New Ground Loop - What Could Have Caused?

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

You fellows are very smart. I can't even begin to explain it technically. Following the "ground loop" , I started losing the FIOS signal sporadically, then entirely. I checked all the connections and noticed a splitter outside running up to my bedroom was burning hot, and the insulation on the coax cable had melted!

When I told Verizon I had a safety as well as signal problem, they showed up within 2 hour. When the technician opened the box attached to the outside of the house where the cable comes in and disconnected the coax cable, he got a nasty shock. Somehow current was running through the coax and he became the ground! He simultaneously blew out the circuit to which all my stereo and TV equipment is connected, requiring finding an electrician on Friday before Labor Day after a hurricane!Miraculously, I did, and he attributed all the problems to malfeasance in the original FIOS installation. Something about a ground wire missing.

In any case, all is fixed, I got 2 new FIOS boxes out of the deal, the audio output on these is MUCH better than the older boxes, the is no hum through the speakers, and I have even greater respect for you fellows (and women) who understand electricity. I resolved to get a primer on electricity so I understand what is going on, at least on a basic level.

Thanks again.

Neal