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POLIVOKS Filter Clone



Special thanks to Allan J. Hall for his great contribution to this project !

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 . 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 controled 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 sligthly adapted to modern modular synthesizer standarts

  1. Added output amplifier-buffer stages for both outputs with a gain of 11, because the audio level on outputs is rather low .
  2. The vintage filter was powered with +/-12.5V. The clone can also work under +/-15V .
  3. CVs calibrated because programmable aop have a range for the Iset pin were they work fine.
  4. Added a reversible cutoff frequency CV attenuator (option)
  5. A fixed attenuator ( 100k ajustable pot ) added to the audio input jack to avoid overload -not on the schematic.


Russian equivalent parts...

European parts suggested here are working equivalents . The first reference proposed is the closest from the original ( hacked)

Russian Ref
Europa/USA Ref
KR140UD8B uA740 , uA741, LF351,... Single standart AOP
KR140UD12 uA776, MC1776, LM4250,NTE888 Programmable low power AOP
KT315G 2N3904A NPN transistor

The LM4250 GainBandwith vs Iset curve is not exactly the same as the UA776: much more sensitive ...So both 110K resistors wired on Iset pin to limit the current flow must be increased at least to 1M ohms. On my prototype ( +/-15V) i have used 1.2MOhm with a couple of LM4250 in metallic rounded box ... There is probably some other programmable opamps on the market able to work here

For the Cutoff CV amplifier, the vintage russian opamp is a hacked UA740, but any single op amp will fit well. The NPN transistor is not very critical too.

This filter is also is great to process directly external audio signal ( -10dB) . The addition of a little mixer or a simple fixed attenuator before the audio input is advised specialy if you use this filter with hi level modular VCO waveforms, to avoid permanent overload !

Front panel

1x5U front panel in MOTM format fit with 3 pots brackets, suggested panel : Polivoks VCF Clone 5x1U Front Panel (fpd)
It looks like this when finished ...

And the sound ?

Allan, who was able to do a direct comparison with the Polivoks synthesizer, report the clone sound very very close from the original. An electronic clean sound is produced at low Q .The filter start to self oscillate with the Q pot set over 2/3.The resonance sound progress with a serie of harmonic steps when the Q pot value is increased. It is a very musical effect, much accentuated if the filter is overloaded ! With Q set to max , the sound suddenly become extremely "harsh" a lot of character... This filter is less noisy than OTA based filters... Curves bellow show a spectrum analysis of LP and BP outputs with Q pot at minimum and maximum with cuttof frequency set at around 1kHz. Clic on the picture to enlarge .

Here are sample sound of the Polivoks filter. Contribution of Raphael ( Paris-France)

      1. Warp633 + Polivoks vcf clone - Loop1 (mp3)
      2. Warp366 + Polivoks vcf clone - Loop3 (mp3)



Polivoks VCF Clone pcb + Assembly manual
are available on order


© Marc Bareille 2003-2007