Originally Posted by Jk7.2
My eventual ’fix’ was moving to fully balanced pre/pro and 10X10 dsp. Still to eliminate the hum, I lifted the ground in the cable. What do you think of that BTH?
Unfortunately you'd have to test each connection with an O-Scope or at least a Volt meter that can read into the 100's or 1000th's of a volt.
There is likely a ground-potential difference between 2 or more of your components.
The cause of this is likely a power supply or the motherboard in one or more of the devices leaking juice into the chassis, and the audio system using the chassis as reference-ground.
This is really only a problem for audio systems. In systems like home networks or business networks / the internet, this isn't a problem since no humans listen to Cat5 cables.
It's a A/V specific issue unfortunately, and all too universal.
All I know is:
My sources are an HDMI BD player, a optical to Cat5 Cable box HDMI, a HTPC via USB/HDMI.
HDMI outputs are: 1 tv and 1 projector
All connected to a 7705.
The USB cable goes to my Motu rig, which goes to my DSP-PC via more Cat5/USB cables (3 routers), bi-directional back to the Motu rig.
BD player and 7705 also has cat5 to same routers.
The 7705 is also connected to the Motu rig via real XLR.
The Motu rig is connected to a dozen amplifiers (FP's and 1 iTech 8k).
No substantive noise in my system, not even if I put my ear up to the subwoofer, mid or tweeter.
No isolators or grounding used anywhere; and I have like a 1/4 mile of interconnects (not even joking!)
That's because the 25ft PE mic cables were cheaper than the 6ft ones! $2 vs $10 You can thank PE for that!
Probably one of the larger / more complicated wiring-jobs on AVS.
Cable management... What's that?
Just wait I haven't even added smart-house stuff yet!
Actually, cable management generally increases noise because the wires become closer together, often in strapped parallel (which is the worst thing you can do for noise rejection, stopping short of large coils.)
One day I probably will find the time/energy to shorten all of these XLR cables. But that's unlikely to be this year.
I'm slowly working towards upgrading from home-grade to business-grade network equipment, and then adding some smart-house power automation, at least the HT-lights and HT-equipment.
I'm actually surprised at how low the noise is with no effort put into it; I was expecting horrible noise levels.
My ISP is optical, and all of my HDMI cables are optical-hybrid, so that helps to a degree I suppose.
I also have a direct dedicated 6-awg grounding cable from that sub-panel to the mains-panel, and most of the wallsockets are dedicated breakers/romex. I also have multiple cascaded SurgeX's cleaning the grid-power. (Soon to be HT-dedicated solar-battery fed.)
That probably all helps to some unknown-degree...