This custom MIDI interface provided the Commodore 64 with a MIDI IN and MIDI OUT/THRU port (connectors not shown here). Via this interface, the C64 was often used as a patch editing system, especially with the Yamaha DX-7. It also allowed for some of dhomas' early exploration with MIDI and SYSEX control and automation.

Numerous modifications were made to the C64, including the replacement of its expansion slot with a female DB37 connector. The problem was that the cards required to connect to the expansion slot were expensive and difficult to find. The DB37 connectors (shown here) were much cheaper and more commonly available.