Korg Poly 800 Oscillators

[>>>marjan<<<]

> 
>     The VCO seems to be a chip labled MSM5232.  It has 8 inputs that come from
> a D/A converter and Sample Hold.  So off hand, I would say the pitch is
> controlled by an analog signal.

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.

I'd say it's DCDO (dig cntld dig osc) as it has 8 data inputs, 4 address
inputs
and 8 inputs for each voice amplitude (here connected to DEG1/2 envelope
mux).

There are some control iputs (reset etc) and two phase clock in. Clever
Korg people
used varying of clock freq for continual modulation of oscillators, as
you have
summed vibrato,bend and manual tune CVs which modulate varicap based
clock cct.
That's where I place modulation of vcos from chorus LFO (yes there's
analog lfo
in there with fixed freq for chorus, I made it variable).

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

I also made FM from VCO1 to expo VCF in, chorus lfo to VCF, variable
waveshape to
lfo, manual control of cutoff and resonance, 12db/oct ouot from filter
option (it's
unused pin5 on vcf chip 2069), lfo amount and resonance to chorus. I
plan to
install additional RAM chip for doubling patch/seq memory and optional
EPROM from
EX800 to choose between standard POLY operation and EX800 mode where kbd
is disabled
but it responds to sysex. 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).

Also made jostick X and Y outs (thou you need to compensate it's offset
in
neutral position at destination mixer). 

Maybe to add midi thru (two inverters), and some sort of cross
modulation - to 
replace reference at + of opamp summer for one voice (I don't use it
with full
polyhony so no problem here) with variable amount of other oscillator.
Add S/H?

Ther's also analo noise in there. 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.

Poly800 didn't need VCA at output as each voice level is dig cntrld with
dig env,
so it was free for noise. I used it to switch between noise to audio and
osc to vcf,
making it have FM programmable and stored in memory!

I guess when I install memory exp and pwm, I'd have to make it online?


Cheers,

marjan