[sdiy] Question to Korg PS-3100 Owners

[jhaible at debitel.net]

Question to Korg PS-3100 Owners


The Korg PS- series synthesizers have a very
unique Voltage Processor (VP), it's function
described as "CV lense" in the user manual.

There are two potentiometers, called "Limiter A"
(A) and "Limiter B" (B).

Now the VP works like this: 
A +/-5V input voltage is processed in a way that
with pots A and B you can set the minimum and
maximum output voltage independently.

Example: 
A = 5V, B= 4V
then
Input = -5V ... +5V  ==> Output = +4V ... +5V


Example2:
A= 1V, B= -3V
then
Input = -5V ... +5V  ==> Output = -3V ... +1V


You can also reverse the polarity:

Example3:
A= -4V, B = +3V
then Input = -5V ... +5V  ==> Output = +3V ... -4V


As you see, it's more or less a scaling of VC plus
a variable level shift.
The *unique* feature is that you really can set
the lowest and highest output voltage *independently*.
(One more brilliant Korg idea!)

This requires a fixed input CV range of -5V ... +5V,
however. Now Korg's own VC pedals (with the 5pin DIN
connectors) apparently put out exactly this +/-5V
range, so the Voltage Processor is the ideal tool
to scale and shift a Pedal CV.

Also, this will work on other CVs which have a +/-5V
range, and the VPs on the PS-Synths have an ordinary
1/4" jacks to feed them, alternatively to the 5pin
DIN jacks.

But there's a rub in it: The PS-3100's own modulation
sources have no +/-5V range!
The LFOs (MG's) have something like +/-3V, the GEG
has 0 ... 5V or -5V ... 0V. So does it make any sense
to run these thru the Voltage Processor?

Yes, you can still do all kinds of scaling, inversion
and level shifting, but that main feature, setting
the uppeer and lower limits of the output CV, is
lost.

So my question to PS-Owners is this: 
How well does it work in practice? (feeding a MG-1 voltage
into the VP, for instance)
Is it still better than the "ordinary" way (which would
be one reversible attenuator pot, and one pot for
+/- DC shift).

Of course I'm asking this for my PS-3200 clone project.
I have 3 options: 
(a) Build the VP as in the original
(b) Build an ordinary Reversible Attenuator + DC shift processor
(c) Build the VP with an extra "Pre-Processor" to adapt
    different input voltage ranges.

What would you suggest?

Thanks,

JH.


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