Big Muff Tone Bypass

[Rodgre]

Can anyone explain where to put a Tone Bypass switch in a Big Muff circuit? I couldn't find a "mod" page on the internet, so I figured someone here could tell me!

Thanks.
Roger

[Skreddy]

I used to think that would be exactly what I'd need to make my BMP sound perfect, but the BMP in question was a black Russian reissue, first of all.  Secondly, I finally got to play with a BMP with a tone bypass switch, and it sounded 100 times better with the tone stack engaged.  A BMP tone stack gives you this subtle mid scoop when in the neutral position, and compared to the tone-bypassed sound, this is actually close to a cabinet simulator.  The tone-bypassed sound is a huge ugly mid-hump.  The moral of the story is get an old BMP or else mod yours to sound better in general; the tone stack probably isn't the whole reason why you hate the sound.  You can tweek the tone stack caps and resistors to tailor the sound to your liking, too.  Visit http://www.muzique.com/ and check his lab notebook section.

Anyhow, to bypass the tone stack, you'll probably want to use a dpdt switch and have it substitute an 8.2k resistor (like the other interstage couplings use) for the whole tone stack (which is a 39k resistor in parallel with a .004 cap, .01 cap to ground, 100k resistor to ground, and 100k pot) leaving the .1uf cap following the tone pot.  There are different layouts for the various BMP models, so I couldn't tell you specifically where on your board to do the mod.  

I do have pictures of the one I mentioned that came from the factory with the tone switch; you'll need either PaintShop Pro (.psp) or PhotoShop (.psd) and a lot of bandwidth to view a layered image of the board and the components, or you can just view the individual .jpg images.
http://happybob.com/skreddy/circuits/ElectroHarmonix/

[Rodgre]

Before I saw your post, I tried just a straight bypass from the X-istor to the center lug on the tone pot and it seemed to do the (very big sounding) trick.

Now, should I still add that 8k2 resistor, or will I not harm anything by just shorting out the circuit like I have?

Roger

[Skreddy]

I assume your switch is lifting the connection to the pot at the same time as it's running the straight wire past the tone stack...

Anyho, if you like it as is, then keep it.  I just mentioned the 8.2k because the other stages use one between transistors.  Probably very little difference if you leave it out (other than a likely volume boost); the interstage resistors probably just contribute to the overall strangled feeling of the 'pi, much like an amp turned up to 11 and about as far from a clean boost as you can get.