decreasing the high end rolloff on the Big Muff Pi tonestack

[mordechai]

I've just built up a veroboard version of the Madbean Krankosaurus (ZVex BOR) project.  Here's the schematic:



The tonestack is effective, but a little too sensitive for me.  At the 12:00 position, a bit too much high end is rolled-off.  I'd like a bit more treble out of it.  Which resistor -- R15 (47K) or R16 (82K) -- should be tweaked to decrease the amount of high end that gets rolled off?  Or should the tweak be one of the caps?

[mth5044]

I can't check it out now, but download the duncan tone stack program, it's free! It has the BMP tone stack, as well as the fender, marshall, vox and a few others. You can modify the component values and it gives a readout of the frequency changes. Very easy to use and very helpful with these kinds of questions.

[GibsonGM]

http://www.duncanamps.com/tsc/

[PRR]

Take out some or all of C9 C10 C11 C12.

That's a high-cut filter. May be too much for your needs.

[mordechai]

Actually, now I am a bit confused.  On the madbean Krankosaurus schematic, c7 is 100n; on the schematic I posted above (from a different site), it is 10n.  When I used the Duncan Tone Stack calculator, it looked like 10n gave a bit of a midscoop, which is what I **THINK** is supposed to be happening with this type of OD circuit (like the BSIAB2).  But on both the Madbean site and on the tagboardeffects blog, this cap seems to be 100n...but that offsets the frequency response quite a bit and really makes the bass response kick in very quickly when the tone knob is turned CCW.

Anybody know which is, in the end, the "proper" value for C7??

[GibsonGM]

Well, you either go with what the designer specified, so it is 'original' and faithful to their idea.   If you can be sure that the schem you have IS the original.  Yes, a bit of midscoop is VERY MUCH what you should get with a BMP style stack, in general.

Or, you do what I do....you mock the tone stack up, make that cap 'changeable', and let your ears decide what is the right cap!!  Esp. since you'll use the pedal with YOUR amp, which may or may not sound best with that original part value.  That's what DIY is all about...

I've seen BMP tone stacks just like this with such widely varying component values, it makes one's head spin, ha ha.   I'd just 'cap to taste', man.   Call me reckless.  Too much mid scoop and you can't be heard in the mix, live.    Too little, and you get honky and lose your 'fluidness'.  So there's a balancing act, and it's up to YOU to find the sweet spot!