Got a ground loop hum, or what sounds like a ground loop hum. Happens with the Zoom interface and the Carver C-1. With nothing hooked to the amplifier's input jacks it is dead quiet. If I hook up any RCA cords a little hum starts. If I hook RCAs to preamp or interface hum gets louder. If unhook one RCA the hum gets quieter.
Now I checked to see if the input jacks are isolated from the chassis, they are. I tried lifting the single point chassis ground and it still hums, I took the copper piece that was between the jacks out and used the solder tabs that came with these jacks (Switchcraft). I also replaced the coax cable between the jacks and the driver board. Still hums......