Moog Opus III Footswitch The MRK-2 has the added

The MRK-2 has the added "Balance" control (basically a tone control that increases/decreases the cymbal sounds)

The unit is nearly mint - looks like it has barely ever been taken out of a box

Often wrongly-credited as being responsible for the sound of the solo by Ernie Isley on The Isley Brothers 'Summer Breeze' (including by us) however we are indebted to eBay user audible23 for setting the record straight:

neatly cased and with universal power supply

This VP-330 and SVC-350 Vocoder page on Vintage Synth Explorer has some useful information and links to demos

Moog Opus III Footswitch The MRK-2 has the addedSafe, powers up, but does not make sound. Clearly needs a service and some general care and attention to get it back to its best.