When connecting a device with a standard MIDI jack to the GT-1000CORE, use a TRS/MIDI cable (BMIDI-5-35, sold separately).
For connecting a device with a 3.5 mm stereo mini-plug MIDI jack (e.g., BOSS 200 series), use a cable with stereo mini-plugs on both ends (RCC-5-3535, RCC-10-3535, sold separately).