The source instrument for Analog Piano is the Crumar ColorSound CompacPiano, an awful name for a wonderful machine.
The ColorSound was intended as a stage piano, but derived all its onboard sounds from good old analogue electronics. It has three preset tones, of which it's the piano that makes you stop and take note: rich, solid, satisfying, and with a natural affinity for contemporary music styles. In many ways it straddles the tonal qualities of an acoustic and an electric piano, sounding more like a "real" piano than a Rhodes or Wurli, but with the same EP-style grunt and heat to the sound. The other two preset tones, HonkyTonk and Clav, are less convincing as instrument emulations.