The hum is probably caused by a ground loop. Due to safety reasons all metal parts of the A-100 cases are connected GND AND to earth
shield of the mains connector. If another component in your system (e.g. mixer, power amplifier ...) is connected in the same way a
ground loop is generated. The problem is that the safety reasons (all metal parts connected to earth shield) contradict to the audio
connection rules (not GND loops). Possible solutions are:

using special cables with GND connected only on one side
DI boxes
disconnecting earth shield (not recommended)

Best wishes
Dieter Doepfer

> I’m still interested in knowing what the original cause of the hum is (and a solution) if anyone knows.
>
> Thanks!!
>
> Scott