A technician would have to answer that, I'm just a user. So far I haven't noticed any hum, my turntable is right next to the Denon DRA F-107DBA which still has a proper phono connection, speakers and the PC are also close by. What I haven't done yet is to connect the PLX-500 to the PC via USB and digitise LPs. But I know from earlier times that hum is possible on the digital recording. Then I had to unplug and remove all other devices. By the way: an ION record player, which was originally created for digital recordings, also has no earth connection.