Review: Kenton MIDI kit for Korg PS-3100

[Tony Clark]

   After a long and restless waiting period, I finally received the 
schematics to this beast (thanks Mark!) and was able to finish installing 
the MIDI kit for this wonderful synth.

   WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING

          This kit is definately NOT for the novice.

   WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING

   Now that is out of the way, let's get started:

   First, I'm going to get a disclaimer out of the way.  The guys at 
Kenton are a good bunch of chaps, they have been helpful with my 
questions and understand some of the issues I brought up.
   Having said that, I'm going to put it bluntly.  The installation 
instructions aren't much of a help at all.  The reason?  It was written 
for the PS-3300 which is (from what I've discerned) totally different in 
every way than the PS-3100!  So all of their diagrams didn't help a bit.
   So anyone thinking of attempting this job better have the schematics 
and a good DMM.  And, BTW, Korg doesn't have any manuals for these 
machines, quoting the service tech, "You do know how OLD these synths are 
don't you?"
   Anyway, that problem past, the first step to getting the MIDI kit 
installed is to mount the circuit boards.  Can anyone confirm that the 
PS-3300 is deeper than the PS3100?  The instructions show mounting the 
circuit board assembly on top of the large card cage, but due to the way 
the PS-3100 is built, it would stick two inches out the backside of the 
cabinet!  So this posed problem #1.
   Solution:  Remove all of the synth cards (9 total).  The left three 
card upper/lower socket sets have to be moved to the left.  This gave me 
enough room to mount the MIDI board against the center metal dividing 
panel.  And to do this, I had to widen the holes in the upper part of the 
metal dividing panel to accept machine screws.  Now I was able to fasten 
the MIDI board to the dividing panel.  Use a rubber bumper (included in 
the kit) to prevent the MIDI board from hitting the dividing panel.
   Now came some of the fun part.  Connecting up wires.  The power supply 
was no problem.  One thing to watch is the multitude of different 
voltages that it puts out.  The PS-3100 has no less than 5 different 
voltage feeds.  Two +/- 15V rails with one +/- being diode protected (use 
these to power the circuitry) and a 10V rail for the panel.
   The MIDI kit comes with two huge ribbons that are used to trigger the 
different keys.  The PS-3100 has a 48 note keyboard and so there are 48 
wires to solder.  This is where the PS-3100 differs from the PS-3300.  On 
the PS-3100 there are 4 gate cards (each controlling one octave).  The 
ribbons must be split into groups of 12 (it actually doesn't work out 
that nicely) and connected to the correct gate card.  No existing wires 
are removed.  Kind of a symbiotic relationship.  The unused parts of the 
ribbon cable can be clipped off.
   Next comes wiring on the small analog board.  The one thing I disliked 
immensely about the MIDI kit was that the analog signals were to be 
routed to a box that sits piggyback on the backside of the synth.  This 
box has 6 1/8" jacks, one pushbutton, and the MIDI IN and THRU.  Here's 
my thing, first, the pushbutton for entering in MIDI setup mode is on the 
backside of the unit.  Not a very convenient place to put it EVEN if you 
don't end up utilizing it much.  Second, I'd have to have special patch 
cables to use AND they'd be wrapping around from the back to the front of 
the synth.  Unacceptable.
   Instead, I decided to use the wonderful aspect of the PS-3100 and it's 
bretheren.  Patchability.
   First, I disconnected the two controller inputs (Really, does anyone 
own a Korg controller??) and rewired them as my MIDI IN and THRU (damn 
convenient if I must say so).  I drilled a hole just above these two 
sockets and mounted the pushbutton in it.  Now I can easily access the 
MIDI setup at any time.
   Now there is an analog board that comes with the MIDI kit and I had to 
mount this on the front side of the card cage utilizing two of the many 
holes along the top side.
   After mounting this board, I had to figure out my strategy for 
connecting in the 6 lines (Pitch bend, Modulation wheel, Aftertouch, MIDI 
Cont. 7 (volume), Cont. 16 (filter), Cont. 17 (resonance)).
   Obviously the Pitch bend line can be routed directly to the wheel on 
the PS-3100.  The Mod wheel and aftertouch lines I decided would be best 
routed to the controller 1 & 2 inputs (which I disconnected the DIN 
sockets but not the 1/4" jacks).
   Cont. 7 goes to control VCA2, Cont. 16 goes to control filter cutoff.  
But instead of routing Cont. 17 to the triple resonant filter, I decided 
instead to divert it to control the frequency of the Sample & Hold 
function (more on this later).
   In order to fully implement the above, I put together a small circuit 
board with 4 non-inverting amplifiers (of the TL082 kind) with two inputs 
each.
   Now I could disconnect and redirect signals so that all of the 
original controls were left fully functional only with the added MIDI 
control.
   With things wired in this manner, I can now patch the Pitch Bend, Mod. 
Wheel, and Aftertouch to any of the other patchable parameters on the 
PS-3100!  And although the Mod. Wheel and Aftertouch use the voltage 
processors, this can be overridden by patching directly into the voltage 
processor inputs.
   The filter and volume MIDI controls can't be overridden but are there 
to allow some programmability via a sequencer program.
   And you're probably wondering why I dedicated a MIDI control line for 
the S&H frequency...well...it was because of all the things they made 
patchable on the PS-3100, this was the one thing they left out!  It was 
there BEGGING to be connected in.  Really you could just drill a hole and 
mount a 1/4" jack there and have a patchable frequency control (maybe one 
of these days I'll do just that).  But in any case, this is something I'd 
make use of.  And as the triple resonant filter already has a patchable 
filter control, I can easily patch in the Pitch bend, Mod. Wheel, or 
Aftertouch to control it via MIDI.
   How does it work?  Pretty good, I must say.  I haven't fiddled around 
with most of the MIDI setup stuff, but setting MIDI channels and 
transposing works well.
   Overall, I would have preferred Kenton to have made a smaller MIDI 
board and worked on a better installation guide (for which they are in 
the process of going through and redoing a number of them).  
Unfortunately I doubt much will be done with the electronics as I was 
told they'd only sold a grand total of "3" PS-3100/3300 MIDI kits.  Oh 
well, I'm not going to complain, I've got a very cool synth that will 
neatly fit into my MIDI setup now.
   Now if only I can solve the massive noise issue of the PS-3100 and the 
crosstalk, I'll be a very happy man...

   Tony

-----------------------------------,----------------------------------
I can't drive (my Moog) 55!        |     
-----------------------------------|     The E-Music DIY Archive
Tony Clark -- clark at andrews.edu    |          COMING SOON!
http://aupe.phys.andrews.edu/~clark| 
-----------------------------------'----------------------------------