The CMU-810 is one of Roland's first Expander type modules. It basically has the same guts and sounds as the MC-202. The overall layout mirrors the MC-202 and SH-101 synthesizers very closely. Along the bottom row are sliders and switches for the Oscillators, 24dB VCF analog filter and ADSR VCA envelope sections. The upper row contains the LFO controls and a simple Mixer section. External audio can also be routed in (but not through the filter). Up to two external sources can be added and their levels mixed in.
This is a rare but capable analog mono-synth. It can generate true MC-202/SH-101 bass sounds which have become very popular in electronic music. The CMU-810's obscurity does not come with a heavy price tag either. In fact, they often make a cheaper alternative to the more common Roland bass/lead-synths. But you'll need some sort of CV/Gate to play any sounds. It has been used by Astral Projection.
Demos & Media
Images from Synthesizer Picture Archive
Thanks to 'Kelly' for providing information.