[sdiy] Looking for OB-8/CEM3320 filter gurus

[ChristianH]

Hi all,

I finally started working on that dead OB-8 filter.
Although the schematic looks a bit weird at first sight, it's starting
to become clearer, once all the 2 pole circuitry is omitted, leaving the
basic 4 pole part.

However, I don't quite understand the way the gain cells are working.
Is there a more complete data sheet than the 2 pages found at synthech.com?
To me each gain cell/buffer combo looks like an inverting op amp (plus
filtering of course), with a summing node, Rc for input, and Rf for
feedback.

But in the OB-8 circuit there are additional resistors (RX44, 59, 58)
that appear to add a negative DC offset current into the summing nodes.
These resistors are not present in the data sheet sample applications, so
they don't seem to be required by the 3320.
What's the use of this? Is it to improve the chip's operation in some way,
or is it to intentionally cause asymmetric clipping in each stage, in
order to spice up the filter's sound?

regards
Christian