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this auction
note the dual level knobs.
"AKAI VX600 is 12VCO (2VCO per VOICE – 6 VOICE) 6 note polyphonic programmable analog synthesizer. It was one of the last Japanese pure analog synthesizers in '80s. Few quantities were built, so very hard to find. This modular matrix analog synthesizer is very similar to OBERHEIM EXPANDER synthesizer and older ARP Odyssey. AKAI adopted basic schematics made by OBERHEIM, so actually the VX600 and OBERHEIM EXPANDER uses the same voice chip, so basically VX600's sound the same as the OBERHEIM EXPANDER MODULE - very fat and warm! But in my opinion, the VX600 is fatter than the OBERHEIM EXPANDER - especially brass, strings, and lead sounds are really great You can use 12VCO for 6 voice polyphonic or unison all 12VCO to a monophonic lead sound (CAUTION! it's very BIG & FAT!) Also it can be used as a multi timbre synth. (6 different voices). It's very flexible. VX600 has a variety of modulation source and destinations to program sound including MIDI control change, so you can use a MIDI controller to tweak cut off etc, and very cool feature is external audio in jack so you can synthesize external sounds using analog filter and other parameters AKAI VX600 is used but in great working condition."
As always, take auction descriptions with a grain of salt. If anyone out has had extensive time with one, feel free to comment.