[sdiy] Korg Poly61 a peculiar design!!

Thu Apr 7 01:39:14 CEST 2011

I'm temped to do this to mine. Dump the digital control for pots - 

http://www.flickr.com/photos/37595587@N00/sets/72157622283778293/

Doug

----- Original Message ----
> From: karl dalen <dalenkarl at yahoo.se>
> To: synth-diy at dropmix.xs4all.nl; Paul Cunningham <paul at cometway.com>
> Sent: Wed, April 6, 2011 3:45:43 PM
> Subject: Re: [sdiy] Korg Poly61 a peculiar design!!
> 
> Uses two 8049 micros, a major rebuild are needed new DAC+mux board.
> Could be done but needs lots of work.More work then to build
> new different from scratch. 
> 
> KD
> --- Den tors 2011-04-07 skrev Paul Cunningham <paul at cometway.com>:
> 
> 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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