Korg Poly 800 Oscillators

[Peter Snow]

Hi Marjan,
Do you have all these mods on the web somewhere?
I have an EX800 that's been lying around unused for a while now.  I would love to start
modding it.
Thanks,
Peter


">>>marjan<<<" wrote:
> 
> >
> >     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