i've been doing a lot of modding the past few years on my Crybaby & Vox wahs. it's not hard if you know how to solder--the boards are an older style of design, with the components accessible. and the mods can make a big difference in the sound.
there's lots of info on the net about most of these mods, but not about others. and it's mostly all from the perspective of vintage cats or blues/rock players, not metal dudes.
so i figured i'd do some posts about it.
first, True Bypass switching....
OK, True Bypass switching:
there's tons of blather about this all over the net. the short version is, most all older pedal designs use a SPDT (single-pole, double-throw) switch instead of a DPDT (double-pole, double-throw) because the SPDT is cheaper. the way the pedal circuit has to be designed in order to use the SPDT, the pedal circuitry is always connected to the input/your guitar signal. (only the output is switched). that pedal circuitry acts like a capacitor or a super-long guitar cable, bleeding off high end from your tone when the pedal is switched off.
some of the vintage cats don't care and blues cats can't hear any difference. but for us metal dudes, playing high-gain amps, any loss in the high end is really obvious. and it sucks!
the solution: replace the SPDT switch with a DPDT, which lets you switch not just the FX output but the input too. so the pedal circuitry is only connected to the input/your guitar signal when the pedal is on. which makes the tone with the pedal off sound the same as if you weren't plugged through any pedals.
a simplified diagram i made 15 years ago to link on Usenet:
this mod is super-common. (all Crybaby and Vox wahs up through the late 90s, and most of them now, use the SPDT.) so there's tons of great resources on the net. and the DPDT switches are easy to find these days.
Crybaby True Bypass: http://stinkfoot.se/archives/546
Crybaby and Vox 847 True Bypass: http://www.wah-wah.co.uk/bypass.html
basically, you make a new wire off the board, by cutting a trace or removing some components. you run that new wire and a new ground wire to the new DPDT switch, plus the three wires that were on the old SPDT switch. those links have details and pics of the boards for different years/revisions of Crybaby and Vox wahs.
this mod also works on many old pedal designs, like MXR phasers. but i never got off my ass to do it on my Phase 100, so i don't have any info on that.
next i'll write about some tone mods, or maybe adding an LED....