KR-55 Modification & Repair Summary
Modification Work
Connected 10 external trigger inputs and 6 parallel outputs to the existing 3.5mm jacks. Triggers implemented using ULN2803, with a dedicated inverter circuit added for the Rimshot channel only. Designed and installed a circuit for external clock input (EXT CLOCK IN).
Repair Work
While building the voltage dividers for the parallel outputs, found 5 volume pots with contact failure and replaced them using donor parts. Replaced 2 capacitors in the voice circuit.
Audio Quality Adjustment
Added filter capacitors to the BD/SD parallel outputs and improved the resulting high-frequency noise contamination by also revising the ground connection routing.
