I knew nothing of this filter and only have the panel (I use the reverse side for a blank panel).  It apparently is an enhanced clone of the Synton Syrinx filter which had two resonant peak filters and a low pass filter originally designed around a pair of CEM3350 dual voltage controlled state-variable filter ICs.  This iteration of the filter appears to use a CEM3328 four pole voltage controlled low pass filter IC instead of the CEM3350 and is normalled to the output of the dual resonant filters.  It also has a three input mixer and two CV inputs for each of the filter sections.

The upper half of the panel layout and legends matches the original Synton Syrinx filter panel.

The bottom of the panel matches the original Synton Syrinx graphics.

Epilog

Interestingly enough, someone sent me one of these filters to repair as it never worked. I have no information on it so it was a bit of trial and error to correct the issues. It works quite well.

Operation

This filter has a lot of character. Each of the bandpass filter outputs is available separately and then combined in the Out jack which is normalled to the lowpass filter. This image is the input (yellow) and the two bandpass outputs (cyan and magenta) and the lowpass output (green).

These next three scope images are of various resonance settings showing the wide variety of waveshaping available with this filter.

This scope image shows just the lowpass filter.

This scope image shows the lowpass filter resonance.

The lowpass filter will self-oscillate from 5 Hz to over 6 KHz. Above 6 KHz the amplitude diminishes and the oscillations stop.

In fact, I liked this filter so much more than my 291M, I bought it.

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