Formanta Polivoks

Formanta Polivoks (with its logo panel missing, unfortunately)

This was Bell Tone’s first Polivoks job, though not my first Russian synth repair as I have a UDS MARSH drum synth of my own. My goals were basically to “assimilate” this Soviet-era Russian for life in the modern United States and correct a few issues with the keyboard.

My first and biggest observation about this synth is that it has the absolute worst-feeling keyboard of any synth, nay, any keyboard instrument of any kind! that I have ever felt. The key feel is absurdly light, yet you feel and hear pieces of thin plastic squeakily scraping against each other as you press the keys. There is very little to push the keys up and it’s very easy for the keys’ reed switches to get stuck in the “ON” position if the key is even a little bit too low.

I’ve never worked on another synth that used reed switches in its keyboard, or even seen a reed switch at all except at some old dude’s electronic surplus stand at a flea market. It’s a mechanism consisting of two (ferrous) metal tabs inside a thin glass tube, sitting just a tiny bit separate from each other. When a magnet comes down close to the tube, the lower tab is lifted up and the switch closes. In this case, the magnets are glued into the underside of each key.

Circuit boards inside the Formanta Polivoks
Circuit boards inside the Formanta Polivoks

Fortunately, the electronics of the synth are organized and built reasonably well. One of my main jobs was to convert the synth from running on the Russian 220VAC to 120VAC and update the power supply. The synth contains a 22-terminal power transformer, which is so quintessentially Soviet in its one-size-fits-all utility! It has many small secondary taps that can be used in myriad series and parallel configurations so that the same transformer could be used for a wide range of devices with different needs. Probably one of the more successful manifestations of a familiar Soviet concept. I replaced it with a nice little 6VA one (Signal Transformer 241-4-24) which is much lighter and smaller.

Original switch from Formanta Polivoks (left); replacement switch (right)
Original power switch from Formanta Polivoks (left); replacement switch (right)

You’ll also see that the power switch interrupts both sides of the AC line. This is because the AC mains in Russia is not polarized, meaning both sides are functionally the same and neither is tied to ground. Here in the US interrupting both sides like this is both unsafe and illegal. Only the line/”hot” side should be interrupted by the switch. The switch in this unit was not making contact anyway, and had to be replaced. E-Switch P197EESB works great after adding a tiny bit of epoxy around the outer edge of the plunger to help it fit into the marginally larger original cap. Let the epoxy dry and sand it back to a square before putting the cap on though! The spacing for the screws on the new switch’s bracket is different, but I just installed it at a right angle to the original switch and drilled new PCB holes. Just take care when measuring as the E-Switch’s screw holes are not centered in its footprint.

Formanta Polivoks power supply update

Left to right: Polivoks’ 22-terminal transformer. Polivoks’ original power supply filter capacitors; power supply PCB with new filter capacitors installed to replace the bolt-on ones!

Finally, it is possible to replace the giant 2000 uf bolt-in power supply capacitors with new ones mounted on the PCB. I just drilled some new holes for leads in the appropriate traces of the main power supply PCB (one of the 200/220 uf capacitors also had to be relocated by ~5mm to make room) and was able to solder some regular sized modern 2200 uf capacitors right into the board as if they were born there, after sanding off a little area of the conformal coating. I am gratified that when you look at the power supply section now, you see what I would say is just a lot less junk.  Smaller transformer, no giant capacitors, significantly fewer wires running everywhere.

The second thing required to “Americanize” this synth was to replace the silly 5-pin DIN audio jacks with 1/4″ jacks. Presumably the Soviets chose to use these jacks for their music gear so that even if some upstart got their hands on a mixer or amplifier from the Capitalist world, they wouldn’t be able to use it with any of their Communist synths. It is not easy to see on the schematics to see what exactly the terminals connected to the original jacks correspond to, due to a combination of blurriness and Russian-ness, so I’ll just stick all that info here:

4 – ground, for all.
16 – low output
7 – high output. Apparently the original jacks had high and low output on different pins of the same jack– not sure how that would have been used in the mixer/amp it was connected to! Even high output is pretty low amplitude, use high.
5 – headphone output. Just double this signal on T and R of a stereo jack.
17/8 – pedal — connect to T and R of a TRS jack. This is supposed to be a resistance pedal and controls the filter.

Thanks to having taken one semester of Russian in college (yesssss) I was able to sound out the Russian words in the schematics. Some of them were pretty self-explanatory but most of them were definitely not words we learned in Russian 101. Here is some fun Russian synth vocabulary that I learned, and now you can too!

питаний (pitaniya) – power supply
клавинатуры (klavinaturi) – keyboard
модулятора (modulyatora) – modulator (LFO)
филътра (filtra) – filter
генератора (generatora) – generator (oscillator)
управляемых усилителей (upravlyemikh usiliteleii) – controlled amplifiers (VCA)

Oh, how does it sound? It definitely sounds distinctive: very gritty, buzzy and sort of bumpy. People will try to describe the sound of any analog synth as “fat” but this is one that I probably wouldn’t call that. Interestingly, the sound reminded me most of two things: a mono version of an Akai AX-60, and a Wasp, even though the Wasp uses a very unusual CMOS filter and this one is just a simple op amp VCF. Definitely a distinctive sounding filter!

16 thoughts on “Formanta Polivoks”

  1. I don’t know why exactly, but this stuff is fascinating. Any chance of posting an audio file of the sounds coming from this keyboard, Comrade?

  2. I’ve been on the “no new synths” bandwagon for at least 10 years, given the crazy prices of the last 15 or so years, but couldn’t resist when a super clean Polivoks came up for sale on Reverb last year. I held my breathe, not knowing if the Seller would perform, but it showed up in excellent nick. Very quirky design and construction, as this article alludes, and befitting its Soviet era military factory heritage. How does it sound? Very raw, lots of character, I like it. I have owned most of the mono synth “heavy hitters”; Mini, 2600, Oscar, OB-1; and the Polivoks can hold its own.
    Now to install the Russian midi kit I purchased. I wish I had a semester or two of Russian language class to help understand the tech documents!

  3. 3 or 5 (for stereo) pin DIN connectors were normal in European consumer electronics from beginning of 60th. 3 pins were here for both input and output. So it was much easier for consumers to interconnect say a radio with their tape recorder. They needed just one cable with with 3 (or 5pin) DIN male connector on both sides. It provided tape recorder with signal from the radio and vice versa.
    When Japanese electronics took over, DIN connector disappeared to dismay of consumers.

      1. hi Alison nice to meet you , i got a plivoks but it seems like the FILTER ADSR is not working , do you have any idea how i can fix this ??,thx

  4. just got one of these and it’s a plastic beast. \very nice synth but rough. great for basslines and drones. The LFO is always very fast, so I am investigating reducing the it’s speed.

  5. Hi Alison.
    Interesting report – thanks.
    Do you happen to have ever seen/used/opened one of the Polivoks’ filter pedals? I got one, but don’t really know how the cable has to be made (which pins for what purpose)…
    Thanks for any help…

  6. I had a Polivoks with faulty PSU, regulation was not operating well.
    As I did not want to buy bathes of 100s of components on Ebay, I changed the controlled power transistor regulation by more modern regulators by Texas instruments and changed the transformer for a toroid. I kept the original diode bridge and trimmers.
    Nice idea for the capacitors, will definitly do it
    Nice job, like you said a distinctive sounding synth that can go crazy

  7. Hi Alison. I am working on a polivoks (I affectionately call it the “Worst Polivoks Ever”). I see you replaced the transformer with a 120v to 24v model. Did you simply NOT use any of the remaining circuit, other than the fullwave bridge rectifier and smoothing capacitors? I ask because tapping the xfrm to give +/-12 v won’t work properly with the power transistors on the PCB. Was the polivoks happy with +/-12v vice +/-12.5 v? Was the output from the rectifier smooth enough to get it to run well with no other conditioning? Thank you for any clarifications.

    1. Actually, once an AC voltage is full-wave-rectified and smoothed, the resulting DC voltage will always be about 1.4 times what the initial AC voltage was. So here it’s +/-12V*1.4 which gives +/-16.8V. This voltage is totally ideal to feed the rest of the circuit including the power transistors so it can be trimmed to a clean +/-12.5V.

  8. Hi! I love reading your repair stories! Kind of like watching this old house for synths. Did you end up replacing the keys/keybed on the synth since had such a crappy feel? I like the sound of these synths but was curious if the keybed could be replaced with something nicer. Thanks again for sharing!

    1. It does use 1V/octave so you could theoretically drop in any keyboard + keyboard circuit (so you can’t just plop in a salvaged Pratt Read keyboard for example without the supporting circuitry) that will deliver 1V/octave.

  9. Hello,
    Great write-up :).

    I’m currently thinking about converting mine to 117 but I can’t seem to find Signal Transformer 241-1-24. Was that indeed the one you used?

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