[sdiy] Korg Poly61 a peculiar design!!

[Paul Cunningham]

I didn't know how to jump in on this thread, but my Poly-61M suffered  
some severe battery damage, and i fear that my motherboard is toast.  
too many of the traces are corroded and as well as the pins of several  
resistors and the CPU... I've seen how some people fix this, and  
perhaps I'm just not up for it.

I would love to just replace the 1980s motherboard with an arduino or  
something similar. Does anyone know actually how dependent the synth  
board is on signals from the motherboard? I've seen some impressive  
Poly-61 mods that basically add real-time control to several  
parameters, but some other oscillator signals are generated by the CPU?

The Poly-61 seems like an awesome sounding synth hobbled by a simple  
programming model. I'd love to augment it with 21st century software,  
or in the least a decent analog-based control system.

I think I have the schematics somewhere, but I struggled a little bit  
to understand how all the circuits were related. Is this what's in the  
service manual PDF? I'll have to figure out what I have...

i'd love to find a working replacement KLM-509A board if anyone knows  
where to find one. -pc


On Apr 6, 2011, at 6:02 PM, Dan Snazelle wrote:

> I actually like the sound of the poly61 for SOMEthings!!!
>
>
>
>
> Sent from my iPhone
>
> On Apr 6, 2011, at 5:46 AM, Tom Wiltshire <tom at electricdruid.net>  
> wrote:
>
>> Have you got a link to some decent schematics for the Poly 61, Karl?
>>
>> I've got a service manual PDF for it, but it's more-or-less  
>> unreadable.
>>
>> Thanks,
>> Tom
>>
>> On 6 Apr 2011, at 01:44, karl dalen wrote:
>>
>>> VCF:
>>> 12db LP LM13600 using a MS20 VCA with limiting diodes in resonance
>>> feedback but before VCA also the feedback not only goes to the input
>>> of the filter but to first cap like half way S/K and no local OTA
>>> gain loops but one fixed over both.
>>>
>>> I have checked trough all other analog Korg products and this VCF
>>> are unique to the P61.It should have a peculiar Bw hump because of
>>> this.
>>>
>>> VCA:
>>> MS20 final VCA. One SSM2056 EG split use VCA and VCF.
>>>
>>> DCO1:
>>> It's a complete saw VCO core, a regular Op amp integrator/comparator
>>> design. The ramp reset comparator also feeds another comparator that
>>> sends this signal back to *both* 1/3 of DCO1 and DCO2 8253 timers  
>>> gate
>>> input, then one of the 8253 timers sends a pulse back to the  
>>> integrator
>>> NPN ramp reset transistor in the VCO!! Odd!
>>>
>>> Could this perhaps mean that half of timers are actually used to  
>>> measure
>>> the frequency of the VCO and if wrong in realtime restart it on a  
>>> per
>>> cycle basis?! It could work if the value are compared to a  
>>> predefined
>>> LUT. Or is it just a bogus thing to distract anyone viewing the  
>>> schematic?
>>>
>>> The output of the ramp integrator are sent to a comparator to create
>>> PW wave.
>>>
>>> DCO2:
>>> DCO2 are made out of 1/3 8253 driving a 4520 divider who's output's
>>> are selected by a switches and summed by a weighted resistor net
>>> acting like a DAC to create saw. A redundant signal goes to divider
>>> reset to actually turn off the chip..
>>>
>>> Apparently resolution of wave are likely dependent of octave  
>>> selected
>>> otherwise only one switch would be needed.
>>>
>>> VCO ramp integrator note CV are a 7bit R2R generated by the same CPU
>>> that scan's KBD that then feed a common expo who are muxed out to
>>> each VCO. (Polysix/Trident)
>>>
>>> The driver for the timer DCO's are a VC RF multi vibrator who in  
>>> turn
>>> are driven by bend and vib voltages, the CLK signal are then driven
>>> into a prog divider to create semitone offsets for DCO2, finer  
>>> detuning
>>> presumably by 8253 timer itself.
>>>
>>> There are no regular muxed DAC for the parameter CV's instead each
>>> has its own DAC trough a bag of 8255 driving a even larger bag of
>>> weighted resistor net's.
>>>
>>> DAC for Cf of VCF are only 6 bits. However PWM, VCF, Vibrato  
>>> modulations
>>> are full resolution from the analog triangle MG.
>>>
>>> In other words an awful sounding poly but a great, peculiar and  
>>> funny
>>> VCO/DCO design.
>>>
>>> Disclaimer: I might be utterly wrong in all that said here.
>>>
>>> Thanks for your attention....G'day...
>>>
>>> KD
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>>
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