Finished January 2006, the What Compressor pedal was something I built based on the David B. Thomas "hack" which again is based on the "Joe Cheep" design. My small variations are that I removed R28 (the one that blends a bit of dry signal with the compressed signal) and I changed R25 from 680 to 27k, and I changed R41 from 1k to 330. These modifications goes against the original design goals of the What compressor, which were to provide a "transparent" compression to vocal tracks. I wanted to be able to get the "over-squeezed" Tony Levin style of compression. The switches on the top corners of the finished unit defeats these modifications, to enable a "nice" compression again, if I should need it.
The electronics were installed into a Hammond aluminum box which had previously housed a prototype of the Quadra phaser, which is why it looks nasty. It has its own power supply with a tiny transformer, giving a bipolar 15 volt power supply. It was a tight fit, as you can see from the photos. The bottom circuit board, as seen from underneath, contains the audio circuit, with a DIY Vactol device (the black tube). The daughter board contains the sidechain.
It looks a bit ugly. But it works very well, and sounds great!