Let's keep the technical description short and concentrate more on the sound:
The System X Filter has three adjustable audio inputs and three CV inputs for controlling the cutoff frequency. It can oscillate at high resonance settings. Like the original it has a 24dB/oct output but the circuit has been expanded by a 12dB output which is 180° out of phase. Mix both outputs will result in a band pass. The circuit uses two LM13700 ICs.
Soundwise the filter is first class! The audio inputs start to distort very nicely beyond 3 o'clock position. It's no dull clipping but beautiful overdrive crating plenty of new overtones. Harmonic material like squares, sawtooths and the product of a wave multiplier get a glassy brilliance. At mid resonance settings and slight overdrive you'll get a gnarly growl which is a little instable.
Our recommendation for "in your face" sounds: two copies of the same signal into both inpus, level to the max, resonance to 3/4 and cutoff modulation with a fast decay envelop. The result resembles a distorted TB-303 a lot. Purists, please don't punish us: of course it's not identical but the typical old Roland character is unmistakable.
For "instant rave" sound just send the mix of three slightly detuned oscillators into the filter, that's it.
three audio inputs, 12dB/oct output, 24db/oct output
three cutoff CV inputs
3U Eurorack module, 10HP wide, 59.5mm deep
Current draw 10mA @ +12V and 10mA @ -12V