DIY Proximity Wah
Because I’m getting so many questions about my “DIY Proximity Wah” video on YouTube, I will use this post to write about it in some more detail.
First of all this is obviously a DIY “interpretation” of the impressive Zvex Wah Probe, so all the idea and mental work comes from Zvex Effects…
The effect unit is basically a simple twin-t wah filter (like the inductorless Colorsound Wah for example). This type of wah circuit is controlled by only one variable resistor. This resistor can be easily replaced by a photoresistor which then allows you to modulate your guitar signal by altering the incidence of light to this photoresistor. There are some solutions out there which just take that photoresistor and lead it out of the enclosure, so the environment-light is your source light and the incidence of light is controlled by the shadow of your foot, however this is not the case on this pedal and it is very likely more unstable because it depends on environment-light sources (e.g. club-stages can be dark or light-shows will influence the resistor) and the response of the filter won’t be that smooth. So on this pedal the photo-resistor is controlled by an LED. This LED is hooked up to a simple theremin-like circuit which alters the intensity of the LED with the use of an antenna that senses your body (just like your foot for example). This solution is way more stable, though it has its limitations too… The antenna reacts with everything that is on ground-potential! That is an important fact that you should keep in mind when your trying to find a suitable enclosure for this circuit. Every grounded part should be kept as far away from the antenna as possible, especially grounded areas that could be in parallel with the antenna plate. That’s why it is not possible to simply put the antenna plate isolated on your common metal enclosures for example!
So here is what I did:
I took a standard B-type enclosure, put all the circuitry in it so it is shielded from RF, mounted an angled plastic enclosure (which I found here) with two screws to the metal enclosure, traced the antenna-lead through a hole to the plastic enclosure and attached a 7.5cm x 10cm (about 3inch x 4inch) PCB-board antenna-plate to it. This way it works pretty nicely…
Here is a video I took while building this circuitry which shows the LED controlled by the theremin-circuit. For testing purposes I used the bottom of a Hammond B type enclosure as the antenna:
The final pedal in action (through the 12AX7, ECC99 MiniAmp):
HERE you can find the schematic for the theremin part I used to drive the LED and HERE you can find the schematic for the modified colorsound inductorless wah I used (the 22nF must be a mistake it should be 2.2nF like in the original CS Wah I would guess).
Finally here are my perfboard layouts and some pictures:
Btw. HERE you can find an interesting forum thread about this topic, which also includes a PCB layout.