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Xaoc Devices Ostrawa & Bohumin

Eurorack Module By William Stokes
Published May 2024

The Xaoc Devices Ostrawa mixer module.The Xaoc Devices Ostrawa mixer module.

Aren’t the full names of Xaoc Devices’ modules just so soothing? Unboxing and mounting the Ostrawa and Bohumin I’m reminded of the Polish developer’s generous ability to make one feel like their system might be edging just a little closer to the fabled European electronic music studios of yore. I favourably reviewed the Sofia Transcendent Waveform Analog Oscillator: Model Of 1955 a while back, and this time around it’s the turn of the Ostrawa Full Stereo Voltage Controlled Mixing Console: Model Of 1966 and the Bohumin Mixing Console Commander: Model Of 1966. You may have picked up on the geographical theme; the city of Ostrawa, by the way, is in the western Czech Republic, adjacent to which lies the town of Bohumin. That should give you a good indication about the relationship between these two modules.

The Ostrawa mixer offers four stereo channels of mixing and a single stereo aux send. It’s a very nicely laid‑out thing, with each channel offering a volume knob, a clickless mute switch, pan pot, aux send attenuator and LED level meter. Below these are per‑channel stereo inputs and CV inputs for panning (or Balance in stereo) and volume, meaning that any of the Ostrawa’s DC‑coupled channels can act as a CV‑controlled VCA if desired. The lowermost row of jacks is allocated to the stereo send and return, sum outputs and also a useful pair of Direct Input jacks for chaining a submix into the equation, or — as I often do — for feeding a module with its own volume control into the mixer without having to use up a channel.

It’s a nifty and compact design that fits a lot onto the faceplate without feeling cramped. I do like the tactility of sliders, but knobs were the right choice here and suit live performance well since they’re well clear of the mixer’s patch points. While it’s fair to say that four channels isn’t masses, there’s a generous amount of I/O to speak of if you really need some workarounds. I’ve never been averse to using two mono signals through a stereo channel, for instance, or to using the aux return as an extra input. The aux send — a huge selling point for those whose workflow is anything like mine — can be pre‑ or post‑fader, switchable simply with a long press on the mute button and indicated by the button LED changing from green to orange.

Xaoc Devices Bohumin expander.Xaoc Devices Bohumin expander.The Bohumin expander contributes an additional aux send, B, though this is far from all it adds to the Ostrawa. It also furnishes both sends A and B with their own master return attenuators and provides jacks (here labelled Active) to mute and unmute any of the mixer channels with gates. I was a little disappointed to find aux B can only operate post‑VCA, but it makes up for this limitation (at least in part) by offering CV control over each channel’s send, which is not possible with aux A and opens up a host of interesting patching potential, particularly when used in conjunction with the Active inputs and the VCA inputs on the mixer proper.

The Ostrawa is a sister module to another Czech‑themed mixer, the Praga (no prizes for knowing where that city is), which is similar in architecture and almost identical in its layout but differs in a number of functions. One thing about Xaoc’s range is that it does very well to build an ecosystem of modules that don’t just work with one another in the conventional modular sense, but in many cases expand one another’s capabilities from within. The Ostrawa is a prime example: it can not only be expanded with the Bohumin via a ribbon cable, it can also be chained to one or more Pragas or other Ostrawas for a mega mixer that can occupy the entirety of your lower 3U if you want it to. The Praga has its own expander to boot, the 10HP Hrad (meaning ‘castle’, with Prague containing the country’s most famous), which ostensibly endows its parent module with a master section including a headphone output.

That’s an astonishing amount of mix‑and‑match flexibility on offer here, and I’d argue that while these are on the pricey side in the first instance, in the longer term it all amounts to something quite budget‑friendly, since you can expand your channel count slowly as your needs grow. I for one would be very interested to see Xaoc Devices consider releasing modules of single channel strips for channel‑by‑channel customisability, anchored by the Hrad’s master bus... I digress. I’ve tested a number of Eurorack mixers, and the Ostrawa/Bohumin team is up there with the very best of them.

Ostrawa £420, Bohumin £230.

Ostrawa $549.99, Bohumin $289.99