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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
jeffloistarca
1,004 posts
 
Good detective work! I think if I were in your shoes, I'd suggest the cable co. attach their cable to a new dedicated ground, perhaps a few feet from your place? A new ground driven three or feet down and used strictly for the cable should decouple it from the rest of your electrical circuits. If that's not possible or practical, and you're using cable for the video content only, perhaps consider a satellite service such as DirectTV? ATB, Jeff
cornfedboy
1,645 posts
 
fpeel: i'm not sure what you mean when you say you "put the tv and cable box in the loop," tho i assume you aren't plugging any cable leads into your sf l-1 (don't think it can be done, can it?). in any event, i agree with jeff that the most plausible problem is with the cable ground. i have my digital cable grounded into a copper rod well away from my electrical boxes; there are no common connections at all. i, likewise, have my telephone lines junction box and all associated wiring segregated from my electrical and coax. i have found an inexplicable reduction in what i assume was rf in my audio system when i recently replaced the cable box to tv coax with composite connections. i'm told that s video works even better but my cable box won't accept such outputs. i think you're on the right track. do check all splitters, too, and eliminate as many as you can. this will also enhance your video output. best of luck. -kelly
andrewucd
6 posts
 
I tried many ground loop isolators and NONE worked for DIGITAL cable. When it lifted the ground loop it interfered with the picture making it horrible or for some reason completely blocking it out. The solution was to use an stereo audio isolator made by Jensen Transformers. It is more expensive than their ground loop isolator but for DIGITAL cable it was the only way I could go. Works great.
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.
sean
6,231 posts
 
If floating the amp gets rid of the hum and does not tear up system performance, don't worry about it. I've seen and read more than a few manuals that specifically state that it might be necessary to eliminate / minimize multiple grounds. As such, ALL of your components are grounded if just ONE component is connected to ground.

Since most designs use a common ground, your interconnects tie all of the components ( and grounds ) together. As such, grounding your preamp and removing / reducing the other grounds seems to be the logical approach. Since ALL of the components ( sources, processors, amps, etc...) are all centrally tied into the pre, that is what you would want grounded. Then again, if they can do the installation "right" and let you keep your grounds, all the better. Sean
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