Direct MIDI Control of MC-202 by hijacking the internal D/A

[Sean Costello]

Hi everybody:

Thanks to all who have written me on this topic.  From the responses I
have received, I realize I need to clarify what I am describing.  I am
also posting this to Synth-DIY - it started as a question on AH.

I know that you can control an MC-202 via MIDI in two ways: either by
syncing up the internal sequences of the 202 with a MIDI/DIN Sync
convertor, or by using like a Kenton Pro-2000 to control the 202 with
voltages.  There are advantages and disadvantages to each method:

DIN Sync Advantages - can use Sync Out jacks to run other x0x boxes; can
use Ext. Synth Outs of 202 to control another synth.
DIN Sync Disadvantages - requires a MIDI/Sync convertor; new sequences
must be loaded for each song (this takes a long time, and is kind of a
touchy process).

MIDI/CV Advantages - allows for unlimited MIDI sequences to control 202
without reloading sequences; portamento and accent can be programmed
into these MIDI sequences also.
MIDI/CV Disadvantages - requires additional sockets for 202 (the CV and
Gate In sockets need to be modified to run properly, + additional
sockets are needed for controlling portamento & gate); sync output and
ext. CV/Gate output of 202 are not useable.

My idea is to basically run the MC-202 directly from MIDI.  The Sync In
jack would become a MIDI In.  Inside the 202, the MIDI In signal would
be converted by (mumble mumble mumble) into the proper signals needed to
drive the D/A convertor of the 202, as well as the other related audio
gates and such.  In addition, the (mumble mumble mumble) would convert
the MIDI clock signal into DIN Sync 24, with Clock/Start/Stop/ available
on the Sync Out jacks of the 202.  As the D/A convertor not only runs
the internal synth of the 202, but also the external outs, the result of
such a modification would be converting the 202 into a 2-channel MIDI/CV
device, that also outputs DIN Sync, with triggerable portamento on each
channel.  All thanks to (mumble mumble mumble)!!!

Obviously, I have no real idea of how to perform such an operation on
the 202.  I don't know if you would replace the internal microprocessor
of the 202, or if you could simply insert a new daughterboard that would
directly control the analog electronics (i.e. by taking the existing
connections between the uP and the analog board, and routing those to
the new section).  

Still, I think it would be a worthy project.  I think that MIDI/CV
convertors usually consist of a microprocessor controlling one or more
D/A convertors.  Since the D/A convertors are already present in the
MC-202, why not access them directly?  This would be entirely within the
realm of digital electronics, done in the analog realm (i.e. I don't
know much about microprocessors, converting MIDI into numbers on a 6-bit
buss that the D/A could use, or even if what I just wrote is accurate). 

I guess the main reason I would want such a project is just the
convenience of it all.  Having an MC-202 that ran directly off MIDI, and
could output 2 seperate CV/Gate channels, plus DIN Sync, would be a very
compact solution to the problems I am encountering with my live setup.
Running the MC-202 directly off of an MMT-8 would be great; running an
SH-101 and TR-606 from that same MC-202 would be even better.

I also believe that such a modification could be done with even greater
ease on an SH-101.  However, I wouldn't know how to do it, and I would
be concerned that such a modification would interfere with the actual
playing of the SH-101 as a keyboard instrument.  But maybe it is
possible.

Any input, analog/digital gurus?

Thanks,

Sean Costello