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
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)
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:
control voltages source and power supply,
blinking LEDs in VCF expo converters.