Discussion about the Korg PolySix synthesizer

Hi Cynthia--I also do design work for Paul Schrieber of SynthTech, so 
I'm also making stuff on the modular front.  Anyway:

On Tue, 26 Aug 2003, Cynthia Webster wrote:

> Wow!  My hat is off to you crow, Well done!
> (What a monumental undertaking you have done!)

  Well, it needed doing a long time ago..but I am very good at
procrastination, especially when there are more pressing engineering tasks
at hand.  The original KLM-367 has a serious design flaw in that 1) they
put a NiCad battery on the pcb and 2) put it near critical circuitry.  I 
finally got fed up with spending an average of 3 hours per KLM-367 repair, 
and decided that the same 3 hours would yield a new, assembled board.

> In fact I've been wanting to add jacks to my P6 to interface it with my
> modular...   Simple mods that I've been wanting to do is add an LED for the
> third LFO and make the LFO outputs available, as well as converting the
> trigger from Moog S-type over to um, "Arp" type.

  Well, 2 LFOs happen to be on the KLM-367: the PWM MG  (Korg calls LFOs 
MGs as you know) and the routable (VCO/VCF/VCA) MG.  Not much would be 
needed to provide outputs for either of these.

> There are many other mods that would be cool, in fact If anyone has some
> cool mods they've done I'd love to hear about them.  (As you can see here I
> am not a purist, as far as keeping my Poly's "stock" looking).
>
> (It would be cool if your new PCB layout facilitated a few mods easily?)

  Well, the initial prototypes are direct KLM-367 clones.  Once I verify 
the clone boards in fact work correctly, I'll start adding in option 
features.  For example, there are two unused MUX S/H outputs that beg to 
have S/H circuitry added so as to create two new control voltage 
parameters.  Ricard Wolf used them for pitchbend and mod wheel CVs, I 
believe.  I would probably provide circuitry for the same.

  Down the road I want to change CPUs as 8748s are getting harder to come
by.  With a CPU change, I can start to do things like add MIDI, integrate
the key assigner (a separate CPU on the KLM-366 board) and generally make
things more efficient such as eliminate the battery-backed SRAM and use
the new MCU's internal user data flashrom area to store patches..many more
than 32 patches, btw.  While doing this I would switch to surface-mount
for most of the board's parts: I can get a factory to build SMD boards
*much* cheaper than to build TH boards.

> It's really refreshing to see this level of commitment to the machine Scott.
> I think would like to get a couple of these new boards when you have them
> made, and am Very interested in facilitating the MIDI mod as well.
> 
> Do you suggest these boards just for units are found broken, or also for
> PolySixes that have already had their battery problems repaired?

  I would suggest the clone boards for repair job first--thats why I made 
them.  For upgrading the Polysix, I would go with the next version of the 
board, once I figure out what to put on it.
 
> I hope that I don't upset anyone here with this next comment, but...
> 
> Does anyone really ~want~ to deal with that cassette interface?  (Gak!)
> 
> I've often thought that that entire section could be replaced with something
> much more interesting, (or even a small floppy disk drive or the little
> flash memory cards thingies that go into digital cameras in order to save
> patches).  

  The cassette interface takes up very little hardware (and not much code
space, either).  It is about the most generic implementation of the Kansas
City Standard FSK data-to-tape I/O routine I've ever seen.  I would leave
it in simply because lots of folks still have patches on tape.

  Anyway, once I have a new board assembled and working I'll figure out a 
repair/replacement scheme.  I can probably still do the $100+old board (I 
would scavenge a few esstentials off the old boards) and send a new board 
to folks...we'll see.

Crow
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