Polivoks [Polivoks filter]

The Polivoks (also known as the Polyvox, or in Russian, Поливокс) is a cult-classic synthesizer manufactured in the the 1980s by the Formanta Radio Factory. Known for its aggressive sound, its unique filter has been replicated in the Eurorack format by several manufacturers. Instead of a typical RC circuit, it uses a Russian K140УД12 programmable op-amp (their equivalent to the classic uA776) as a current-controlled slew generator to filter out the desired frequency range without the use of capacitors. This is then placed in a typical two-pole state variable multimode filter design. The Polivoks filter is known for its eager and occasionally unstable resonance – I wrote a post and created a video detailing this using the Erica Dtech version of the Polivoks VCF.