The Tinkering PRK
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The Unique MIDI Tinkering PRK

This is a very special piece in my collection - a PRK that I obtained from Andy Scholle, together with a defective Wave 2.3 and an 8" Waveterm B.

A normal PRK has no MIDI... this one has not one, but two MIDI Interfaces: an internal and an external.


According to Andy, the first one has been implemented by PPG, since he was sometimes (ab)used as a test person for PPG back in these days. This interface consists of an additional processor board that's activated by a switch that routes the keyboard either to the normal PRK processor board or to the MIDI processor board, which sends them on to MIDI Out. The control section of the PRK has been heavily modified:

As you can see, there's a "MIDI ON/OFF" switch. During the decades, it has unfortunately lost the attached knob, so it's quite difficult to move it. On the right side, there's a series of switches and buttons, but they are not connected to the MIDI processor board internally. Therefore, it's unfortunately impossible to tell the buttons' intended use.
The switch itself is not exactly a simple one - it switches the complete 16-pin cable leading from the keyboard's switchboards to either the normal PRK or to the MIDI processor board.

Here's another view, from a different angle, to better show the switches:

and now let's see the inside, which has been done in a very... well, makeshift way. The add-on board has simply been glued to the case with a fragile wooden support frame. Yes, glued. Not very repair-friendly.

The MIDI processor board seems to be a generic microcontroller development board, unfortunately without any text on it that would aid in finding out its origins. In any case, it has a series of connectors, obviously for some I/O ports.

Unfortunately, the internal interface doesn't work completely... sometimes, it seems to deliver the correct keys, but it delivers a lot of intermediate garbage, too. Well, this needs quite some additional restoration work...


Some fine day in the 20th century, a second MIDI interface was added... you just can't get enough of these :-)... but this one didn't use the original PPG keyboard logic but went a completely independent way. For that, a series of rubber contact strips was screwed into the PRK (framed yellow in the picture):

and a control cable was added that goes through the case and is plugged into a nice hand-made add-on device:

... where you can adjust quite a lot. Unfortunately, there's absolutely no description for it, and the display is less than self-explanatory. The MCB-200 was applied by:
    Tonstudio - Bauer
    Eitel-Fritz-Str. 20
    1000 Berlin 38
(it kindly tells that when you turn it on  :-).

This interface seems to work to a certain degree; some keys work better, some need a really hard beating... obviously, it would need some contact cleaning. I'll do that someday. It's just too bad that I don't have a description for it, and Andy can't remember a thing - the device seems to be rather intelligent. It looks like it can handle up to four keyboard zones with different channel and transposition assignments, but programming it is an experience in head-scratching. If anybody has a manual for that baby, I'd just love to get a copy!



Last update: 10/23/02