The Wah effect is a natural continuation of the probe series... the fuzz factory probe, the volume control/manual tremolo probe, and now a wah

It's probably exactly what you think it is: a theremin-style antenna controlling a wah, getting brighter as your foot approaches. It has one extra feature, however. There's a Super Hard-On boost circuit in front of the wah, with a knob to set the exact level of boost for driving your wah sound. It can be turned up high enough to make the wah crack up a little for that "something's gonna blow" sound. It gets pretty darn loud!