That actually makes sense. Now disconnect all the inputs to the preamp. :)
Ground loops are caused by alternate current PATHS not sources. Are your monoblocks plugged into the same outlet?
Weirdly Specific HUM issue
I have a pair of KEF LS50 Meta's driven by (2) Schiit Audio Lidar amps configured as monoblocks, coming through a Schiit Freya+ preamp. I use an Ompower EM1100 conditioner and Audioquest shielded power and interconnect cables.
I get a slight but noticeable hum in the Left speaker only (farthest from the preamp), but ONLY under these conditions:
Plugged into (powered on) power amp only (no source connection) - NO HUM
Preamp connected (balanced XLR) and powered ON - HUM
Preamp connected (balanced XLR) and powered OFF - HUM persists
Hum only stops when I physically disconnect the input from the preamp (same with both preamp output channels)
Thoughts? Why would the hum persist even with the preamp powered down?
Thanks in advance.