This module is used, in excellent condition, cleaned, and fully functional.
Inspired by the legendary SSM2040 filter chip, made famous by the Sequential Circuits Prophet 5 Rev 2, and the SSM2044 filter chip, made famous by the PPG wave 2.2, the Z2040 is highly versatile 4-pole filter that is more than just a by rote copy. The first, and indeed primary, point of departure is the all discrete design at the core of the circuit. Beyond that is a fully blown out complement of modulation inputs, engineered to handle CV and audio rate signals.
Standard filter sweep applications can be realized at the FM input, and the VC-FM input adds modulation of incoming FM signals. Voltage control of resonance is also available, which can be used to modulate and even clip the sine wave produced by the self-oscillating circuit. Lastly, the VC gain input means the Z2040 also has an integrated audio VCA, which can be configured to affect the input or output of the filter.