teePolivoks VCF
In 2016 we built the Polivoks VCF by ericasynths. This is a VCF (Voltage Controlled Filter) powered by old soviet era programmable opamps. Most resources can be found on ericasynths site, the module is also on modulargrid.
The module has a switchable LP/BP Filter (see Filter Article and can be used as crude VCO if the Resonance Knob is cranked up.