Irrespective of location (to eliminate mains hum from other sources) tests give the following:
Bass with ordinary mag pickup - plugged directly into any mixer or amplifier = no hum.
Bass plugged into T1 fed input/output from L1 Model II via its ethernet cable = no hum on any outputs.
Bass plugged into T1 fed from T1 external power supply = hum, on all outputs including USB, irrespective of what amplifier it is feeding or none. Even with no outputs connected, the hum level can be seen on T1 "Tuning" selection, it overpowers the input signal from the bass.
Any ideas folks, have been trying to overcome this for ages, been on the tone.ca wiki, tried everything.
It sounds like you've done everything possible to isolate the issue. I agree. It's probably a fault in the T1 Power Supply.
If the T1 Power Supply is less than 2 years old, it may still be under warranty. You'll have to contact Bose in your location to see if you are covered. If that isn't applicable, then I'd go to an authorized Bose dealer and test the T1® with a new T1 Power Supply. If that works, buy it.
I'm sorry that I don't have better news.
ST
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