The 4075 filter is a discrete, voltage controlled, 24/db/oct cascaded transconductance low-pass filter, employing six pairs of hand-matched transistors. In its lowest FREQUENCY setting it shaves off higher frequency harmonics; its RESONANCE or “Q” circuit pushes those harmonics past the self-oscillation boiling point, projecting a thumpy, thrashing squeal, with explosive low to mid-range power and depth. The design is actually pulled from the four-pole ARP 4072 (better: more parts and trims), sans the 12kHz design flaw which hamstrung the original’s high end.