The 3224 is a 4 pole dual filter which uses a pair of CEM3320 ICs. The high pass is in series before the low pass. They have independent resonance controls and the LP has a resonance CV input.

This description is from the Series 3000 Modular Synthesizer Instructions Manual.

A later revision of the board shows that added resistor incorporated.

I do not have a reference diagram for the 3224 but do have a schematic. There were a number of errors in it that I corrected on this copy.

3224 Schematic

Calibration

The CV Bleed trimmers set the frequency input control voltage rejection. Disconnect signals from the INP, Fhp, Flp, and RES LP inputs. Set the trimmers to the middle of their range. Set the FREQ and RES controls fully counter clockwise. Apply a sawtooth unipolar waveform in the audible range from an oscillator to the FHP input. Adjust the HP trimmer for a minimum output signal at the - terminal of the 10 uF capacitor at the top. Apply the sawtooth to the FLP input. Adjust the HP trimmer for a minimum output signal at the OUT connector.

Adjust the Scale trimmers for 1V/Oct when self-oscillating.

Operation

I didn't take very many scope images as the operation is straightforward. This scope image shows both the HP and LP filters set to maximum for an all pass operation.

This image show a combination of the HP and LP filters.

This images shows a sweeping input and the filters adjusted to bandpass.

This image shows the self-oscillation.  The LP filter will self-oscillate from 7 Hz to 12 KHz.  The HP filter will self-oscillate from 4 Hz to 1500 Hz.

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