KORG Micro Preset M500 SP

Click here for shots via this auction.

Update: Some interesting bits on the M500 just in via The Most Underrated Synth post.
"It has one oscillator, 2 2-pole resonant LP filters (one for the synth preset, one for the brass preset), and four fixed (organ-style) filters. The 2 filters have VCAs built in, and each of the fixed filter circuits had its own VCA and (fixed) envelope generator. The brass voice and synth voice also had their own envelopes. The envelope attack and release controls affected the synth and brass VCA and VCF.

They could afford 6 VCAs because, for a fixed-voice, fixed-envelope monosynth, they could get away with one-transistor VCAs and RC (NO active component) envelopes, and the VCF/VCA chip I imagine was used in other synths as well.

OMD used this synth a lot on their first few albums. You can recognize it easily in their stuff before they got into samplers, which you can also recognize (Dazzle Ships onwards)"