Serpens Modular

Sirius Low Pass Filter


The Sirius filter uses similar analog architecture found in a number of classic 80s synths such as the Korg PolySix, Mono/Poly and the PPG Wave 2.0. We've then tweaked the design to integrate a germanium diode distortion stage to give this traditionally smooth filter some real bite as well as extending the resonance range so that it goes into self oscillation. This can turn the Sirius into a ground shaking sine wave oscillator that can track pitch at 1v/oct via the frequency cv inputs. The Bias knob allows users to not only set the pitch tracking themselves but to also tune the filter resonance, meaning resonance pings can be easily tuned to the key of your song. Two outputs are also available - a 'dirty' which passes through the distortion stage, but also a 'clean' which bypasses the distortion if you're looking for a more traditional filtered sound or want to patch the filter back into itself for interesting results.


  • 4 pole low pass filter with germanium diode based distortion.
  • Two individually attenuated CV inputs for both cutoff and resonance (four in total).
  • Two attenuated audio inputs for precise signal mixing.
  • Clean and dirty outputs allowing users to bypass distortion circuit and for self patching.
  • Sine wave oscillator with 1/v oct tracking via the fcv inputs.
  • Bias knob for resonance tuning and adjusting pitch tracking.


  • Width: 12HP