Big Muff Pi for Bass Guitar Mod

[heyniceguy]

question...

i've read in many places that the "Bass Guitar Mod" for any distortion/overdrive pedal is to increase the input DC blocking capacitor to "let more bass in". and in another case, it stated to also increase the output cap as well. that said, looking at the green russian BMP schematic, there are multiple serial gain stages, each with a coupling cap of 0.1uF. To mod this circuit for bass, would we have to increase the value of ALL the stage coupling caps, not just the first/last? Since the stages are all in series, does it follow that any coupling cap with a lower value will be the frequency-sensitive "bottleneck" cap as far as bass is concerned?

[Barcode80]

i think only the in and out caps should be adjusted.

[Meanderthal]

 The BMP is usually pretty bassy right outa the box, but if you want more the output cap is usually enough to do it. If you lower all the caps for every gain stage you run the risk of getting downright muddy! But, each muff is a little different, by all means tune to taste!

[sfr]

Seems to me that the BMP lets plenty of bass through, and that the real cincher for getting a good bass guitar sound out of it would be altering the frequency of that tone control, to make it more useable.  (Or maybe just seperating the tone control into two separate ones instead of the funky blending one?)

[Meanderthal]

 Yes yes(good point), the stock tonestack  does create a mid notch which can get you lost in the mix. Yun just posted his supermuff mods, and the 2 knob tonestack in there looks great for compensating for this!

[lowstar]

muff in the flavour of green russian muff is perfect for bass guitar without any mods. 

cheers,
lowstar

[runmikeyrun]

agreed.  The new ones (russian and USA) suck for bass.  I had a green one until it was stolen   but simple to mod... if you don't like it and there's not enough low end, start with the output and input caps (one at a time) try 1.0uF.  Here's a trick: piggybacking/parallel caps add up in value, so you could tack a 0.47 onto a 0.47 and have a 1.0 to try out without and unsoldering from the pcb.  Or if the leads are long enough get some test clips on the leads and try different values.  Get an assortment of leads at the store and clip on to every coupling cap and just experiement, just do one at a time to notice what changes what.

The tone stack is somewhat unusable for bass but you can bypass it and use an eq pedal if you have one.  I've found that modifying them really doesn't make them any better.

good luck.  fun circuit for bass. 

[moosapotamus]

In addition to going with bigger input/output caps, you can also make it more bass friendly by getting rid of the mid freq notch by modding the tone stack for a flat response in the mids. Others have done it and posted their values, so try the search function. The tone stack calculator at Duncan Amps is very useful for this, too. But, the best mod for bass is probably to add a clean blend.

~ Charlie