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Ground Loop - New Twist?

In a recent discussion I pointed out having lost a 60Hz speaker hum from my stereo after moving to a place with a better electrical system. Well, that claim was premature. The cable company was out yesterday, did their thing and OUCH! things are worse than ever. With the TV and digital cable box in the loop the 60Hz hum is LOUD. Putting a ground isolator on the cable connection helped, but doesn't completely remove the noise. The installer tried to ignore the problem, even said it is normal, but finally relented after much insistence on my behalf, called his supervisor and a technician is supposed to be assigned to investigate the problem. What I'm hoping for with this post is a little guidance on the best path(s) to take when the technician comes out.

Before the cable installation there was a *minor* speaker hum audible from a couple of inches away. It was about as loud as the tube rush from the pre-. Floating the ground on the amp or pre- does remove it. With the pre-'s ground floated there is a lack of life to the sound, so that isn't an acceptable fix. I tried floating the amp's ground this morning, against my better judgement, and while the hum is gone this is really not my preference. Too unsafe; the ground is there for a reason.

In conjunction with this the ballasts for the flourescent lights in my office and garage all started buzzing, too, right after the installation. Something is plain not right.

The installer said the cable connection is grounded to "the power mass". This was not a familiar term, so had him show me the ground connection. It is attached to the outside of the breaker box next to the power meter. Somehow that doesn't seem right.

What are the available options and what should I say to the tech to get this fixed? BTW, I do have a basic understanding of what causes ground loops. Also, the equipment is a McCormack DNA-1 and the pre- is a Sonic Frontiers Line 1. Thanks in advance for walking me through this one.
fpeel

Showing 5 responses by fpeel

fpeel OP
455 posts
 
Well, I'm not giving up the TV. At least not until hockey season is over. ;-)

As for the RS fix, tried it and while the sound improved the picture quality was unacceptably poor. Eventually bought a ground isolator, but in this case even it is not enough. Thanks for the link in any case.
fpeel OP
455 posts
 
Cornfedboy: That phrase meant connecting the audio outputs of the TV to one of the inputs on the pre-. Sorry it wasn't clear. Thanks for the ideas, too.

To everyone: Went out today and looked even more closely at how the cable hook up is grounded. I was mistaken before and it isn't grounded to the main breaker box cabinet at my meter. It's grounded to MY NEIGHBOR'S main breaker box cabinet (we share a wiring closet). Of course, my neighbor's cable hookup is also part of this cluster, oops, can't use that word. But you get my drift.

Given that the manager at the cable company didn't call back with an update on getting a tech to come out as promised (big surprise there), I came close to changing the set up myself. Decided at the last minute to wait a day or so and see if they come through. Do you think moving the ground to my side of the electrical system would make much of a difference? My hunch is it won't hurt. It'd at least be a step toward isolating mine from the neighbor's.
fpeel OP
455 posts
 
Sean: That is pretty much my philosophy on the situation. I prefer to use the equipment as designed, but do want the best sound.

Given that the cable co. fails to fix the problem I am considering taking this to the extreme. Everything is plugged into a PLC except the amp. I have thought about floating the ground on it (and thus everything plugged into it). Then the amp would be the central gound point and the rest of the system grounded through it. Comments on whether this would be a good idea would be appreciated.

Of course, the $20,000 question is "Where does one buy a high grade cheater plug?"

Acas: That's what I said to the installer (admittedly out of frustration rather than actual knowledge), though it does seem they are in compliance with the National Electrical Code. It calls for the cable to be grounded at the entry point to the house. Unfortunately, the full text of the code is unavailable online except for a fee, so exactly what beyond that is required in as of yet an unknown. Any electricians out there that can help here? Thanks.
fpeel OP
455 posts
 
Thanks, Sean. Your suggestion makes sense even to a non-techie like myself. Along that line, it would seem lifting the ground at the IEC inside the amp would accomplish the same thing. This is just me looking at options. The PC has heat shrink over the IEC that would have to be cut away, something I am reluctant to do. Not sure about the connection in the amp, but it may be easier to return to stock form than the PC. Is there a reason not to disconnect at the amps IEC?
fpeel OP
455 posts
 
Update: The tech from the cable company never called as promised. BUT he did visit. There is now a ground connection from the cable entry to my power meter's junction box instead of the former daisy chain to my neighbor's. Removing the cable ground isolator at the digital cable box and the cheater plug from the amp power cord as a check of the results showed there is a very minor hum audible only if I put my ear next to the speaker. This existed before and is a known system issue. It's better now than it was at the last house, albeit just barely so. Overall, an improvement. I also learned that the digital cable box has audio outputs. Using these is quieter than plugging into the back of the TV. Could be the age of the TV, could be a difference in ground potential. Either way it's quieter.

Thanks for all the ideas, guys. I'll most likely float the ground at the amp in one way or the other to create as low a noise floor as possible. Hopefully this discussion will serve as good reference for others having similar problems in the future. Again, thanks for helping sort this one out.
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