Elta Music Polyvox PF-3

Elta Music have put the heart of the celebrated Soviet synthesizer into a convenient desktop box.

I’m surprised that desktop standalone filters are not more of a thing. I remember having a lot of fun playing with the Waldorf MiniWorks 4‑Pole filter in the back room at Turnkey [a London retail store] where I worked in the late ’90s. There have been a few others along the way like the Moogerfooger, the Fat Resonator, Sherman Filter Bank and more recently the Analogue Solutions Mr Hyde, but considering the explosion in DAW‑free, hardware jamming I would have thought standalone filters could fit in there quite nicely.

The most obvious reason for their lack of proliferation is that everything already has a filter. And most things with a filter let other things use that filter via an external input. So, have I already talked myself out of the need for a Soviet‑inspired, stereo‑linkable/mono‑decouplable, multi‑mode, noise‑infused, CV‑controllable filter in a bomb‑proof box? Or could Elta Music convince me otherwise?

Polyvox PF‑3

The Polyvox PF‑3 is based on a filter design pulled from the much sought‑after Soviet‑era Polivoks synthesizer (apparently the spellings are interchangeable). It uses the same UD1208 chip, which gives it that unique about‑to‑fall‑apart‑at‑any‑moment tone when you seek out the edges. Elta advise you to let the PF‑3 warm up for at least five minutes or you will get some horrendous feedback when the frequency knob approaches zero in Soft mode. I can attest to that; it’s definitely best to turn it on and go and make a cup of tea.

Apparently no two examples of the UD1208 are the same, which means the two filters will vary, something that Elta count as a feature rather than an issue. You can use the filters independently, as a linked pair for parallel mono processing or stereo filtering, or in series by plugging only into input 1 and out of output 2. However, it has no mono‑to‑stereo ability. Two Link switches will let the first filter CV and cutoff knobs control both filters.

Layout

From left to right you have a CV input tied to a CV attenuation knob and activity LED. The LED seems to be post attenuation so it disappears once you wind back past the number 2. That seems a little odd to me. Next is the cutoff frequency knob with enlarged numbering around it to draw the eye, and its companion, the resonance knob. Then we have the filter mode switch, which adds high‑pass and notch options to the Polivoks’ original low‑pass and band‑pass. The row is finished off with a level control and a wet/dry mix knob.

In between the two filters you have the Link buttons and a Hard/Soft switch. Hard mode follows the character of the original Polivoks filter whereas Soft loosens it up a bit to give you a bit less aggression. The difference is only really noticeable at high resonance levels, and at less extreme settings, the PF‑3 feels remarkably well behaved in either mode. Next to that is a noise generator with pink and white noise, a level control, and a balance setting to push it between the two filters.

The look, from the knobs to the face paint, are all pure Polivoks. If only the original was this sturdy more of them would have survived. I imagined it would be larger but it’s actually quite compact — about the size of a Korg Volca — and finished off with an over‑large domed blue power light. I like the ordered nature of the knob numbering. As on the synth, all the knobs go up to six. I asked the wizened synth nerds of the Internet if six was significant in Soviet machines but no one seemed to know. In any case it’s very aesthetically pleasing.

At the back are two quarter‑inch inputs and two quarter‑inch outputs.

In Use

My first instinct was to use the PF‑3 in a modular setup. It’s easy enough to drop it on the master outputs of a Eurorack case and run everything through it. But for this I was using a single bass line sequence with an envelope patching in the CV input, just like I would with any modular filter. Coming in and out in stereo at line level produces a nicely full and solid sound. The variation in the two filters gives it a lively, animated sound and never feels placed or static. I’m surprised at how smooth this is. I was prepared for grit and chaotic cascading resonances, but with a little restraint the PF‑3 is gorgeous.

Routing the master outputs through the PF‑3 is not particularly versatile, so I tried patching it directly into the oscillator path before the VCA. The leap in volume was quickly dealt with using the PF‑3’s level knob, and then it was operating perfectly as part of my rack. Blend in a bit of noise for ballast and you’re having a fabulous time. So, you can definitely use the two filters as a 0HP addition to your modular. And the nature of the stereo output is really quite lovely.

I have an Erica Synths Black Polivoks VCF and they are strikingly similar in tone. If anything, the PF‑3 felt more responsive and predictable. Sometimes I find myself fighting with the Erica to find that sweet spot, but I had no such trouble with the PF‑3. The Erica likes to go into distortion when the resonance is pushed, whereas the PF‑3 is more partial to screaming feedback. Each to their own, I guess.

With more conventional synthesizers you can only really use the PF‑3 on the outputs, which is interesting in itself. But it’s not as if you can bypass internal synth structures and use the Polyvox instead. Synths rarely have envelope CV outputs and so it’s a hands‑on, mix filtering affair, which does give you some cool things to do in performance.

However, when paired with a groovebox the PF‑3 becomes a proper Polivoks party. Low‑pass and high‑pass modes are blisteringly smooth and let you create effects ranging from subtle tonal changes to surgical strikes on your bass or hi‑hats. You really appreciate the lack of volume drop as you push up the resonance to pick out the snare in low‑pass or push a tsumani through the bass and kick drum in high‑pass. It’s terrific fun.

The band‑pass plays really nicely, giving you that solid sweep across the frequencies. The band is quite narrow, letting you isolate various elements of your track. In notch mode, though, I can’t really hear it doing very much. At full resonance it brings in some low‑level chaotic squeals, which are quite interesting, but otherwise the usefulness is lost on me. I should also point out the dry/wet mix knob, which is a great way of getting a bit more subtlety into your filtering.

At half past five on the resonance knobs in any mode the filters start to self‑oscillate. And they don’t just start oscillating, it’s as if the notion is being dragged out of them so they have no choice but to expel these oscillating tones. If you have something running through the filters it turns into a rough, gritty and unstable sound. However, on its own it’s pure and playable with the cutoff knob. You can tune the two filters together for some unholy wonderful melodies. If you link the CV and decouple the cutoff, you can play it like a dual VCO with some very gooey detuning. You get a quite interesting effect when you introduce some of the noise back in. It quickly descends from a pure tone into a nest of hornets. There is a small shift in tone and pitch when swapping between Hard and Soft modes but I’m not deeply appreciating the difference.

The PF‑3 is a great stereo filter that’s enormously fun to play with. It’s robust, easy to use and sonically solid until you push it to the edges.

Conclusion

The PF‑3 is a great stereo filter that’s enormous fun to play with. It’s robust, easy to use and sonically solid until you push it to the edges. It’s not as unruly as I expected, but that’s more to do with my presumptions about Soviet‑inspired tech, and I’m not in any way disappointed by how musical and useful this thing is. The CV control really elevates it to being a nuanced part of a modular setup rather than just a filter for doing crowd‑pleasing drops on your mix.

The two filters in my unit here were quite different, which added nicely to the character of the stereo output. But filter number 2 never got over the feedback when the cutoff was at zero in Soft mode, regardless of how long I left it on to warm up. It could have done with a bit more CV control, maybe even an internal LFO. But then this is designed for hands‑on manipulation. In which case the only thing really missing for me is a bypass switch.

So, could the PF‑3 prompt a slew of desktop filters? Well, we do have filters. Most DJ and performance‑oriented gear is going to have a filter of some sort on the outputs, so is the PF‑3 really adding anything? Yes, I believe it is. This is 100 percent analogue; you’ve got the versatility of running all sorts of things through it and it sounds awesome. It’s a great tool for any desktop musician.