Offered here is an exceptionally rare Korg MU-5000 Expander, an undocumented and never-released unit, widely believed to be the only existing prototype.

This exact unit is the same MU-5000 featured in Alex Ball’s YouTube video dedicated to this mysterious Korg device. I personally loaned this unit to Alex Ball for the purpose of producing that video, and the serial, condition, and behavior are identical to the one shown and discussed.

The MU-5000 represents a fascinating “what-if” moment in Korg’s history: a standalone expander whose design philosophy sits somewhere between late-70s/early-80s Korg analog experimentation and concepts that would only fully materialize years later. It is not a production model, not a modified commercial unit, and not a replica — it is a genuine prototype.

Is is fully working but I have not any original box.

Due to its nature, this unit is intended strictly for serious collectors, museums, or historically focused studios. It is not being sold as a conventional, documented product, but as a unique artifact of synthesizer history.

Please feel free to contact me for any additional information, detailed photos, or technical discussion. Serious inquiries only.