Voltage controlled state variable filter with all the bells and whistles.
The filter can be controlled by playing dynamics (envelope follower), voltage controlled LFO/Sample&Hold or manually with a knob/external expression pedal. Also has a buffered effect loop, wet/dry mix and active volume control.
The envelope follower circuit is pretty complex, at least in the stompbox world..
Frequency specific somewhat log. amplification/attenuation, full wave rectification..
Attack and release times are completely independent and non-interactive. The release is linear (as opposed to the 1/2piRC discharge), which means the effective filtering is more effective and any residual 'ripple' or AC components in the envelope voltage is reduced.
However, the change in release time for a given rotation of the release-knob is exponential, which means the response seems natural and useful.
It has dawned on me that voltage controllable everything is way beneficial..
I've spent a lot of time with the sidechain and I'm very proud of the result.
The LFO/Sample&Hold rate can be modulated by the envelope follower. The initial frequency is set with a knob. Another knob then sets the amount of modulation. Set fully CCW, the rate decreases from the initial frequency when picking harder. Set fully CW the rate increases from the initial frequency when picking harder. And set to the 12'oclock position the modulation is disabled. Other controls work in a similar way. Switches < Pots.
All analog. 22 ICs, 28 Transistors.
|Filter block diagram|