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Discussion about the Korg PolySix synthesizer

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Tuning issue.

Tuning issue.

2014-12-16 by pasitive@gmail.com

Hi,


I've got Korg Polysix here, with clone KLM367. 


There's something wrong with tuning. C-keys are something like F and octave is couple semitones shorter than it should be. It's impossible to get it tuned right. I've been following several calibration instructions without any success. 


VR2 has no effect at all.


Is it photocoupler? IC18 pin 7 gives +12v. As I understood it should give something like -2v - -5v, but this one gives something else..





Re: [PolySix] Tuning issue.

2014-12-16 by Jed Jorgensen

This is the note from the files section:

From a user (the solution refers to the problem of not being able to get correct scaling of the Polysix keyboard):


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!




On Tue, Dec 16, 2014 at 5:27 AM, pasitive@gmail.com [PolySix] <PolySix@yahoogroups.com> wrote:
 

Hi,


I've got Korg Polysix here, with clone KLM367. 


There's something wrong with tuning. C-keys are something like F and octave is couple semitones shorter than it should be. It's impossible to get it tuned right. I've been following several calibration instructions without any success. 


VR2 has no effect at all.


Is it photocoupler? IC18 pin 7 gives +12v. As I understood it should give something like -2v - -5v, but this one gives something else..





Re: [PolySix] Tuning issue.

2014-12-20 by pasitive@gmail.com

PC-1 replaced, without any effect.

Cannot get basic tune to C at all. It's A or A#. 

Very strange.

Re: [PolySix] Tuning issue.

2014-12-21 by Bob Grieb

How about IC18 and Q3?   Are they OK?   Also,
there is a 4051 (IC31) in that feedback loop.   Maybe it's gone
bad?

    Bob

From: "pasitive@gmail.com [PolySix]" <PolySix@yahoogroups.com>
To: PolySix@yahoogroups.com
Sent: Saturday, December 20, 2014 8:56 AM
Subject: Re: [PolySix] Tuning issue.

 
PC-1 replaced, without any effect.

Cannot get basic tune to C at all. It's A or A#. 

Very strange.


Re: [PolySix] Tuning issue.

2014-12-21 by pasitive@gmail.com

Actually it's fixed now. There was acid-trace in KLM-366B. It's is now in tune, but there's something that causes slight but very audible  fast modulation in higher octaves. It seems to be connected with antilog somehow, because when turning on Polysix, pressing few keys to hear that "warm up sweep", the notes are absolutely clear. But when it goes to "stable" mode, the modulation starts. I noticed that sometimes it will go away after 10 minutes, or sometimes it will stay without fading away.

Re: Tuning issue.

2014-12-26 by andrijapusic@yahoo.com

Can you explain, what is your final solution? Which optocoupler and which resistor? 

Re: [PolySix] Re: Tuning issue.

2014-12-27 by <backshall1@bellsouth.net>

I believe he said the real problem was some acid trace damage on the 366 board, and it is working fine now with the original photocoupler and resistor. He didn’t mention where the damaged trace was.
Don B.
 
Sent: Friday, December 26, 2014 4:57 PM
Subject: [PolySix] Re: Tuning issue.
 
 

Can you explain, what is your final solution? Which optocoupler and which resistor? 

 

Re: Tuning issue.

2014-12-27 by pasitive@gmail.com

The real problem was bad trace on KLM-366, -15V trace near connector from PSU. It's now with original optocoupler and original resistor. No problems anymore. Tried with VTL5C9 and original resistor, but only three lower octaves are ok. I've been told that VTL5C9 will be fine with original resistor, but it seems that it's not true. At least in this case. Or my VTL5C9 was bad.

Thanks everyone!

Re: [PolySix] Re: Tuning issue.

2014-12-28 by jw_dewdney@yahoo.com

THIS should give some really interesting context to the question of trace damage with acid. It's actually quite surprising just how MUCH the cross sectional area of traces affects the signal (!!)

EEVblog #317 - PCB Tinning Myth Busting
EEVblog #317 - PCB Tinning Myth Busting
Forum Topic here: http://www.eevblog.com/forum/blog-specific/eevblog-317-pcb-tinning-myth-busting/ Dave does some measuremen...
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