Ketron SD90 module is the easiest arranger module to setup to practice piano, bass, and drums only arrangement with its built-in styles.

With the "Chord" slider on the left completely pulled down at its lowest, only the right hand voice (piano), bass, and drums of the selected style will sound. With the "Pianist" button pressed (and lit), you can extend the right hand voice (piano) to the entire keyboard. You can also combine the "Lowest" button with the "Pianist" button to keep the lowest bass note of your left hand playing.

If you want to practice walking / running bass on the left hand, you can press the "Manual" button. The "Manual" button can combine with the "Lowest" button. The "Pianist" and "Manual" buttons are mutually exclusive.