[Gmd]

So I recently hooked my tube amp to my dvd player and television. Unfortunately I have noticed if my amp is connected to anything, and I mean anything that is connected to the coax line (either audio or video cables) then it produces a hum. So say I have the coax line going to my cable box which goes to the tv, well the dvd player goes to the tv as well and if the amp is connected jsut to the dvd player it produces a hum. I think I know the problem in that we had poor signal quality so cox communications came over and amplified the coax signal outside to some insane level so the noise is really powerful now. I am wondering if anyone knows anyway to get around this? Right now for dvd movies I unplug the coax line from the wall but for regular tv I cannot use the speakers because of the loud hum.

 

[morphsci]

First thing is to make sure the cable feed is grounded properly and that the ground they are using for the cable is also tied to the earth ground for the house. If not you will almost surely have a ground loop. After, that you may still have some hum that may require running the cable coax through a power conditionaer that is also tied to the house ground through its three-prong plug. This worked for me to remove the cable hum I had when I lived in SC.

 

[rickcr42]

Quote:

First thing is to make sure the cable feed is grounded properly and that the ground they are using for the cable is also tied to the earth ground for the house. If not you will almost surely have a ground loop.

no doubt it IS a ground loop.SATV and CATV are brutal when added to a multimediia system becasue since they come in from outside the house they have an additional ground to protect against lightening strikes riding the cable in to your home.You need a "ground eliminator" isolation transformer.

Jensen Transformer has the best out there with the Iso-Max line but others can be had also.
Do NOT disconnect the outside ground but address the problem inside the house .

 

[bg4533]

I have the same problem. On the recommendations of a few people i put together a little adaptor. It cost about $8 and fixed the problem. It consists of a 75ohm->300ohm adaptor connected to a 300ohm->75ohm adaptor from radioshack.

 

[rickcr42]

how is the bandwidth of the transformer ? Will it pass a digital cable signal ?

 

[bg4533]

I used it with my Time Warner digital cable. I didn't notice any loss in quality. My TV is a 10+ year old Samsung, it is good, but not the best. Your results may vary if you have a nicer TV.

 

[Jasper994]

Quote:

Originally Posted by rickcr42 no doubt it IS a ground loop.SATV and CATV are brutal when added to a multimediia system becasue since they come in from outside the house they have an additional ground to protect against lightening strikes riding the cable in to your home.You need a "ground eliminator" isolation transformer. Jensen Transformer has the best out there with the Iso-Max line but others can be had also. Do NOT disconnect the outside ground but address the problem inside the house .

http://www.jensen-transformers.com/iso_vid.html

 

[rickcr42]

should add to that :

You can make the same product if you are up to it using the Bulk Jensen Tranformers and a must read is this ;

http://www.jensen-transformers.com/faqs.html

All transformers are NOT created equal and other than the jensens I only use the CineMags for line level/inline isolation/balancing/driving applications

 

[morphsci]

Quote:

Originally Posted by rickcr42 Do NOT disconnect the outside ground but address the problem inside the house .

Just to make it clear, I was not suggesting that the outside CATV ground be disconnected, but that the CATV ground rod be tied to the house ground rod via some substantial copper wire. This should remove the ground loop at the source, in theory, in practice you may still have some hum.

You can clear that up in various ways including various transformers and ground loop "blockers" as listed above.

 

[rickcr42]

Quote:

Just to make it clear, I was not suggesting that the outside CATV ground be disconnected, but that the CATV ground rod be tied to the house ground rod via some substantial copper wire.

sounds good in theory but not workable in practise.the local grounding rod for CATV and SATV is right near the inlet for a reason and that is to dissapate a lightening strike right there where the cable enters the dwelling.
With a dish it is easy to see how it could be an attractor for lightening but with cable less so until you think how these things work.
A lighteneing strike miles away can still ride in on the cable unless the energy is dissapated into the ground right there as it enters.Fail to have the rod below the frost line of your locality and you accomplish nothing in clod climates.

There is a reason why electricians get paid a lot of loot and must pass a test AFTER apprenticing for a period of time under a liscenced electrician before they themselves are liscenced.
These are not things for untrained "civilains" to be mucking around with becasue the end results can be way more disastrous than having a small system hum problem.And if the modifiaction IS done by someone other than a liscenced electrician and the house gets hit and burns down or at the minimum takes out all your electronics your home owners insurance will not be worth the paper it is written on.

I am totally a beleiver in both the proiper earth ground surge supressor since having a VCR take a hit about ten years ago.
It was first electronic device in the line from the cable inlet and how the TV survived was most likely pure dumb luck but when nothing worked I opened up the VCR and what i found was every single capacitor had "popped" and they looked like a bunch of Q-tips had moved into my VCR when no one was looking

every single one had the internals sticking out the top,little "fuzzies" which was the internal dielectric of the cpas.Obviously repair was not on the list and i ***canned the whole deal,went out and immediately purchsed a couple of surge supressors that had protection for cable and phone lines as well as the AC.Taking no chances after that experience.

Anything that leads in from outside in a potential source of lightening riding in unless locally grounded

 

[bundee1]

use the bg4533 method. It worked when I had the Philips 963sa hooked up to both my TVw/cable and my stereo. You may lose some channels from time to time but if you are only going to use it when you listen to music, it shouldnt be a problem to switch it in and out.

 

[morphsci]

Quote:

Originally Posted by rickcr42 sounds good in theory but not workable in practise.the local grounding rod for CATV and SATV is right near the inlet for a reason and that is to dissapate a lightening strike right there where the cable enters the dwelling.

Actually I did the grounding work myself but the the grounding scheme was certified by both my master electrician (who also certified my work after completion) and the local building inspector. The reason it works is that there is still a local ground for the CATV but you tie that local ground to your central house earth ground. The electrician explained to me that this is not routinely done because it increases the cost and is not required by the local codes. Actually it provides a backup earth ground to the local CATV ground that is actually above code, which was confirmed by the local building inspector. They may be full of it but I survived two close lightening strikes over a five year period that took out one oak tree in the front yard and one pine in the back with no (absolutely none) equipment loss. I also have a whole house surge suppressor and all electronics have their own local surge protection which includes all coaxial and telephone lines in addition to the electrical circuits. I guess YMMV.

 

[lini]

Gmd: That's a common problem - the usual solution is something like this: http://www.partsexpress.com/pe/showd...number=180-075

Greetings from Hannover!

Manfred