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Poly-61 Episode IV: The Return of the Tones
StoreTags: korg, poly61, repair, synth
Author: delete on June 29 2007 Viewed 1518 times. 6 people liked this blog. You can rate it below if you haven't already.
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this moring i woke up because of the heat (~45 degrees celsius in the shade = ~115 Fahrenheit) so i had plenty of time to inspect my poly61 more closely. like jcd's poly61 mine also had the "6th note" problem (here are the previous 3 episodes from jcd: link link link ). apart from that, there's another issue: it shifts octaves every 3 times i press a key (wtf?).
time to open up the synth and have a closer look. this is the first piece of analog music-making equipment i've ever opened up so i'm a little excited. ok, i'm in (pic 1).
first thing i wanted to check is the condition of the battery. i don't really know where it is so i look around for a varta logo. i also take off the keyboard but nothing. i searched a little bit on a korg yahoo group (lots of info there: link ) and found a pic showing the whereabouts of the battery. i find the same spot on my synth's boardh but... uhoh! no battery (pic 2)! i freaked out a little bit about it at first but then i realised that it's better than possible corrosion from a bad battery. however, the resistors around that area aren't in good shape, the legs are rusty and the pcb looks weird. who knows what this grandpa has been through.. maybe i'll buy a new Li battery but for now i think i'll save my presets on a piece of paper instead. it'll be knid of primitive and fun.
now, lemme check that 6th note mystery. on episode 3, fly talked about a cable that connects the 2 boards. yep, that cable is damaged by the solder joints of the buttons' pcb (pic 3). i don't have a spare one so i'll try to make sure this one works as well as possible. i play the keyboard while the synth is open, sounds good, no 6th note crazyness. i place a little foamy disc (the ones found in cdr packs) on the ribbon cable with a tiny bit of glue to keep it in place (pic 4).
the hard part (and probably what the sequel will be about) is the 3 notes octave up / 3 notes octave down problem. playing some preset programs i noticed that only 1 osc seems to have the problem. i disabled DCO 2, still octave shift. so, every 3 times there's signal from DCO 1 the octave is changed. i can think of 2 possible scenarios: either the cable mentioned above affects the signal or the DCO is freaking out for some reason. i don't think that the cable damage would cause such an exact repetition. any ideas here?
like all flicks that are followed by a sequel, this blog must end abruptly at this point in order to create suspense and mystery (...). i hope you enjoyed reading about my first not so exciting adventure with analog synths.
ps: (pic 5) poly61 and asr-10 makin' deals | |
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06/29/07
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monkvolcano
lol at the fanned out money.
edited: Jun 29 2007
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delete
note: there has to be a chip or sth that controls how the key presses are distributed to the voice circuits. i assume that this had to be included so that all voice circuits are equaly used, otherwise some of the would fail sooner. so, i was thinking that if someone bypassed / bent that some interesting results would occur, for example using the "glitchy" 6th voice circuit (if it actually is faulty) at will. or combining some of the voices and switching through different "synth modes". less polyphony, more versatility! now i see why some people are so into messing around with synth circuitry 
06/29/07
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RogerRoger
If you put it in chord hold and hit the same note six times(unison mode), do all of the notes change octaves in unison or just some? This could either be a keyboard scanning issue or a voice tuning issue.
06/29/07
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delete
RogerRoger, i tried that but i forgot to write it before. the first 3 notes played are normal and the next 3 are an octave up.
06/29/07
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RogerRoger
And does it continue to play them the same range apart if you played repeated unison notes?
What I'm getting at is the chord memory may be storing 3 lower octave and 3 upper octave note values, so you have to continue playing unison to see if the notes continue to transpose as a group, or stay the same half lower, half upper.
If they stay the same range apart and don't transpose as a group in unison, then it's a voice tuning issue, and doesn't relate to the keyboard tracking.
edited: Jun 30 2007
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no, when in unison mode there's no transposition. when a chord is stored the problem disappears. this is super-cool, because this way i can store 1 note "chords" and the poly61 is perfectly usable. many thanks for the tip RogerRoger
it seems the chord memory is storing 3 lower / 3 upper octave note values, because with any key pressed in unison mode, half the voices play a lower octave note and the other half a higher octave one.
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