Korg KPR77 a very underrated drum machine with, from my point of view, some cool hand claps (sounding like shaking a matchbox!), a great snare and cymbals… The bassdrum sucks nevertheless.
The extension is intended to makes that little machine a bit more versatile, in it’s original configuration it isn’t really mindblowing.
I think I modified already 3 KPR’s this way, the one pictured is the one with the nicest frontpanel.
It also features a built-in Midi-Sync converter from this project.
I was asked by several people about the modifications I made, that’s why I decided to share this info here.
At the time I did the modifications, I did not have any schematics available, so I had to analyze the circuits and compared it with some common well known drum machine circuits, where I already understood the working principle, in order to find out which changes to apply. Comparing what I did back then with the schematics now available, I have to say, I did quite a good job, but not a perfect one. I am sure some modifications could be better or more effective by choosing some other parameters than I did back then.
Of course, there’s a disclaimer just to make sure :
I can not be held responsible for any resulting damage you do to your machine or to yourself by trying to apply these transformations nor are these instructions to apply changes, it is only a listing of changes I made myself.
I will also not post the schematics for the KPR77 on this website, since the copyright of the service manual belongs to Korg. If you require the schematics, please look somewhere else.
So here a list of modifications with part numbers and exchange values:
Here the KPR77 with extension box and Frontpanel:
The new frontpanel in closeup:
Extension box also holds my Midi-Sync converter:
Some pictures of the KPR77 internals after modification:
You will notice that I left the original parts actually on the PCB, I just bent one pin upwards on the resistors. That way it is easy to put the unit back into it’s original state. Remember that collectors do generally not like modified equipment, at least as long as it hasn’t been modified by Bill Putnam or some other world renowned audio-guru.