My polysynth was a long term project taking slightly more than 5 years. Finally finished in 1994. Here's few words (and sounds) about it.
Please take look at these two pictures of its interior:

• Overall view of PCBs and keyboard
  On the left - power supply and little computer with control voltages source, in the middle - top PCB with EGs and VCFs, on the right - main VCO, dividers, LFO regulators. All DIP8 devices you can see are CA3080
• If it wasn't poor quality picture, you'd see 4 layers of PCBs, uC and power supply. But here you can see it clearly (different cammera)
• Top PCB
  VCF and ADSR (6 voices visible), tone frequency dividers and LFO's VCAs.
• Most of digital circuitry is stacked under VCF board in 4 layers. Counting from the bottom: keyboard scanner, voice assignement logic, DCOs, samplers. VCF board is covered with protective PVC foam foil, so you can't see it there.
• Look at dividers (right), LFO regulators (top) and from-keyboard-to-vcf stacked PCBs (left) or from a different perspective

Few other pics: VCF+EG board, control voltages source and power supply, blinking LEDs in VCF expo converters.

Samples