The filter abuses digital inverters as operation amplifiers what is very formative to the sound. The filter is equipped with a band pass output and a combined low/notch/high pass output. A control knob defines the relation between low and high pass signal for this output. In the middle position of the mix knob one obtains a notch filter. The volume of the audio signal can be controlled with a knob and even distorted. Of course the filter features resonance but this one can´t self-oscillate (see misc..).
The module can be modified to allow self-resonance. "Soldering a 10k resistor in parallel to R13 (27k) leads to self-oscillation of the filter at the max. resonance setting of the resonance control. R13 is located in the gap between IC1 (CD4069) and IC2 (i.e. the upper CA3080, close to C4/100pF)".
audio input, bandpass output, lowpass/notch/highpass output
two cutoff CV inputs: one with 1V/octave and one with attenuator
3U Eurorack module, 8HP wide, 45mm deep
current draw 30mA