New Ground Loop - What Could Have Caused?

Nglazer,

Somewhere outside your house there should be a grounding block for the Verizon FIOS incoming cable before it enters your house.

The ground wire that connects to the ground block is supposed to connect to the main grounding electrode system of your main electrical service.... You might want to check and make sure that is how it was done.

The ground block should not be connected to a dedicated ground rod that does not tie back the main grounding electrode system. Not only can a dedicated ground rod cause ground loop hum problems especially when the soil is dry but it also can add an alternative path for lightning.
Bad news for your audio equipment and TV.

If the grounding block is properly connected to the main grounding electrode system and was working just fine until you came back from vacation then the ground wire connection at the grounding block could be loose or corroded causing resistance at the connection. A difference of potential, voltage, then may exist from the Verizon FIOS cable and the equipment ground of the electrical system of your house.

If there is a difference of potential and a closed current path is provided then you will have a ground loop and the dreaded hum.

Best thing to do is buy a ground isolator for the Verizon FIOS incoming cable line.....

It was the Verizon FIOS box. Once I disconnected IC's running from FIOS box to pre, problem solved. No music stations through stereo, though.
08-29-11: Nglazer

Nglazer,

Is it? Or is it actually caused by a difference of potential between the shield signal ground of the FIOS cable and the equipment ground of the 120V AC grounded system.

Did you disconnect the FIOS cable from the box, with the ics still connected from the box to the preamp, and check for the hum? If you did and the hum was still present then the hum could be blamed on the box.

I did read your response on AA..... I don't believe the problem is the Verizon FIOS box.
Jim

Whoa. Nothing ever is simple, is it. I will first try Jim's FIOS box suggestion, because it is easier and I know what to do. Jim's other suggestion probably is beyond my technical competence, but I know where the FIOS cable connects to the house.

Thanks again. I would like to go back to where I was.

Neal

Neal- A cheapo way to experiment w a ground iso xfrmr is to put two of those 75 - 300 ohm (aka F to twin lead) converters back to back into the FIOS cable run. Incoming cable to F input to 300 out to 300 in to F output to cable out. If it substantially reduces or eliminates the hum, you can pay RS a ten spot for one, or buy a more expensive one from Jensen or find a used Mondial MAGIC.

Jim's comments are right on, IMO, as usual. Good suggestion by Michael (Swampwalker) as well.

Given that the problem appeared out of the blue, after everything had been fine for a long while, my bet is that the root cause is the possibility Jim suggested of corrosion/poor connections at the ground block outside. If so, the fix could be as simple as tightening a screw or nut on it.

Dealing with a ground block doesn't require much technical expertise. It's just a pair of back-to-back coax connectors connected between the cable from the pole and the cable that goes into your house, with a ground wire clamped onto the block via a bolt or screw.

Regards,
-- Al