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Classic SEM-style filter

A fat 2-pole state variable filter which invokes the classic sounds of the synthesiser ‘golden years’, twisted and mutated to reflect the future. Multi-mode, state-variable topology and ‘hot-rodded’ resonance for self oscillation. Humpback is made with high quality components including silver mica capcitors.

Humpback has a sound all of it’s own. Low input levels will give you a traditional 2-pole filter sound – warm, but clean. As the filter is driven and resonance increased, the distinctive character of the filter is revealed – a ‘rubbery’ resonance which seems to pluck out harmonics.

The Humpback multimode voltage controlled filter is a 2-pole, CA3080 based implementation of the classic state variable architecture. The controls of the filter are as follows:

  • Filter cutoff – a hardwired DC voltage frequency control
  • CV inputs – two frequency CV inputs are included on the panel and controlled by attenutators.
  • Outputs – lowpass, bandpass, highpass and notch are available simultaneously
  • Signal input – one signal input is available on the panel
  • Resonance-resonance control is included and is hot-rodded to allow self-oscillation. In self oscillation the filter will produce a sine wave output.


  • width: 8hp
  • depth: 38mm
  • power: +72mA -70mA + @ +/- 12V