Help with switch placement on a Big Muff Tone bypass switch.

[daryl]

I'm modding a Big Muff pedal clone. (its the BMP by General Guitar Gadgets)

I wanted to do the 'Tone bypass mod' to see what it sounded like, using a DPDT toggle switch.

1. Where is the best place in the circuit to put the switch?
2. Do I need to add a resistor to my bypass cable?


This is what I was thinking:



Or should the first part of the switch be before the 0.1uF cap?

[Electron Tornado]

Your switch there looks correct, and you don't need to add a resistor.

You might also consider this mod to the tone section for flat mids:  http://guitarkitbuilder.com/content/big-muff-pi-mod-more-mid-range-tone

You can also do the tone wicker mod by using a 3PST or 3PDT switch to disconnect the 470pf caps. 

[Fender3D]

Your switch there looks correct, and you don't need to add a resistor.
...

EH used a 150K resistor between switch lug 1 and 4

[daryl]

Thanks for the confirmation and the info.

I thought i'd seen a resistor used there on one of the schematics I looked at.
Any idea if its needed? or why they used it?

[nocentelli]

The BMP tonestack is quite lossy, so if you bypass it you get a large jump in volume output. The resistor reduces the volume jump when tone bypass is engaged.

[Electron Tornado]

The BMP tonestack is quite lossy, so if you bypass it you get a large jump in volume output. The resistor reduces the volume jump when tone bypass is engaged.

I didn't realize EH actually used a resistor. I saw a video demo of the BMP with tone bypass, and thought part of the point of bypassing the tone section was the increase in volume. I put a mid range control switch in mine instead.

[nocentelli]

If you're going to drill a hole for a switch, it might be more worthwhile to add a mid pot (see AMZ for details). Bypassing the tonestack adds mids, but also allows a lot of high end hiss that is usually tamed by the tonestack. A mids control gives you the mids back, but you can still use to tone pot to tame the high end.

[runmikeyrun]

I used a 100k resistor and it sounded just about right.

[Mark Hammer]

I modded/repaired a buddy's op-amp BMP recently.  Whoever had it previously had misconnected some wires so I needed to restore the tone-bypass function.

The level-shift can be looked at a few ways.  If you simply want it to be a tonal variation of the basic sound, then use of a voltage divider after the 100nf cap is appropriate, so one can go back and forth between what the tone control delivers, and a non-filtered tone. without blowing ears out.  That's what you see on a numbmer of older fuzzes like the Superfuzz.

On the other hand, and as we found out with my buddy's BMP, a straight tone-bypass without volume compensation provides the option for a very light overdrive with high output for pushing an amp harder.  Six of one, half dozen of the other, really.  Like I say, it would depend on how you plan to use the pedal.

[daryl]

Is it enough of a volume increase to wire it to a footswitch and use it as a solo boost? or does it alter the sound too much? if so I will probably wire it as a different sound at the same volume.

[daryl]

I had a look at the AMZ Presence Control.

I'm finally starting to see how the tonestack in the big muff is manipulated.

But what I don't have the musical experience to know is how that translates to sound.

But thats for a different thread.......

[nocentelli]

Search for Duncan's tonestack calculator, download the calculator, and you can see the effect of altering the values of the tonestack components upon the frequency response of the filter. If you go for the presence control, you can fiddle the cap values to give a classic BMP midscoop and have the presence pot return the mids so the response is "flat" with the tone control at 12 o'clock, or you can have the 12 o' clock flat, and the presence acts as a mid boost, or a compromise so 12 o clock on the presence pot is flat, with mid cut and boost available at either extreme. It's far easier to see how this is done by playing with the calculator than explaining it in words. Another useful site is "kitrae's big muff page".

[runmikeyrun]

it gives a very large volume boost when bypassed, which might be good for a lead boost, depending on how your amp takes it.