Schematics / Polivox VCF Layout
This filter is a clone of the famous vintage russian analog synthetiser named .Inside this synth there is an incredible and very original filter invented by Vladimir Kuzmin. Please visit his web site at http://www.muztech.com . It is a Lowpass ( LP) and Bandpass (BP) voltage controled filter with a special design and sound . A Vodka filter...The clone contains only cheap common parts, and it is very simple to build... No calibration trimmers or accurate tempco stages required, it is not the spirit of this beast from the far East ...
Unlike most of Voltage controlled analog filters who use a combination of a fixed capacitor with a variable resistor element ( OTA, opto,etc..) the filter core here is just a pair of programmable low power operational amplifiers ( PLPOA?). At first sight, it look like a classic SVF but with a difference: there is no capacitors ! CV modulations are applied on the current setting pin (Iset) to reduce or increase the GainBandwith of the aop who act as a variable time constant RC element. It is a 12dB filter. Sound as well. A bit wild at extreme Q, remind a little bit the Korg MS20 on this point . Frequency modulation on CV inputs work well with this filter!
The vintage schematic has been slightly adapted to modern modular synthesizer standards
Added output amplifier-buffer stages for both outputs with a gain of 11, because the audio level on outputs is rather low . The vintage filter was powered with +/-12.5V. The clone can also work under +/-15V . CVs calibrated because programmable aop have a range for the Iset pin were they work fine. Added a reversible cutoff frequency CV attenuator (option) A fixed attenuator ( 100k ajustable pot ) added to the audio input jack to avoid overload
This the thread on the Forum ,the layout is built and confirmed Sebo : http://www.electro-music.com/forum/viewtopic.php?t=47831