From the Synthtech website:
The MOTM-420 is a switch-selectable LP/NF/HP (lowpass/notch/highpass) voltage-controlled filter. Using the same filter structure as the MS-20, the MOTM-420 has a unique “cutting” sound that is perfect for techno, acid, house, and other dance music. The VCF will over-drive/distort in all modes, and the resonance can be cranked into self-oscillation. The LP/HP slopes are -12dB/oct and the NF is -6dB/oct.
The MOTM-420 includes two on-board three-channel mixers: one for audio and one for control voltages. Having three separate audio inputs eliminates the need for a separate mixer module in most patches. Multiple MOTM-420s can be chained in series to exactly emulate the MS-20 filter (a HP followed by a LP).
The MOTM-420 has a bright, “glassy” sound. This is due to the selection of parts used, and the filter design. The VCF will alter its resonance as the input amplitude varies. This was a “flaw” in the original design, but is the main reason for the sound!