Sovtek Big Muff Pi Mods for Bass

[soundboy.massacre]

My friend asked me to fix up his 90's era Sovtek Big Muff Pi to sound better with his bass - I did some quick recordings with a fender jazz bass going through the pedal into a yamaha 115b-50 bass amp before and after I worked on it.
In the before clip; you hear a lot of hum due to the unregulated power supply that was connected via bare wire to the board where the battery used to be.
I started by removing the first stage soft clipping diodes, this allows more low frequencies to pass and reduces compression. For the second stage of clipping diodes, I changed the series cap from .047uf to 1uf, this gave the dirt a fuller spectrum.
I reduced the value of the emitter resistors on Q1 and Q2 from 390 ohms to 300 ohms (this mod makes more difference on bass than it will with guitar) to increase bass saturation.
Finally I added a switch to bypass the big muff tone stack for 6db of boost without the frequency loss imposed by the tone stack. and a 2.1mm power jack with a regulated 9vdc supply killed the hum.
= this page was very helpful ; http://rkerkhof.ruhosting.nl/Taas/Mods/Big%20Muff.htm
Before[soundcloud]http://soundcloud.com/soundboy-massacre/before[/soundcloud]
After[soundcloud]http://soundcloud.com/soundboy-massacre/after[/soundcloud]

[greeny23]

change the input cap at all?

[soundboy.massacre]

I didn't change it...it's .1uf ,not too bad for bass.
To me bass fuzz sounds best when it's a little on the bright side.
But something like this could sound even better

the earthbound supercollider , which is a modded big muff, uses a pot to blend two different input cap values;
I saw a youtube demo of it with a bass and it was a good mod.

[ural]

My friend asked me to fix up his 90's era Sovtek Big Muff Pi to sound better with his bass - I did some quick recordings with a fender jazz bass going through the pedal into a yamaha 115b-50 bass amp before and after I worked on it.
In the before clip; you hear a lot of hum due to the unregulated power supply that was connected via bare wire to the board where the battery used to be.
I started by removing the first stage soft clipping diodes, this allows more low frequencies to pass and reduces compression. For the second stage of clipping diodes, I changed the series cap from .047uf to 1uf, this gave the dirt a fuller spectrum.
I reduced the value of the emitter resistors on Q1 and Q2 from 390 ohms to 300 ohms (this mod makes more difference on bass than it will with guitar) to increase bass saturation.
Finally I added a switch to bypass the big muff tone stack for 6db of boost without the frequency loss imposed by the tone stack. and a 2.1mm power jack with a regulated 9vdc supply killed the hum.
= this page was very helpful ; http://rkerkhof.ruhosting.nl/Taas/Mods/Big%20Muff.htm
Before[soundcloud]http://soundcloud.com/soundboy-massacre/before[/soundcloud]
After[soundcloud]http://soundcloud.com/soundboy-massacre/after[/soundcloud]

well, "before" sounds better..

[soundboy.massacre]

...and einsturzende neubaten thought amplified shopping carts sounded better, but that doesn't mean they were right

[Boxbie]

[Chankgeez]

Love this thread.

[soundboy.massacre]

Had some more time to alter the pedal today,
so I reduced the resistor in the feedback loop of the first stage from 470k to 360k, and upped the coupling cap to the second stage from .1uf to 1uf, then took the diodes I removed from the second stage and added them in series with the diodes in the third stage to make the clipping less harsh; have a listen...
[soundcloud]http://soundcloud.com/soundboy-massacre/double-diodes[/soundcloud]

[Boxbie]

Its hard to tell from my crappy headphones how the low bass is holding up. Keep it happening!