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.
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 241-1-24) which is much lighter and smaller.
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.
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!