[sdiy] JH-3200 PolyKorg Clone finished

[jhaible]

> > Well, it's rather noisy, especially on the triangle waveforms.
> > That's the price to pay for full polyphony. (Triangle waves,
> > in addition to having low harmonic contents, are also just half the
> > amplitude of the saw waves here, which doesn't make the situation
> > better ...)
>
> Sure. I'm more impressed how flexible it is, with all that interesting
> little differences to a more ordinary implementation.


I was surprised, too, that even rather "dark" sounds are possible.
When I started building it, my focus was on String Ensemble and
Organ sounds. Now it turns out that my ES-50 Lambdas (I have
2 of them meanwhile!) still make better Strings, and Organs with
fast attack and *no* percussion added are very difficult on the PolyKorg.
This unusual ADSR has some strange side effects indeed, with
a severe overshot (above maximum Sustain level) for short Attack
times, so ironically organ sounds without percussion are nearly
impossible. With slightly longer Attack times - yes.
Maybe I can cure this, but one PS-3100 owner has told me that
this overshot also happens in th eoriginal, at least to some degree.

Other problem is with too low cutoff frequency. When the filter is
modulated to sub audio cutoff frequency (easy, when you have
a ADSR that changes its depth with attack time!), it starts to
produce pop-corn noises. These are so strong that they even cut
thru the closed (!) one-transistor VCAs !!
A strange effect indeed, and I'm axious that this will not degrade
transistors (backward zener diodes conducting ??).
I could cure this with resistors in each filter (/&%/&%/%(!!!),
but I'm lookinhg for a better solution to do this in the common CV
part of the filter controller circuit.

JH.