PS-3100 Resonator Section Clone

[Haible_Juergen#Tel2743]

Hi!

Over the weekend, I did the first tests with my PS-3100
Resonator Clone. (Thanks to Romeo, who came up with the
idea to clone this thing!)
Many people love the PS-3100 mostly for this Resonator section
that allows very unique phasing-like sweeps. Like on a 6-pole
Phaser, you have 3 peaks in the frequency response, which are
swept by a common CV. And also like on a Phaser, you have
a common Resonance control for all peaks together. The great
difference is that you can manually adjust the initial position
of each individual peak. The reason is the completely different
implementation. (And to be honest, the peaks of a Phaser are
also shaped in a different way ...)
The resonator consists of 3 voltage controlled BP filters that are
connected in a parallel way (i.e. outputs summed up). The Q
factor of each BPF is fixed to approx. 50. You change the shape
and height of the peaks by simply mixing the filtered and the
unfiltered signal.
The voltage control is made with dual-type optoisolators
(a center-tapped LDR and a LED in a black enclosure).
Now a single BPF only consists of 4 (four!) components:
two capacitors, one opamp, and the optoisolator that replaces
the two resistors of a garden variety BPF.
The ideal thing for DIY experiments!
Of course, there is a little bit of something else around this:
exponential current sources for voltage control, a Low-cut
filter in front of the BPF's to avoid killing your speakers
when all 3 resonators go to the subsonic range.
I plan to make a stand-alone unit, so I added some other useful stuff,
that is a MS-20 style LFO with contiously variable waveshape,
external modulation inputs, and a sophisticated Pedal control
routing that can work on LFO amount and/or directly, both
with different amounts. If you don't plug in either an external signal
or a pedal, the respective potentiometer becomes a manual
control for all 3 bands together.
I also included a tri/sine shaper with a switch to choose sharp
or rounded corners on the LFO.
With these additions, an Eurocard is pretty filled.

As I said, I tested the basic functions (filter and LFO), and it
works just as intended. Does sond different than a Phaser
(I don't have a PS-3100 for A/B comparison). Very good
SNR. I will lay it aside until I get a front panel in a few weeks.
Then I will test the full functionality.

JH.