What happens if you take your equipment to a different location, a whole other building?
Start a process of elimination and only change one thing at a time.
With just the amp plugged in, try a different bass using the same cord.
Try a different cord
Try your bass in a different amp.
You said the amp and bass are new so I can assume the amp has a grounded plug. What about the wiring in the building?
Years ago, before grounded receptacles and polarized plugs, just flipping the plug 180 deg sometimes reduced or eliminated hum.
Start a process of elimination and only change one thing at a time.
With just the amp plugged in, try a different bass using the same cord.
Try a different cord
Try your bass in a different amp.
You said the amp and bass are new so I can assume the amp has a grounded plug. What about the wiring in the building?
Years ago, before grounded receptacles and polarized plugs, just flipping the plug 180 deg sometimes reduced or eliminated hum.
