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XAOC Devices Batumi II & Poti II

Eurorack Module By Robin Vincent
Published November 2024

XAOC Devices Batumi II & Poti II

It’s been 10 years since the original Batumi quadruple low‑frequency oscillator appeared. It was a solid, four‑channel LFO with sine, sawtooth and square outputs with the option of switching out the saw for a triangle or trapezoid shape. It had four different modes: free running, fixed phase, variable phase and time division, and had CV control over reset, sync and frequency, which could push the range all the way down to 53 minutes. The Batumi has been a reliable purveyor of Eurorack modulation.

Prompted somewhat by the unexpected release of a clone, XAOC decided to reassert themselves with a new version that pulls in the expansions of the past while pushing it into the realms of audio as a four‑channel VCO.

Batumi II

The Mode is now reflected in the four colours of a single LED on the left of the module, and our choices are Free, Variable Phase, Divide and Multiply. On the right is a Wave selector button which, through a six‑colour LED, sets the assignable output waveform. On the original you could only set this, very inconveniently, on the back of the module via a jumper. XAOC introduced the optional Poti 1974 breakout expansion to bring the switch to the front, which certainly helped. This is now built directly into the front panel. You can choose from triangle, saw in both directions, trapezoid and stepped or smooth randomisation.

With those small adjustments, the Batumi II feels like it’s been perfected. Any criticism that could be levelled at the original has been smoothed away and it remains a completely solid four‑channel source of slightly more modulation. However, two new aspects elevate this no‑nonsense LFO into a surprisingly creative device.

As a four‑channel VCO it gets a completely new lease of life. Each channel can be fed 1V/oct sequences and act completely independently as a melodic oscillator with sine, square or one of the assigned waveforms. While the range of the oscillator on the slider only goes up to 100Hz, it can be pushed all the way up to 5kHz with an input voltage, giving it a useful range of octaves. Tuning can be a bit tricky as you’ve got very little room to play with on the slider at audio frequencies. I found putting the sliders all the way to the top gave a slightly sharp G2, but all four were consistent. Outside of Free mode, you could run them as an out‑of‑phase four‑oscillator cluster with channel A dictating the melody, or, in Divide mode, you could find octave‑down sub‑oscillators.

Poti II

The other remarkable aspect can be found in the new and completely different Poti II expander. The Poti II adds a button so you can select each channel individually and set its own assignable waveform. Once selected, you can attenuate the incoming CV, the sine output and the assignable output level for that channel. It also adds a modulation input for each channel with a three‑way switch that lets you set either wavefolding on the sine wave, wave selection on the assignable or pulse‑width modulation on the square wave.

So, in playing with the Batumi II, I found myself doing all the usual modulations and nodding my head in response to the predictable, solid outcomes. I very much enjoyed using the four VCOs because it becomes a great tool for chords, intervals and harmonies. All great stuff. But then I started to work it back into itself and realised that it has a phenomenal amount of power as a self‑driven generator of waveforms. With a couple of patch cables, I could have a tuneful sine wave oscillator on channel A, being played by stepped voltages from channel B, while being folded by the sine wave LFO from channel C and reset by a pulse from channel D.

The ability of the Batumi II to interweave with itself is very satisfying. The Poti II is an essential companion that gives it so much tonal potential and more nuanced modulation through attenuation and shaping. It can be all sorts of things like a pair of VCOs with self‑modulating wavefolding or PWM, it can be an FM sound source, a fat pulse wave machine, or a source of sound, randomness and modulation all coming apart in different directions. The Batumi II is overwhelmingly useful in a small system but superbly multi‑functional in any setup.

Batumi II £289$369.99, Poti II £75$99.99.

www.xaocdevices.com