big muff tone bypass mods - different methods

[fuzzmonger]

Hello again, my fellow tinkerers,
Just got my hands on a vintage IC Little Big Muff Pi and looking to add some tone and sustain controls by way of internal trimpots on a separate board to keep it all as original as possible 

To make use of the tone switch (currently for switching between full bass or full treble.. Go figure) I'm going to repurpose it as a tone bypass. I, as I'm sure many of you, have seen this PowerPoint knocking about detailing a method of doing this by effectively jumpering all three tone lugs together, which appeals to me as it doesn't require lifting any of the 40 year old and likely fragile components as with other methods

http://docs.google.com/EmbedSlideshow?docid=dhrp52kc_14rg8b3gm&size=l

Question is; does this properly bypass the tone stack? I can't see how it could (but, for some reason, switch wiring always baffles me. I can make and design fairly complex circuits but draw a blank when I have a switch on front of me. Anyone else have this problem? Anyone? No? Oh..)

Regards,
Fuzzmonger

[Mark Hammer]

So here is our basic BMP tone control:

The 4000pf/22k network forms a hihpass filter section, the 39k/.01uf network forms a lowpass filter section, and the tone pot pans between them to jugle the amount each contributes to the final sound.  I don't know what issue pedal/circuit you are using so the component values shown may be a little different than what you have, but it's the same circuit and function.

If the ground connection for the .01uf cap is lifted then there is no treble cut at point B, and it the 22k connection is lifted, there is no substantial bass cut at point A.  Lift both of those connections and there will be a signal that is essentially a bit brighter and louder than if the entire network had been bypassed, simply because the cap makes for a more efficient path for the treble than the 39k does.

But there will be no midscoop, and that can radically transform your tone and signal level.  Is a complete bypass better?  Who is to say.  Certainly you are not aiming for some audiophile flat frequency response, so the only thing that really matters is if it provides a useful change.  And lifting both of those connections to ground will do that.

I modded a buddy's op-amp BMP last year to fully bypass the tone control, and we both liked the manner in which the added signal level allowed him to push the input stage of his amp without requiring high drive levels in the pedal, so there's that side of it too.

[fuzzmonger]

Thanks for the info!
I've used this method before on other muffs but I was curious about this other route which didn't require lifting for the sake of not playing with the board and original components
-Fuzzmonger