This module is a variation on the Serge Voltage Variable Q VCF module (VCFQ).

The VARIABLE Q VCF (VCFQ) is an excellent general-purpose VCF offering simultaneous low-pass, high-pass, band-pass and notch (band-reject) outputs. The resonance (Q) of this filter is dynamically variable by manual or voltage control. The VCFQ has two signal inputs. One incorporates an automatic gain control to prevent the filter from overloading at high Q settings. The second input has a level control so that the percussive effects of overloading the filter can be exploited. When a pulse is applied to the Trigger input, the filter will ring, producing a damped waveform similar to that produced by striking a resonant object. The nature of this ringing is controlled by the Q and the filter frequency. Percussive effects ranging from clicks to the sound of wood blocks and bell tones can be produced and controlled. This ringing effect can be used in conjunction with signals applied to either of the audio inputs to achieve highly controlled complex tonal qualities.

The VCFQ also includes offers an extended range featuring a sub-audio range. This low-frequency range is selected by setting the [RANGE] switch to 'LO' and allows the filter to be used as a control voltage processor. A fast envelope or trigger applied to the filter in the low range at high Q settings will cause low-frequency ringing, generating complex envelopes and damped vibrato effects.

NB: The GAIN Cells are no longer available as a DIY kit and will now be supplied as pre-built sub-assemblies along with the CGS512 PCB and are factory calibrated units.