Bastl Partially Open‑Sources Kastle 2 and Citadel, Launches Affordable DIY Kits

Bastl Instruments opened the door on deeper community involvement by partially open-sourcing its Kastle 2 and Citadel platforms and offering affordable DIY kits that put repair, modding, and firmware hacking within reach. The company published most of the core code under the MIT license and released comprehensive documentation, while retaining certain commercial assets such as board layout files, final artwork, and selected factory sample banks.

The move, announced January 21, 2026, preserves the three main firmware/apps - Alchemist (synth), Wave Bard (sample player) and FX Wizard (multi-effect) - as cross-flashable across Kastle 2 and Citadel hardware. That compatibility means a single community of developers and tinkerers can swap firmware between pocket instruments and rack-friendly modules without rewriting patches from scratch, accelerating creative work and bug fixes across both product lines.

Bastl also introduced a Citadel Eurorack Alchemist module and kit options to accompany the software release. Kastle 2 DIY kits are priced at about €128, while Citadel kits come in around €194. The pricing positions both kits as accessible entry points for makers, repairers, and anyone suffering from GAS for hands-on tools rather than turnkey gear. Kits lower the barrier to learning soldering, EEPROM flashing, and front-panel customization, while keeping a fallback option for users who want finished units.

Practical value is immediate. With source code and documentation available, you can inspect algorithms, create alternate UIs, or modify signal paths in Alchemist without waiting for vendor updates. Wave Bard access streamlines sample loading and personal bank creation, and FX Wizard code opens up multi-effect chains for experimentation in feedback effects and live routing. Cross-flashing simplifies testing across form factors, so a tweak that improves aliasing on Kastle 2 can be evaluated quickly on Citadel.

The retained proprietary items matter too. By withholding board layout files and final artwork, Bastl protects its production design and branding, and by keeping some factory sample banks closed it preserves commercial content that supports sales of finished modules. That balance allows community-driven software innovation without undermining the company’s ability to sell assembled products and curated sound libraries.

For the Vintage Synthesizers community, this is a pragmatic compromise that expands creative possibilities while keeping supply and income streams intact. If you want to mod firmware, fix a flaky component, or build a skiff-friendly Citadel Alchemist, the parts you need to tinker with are now visible. Expect a faster cycle of community fixes, third-party patches, and new sample sets from independent makers; just remember that some hardware files and factory banks remain off limits for now.