Selling a beautifully built and fully calibrated x0x‑Heart with the EI‑303 interface by
jean.pri, with few tweaks — a complete, performance‑ready TB‑303 voice in Eurorack format.

v.1.1
Implemented some mods kindly given by P4L modular.
Tuning control sensitivity decreased.
Max resonance increased.
Max decay increased.
Calibration stability improved: clean 4 octave doubling, ~ 2 cent deviation.
Added:
authentic tantlm capacitors,
precision 0.1% tolerance resistors,
high quality Alpha potentiometers.

EI‑303 adds:
- 303‑style control panel
- controls and CV for Saw/Square mix,
- overdr1ve, Filter FM controls
- Invertible Accent/Slide knobs with led illumination,
and more intuitive, ergonomic layout for live tweaking.
- calibration controls - easily accessible.
Condition: fully working, clean build, accurately calibrated across 1–5 V, power cable + screws.