I built my first analog synth back in 1998; it was a PAIA Fatman. In 2006, I got the itch to build another.
The sound-producing electronics are mostly from a Soundlab PCB from Music From Outer Space (aka Ray Wilson). This is a great little project and you can take it a lot of different places by adding various mods. I added a sample and hold from Ray's site, as well as my own PT2396-based echo. The soundlab only has a single AR envelope generator. It is more useful than normal because it has a repeat function, however, I really wished I had added a second envelope. The soundlab filter is okay - it has both highpass and lowpass modes, but it is only a 2-pole design.
My panel design ended up being sort of a hybrid of my favorite synths. I used the Moog-ish Futura font and PKES knobs (Cosmo are too expensive), and late-period ARP black/orange/white color scheme. I collected all of the modulation routings into a matrix of switches like on a EMS Synthi or VCS3. The panel was designed using Front Designer and printed off on nice paper at a photo lab. I then glued the paper to a sheet of aluminum (Online Metals) and drilled the holes with a drill press. This is a very cost-effective way to make a panel, but it takes a while to drill all those holes. Also the paper has started to crack/peel slightly around the edges after several years of use.
I wanted this to be a performance instrument, and not just something to sequence with MIDI, so I opted for a built-in velocity-sensitive keyboard. The keyboard and pitch-bend wheel are from Doepfer spare parts. I designed the matrix-scanning electronics myself. A PIC microcontroller does most of the work, and outputs a gate signal, pitch CV, and velocity CV. All three of these are available as ins and outs on the back panel. So I can use the keyboard to play my modular synthesizer, while I drive the Soundlab with an external sequencer. Or I can play the modular and soundlab in unison to get all five oscillators going at once.
I tinker with woodworking, and the design for the case was the first thing I came up with. I had in mind the Moog Prodigy and Jen SX-1000. However it was the last part to be built. The case is made out of walnut. I covered screw holes with side-grain dowels, and rubbed in a tung-oil finish.