Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

Hello,

Thank you for the info!

Best regards,

Johannes


Peter Andersson wrote:

> Hi,
>
> I wanted to let you know that I've finally managed to repair my
> Precious (Polysix). It was indeed the opto resistor, the PC-1, that
> was faulty. It was suggested to me that I replace the old mysterious
> PC-1 component with a VTL5C3 and change R93 from 4k7 to 1k2 (to get
> the VTL5C3 working properly). I did and then the synth was as good
> as new!
>
> Appearently, the PC-1 is what stabilizes the expo-converter circuit.
> If it's broken, the circuit can't manage to keep the synth in tune
> as the voltages vary (which is especially noticeable during the time
> the machine is warming up).
>
> Thanks for the help!
>
> Peter
>
> --- In PolySix@yahoogroups.com, Johannes Hausensteiner
> <jo.synth@c...> wrote:
>
>>I would not start to replace all components; I would rather try
>>to find out the faulty one. Heat up the whole area of the PCB
>>using a hot fan. Then you can selectively cool down single
>>components with cooling spray. If you start the Arpeggiator
>>before you can let play the Polysix for its own and hear changes
>>immediately.
>>
>>Johannes
>>
>>
>>Peter Andersson wrote:
>>
>>>You're right, searching for "2SC1583" does give me a bunch of
>>>interesting matches. No seller in Sweden but there are shops in
>>>Germany, for example, selling both that and the 2SA733. I'll ask
>
> a
>
>>>friend to get them and post them to me. Like you say, the opto
>>>resistor (PC-1) could be tough to get hold of, though. I'll
>
> start by
>
>>>replacing the transistors anyway and see if that does anything.
>
> Oh,
>
>>>and what about those amplifier ICs? Is that a long shot you
>
> think?
>
>>>Peter
>>>
>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>>><jo.synth@c...> wrote:
>>>
>>>
>>>>I read from the schematic:
>>>>∗ Q12 is a dual npn transistor, common emitter.
>>>> The used type is 2SC1583.
>>>> I found a company Dönberg Electronics, who does sell this
>>>> component, by entering "2sc1583" into Google
>>>>
>>>>∗ Q3 is a standard (Japanese) pnp small signal transistor,
>>>> type 2SA733. Dönberg also do have this one or you can take
>>>> a BC557 as a substitute. But be careful, the pinout is
>>>> different:
>>>> 2SA733 BC557
>>>> B-C-E E-B-C
>>>>
>>>>∗ PC-1 seems to be a Korg custom component. Doesnt it have a
>>>> black rubber tube on it? It is drawn in the schematics as
>>>> an LED optically coupled to an LDR. Hm.
>>>> Maybe someone of the list has a spare?
>>>>
>>>>Johannes
>>>>
>>>>
>>>>
>>>>Peter Andersson wrote:
>>>>
>>>>
>>>>>Wow, that's very useful info! Thanks Johannes!
>>>>>
>>>>>The control voltage must be crucial for the expo conversion to
>>>
>>>work
>>>
>>>
>>>>>properly then. If any of the amplifier circuits would be broken
>>>>>(IC17, 18 or 19), could that cause this behaviour do you think,
>>>
>>>or
>>>
>>>
>>>>>would that just make everything fail "from start"?
>>>>>
>>>>>Well, speaking of which... The synth no longer tunes up
>>>
>>>correctly
>>>
>>>
>>>>>after 20 minutes. Now the tuning and the note intervals are
>>>
>>>screwed
>>>
>>>
>>>>>up period. So whatever needed "warming up" a few days ago seems
>>>
>>>to
>>>
>>>
>>>>>have failed permanently now.
>>>>>
>>>>>I just went over the soldering points around the components you
>>>>>pointed out and resoldered most of them to be sure. I still get
>>>
>>>the
>>>
>>>
>>>>>same problem, though, so I guess it's time to start replacing
>>>>>components. I'll definitely try testing with cooling spray.
>
> Good
>
>>>>>suggestion!
>>>>>
>>>>>BTW, it seems I can replace all components in the expo
>>>
>>>conversion
>>>
>>>
>>>>>circuitry easily except Q12, Q3 and PC-1. Can't seem to find
>>>
>>>info on
>>>
>>>
>>>>>these anywhere. You wouldn't happen to know of components
>>>
>>>compatible
>>>
>>>
>>>>>to any of these three, would you?
>>>>>
>>>>>Peter
>>>>>
>>>>>
>>>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>>>>><jo.synth@c...> wrote:
>>>>>
>>>>>
>>>>>
>>>>>>The hold capacitors are C56 in unit0..5. But I do not think
>
> that
>
>>>it
>>>
>>>
>>>>>>is the hold capacitors very likey. If it were, not all six
>
> voices
>
>>>>>>would be affected equally. No, it must be something common. If
>
> it
>
>>>>>>is not the wires to/from KLM-396, then the "expo converter" is
>
> my
>
>>>>>>no.1 candidate. KLM-396 seems to be a part of it. The KBD works
>>>>>>logarithmically; that is going up a certain number of keys
>
> (e.g.
>
>>>>>>12 for one octave) multiplies the frequency of the generated
>
> note
>
>>>>>>by a certain factor (times 2 in case of an octave). So the KBD
>
> CV
>
>>>>>>logarithmic by its nature, whereas the oscillators work linear;
>>>>>>that is, the generated frequency changes linearly with the
>>>
>>>control
>>>
>>>
>>>>>>voltage (e.g 1V gives 1000Hz, 2V give 2000Hz, 3V give 3000Hz,
>>>>>
>>>>>etc.).
>>>>>
>>>>>
>>>>>
>>>>>>These two schemes are not compatible to each other but it is
>>>>>
>>>>>possible
>>>>>
>>>>>
>>>>>
>>>>>>(and necessary) to convert from one to the other. When
>
> converting
>
>>>>>>from logarithmic to linear you have to do the opposite of
>>>
>>>logarithm
>>>
>>>
>>>>>>which is exponential function. It happens that diodes and
>>>>>
>>>>>transistors
>>>>>
>>>>>
>>>>>
>>>>>>have exponential transfer curves, so they can be used for this
>>>>>>purpose. But the exponential function is extrem sensitive to
>>>
>>>small
>>>
>>>
>>>>>>variations; a small variation of the input causes a big change
>
> at
>
>>>>>>the output. Furthermore the human ear is very sensitive to
>>>
>>>changes
>>>
>>>
>>>>>>in pitch. This means that there must be taken special measures
>>>
>>>that
>>>
>>>
>>>>>>the whole thing does not run out of tune.
>>>>>>The expo converter in the Polysix is made of IC17, 18, and 19,
>>>
>>>Q12
>>>
>>>
>>>>>>(the expo component), PC-1 (kind of an opto-coupling device),
>
> Q3,
>
>>>>>>and surrounding components. In case of "old production" units
>>>>>>KLM-396 belong to this circuitry, too. Polysix has 6 voices but
>>>>>>the analog (de)multiplexers for the CV have 8 inputs/outputs.
>
> The
>
>>>>>>additional 2 inputs/outputs are used for some kind of
>
> calibrating
>
>>>>>>the exp. amplifier and thus stabilizing tuning of the
>
> instrument.
>
>>>>>>I am not 100% sure how this works as the CPU never measures any
>>>>>>value and therefore cannot adjust to changing values. From
>
> what I
>
>>>>>>can see from the code there is always the value 0 ouput
>>>
>>>to "voices"
>>>
>>>
>>>>>>6 and 7.
>>>>>>
>>>>>>According to what you tell, it may be a thermal problem. So I
>>>
>>>would
>>>
>>>
>>>>>>carefully check all solder points and try to heat up / cool
>
> down
>
>>>>>>the PCB in the area where these components are located. With
>>>>>
>>>>>cooling
>>>>>
>>>>>
>>>>>
>>>>>>spray you may identify a faulty component.
>>>>>>
>>>>>>Johannes
>>>>>>
>>>>>>
>>>>>>Peter Andersson wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>Yes, it's an old production unit alright. I've checked the
>>>
>>>wires
>>>
>>>
>>>>>>>between the 366 and the 396. It seems ok, the solder joints
>
> too.
>
>>>>>>>Can you tell me which major components are actually involved
>
> in
>
>>>>>the
>>>>>
>>>>>
>>>>>
>>>>>>>lin/log conversion/tuning? I've been told to "check" the key
>>>>>
>>>>>voltage
>>>>>
>>>>>
>>>>>
>>>>>>>selector chip, the DAC and the S/H capacitors as well as
>>>>>
>>>>>something
>>>>>
>>>>>
>>>>>
>>>>>>>called an expo converter. (I don't understand half of this
>>>
>>>stuff
>>>
>>>
>>>>>to
>>>>>
>>>>>
>>>>>
>>>>>>>be honest - I know you're not surprised. I'm learning,
>>>
>>>though...
>>>
>>>
>>>>>>>quickly!). These are some of the key components of the 366 as
>>>>>
>>>>>far as
>>>>>
>>>>>
>>>>>
>>>>>>>I understand. Do they handle the conversion/tuning you're
>>>>>
>>>>>refering
>>>>>
>>>>>
>>>>>
>>>>>>>to? I thought I'd start out by replacing the S/H capacitors.
>>>
>>>The
>>>
>>>
>>>>>>>cheapest and easiest operation to start with, I thought.
>>>>>
>>>>>However, I
>>>>>
>>>>>
>>>>>
>>>>>>>haven't even been able to locate them. It's nearly impossibe
>
> to
>
>>>>>read
>>>>>
>>>>>
>>>>>
>>>>>>>the numbers on the 366 schematics I got off the Old Crow web
>>>>>
>>>>>site.
>>>>>
>>>>>
>>>>>
>>>>>>>(Man what a fantastic resource his site is, btw!).
>>>>>>>
>>>>>>>Again, thanks for helping!
>>>>>>>
>>>>>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>>>>>>><jo.synth@c...> wrote:
>>>>>>>
>>>>>>>
>>>>>>>>From what you tell I would say it is a problem on the KLM-
>
> 366,
>
>>>>>in
>>>>>
>>>>>
>>>>>
>>>>>>>>the log/lin conversion/tuning section.
>>>>>>>>Or maybe you have one of the rare "old production" units. Is
>>>>>
>>>>>there
>>>>>
>>>>>
>>>>>
>>>>>>>>a small add-on board "KLM-396" to the KLM-366?
>>>>>>>>It could be a lose wire (if "old production") and/or a bad
>>>
>>>solder
>>>
>>>
>>>>>>>>joint.
>>>>>>>>I can see that you are located in Sweden; maybe you ask
>
> Ricard
>
>>>>>>>>( http://home.swipnet.se/ricard2/p6index.html ) for
>
> technical
>
>>>>>help.
>>>>>
>>>>>
>>>>>
>>>>>>>>Peter Andersson wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>Actually, tones are quite stable even during the first 20
>>>>>>>
>>>>>>>minutes, but
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>the synth is not in tune generally. Also, an octave is a
>>>
>>>quite
>>>
>>>
>>>>>>>stable
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>major 7 interval for the first 20 minutes, until suddenly,
>>>
>>>the
>>>
>>>
>>>>>>>synth
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>goes into tune and then the octave is correct as well. I'll
>>>>>
>>>>>check
>>>>>
>>>>>
>>>>>
>>>>>>>>>tonight if a single generated tone changes a lot during the
>>>>>>>
>>>>>>>first 10
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>sec.
>>>>>>>>>
>>>>>>>>>All six voices are affected. If I play a chord when it
>>>
>>>suddenly
>>>
>>>
>>>>>>>slides
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>out of pitch, all notes follow. It actually sounds like I'm
>>>>>>>
>>>>>>>turning
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>the pitch wheel. (I disconnected the pitch wheel, btw, just
>>>
>>>to
>>>
>>>
>>>>>>>be sure
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>it wasn't playing tricks on me).
>>>>>>>>>
>>>>>>>>>It is not related to the MG setting and I've played around
>>>
>>>with
>>>
>>>
>>>>>>>all
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>three - VCA, VCF and VCO. I'm quite sure it's not affected
>
> by
>
>>>>>the
>>>>>
>>>>>
>>>>>
>>>>>>>>>waveform setting either (whether I use a saw or a pulse)
>
> but
>
>>>>>I'll
>>>>>
>>>>>
>>>>>
>>>>>>>>>double check that tonight. The PWM setting does not make any
>>>>>>>>>difference.
>>>>>>>>>
>>>>>>>>>Does this give you any clues? Thanks for helping!
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>--- In PolySix@yahoogroups.com, Johannes Hausensteiner
>>>>>>>
>>>>>>><jo.synth@c...>
>>>>>>>
>>>>>>>>>wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>It is not normal that it takes 20 miuntes to tune up.
>>>
>>>Usually
>>>
>>>
>>>>>it
>>>>>
>>>>>
>>>>>
>>>>>>>>>>takes about 10sec to tune and then it is quite stable.
>>>>>>>>>>Check the following: hold a key down when switching power
>>>
>>>on.
>>>
>>>
>>>>>The
>>>>>
>>>>>
>>>>>
>>>>>>>>>>generated note should change quite a lot until it
>
> stabilizes
>
>>>>>>>after
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>a few secs.
>>>>>>>>>>Are all six voice affected? Is the effect related to the
>
> MG
>
>>>>>>>setting
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>(VCA/VCF/VCO)? Is it related to PWM setting?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>Peter Andersson wrote:
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>Hi all,
>>>>>>>>>>>
>>>>>>>>>>>I'm the proud new owner of a Polysix. I love it! Can't
>
> take
>
>>>my
>>>
>>>
>>>>>>>>>hands
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>off those knobs - the filters are just great! But I'm
>>>
>>>having
>>>
>>>
>>>>>a
>>>>>
>>>>>
>>>>>
>>>>>>>>>>>problem with it and I'm hoping someone can tell me what
>
> it's
>
>>>>>>>>>about
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>and maybe even what can be done...
>>>>>>>>>>>
>>>>>>>>>>>After I've played the synth for a while, notes start to
>
> go
>
>>>>>out
>>>>>
>>>>>
>>>>>
>>>>>>>of
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>>pitch every now and then. It happens randomly every 10-30
>>>
>>>sec
>>>
>>>
>>>>>or
>>>>>
>>>>>
>>>>>
>>>>>>>>>so.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>The notes go off pitch with a note or so and always jump
>
> or
>
>>>>>>>slide
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>>back to the original pitch again within half a second.
>>>>>>>>>>>
>>>>>>>>>>>At first I thought it was some filter setting of mine
>
> that
>
>>>>>>>caused
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>>>>>it, but as it turns out I get this no matter how the
>
> Poly6
>
>>>is
>>>
>>>
>>>>>>>>>>>programmed (or if I use a preset or a fresh "manual"
>>>
>>>sound).
>>>
>>>
>>>>>(By
>>>>>
>>>>>
>>>>>
>>>>>>>>>the
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>way, it takes about 20 minutes for the unit to get in
>>>
>>>perfect
>>>
>>>
>>>>>>>>>tune
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>after a cold start. Don't know if that's normal or if it's
>>>>>>>>>
>>>>>>>>>related
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>>>to this problem in any way).
>>>>>>>>>>>
>>>>>>>>>>>I'd be truly grateful for any help!
>>>>>>>>>>>
>>>>>>>>>>>Peter
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>PolySix "Digiest" Page:
>
> http://www.acc.umu.se/~amber/Poly6
>
>>>>>>>>>>>
>>>>>>>>>>>Yahoo! Groups Links
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>>>>>>>>>>>
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>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
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>>>>>>>>>
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>>>>>>>>>
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>>>>>
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>>>
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