Korg KPR-77 MIDI Interface (updated September 2022)
The Korg KPR-77 is a neat little analogue drum machine from 1983. Sound-wise it shares a lot in common with its predecessor, the KR-55, while adding the ability to program your own patterns into it. It gets a bad reputation as being hard to use, but I don’t think it’s any more difficult to program than the then-competing Roland TR-606, just different.
This MIDI kit allows you to trigger all of the drum voices from MIDI notes, including the two metronome sounds, with accent if the note velocity is greater than a user-specified threshold, as well as sync the on-board sequencer to MIDI clock. As space is rather limited inside the machine, the MIDI board installs in the battery compartment. The MIDI receive channel is set with a learn button, accessible through the battery compartment door.
Conveniently, the two pins of the DIN socket which MIDI uses actually go unused on the KPR-77’s SYNC socket, so it’s able to serve double-duty for both SYNC and MIDI IN (original SYNC IN and OUT functionality remains intact, but you can't use both SYNC and MIDI at the same time). Other than drilling two 3mm holes on the underneath to mount the MIDI board, there are no permanent modifications to the machine.
Non-volatile RAM modification
As the MIDI board installs in the battery compartment, you can no longer run the KPR-77 from battery power. This also means that programmed patterns won’t be remembered for more than a day or two as the main batteries are also used for maintaining the memory contents when the power is turned off.
It is possible however to replace the original RAM IC on the CPU board (a standard 24-pin 6116-type 2kB SRAM) with a modern ‘F-RAM’ replacement module which will retain its contents almost indefinitely without any backup power needed at all! These modules are quite easy to come by as they’re popular with pinball machine enthusiasts, just do a search on eBay for ‘6116 NVRAM replacement module’. I paid about £15 for one at time of writing. You will need quality de-soldering gear to remove the original RAM IC without damaging the board though (I use a Hakko FR-301). Note that there’s not enough vertical height to fit it in a socket.
- Installation & user instructions (for older 'Rev 3' kits sold before May 2022)
- Installation & user instructions (for new 'Rev 4' kits sold September 2022 onwards)