MDDN 251 - Wah Circuit

I've been looking into different Wah Circuits and trying to understand how they work. Some of them seem to be much more complex than others. Ideally I would like to apply the most basic form of a Wah-Wah circuit to my project so it would make it easier to develop it further. Here are a few interesting circuits that I found that seem to be quite similar to my Wah Wah: