Discussion about the Korg PolySix synthesizer

And here's the voltage for all "C" keys, starting from the lowest C and 16'
to the highest and 4'. Measured on the new production board, after the
demultiplexer. Stretch tuning is off (this is important!). Multimeter
ground is TP4 (-10V).

0.018
0.042
0.090
0.185
0.375
0.755
1.513
3.03x

The doubling of the voltage for each octave is easy to see. I think this
antilog amp has a good calibration; perhaps at the bottom there is a little
bit of room for improvement.

So we have essentially a doubling for every 0.5V at the input.


With VR1 to VR3 we can change the relation of those voltages for certain areas.

The service manual says:

VR1 ADJ. CENTER
VR2 TUNE HIGH
VR3 TUNE LOW
VR15 TUNE MID

However I'm not a 100% convinced that the functionality of VR15 and VR1
isn't switched.

VR15 seems to control a general offset while the other VR's indeed control
their respective ranges. They're affecting the tuning a bit outside their
range but not much.

A comparison of the old and new production also hints at this:

VR1 MID
VR3 LO
There seems to be no VR2 for the old production.

And the addendum says

"VR15 on KLM-366 is equal to VR1 on KLM-396."
The latter is the daughterboard for the old production; hence VR15 is NOT
the same as VR1 (which is simply labelled "MID") on the old production
KLM-366.

So my guess is that the four VR's for the new production should better be
labelled:

VR1 TUNE MID
VR2 TUNE HIGH
VR3 TUNE LOW
VR15 ADJ. CENTER