Korg Poly 800 Oscillators

[WeAreAs1 at aol.com]

In a message dated 10/7/00 2:21:56 AM, urekar.m at EUnet.yu writes:

<< I've been modifying my Poly exstensively over the years. MSM5232 
(made by OKI) is 8 voice tone generator (IT would be very nice to see if 
anyone has datasheet for it), it's configured with outputs for each 
harmonic (2,4,8,16) of each osc. >>

Roland also used that chip in a little sound module they made in the 
mid-1980's.  I cannot quite remember the model number of the Roland module 
right now (EM-101, or something like that), but it was a little 8-voice 
tabletop unit with preset sounds (strings, brass, flute, etc.) that was sold 
primarily as an accessory for the digital home piano market.  

It used the MSM5232 chip for tone generation and had one Juno-2 (or maybe 
Juno 106) filter/VCA chip and a nice analog stereo chorus at the output.  
Anyway, since Roland was also using the OKI chip, it must not have been a 
custom-made proprietary Korg part.  It's quite possible that they also sold 
the chip to some other manufacturers - possibly some organ makers, most of 
whom were eager to add "synthesizer" features to their organs around that 
time.

And yes, it is purely clock-derived DCO.  Any analog CV inputs it has are 
used to control its internal volume VCA's, and are not used for pitch 
control.  Much like the often-used 8253 triple timer chip, the Poly 800's 
individual voice pitches are determined by an externally-provided 8-bit 
binary word which is multiplexed to each voice via a 3 or 4-bit word, then 
latched into the the chip at a very high rate.  The master tuning, pitch LFO 
and pitch bender CV's are used to modulate a high-frequency clock, which 
determines the overall pitch range of all the voices (just as it's done on 
the 8253-basd DCO's in the Juno60, Juno106, JX3P, JX8P, GR700, MKS30, JX10, 
MKS70, MKS10, MKS7, Juno1 and 2, Matrix 6, Matrix 1000, and a few others).

<<I wish to see from datasheet what are the unused inputs of MSM5232 
are, maybe some level of modulation could be acomplished or pwm? >>

The Poly 800 service manual has an internal block diagram of the chip.  Would 
this be at all helpful to you?  It may not show all of the pin I/O's, though. 
 The Roland module's schematic doesn't really say much at all about the chip. 
 I doubt that you would be able to achieve any sort of individual voice PWM 
in there, since the individual voices are not brought to output pins until 
after going through the internal VCA's.

<< Also I have a plan to install sort of dynamic harmonic PWM (based on 
John simonton's simple ADC - but more about it when I test it). >>

Yes - please explain more!  It sounds interesting.

<<It uses VCA section of VCF chip which is powerful
selfconained CEM type chip. Two audio inputs with 2 CV ins for level control 
of each,
4 stage VCF with separate 12 and 24 db/oct outputs, 4 nodes for cutoff 
capacitors,
lin and log cutoff CV ins, resonance CV in, separate VCA with input, ouput, 
lin and
log CV ins. It's powerfull analog filter/vca chip (NJM2069) quite nice for 
external
processing (made that mod too). I don't know if it was used in any other Korg 
synth,
but if you find any spare chip you can build nice module or processor with 
it. >>

That's a very nice filter chip.  To my ears, it sounds much better than the 
CEM3320 and all of the other Curtis chips that contained both VCF's and VCA's 
(CEM3372, CEM3379, CEM3396, etc.) - better low end and squishier resonance.  
The NJM2069 was also used in the DW6000, DW8000, EX8000, and the old Korg DSM 
12-bit samplers.  I really love my EX8000!  I wonder if Korg still has those 
chips, and how much they cost?

Please keep us informed about your Poly 800 mods.

Best regards,
Michael Bacich