And now, as we turn back to messy old reality, the reading list:
- Balancing Act - excellent explanation; if you know nothing, start here
- How to get rid of ground loops (50 or 60 hz hum)?
- Wikipedia "Balanced audio" article
- The War on Hum
- How to Eliminate Hum or Buzz
- Ground Loops - Eliminating System Hum and Buzz
- Balanced, Unbalanced, Stereo? what are they?
- AVS Forum Hum FAQ
- Ground loop problems and how to get rid of them - lots of information here
Grounding wires are like antennas!
The standard electrical grounding system throughout the building isn't designed to have current constantly flowing through it--and yet it does, you cannot stop it. The reason a ground will not and never be perfectly noise free is that the grounding electrode conductor is nothing more than a long wire from point A to point B. And the longer the wire the more noise it will pick up.
Unify your grounds:
The best solution is to unify the grounds in your system. First and foremost be sure your CATV/SAT/ANT is properly grounded to your main house ground. You can find your main house ground next to your utility meter. It’s a copper rod driven into the ground and it has a large gauge copper wire connected to it. You can run a wire from the splitter for your video source to this grounding rod. All the ingredients are available at your local hardware store, Home Depot, or Lowes. Frequently this will solve the hum. If you don’t feel like doing this yourself, call you cable or satellite installer. It’s code- they are supposed to do it correctly.
It is important for safety reasons to have all the grounds bonded together. Say, for example, a bolt of lightning struck the earth near your service entrance. This is going to cause a large voltage surge at the ground. As long as everything is connected and bonded to that ground- no problem. There will be no difference in voltage and no current over the systems in your house. But if you have a CATV or satellite dish ground somewhere else you have a problem. That ground is going to be at a dramatically different potential than your main house ground. Guess what those grounds are connected through… your equipment! Now you have a surge of up to 6000 volts traveling from one ground site to another through your house and equipment. Equipment damage is likely and you or your family could be injured or killed. “Cheater plugs” are OK for troubleshooting and testing, but should not be used for a long term solution.