Grounding problem?

[subynube]

I just moved into a new apartment, and it is very old and outdated. It has the old outlets, with only 2 prongs, and cannot accept a plug with a third prong. I tried to correct this issue by buying an adapter that converts a 2 prong plug into a 3 prong outlet. The adapter has a small metal loop on the top that screws into the face plate, which should ground the plug, I think?
The problem, is that I am getting an audible hum through my subwoofer, which is powered by a plate amp. The hum is not audible from the listening area, but is audible up to a few feet away. My question, is what else do I have to do to get a good ground? Is there something else I have to do to ground the outlet properly, other than just connecting the plug adapter to the face plate? Thanks for the input. ;x(

[subynube]

OK, wow, strange things are happening, but in my favor :T I have isolated the problem, and the problem is the cable TV signal. When I unplug the cable from the TV, the hum immediately goes away.I guess this has nothing to do with a grounding problem after all. Now I have to figure out how to listen to the stereo and have the cable TV on at the same time. That is the new question.

[Kevin D]

Common problem and it does have to do with a grounding problem, the cable company didn't ground the cable right at the entry point (or do to the age, the ground at entry is not the same inside).

One of our sponsors up top, Parts Express, has cable ground isolators. Screw it in-line and you should be good to go.

Kevin D.

[Glen B]

On the matter of your outlet, instead of using the adapter, you may be able to install a new grounded receptacle. Older houses in some areas of the United States were wired with BX cable (a type of armored cable with a flexible outer steel jacket which serves as the ground conductor). Although you may have two-prong outlets, the metal receptacle box may be grounded if your circuits are wired with BX cable by virtue of the cable jacket being clamped to it.

Obtain an inexpensive outlet tester and plug it into the adapter. If the tester reads "wiring OK" that means the ground is present and you can replace the two-prong receptacle with one that has the ground pin. These testers are available at your local home improvement store, hardware store or lighting and electrical supply house.

http://www.amazon.com/AEMC-Outlet-Tester-100-125V-Receptacles/dp/B0000WS7M6

[subynube]

Kevin, is this the cable ground device you are talking about? http://www.partsexpress.com/pe/pshow...TOKEN=47290701

This is part is actually also recommended in my sub-amplifier instruction manual in the troubleshooting section. I will go ahead and buy it.

Glen, that is also a great idea. I actually have the circiut breaker right inside my aparment, and can shut off power to those receptacles easily, to change them over to 3 prong recepticles. I may buy that outlet tester first as well. Thanks again.

Josh

[Kevin D]

Kevin, is this the cable ground device you are talking about? http://www.partsexpress.com/pe/pshow...TOKEN=47290701

Josh

That's it!

Kevin D.

[whoaru99]

Kevin, is this the cable ground device you are talking about? http://www.partsexpress.com/pe/pshow...TOKEN=47290701

This is part is actually also recommended in my sub-amplifier instruction manual in the troubleshooting section. I will go ahead and buy it.

Glen, that is also a great idea. I actually have the circiut breaker right inside my aparment, and can shut off power to those receptacles easily, to change them over to 3 prong recepticles. I may buy that outlet tester first as well. Thanks again.

Josh

There is no benefit to install grounding receptacles if there is no grounding circuit to that box - in fact, I believe it's against code unless the grounding hole is plugged or the receptacle is labeled as a non-grounding.

Get the tester and check before you buy any receptacles...

Also, it wouldn't hurt to try to have the cable ground fixed by the Cable Co before spending your $ on it.

An isolator can also be built by connecting two 75-to-300 ohm baluns back-to-back using the twin-lead ends.

EDIT: Important info about making your own isolator.

One must be sure both conductors of the twin-lead are isolated (no continuity) to the threaded part of the F-connector. Most don't, but there are some baluns that do. If they do, you have not achieved the isolation. A final test is to be sure there is no continuity between the threaded part of the F-connectors at each end of the final assembly.

I no longer use the isolator because the grounding issues with the cable system were fixed.

[Glen B]

There is no benefit to install grounding receptacles if there is no grounding circuit to that box - in fact, I believe it's against code unless the grounding hole is plugged or the receptacle is labeled as a non-grounding.

Get the tester and check before you buy any receptacles...

Did you even read my original post ? Read the beginning of the second paragraph, where I advised the OP to obtain an outlet tester and check first. Alternately I could have advised him to get a DVM and check between the two slots and center screw/receptacle box. He should get 120V between the two slots, 120V between the right hand slot and ground screw/box, and 0V or very close to zero between the left hand slot and center screw/box. Opposite readings could indicate a miswired outlet. This accomplishes the same thing as the outlet tester.

[whoaru99]

Did you even read my original post ? Read the beginning of the second paragraph, where I advised the OP to obtain an outlet tester and check first. Alternately I could have advised him to get a DVM and check between the two slots and center screw/receptacle box. He should get 120V between the two slots, 120V between the right hand slot and ground screw/box, and 0V or very close to zero between the left hand slot and center screw/box. Opposite readings could indicate a miswired outlet. This accomplishes the same thing as the outlet tester.

Yes, I certainly did.

I was responding to this:

I actually have the circiut breaker right inside my aparment, and can shut off power to those receptacles easily, to change them over to 3 prong recepticles. I may buy that outlet tester first as well. Thanks again.

In which it seemed to me the OP was going to replace the receptacles with grounding-style, and MAY buy the tester.

Perhaps I just interpreted his response incorrectly, but better safe than sorry, IMO.

I was not questioning your expertise.

[subynube]

Thanks for all the input. I have definately decided not to touch the outlets after all. I know just enough to be dangerous :roll: I do know that if the outlets are not grounded now, then putting in new 3 way receptacles wont work. If there is a problem in the future, I will contact the landlord.

On the other note, I will definately call the cable company, as they are definately the cause of the problem. Is it possible for an intense cable signal, that IS properly grounded to cause this hum? The cable guy said the other day that this area has an unusually intense cable signal. Also, is it bad for my system just to do this temporary fix with this cable ground connector, and can it cause further problems? Either way, I am calling the cable company!!

Thanks again

Josh

[subynube]

One more question to whoaru99? Why would you get baluns that range from 75 hz to 300 hz, if the grounding problem is probably from a 60 hz "hum" introduced through the cable, which it says in the parts express link:

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=180-075&CFID=477000&CFTOKEN=47290701

Thanks

Josh

[whoaru99]

The 75 to 300 balun is in reference to the characteristic impedance of the circuits they were designed to match.

Older TVs had inputs that were designed for 300 ohm twin-lead cable that was commonly used for antenna lead-in at the time. Cable TV uses (these days) RG-6 cable that has characteristic impedance of 75 ohms.

So, these baluns were developed to allow impedance-matched connection of newer cable systems to older TVs.

They just happen to be useful to make the isolator, but they're not commonly used anymore for their original purpose because TVs have been "cable ready" for many years.

The most common use these days is probably to match an antenna to a RG-59 or RG-6 lead-in to the TV or FM tuner.

[Kevin D]

Little odd this happened while having the discussion. I've seen the 75-300ohm adapter solution before but have never tried it. I've got a Jensen isolator in my system (more expensive version of the same thing on Parts Express). I had a customer today with some issues with video lines when the cable was hooked up.

I said no problem, I've got an isolator at the house I'll grab it at lunch. Cleared up their problem fine. Get home tonight, dig out two ohm adapters, and hooked them up. It does not get rid of my hum and as far as I can tell doesn't make a difference at all.

So in the future I would recommend trying the adapter route if you have some available, but don't spend an money on them.

Kevin D.

[subynube]

Thanks Kevin,
I just ordered the adapter from PE. If it works, great. If not, oh well. I also called the cable company to send over a tech. Ill post results when all is done.

[whoaru99]

Little odd this happened while having the discussion. I've seen the 75-300ohm adapter solution before but have never tried it. I've got a Jensen isolator in my system (more expensive version of the same thing on Parts Express). I had a customer today with some issues with video lines when the cable was hooked up.

I said no problem, I've got an isolator at the house I'll grab it at lunch. Cleared up their problem fine. Get home tonight, dig out two ohm adapters, and hooked them up. It does not get rid of my hum and as far as I can tell doesn't make a difference at all.

So in the future I would recommend trying the adapter route if you have some available, but don't spend an money on them.

Kevin D.

Just out of curiosity, do you have an ohmmeter to check for continuity between the twin-lead conductors and the F-connector threads?

If there is continuity between any of them, the baluns are not isolated. The non-isolated style won't work...

[subynube]

Well, Im happy to say that the parts express isolator worked perfectly. Absolutely no hum throught the sub. The cable guy was here the other day and could not figure out what was wrong with cable, and thought the grond was fine. I guess not :roll:
Here is the link again!

http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=180-075&CFID=477000&CFTOKEN=47290701