is a 1st order low pass and a 1st order high pass blended together with a pot, one could find a million different combinations with the same cutoff frequencies, from very low resistor (and "high" cap) values to very high resistor (and very low cap) values.
what i'm also looking for is a different set of values to get a flat mid response with a switch, exactly like in the original circuit, but still have that tone pot active, i don't want a tone bypass.
Mark proposed to add a 50k pot to smoothen the scoop but this addition does not allow me to "dial" the tone like in a BMP, a tube screamer, etc.
i read a lot of articles about he BMP tone stack, different scoop frequencies, how to mod it, etc, i even did the AMZ mod on my big muff pi with the extra mids pot, but that's not what i'm looking for here, with this build.

so i was wondering, how shall i choose my sets of values in the first place?
the BMP tone stacks usually have values from 8.2k to 33k, for instance. with the appropriate cap values, shall i keep them (resistor values) low, high, in the middle? doesn't it change anything at all?
to go from scooped to flat, would i rather toggle between 2 different sets of resistors or between 2 different sets of caps (since i'm not looking for a continuous sweep of mids like in the AMZ mod)?

i hope this makes more sense to you...
i'll try to draw something on eagle if not.

cheers

[PRR]

> how shall i choose my sets of values in the first place?

Around mid-way between the driving impedance and the load impedance.

Probably not 10 Ohms, probably not 10 Megs.

You may want to sketch-up the circuits in front and back of the tone control for study.

[cleverbeefalo]

Frances, if you're looking for flat mids in the BPM this article might be helpful:

http://guitarkitbuilder.com/big-muff-pi-mod-more-mid-range-tone/

This is the mod I used for my most recent BMP build for a friend. I don't own an original Muff, but I compared it to a couple other pedals that have scooped toggles. It definitely eliminates the scooped Muff sound and is a very simple substitution mod, so if you're looking for simplicity I'd also recommend this.