Some more bypassing

Hello again! It’s been a while, I’ve been busy with family and stuff. Well mostly family. But the other day I decided to finally convert my CryBaby into true bypass. This is a common mod, and it has been explained in depth many times all over the internet, but I took a slightly different approach to things. The CryBaby (gcb95) basically has two circuits connected in series, a buffer and a filter. The filter part is what makes the wah-wah sound, it’s a resonant filter that amplifies mid frequencies. The rocker on the pedal changes the center frequency of this mid boost. The problem with the filter is that it

• a: isn’t bypassed properly
• b. has a very low input impedance

One of these two wouldn’t necessarily be a problem but the two of them combined is trouble. When the pedal is bypassed, the input is still connected and as the input impedance is low, it will load down the guitar signal. This is why the buffer is added to the circuit. The buffer lifts the input impedance to acceptable levels (ca 1 megaohm). However, if the circuit was bypassed properly, the buffer wouldn’t really be needed at all. Here’s how I did it: First of all, I tend to be somewhat reluctant to making too drastic changes to my pedals. By this I mean that want to be able to mod the pedals in such a way that they can easily be returned to their original state. So I wanted to keep the buffer but still have true bypass and be able to play without the buffer when needed. Sounds reasonable, right? What I did was to disconnect the two circuits (buffer and filter). This was the most drastic thing i did to the pedal, as it included cutting traces on the circuit board. I cut the trace between the input of the pedal and the input capacitor of the buffer circuit. The other cut i had to make was between the output of the buffer (at the emitter of the first transistor) and the 68k input resistor of the filter part of the circuit. I also had to add wires to the input and output of the buffer and the filter input at the mentioned points. See picture below. ( sorry for the bad pic) There was no need to add a wire for the pedal input, as it already existed (the green wire on the ribbon contact). This was really all i had to do to the circuit board, the rest was done around two switches. The original bypass switch is a single pole switch, so this had to be replaced. I happened to have a couple of double-pole switches so it was an easy operation. Here’s a schematic of the switching: As you can see there are two DPDT switches, the first one (S1 in the schematic) bypasses the buffer, and the second bypasses the filter (this is the switch that is in the place of the original SPDT switch). The first switch is a small one, placed on the left side of the pedal, right next to the output socket. The capacitor on the small switch is simply an output capacitor for the buffer circuit. It was easier to solder it directly to the switch. And that’s it! Now I have two bypassable circuits in one. The buffer can be on all the time or bypassed by the flick of a small switch. The filter part can also be used on it’s own. The reason why I wanted it this way is of course mainly to prevent loading on the guitar pickups in bypass mode, but also to be able to use the pedal as an input buffer for the whole pedalboard. The wah now sounds slightly different, not necessarily better (or worse), but the big change is in how the pedals connected after the wah sounds. My fuzz sounds way better now when there’s nothing stealing signal between the guitar and the fuzz. When I don’t feel fuzzy, I can add the buffer and have some more treble to use with other overdrive pedals. There’s one tiny problem still. When the buffer is activated, there’s an audible thump noise when the filter is activated/bypassed. Can probably be fixed by adding a large resistor in a strategical place. I’ll get back to you on that one. Stay tuned (as always!) (and yes, I will continue with the tremolo project soon…) Edit: Corrected some major spelling errors (seriously, in what state did I write the original post?). I added a 1M resistor between buffer output and ground. This drains any build-up voltage on the output capacitor to ground. This solved the click-problem mentioned above. (kind of, there is still a bit of a thump when the filter is turned on and off, but it’s no worse than you would usually expect from a mechanical switch)