[sdiy] Korg Poly61 a peculiar design!!

karl dalen dalenkarl at yahoo.se
Fri Apr 8 18:52:53 CEST 2011 

I agree that you agree however i do not agree it's a 
being a genuine ramp-core-with-timer-reset, as previously
mentioned it's complete VCO with timer reset and timer
signaling and i still wonder why?..

OSCare oscillators are PLL driving a timer who read out a LUT
who suffers from rubberband effects if you rappidly switch
between hi and low note on the KB.

But i do agree to your assessment why didnt they use the
SSM or NJM chips? The mysteries with Korg , next episode
nest week!
 
Reg
KD 
 

--- Den tors 2011-04-07 skrev Tom Wiltshire <tom at electricdruid.net>:

> You've really got to do *something*
> to it. I've just been reading the user manual. It's
> interesting to compare with the service manual.
> The main problem is definitely the incredibly low
> resolution on most parameters. (Osc detune in 7 steps,
> filter cutoff in 63 steps, resonance in 7 steps, etc etc).
> Dumping the presets and adding pots for the CVs isn't a bad
> option for this particular synth, I'd say. Certainly it's a
> lot easier than building a new master uP board, although
> that wouldn't be impossible, if you had half-way decent
> schematics. Neil J has such a project on with his Opera 12
> voice.
> 
> One thing that struck me was that although the two
> oscillators are quite different internally this isn't
> exposed to the user at all (one being a genuine
> ramp-core-with-timer-reset (Juno style) DCO, the other is a
> sum-of-octave-squarewaves (OSCar style?) DCO. I wonder why
> they did them differently.
> I also wonder why they used a fairly complicated filter
> design (although only 12dB/oct) when they must have had
> thousands of SSM2044s sat around the factory that they were
> using in virtually everything else they built around this
> time.
> 
> All in all, I agree with Karl's assessment; "a peculiar
> design".
> 
> T.
> 
> On 7 Apr 2011, at 01:25, karl dalen wrote:
> 
> > Nice but why not move the knobs ontop of panel print.
> > 
> > KD
> > --- Den tors 2011-04-07 skrev Doug Terrebonne <dougt55 at yahoo.com>:
> > 
> >> Från: Doug Terrebonne <dougt55 at yahoo.com>
> >> Ämne: Re: [sdiy] Korg Poly61 a peculiar design!!
> >> Till: "karl dalen" <dalenkarl at yahoo.se>,
> synth-diy at dropmix.xs4all.nl
> >> Datum: torsdag 7 april 2011 04:09
> >> 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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