Ground hum on OTA antenna cable

[Galu]

Hi Hogwild!

Baffling indeed! Perhaps it's time for a summary?

(a) With CD connected to preamp you get no hum.
(b) With TV connected you get hum, but it's less since fitting the antenna isolator.
(c) The volume of the TV system is much louder with the antenna isolator fitted.

Would you confirm if this is a correct summary and answer the following question please?

Which output on the TV are you using? RCA line level? Headphone jack?

 

[Hogwild]

Galu:


Thanks for doing that. Yes, I'd say that's accurate. I hope I'm not missing anything.
Yes, RCA line level. There are no digital/optical inputs on the Crestrons, so that

eliminates trying that.



I'm using the cheapest of RCA cables. Maybe I should try better ones?


Strangely, the hum was quieter yesterday when I tested it than it was a few days
ago. I think it would be acceptable for watching TV. And I could just disconnect
the cables to listen to CD for a really quiet signal.


Also, I'm moving, hopefully in a few months, so I don't want to put too much

more work into this.

 

[OffGridKindaGuy]

Try a ground loop isolator between the TV and the Preamp in the RCA connections.

I don't know how you are powering the Preamp. Is it through the wall outlet? Is the ground connection in the 3 prong plug connected to the preamp grounding?

Can you hear the hum with the volume turned down all the way on the preamp with everything connected? Does the TV have a 3 prong plug?

I'm sensing a ground loop between the TV and the preamp..

 

[Galu]

I agree with OffGridKindaGuy that you could try a ground loop isolator (a transformer isolator for audio use) between TV and preamp.

(Since it is a passive preamp, and gives no problems when your CD player is connected, we may rule it out as the culprit.)

In order to rule out any problems with the TV itself, I suggest you temporarily substitute it with another.

 

[Galu]

P.S. Before spending money on expensive RCA cables, try substituting your present TV cable with another (the one you're using with your CD player perhaps?).

 

[Hogwild]

Galu:


I think I did swap cables, but just in case, I'll do that again and report back. Good idea, thank you!


As for a ground hum isolator-I'm using one. See earlier posts.

 

[Galu]

I've looked again at the earlier posts, but I'm not clear on the isolator situation. Sorry if I'm missing/misinterpreting something.

Are you saying you have both of the following fitted?

(a) An antenna isolator between antenna and TV.
(b) An audio signal ground loop isolator between TV and passive pre.

 

[Hogwild]

See post #53:


I installed an MI 2120V cable isolator, between the antenna feed and the television.
That's it.


Specs here:

RMS Communications Inc. Model 2120V

 

[Mark Whitney]

What is the residence between the input GND and output GND?

 

[Galu]

Hi Hogwild!

We are recommending that you also insert a stereo audio ground loop isolator between your TV RCA outputs and the passive preamp RCA inputs.

This is different from an RF antenna isolator and uses transformers to pass the audio signal while breaking any troublesome ground loop.

Search for a 'Stereo audio ground loop isolator with RCA plug inputs and RCA socket outlets'.

Like this one:

Stereo Audio Ground-Loop Isolator & Filter with RCA Connectors

 

[OffGridKindaGuy]

Hogwilds post (53) confirms a ground loop... "The vol. got louder.."

Hogwild had mentioned that he didn't want to insert a isolation transformer in the audio chain because of fidelity loss. I can relate, because the cheap ones do! But, for a test, a cheap one would tell the story..

I found some isolation units that are fantastic! No fidelity loss that I can notice and in 2 cases, I have 2 in one audio circuit and you can't tell that they are in there..

KROAK Car Auto 3.5mm Aux Audio Noise Filter Ground Loop Isolator Eliminate Car Electrical Noise-in Bluetooth Car Kit from Automobiles & Motorcycles on Aliexpress.com | Alibaba Group

 

[Hogwild]

Thanks again. I am reluctant to be installing additional new gear, simply because I'm soon moving. For that reason, I thought I'd save the money. When I move, there will be no TV antenna, and I may use cable. So my thinking is that if the antenna amp is the source of the hum, I will be eliminating that when I move to a new home.



For now, I think I'll just hold off. At least now the hum is very tolerable. I usually don't even notice it unless I have my ear right near the woofers. I will look into those RCA-level hum isolators, though, just in case. Again, thanks everyone.

 

[Galu]

Thanks again. I am reluctant to be installing additional new gear, simply because I'm soon moving. When I move, there will be no TV antenna, and I may use cable.

Oh well, at least we had the opportunity to throw some ideas about!

Hope your move goes smoothly.

 

[Audio1Man]

Just remember that the Outside Antenna is still grounded, as the mast is usually connected or mounted to the sewer pipe vent that connects to the soil. This is similar to the TV Cable Service and similar ground currents paths are made.
Duke

 

[PRR]

Just remember that the Outside Antenna is still grounded, as the mast is usually connected or mounted to the sewer pipe vent that connects to the soil....

Conditions vary. Your point is quite true many places. I would not trust the old hemp/lead joints on heavy iron sewer pipe. And rubber couplers are very common in repairs or changes. Me I just hoisted 15 feet of heavy iron pipe up out of an old house to re-plumb in PVC plastic (to ease future changes). FWIW that old iron had already been re-connected in rubber and PVC down in the cellar when the old cesspit was required to be changed to a septic field.

I once bonded to an underground water pipe, then later learned the copper turned to plastic less than a foot outside the foundation, under a dry porch. So just enuff conductivity to stop your heart, not enough to drain-off unwanted potential.

Bizarrely, this house had multiple cable and satellite feeds and all were correctly bonded near the meterbox and a nearly-NEC dirt-rod system. (They are a little too shallow, because of rock; but there are two full-length with tight clamps.)