Discussion about the Korg PolySix synthesizer

Hi folks,

I have successfully implemented my unison detune mod. And its very easy
to do.

You need one 5K linear pot and a knob of some kind, I used one from a
Monopoly (thanks Andrew who gracefully answered my request for one the
other day). One 3.9K resistor. A 80cm piece of screened audio cable.

Remove R116, a 220 ohm resistor, from the voice board. You can do this
without taking out the board, but you will need to (re)move the
keyboard, as it sits under there. Take it out, and use wick to clean the
holes from solder. Now solder the 3.9K resistor in the same place as
R116. Solder the pot to the screened cable, the wiper should go to the
core, and the CCW pin to the screen. Now solder the other end of the
cable to the voice board. The core should go to the bottom solder pad of
the new 3.9K res, and the screen to the top pad. Make sure nothing will
short out, when the keyboard is put back on.

Now fit the pot somewhere on the front panel. I used the location used
by the LFO's LED. I simply removed the LED and fitted the pot in its
place. I used a low profile Alps pot I had from an old guitar effects
pedal that had died. I can live without the flashing LED, although I may
put it back on at a later stage in a different location.

How it works: The original 220R resistor changes the currents created by
the four tune setting resistors in the unison detune circuit to voltages
that control the pitch of each voltage. A larger value than 220R will
give greater detune, and no resistance (a short) at all will hold the
VCOs at the same pitch. By fitting a 3K9 and a 5K pot in parallel, you
can change the detune resistance from 0 to 2 200 ohms.

Have fun.

Regards,

Tony Allgood Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan

On Sat, 9 Jun 2001, Tony Allgood wrote:

> VCOs at the same pitch. By fitting a 3K9 and a 5K pot in parallel, you
> can change the detune resistance from 0 to 2 200 ohms.

How greatly does this affect the pitch of the voice (which one did you
change BTW?)? I have tried this before with some value I cannot remember
but I can detune one of my voices down 7 semi-tones with the pot. But I
would like to be able to detune it down an entire octave to be able to
produce fat subs for the other voices...

Happy modding!
regards,
Kristofer Ulfves, Uppsala, Sweden

>How greatly does this affect the pitch of the voice ...

It detunes four of the six voices by a different amount. It works by
controlling the unison detune circuit and not by any individual detune
of a single VCO. I didn't actually measure the amount of detune, I did
it by ear alone, but its more likely to be measured in cents rather than
semitones. I guess maximum deviation is around half a semitone. Its
actually quite tricky to measure individual detune, you'll need to tap
into the separate voice outputs.

Individual detune of each VCO is a worthy mod, but rather heavy in
additional pots. I wanted one simple detune pot. Its easy to use and
doesn't affect any other key assign modes. Its also very easy to do.

It is possible to use the unison detune circuit to control each voice,
and this may be a good way to add significant detunes if you can spare
the pots.

Cheers,

Tony

On Wed, 13 Jun 2001, Tony Allgood wrote:

> Individual detune of each VCO is a worthy mod, but rather heavy in
> additional pots. I wanted one simple detune pot. Its easy to use and
> doesn't affect any other key assign modes. Its also very easy to do.

Hmmm...how exactly does your mod work? Which resistor have you replaced
with a pot?

I myself based my mod on the information I retained from this list and
which is stored at my digest page at the following adress:

http://www.ing.umu.se/~me96kus/stuff/p6digi29

What I actually did was to change the R120 to a 1 meg pot which (as I
mentioned in my last mail) gave me a detune span of 7 semitones. But what
I really wanted was something like 12 semitones so I guess using a 2 meg
pot would do the trick. Haven't get around to try it yet, though.

Happy modding!

regards,
Kristofer Ulfves, Uppsala, Sweden

Hi Kristofer,

Right the resistor you are changing to get your 7 semitones detune is
simply one half of a potential divider. By changing R116, a 220R
resistor, you can alter the bottom half of that divider. By just over
doubling the value to 470R, you will get twice the detune range for ALL
four of the detuned voices.

If you want twice your detune range just alter that one resistor to 470R
and keep using your 1M value. But my reckoning was that if I wanted that
amount of detune I would use the chord hold function on the mode
assigner.

Now what you really need is six sets of pots connected to that unison
circuit. Six 47K linear pots between the power rails, +/- 5V. Feeding a
100K resistor from each wiper to each of the de-mpx inputs in the unison
circuit. This way you would detune either side of perfect note. You
would need some track cuts, but if you can afford the extra panel space
it may be worth it. You could still use my original mod to control the
overall level of detune.

Regards,

Tony Allgood Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan

On Thu, 14 Jun 2001, Tony Allgood wrote:

> and keep using your 1M value. But my reckoning was that if I wanted that
> amount of detune I would use the chord hold function on the mode
> assigner.

Well, that'll work if you detune the different voices by the fine-tune
pots found on the voice-card, but really is no option if you want to
change swiftly from rock-steady tuned polyphonic to fat monophonic the way
I described. But thanks for the info about the other part of the unison
mode...

regards,
Kristofer Ulfves, Uppsala, Sweden