via BugBrand
"The FilterQAmp (FQA) combines a 2-pole State Variable VC Filter with a Linear VC Amplifier and an inbuilt variable-decay Envelope Generator. It is capable both of processing and, when the filter is self-oscillating, generation of synthesised sounds such as drums.
The VCF section contains a State Variable Filter (similar to my other designs) – this offers switchable Low or High Pass responses and covers the full audio range. It is temperature compensated & tracks 1V/Oct accurately. The Resonance/Q is voltage controlled with a linear response up to self-oscillation – this creates a pure sinewave, useful for synthesis.
The VCA is linear in response and takes the Low/Hi-pass output from the VCF section. It can either be set, via rear jumper, to a clean response (gain from 0 to +1) or saturation (gain from 0 to +1 then +/-5V zener clipping beyond – unity at approx 10 o’clock rotation).
The Filter, Q and Amp sections each have a CV Modulation depth control with switchable polarity (centre off) – the Filter has an additional 1V/Oct control input. In addition there is a simple variable-decay Envelope Generator which can be fired either with the manual Trig button or via the Trig input – this has a comparator so triggers on any signal over c.+1V. Decay time is variable between approx 15mS and 3Secs with an amplitude of 0 to +10V. The envelope is internally routed to modulate the Filter and Amp sections via individual depth controls – it could be manually patched to QCV with a 0.75″ shorting bar or cable.
When Q is set to full, the self-oscillating filter makes good sound generator – it can also ring when set below self-oscillation & fed with sharp edges such as gate signals. A basic drum synth can be achieved with self-oscillation and the decay envelope opening the VCA – try varying how much the envelope modulates the filter cutoff too. You can feed the main output back to the FCV input to self-modulate, resulting in an interesting peaky waveform."
