On 1:00 in the Video you can see Frank using a Maestro Boomerang Wah. He also said this in an interview: "Which one to use depends on what kind of sound you want. They all have different responses. In the very beginning I used the original Vox pedal, and then later I moved to the Boomerang, because when I didn't have the guitar with the pre-amp it added a certain amount of distortion, and I liked that. I'll be using a Boomerang tonight. " ( http://wiki.killuglyradio.com/wiki/Shut_Up_And_Play_Your_Guitar ) - That is the Guitar Player interview form 1977 (May-June), written downj on the Zappa Wikimore
I'm not sure when I got this. Its the shaft wah, or so I'm told. It isn't working right, but when it DOES work it sounds like Isaac Hayes. When you disengage the wah effect its a volum pedal, but its active and with the toe all the way down the thing gives a gentle boost. Old school tone coloration in bypass, but in a good way. Need to fix it. There's something wrong mechanically on top of a dying switch and crackly pot... maybe that's why I put it in a box and forgot about it. Might be too hard/expensive to restore.