[sdiy] Korg Poly61 a peculiar design!!

karl dalen dalenkarl at yahoo.se
Thu Apr 7 00:45:43 CEST 2011


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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