Bastl released firmware 1.7 for its Kastle 2 hardware modular synths, plus some alternative engines to try.
The Kastle 2 is a small, patchable, battery-powered modular synth or effects, depending on the loaded firmware. The Eurorack version is called Citadel.
Both Kastle 2 and Citadel are more than modular synths and effects; they are programmable environments that have been open-source since early 2026. The system firmware 1.7 is out now for the Bastl Kastle 2 and Citadel series with new additions
Bastl Kastle 2 firmware 1.7
Firmware 1.7 is a free update for existing Bastl Kastle 2 and Citadel users. It’s compatible with all versions: the Alchemist, Wave Bard and FX Wizard. It introduces some neat new features to these instruments.
A big new addition is Humanize and Swing in the sequencer engine. Humanize, for example, turns an existing pattern on its head by shifting all the triggers with a knob twist and gives you a new, fresh output. You can also control both humanize and swing with MIDI CC32.
Then, it introduces assignable LFO modulation to the Kastle 2 and Citadel hardware. You can now freely assign an LFO to a parameter, giving users more ways to add animation to sounds.
Alongside small bug fixes, the Alchemy firmware also now supports MIDI velocity and sustain.
Alternative Engines
The Bastle Kastle 2 engine is open-source, which has motivated third-party developers to build exciting alternative engines you can explore for free by flashing them onto your hardware.
Knoscillator, for example, is a synth powered by a unique stereo oscillator that oscillates over a parametric 3D curve called a knot. It also includes the original Citadel sequencer and a stereo delay to round out the synth voice.
Glazmo_Kastle2_Skrub by Oliver Torr records incoming audio continuously to a buffer and plays selected sections from that buffer. Harmonic mode adds two varispeed playback voices with selectable interval groups.
Chaotic mode provides clock-synchronized segment repeats, reverse playback, variable playback rates, stereo offset, timing variation, and feedback.
Another upcoming alternative firmware from Oliver Torr is Glazmor_Kick. It features a replaced sample player with a synthesized 808 kick engine with various styles and other features. Lastly, there is Kastle Chan v1.0 by sxilence6, which is a patchable vocal engine.
First Impression
Great new additions for the Kastle 2 and Citadel series. I hope there will be more alternative firmwares in the future. Currently, there are still relatively few even if the engine is open-source.
The new Bastl Kastle 2 firmware 1.7 is available now as a free download for existing users.
More information here: Bastl Instruments
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Thomann
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