On 02/08/2015 09:06 AM, Len Ovens wrote:

Beware old building with additions  :P  It appears we have power coming
from two power entrances with two different earth grounds to the panels.
I had found two power cords with the ground pin pulled which I
replaced... big ground loop noise. I tried (as read from a number of
sources) making unballanced cables with a small resitor in the ground
path but this made things worse not better. I will be running a power
cord from the stage back to the mixer next. All of our signal in paths
are already isolated. It is only the two monitor mixes to powered
monitors that are unballanced and causing problems. The outputs from the