Originally Posted by Cpartipilo
Thanks memphisindie i understand grounding schemes but i isolated the unit completely. I don't have any other hums in my whole setup. (7 preamps)
My test Chain ART MPA > Presonus HP4 > mdr 7506.
both units plugged into the same AC outlet with NOTHING connected to the ART, no mics, no nothing.
Gain and impedance are all the way down. Balanced cable from ART to HP4 (mogami) and as soon as output gain is around 11 o'clock the hum starts, when it's all the way down is strong enough that i could not hear someone talking in the room and if i dare to press the +20db switch at that point is about the level i listen to music at. (remember input gain is at zero)
With the +20db switch out the input gain knob does not affect the hum but i can hear a sligh change in the hiss waaay in the back.
I did the same test in my home, neighbors and my office. Same result.
I'm only guessing, not being able to put my hands on it, but, either way, you need to contact ART and see what they can do if it's in warranty.
OK, if it isn't an accidentally reverse wired cord between the units, which I'd check,
it might be that the ground wire that should be connected to the input is not making connection also it sounds like it may be further down the line to me, like where all signals need a ground before the output section.
Could be a fractured solder joint.