LESS gain from a Big Muff Pi (Russian Modified)

[amonte]

Hi guys,

I've got a Russian Big Muff that I've modded to match the schematic of the 1970's "#3" BMP.  I like the way it sounds - nowhere near as dark or muddy as it did originally - but for my purposes, there's way too much tain on tap.  Rolling back the sustain solves the gain problem but it does seem to muddy up the sound a bit.  I've found a lot of success by runing the BMP at around halfway on the sustain knob and then rolling back my guitar knob, but that's really not going to work in a live setting when I need to switch pedals quickly.  So I've been going over the schematic and trying to come  up with some possible solutions.  The goal is to mimic the effect of the guitar volume rolled back within the circuit, or simply find a way to get a similarly unmuffled sound at lower gain settings. 

Idea #1 : Add a treble bleed cap to the sustain knob to prevent it from getting muddy at lower settings.  This isn't really the same change as what I described above but I thought it might be a good alternative to some of my other ideas.

Idea #2 : increase the 39K resistor on input, or replace it with a trim pot to allow a variable resistance on input.

Idea #3 : Change the 100K Sustain knob to 50K.  Actually I just read that some Russian Muffs came with 150K pots - so it might be worth looking into.

Idea #4 : add a voltage divider to ground or a trimpot before the 39K resistor on input.  I'm not sure this will work though because it will mess with the input impedance of the pedal

Idea #5 : bleed some of the signal to ground coming out of the first input stage before the sustain knob with a voltage divider.

Any thoughts?

[bufferz]

bump, I too am interested.

[LucifersTrip]

i'd first try the simplest. #2

but try #4 and see if that works for you, possibly instead of the 39K rather than before. that's used in many fuzzes.

[defaced]

Skip over one of the gain stages.

[Pyr0]

All of the above, also study this page
http://www.kitrae.net/music/big_muff_guts.html#Circuit
and try replacing the components marked for gain, increase the values of the emitter resistors, or reduce the value of the feedback resistors.

[Pyr0]

Also, this artical on determining the gain factor for a big muff might be useful

http://sovtek.webs.com/bmpgainfactor.htm

[R O Tiree]

How about just putting a 250k guitar pot at the input? Lug 3 to input jack tip terminal, lug 1 to GND and lug 2 to the BMP's input. Adjust to taste.

[amonte]

Wow this post exploded over night...  

How about just putting a 250k guitar pot at the input? Lug 3 to input jack tip terminal, lug 1 to GND and lug 2 to the BMP's input. Adjust to taste.

This is ideally what I want to do, as it seems like it's the closest thing to rolling the volume back ont he guitar - but I don't think I can just insert the guitar pot on input - wouldn't it load down the signal too much and lower the input impedance?  

All of the above, also study this page
http://www.kitrae.net/music/big_muff_guts.html#Circuit
and try replacing the components marked for gain, increase the values of the emitter resistors, or reduce the value of the feedback resistors.

Thanks, I have read through this page.  I thought about doing this to, but I remember having read that the values selected for the Russian Big Muff give it a lower gain, which in turn gives it the darker/murkier sound when compared to the American version.  I pretty much rebuilt my Russian Big Muff into a Version 3 BMP and I like the sound a lot - much more than the stock Russian version - I just don't want/need/use this much distortion.

Skip over one of the gain stages.

This is another interesting idea that I'd like to try.  Maybe there's a way I can jumper over a big chunk of the circuit to test it.  

i'd first try the simplest. #2

but try #4 and see if that works for you, possibly instead of the 39K rather than before. that's used in many fuzzes.

This is the idea that I come back to the most.  It wouldn't be hard to try either.  If I get a chance I am going to try this over the weekend - I'll report back what I find.

[jumpchamp]

You could also mess around with the clipping diodes. I modded an NYC to green russian tone stack specs and  replaced D1 and D3 with germanium and left D2 and D4 empty (all germanium reduced the overall level too much for me).

[R O Tiree]

Wow this post exploded over night...  

How about just putting a 250k guitar pot at the input? Lug 3 to input jack tip terminal, lug 1 to GND and lug 2 to the BMP's input. Adjust to taste.

This is ideally what I want to do, as it seems like it's the closest thing to rolling the volume back ont he guitar - but I don't think I can just insert the guitar pot on input - wouldn't it load down the signal too much and lower the input impedance?  

Surely, anything "to the left" of the input jack can be considered as a single AC voltage source together with a single complex impedance (coil, resistance of the coil, tone cap/R to GND, parasitic resistance/capacitance of the guitar cable), part of which is a Vol pot, usually 250k for a single coil guitar and 500k for a humbucker-equipped guitar... All other things being equal, there should be no snag putting another pot in parallel with the Vol pot, which is effectively what I'm suggesting.  Thinking about it, a 500k or 1M would be better.