Review AcidboxII Polivoks VCF emulation


Erica synths is a Latvian company that create boutique synths, modular components and DIY kits. In December last year they announced a MkII version of Acidbox a Polivox VCF replica filter. I just had to order one and played a couple weeks with it and wanted to share my findings because it’s very much gearjunkies worthy.

Black box
The unit is a smallish sturdy black metal box which is clearly is meant as a tabletop unit because the adapter that comes with it has a very short cable. On the back you have the adapter input, off/on switch, (balanced) input, LFO sync in, control in and (balanced) output. So it’s a mono filter in case you wondered. On the front is a LFO section with knobs to control the LFO speed, LFO speed multiplier, LFO shape and LFO level. You also can adjust the LFO speed with the tap tempo button or use the LFO sync input. The filter section has of course a cutoff, resonance button and two switches to enable LPF or BPF mode or bypass the filter. This implies that the filter itself is 24dB in LPF mode and 12dB in BPF mode but I’m not 100% sure about that. You also have two knobs for input level and external control level. And to top it off you have also a level knob for white noise. The manual is a bit too short but covers all the basics.

Crazy resonance
The Polivox filters are known for its crazy resonance filter sweeps. With the AcidboxII you can get well into self resonance land and be abusive to your speakers. With the external control input you even can use the self oscillation as a tone generator but that seems a bit silly to me. I rather like to use to crank up the input level and get a very gritty and next to distortion type of sound. LFO modulation has various shapes like sine, triangle, saw, square, envelope and random. The combination of the LFO options there are a plethora of ways to shape the filters from subtle and slow to crazy fast

This unit is not a modular format but can fit in a modular setup quite well. You can order a version with a LFO output and basically have a modular unit with a filter and LFO. Maybe you would want to control the resonance level externally as well but that’s the only drawback I could come up with it. Using the CV inputs to control work pretty straightforward as you could expect. Did a little test trying to use the sync input with clave output of my 808 but I guess the output voltage was too low to trigger the LFO sync input.

What I very much like is to hook the filter up to an older rompler synth and combine the rich but very digital sound with a nice and creamy analogue filter. Add a tad of slow LFO modulation to it and you get this nice organic sound. Add a little bit of noise to it will give it even more charm. Or if you happen to have a synth with analogue filters you can bypass those and use this filter to get another sound because this filter has a rather unique sound to it.

The AcidboxII is a creative little black monster with an extraordinary sound. Two small drawbacks are the adapter chord is a bit too short and you cannot control the resonance externally.

Erica Synths AcidboxII Msrp €250

Post Your Thoughts