The Kastle can operate alone or with another tiny synth or drum machine.

Boutique Czech synth company Bastl Instruments has unveiled its latest device, a tiny modular synth that’s the size of the three AA batteries that power it.

The Kastle costs just €65, and is billed by Bastl Instruments as being ideal for newcomers to modular synthesis, but should also be useful to those who already have an existing Eurorack system. It can also be hooked up to other small synths, such as Teenage Engineering’s Pocket Operators and Korg’s Volca series.

The open-source device has a lo-fi digital sound that lends itself to soft or harsh tones. It runs off two chips that can be reprogrammed with an Arduino, allowing coders to change the synths’ sound generation and modulation parameters.

Pitch, timbre, wave shape and LFO can all be patched using the 10 tiny cables included in the box, while those with a larger modular system can connect the Kastle via two I/O CV outputs at the rear of the device.

The Kastle is the latest in a long line of unique products from the Czech company, whose products range from handmade wooden synth modules, to a tiny sampler called the Microgranny.


Read next: The 13 best affordable, pocket-sized, hackable, off-the-wall synthesizers



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