Available as an assembled Module and as a DIY project.
This Module is currently available.
Four pole VCF and quadrature oscillator
The Feague is a 4 pole VCF and quadrature oscillator with 0, 90, 180 & 270 degree outputs. It is based on the design in Electronotes 41.
It features a Lo/Hi switch to run it at audio rates or LFO rates, plus a nonlinear Q pot which makes for interesting behaviour when using as a VCF.
When using as a QUO, the nonlinQ pot is used to increase the amplitude of the output signal, which is known to shrink somewhat at low frequencies in these kind of oscillators.
https://www.nonlinearcircuits.com/modules/p/feague?rq=feague
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These merchants probably sell this module. Huh?
Nonlinearcircuits Feague
Nonlinearcircuits Feague