The Toppobrillo Multifilter is a eurorack state-variable filter - the original version from Toppobrillo
This module is pre-owned and in excellent condition.
The original manual can be found here: http://sdiy.org/toppobrillo/multifilter.html
Some features from Toppobrillo's original site:
-4 outputs: -12dB/Oct Lowpass, Hipass; -6dB/Oct Bandpass and Notch
-Notch "Balance" control dials in the H/L ratio with constant power design
-voltage-controlled resonance from none to oscillation
-clean self-oscillation over entire range; ~15-15kHz
-calibrated 1V/Oct input; tracks ~4 octaves
-CV input with reversing-attenuator
-voltage-controlled input gain available at the main signal input. 'overdrive' available for extra processing
-user-selectable gain mode; "standard" or "gain compensated" via special gain-compensation loop
-user-configurable "Aux" input; either a 2nd audio input or a 2nd control input
More from their site:
the Toppobrillo Multifilter is a new/ traditional state-variable design based on a great modern quad VCA chip, the SSM2164. this, in part, helps make the Multiflter what it is, a clean, quiet, stable and very controllable filter at it's core, without limiting its palette, well suited for processing anything you can run through it. much attention was paid to the range and feel of the controls, inputs and overall usability, including all options standard and more; a very versatile processing tool with amazing sound in a small package.
the so-called state-variable filter has a long history in electronic music- traditionally the most versatile voltage-controlled filter at any analog synthesist's disposal. there were several classic design examples and variants produced throughout the heyday of analog synthesis, such as those implemented in the Oberheim SEM, the EDP Wasp, and the fabled,albeit lesser known filters such as the famous Serge filters and Arp 1047; the classic SVF configuration is simple and versatile- with several different filter responses available simultaneously 'for free' by nature of it's design with no elaborate mixing schemes. traditionally there have been some considerations when designing a wide-range filter with variable Q using this topology, for instance, relative instability/ generally poor sound and behaviour at very high Q, many designs get around this by limiting the maximum Q available, among other things. those that are designed to allow for self-oscillation will often become unstable at the threshold and have inconsistencies initiating or mantaining oscillation across the entire audio range.