Here is how you change the Midi Clock source in the JX-03.
System Settings
1. While holding down the [MANUAL] button, press [3] button
* Keep holding down the [MANUAL] button.
2. Press a numeric button to select the value, and release the [MANUAL] button to confirm the value.
[1] (AUTO)
If MIDI clock is being input to the MIDI IN connector or the USB
port, the JX-03’s tempo will automatically synchronize to MIDI clock
(default).
[2] (INTERNAL)
The JX-03 operates at the tempo specified on the unit itself. Choose
the “INTERNAL” setting if you don’t want to synchronize to an external