HDMI hum from BI PC at AV Receiver

[Jose R.]

So I have remotely located my BI machine in a closet and ran an HDMI cable from the PC's DisplayPort (with adapter) to the TV in the living room. This works great however...

If I turn my my receiver, there's a 60Hz hum from the speakers. This happens even if the TV and PC are off. These are the only ways I could silence the noise:

1. Unplug the HDMI cable at PC.
2. Unplug the PC power cord.
3. Power both the AV Center and PC from the same receptacle via extension cord (same ground). (They are in different rooms)
4. Ground the PC from an extension cord from the A/V receptacle. (same as 3., but just using the ground)

So, obviously there's a ground potential difference between the two outlets. (3 bulb checker says my grounds are good all around) Apparently this is a common issue. Before I do this the hard way of repowering the closet outlet from the A/V outlet by running a new romex feed line across the house, any other suggestions?

I considered moving the PC to the a/v center but it's just too big to situate in a pleasing manner. Plus I already have some cameras wired up to the closet location.

I tried finding some HDMI ground loop isolators that don't exist or are supremely expensive.

I could use another type of cable but I'll lose PC sound at the TV.

Repowering the outlet shouldn't be a huge deal, I have the romex and electrical experience. I'd side tap the A/C Center's receptacle and run up and over to the BI closet. Won't be fun, but totally possible.

Perhaps just grounding the two outlets together instead of repowering? Is that code legal? I mean, they are all grounded together in theory so a ground from another circuit (4. above) could solve it but I'm not sure if that's dangerous or not. I could run a romex but only use the ground wire inside and connect the two receptacles ground screws together.

What say ye?

Thanks, all!

 

[fenderman]

You might try running hdmi over cat...

 

[Jose R.]

Thanks, Fenderman.

Being that both are over copper, how would that be any different than what's there now? The signal over the single HDMI makes it just fine to the TV otherwise.

Am I missing something here? The twisted pairs or something?

An optical type of connection would do it but that's only for audio.

 

[fenderman]

Thanks, Fenderman.

Being that both are over copper, how would that be any different than what's there now? The signal over the single HDMI makes it just fine to the TV otherwise.

Am I missing something here? The twisted pairs or something?

An optical type of connection would do it but that's only for audio.

How long is your HDMI cable?

 

[Jose R.]

35 feet.

 

[fenderman]

35 feet.

At that distance the length could be the issue... Try using CAT5.. it cannot hurt.

 

[Jose R.]

I could give it a shot altho I'd have to buy the extender modules. Are there any favorites everyone uses on here?

 

[NoloC]

Seems weird there is a ground potential difference in what seems to be a short distance. Maybe one outlet is not properly grounded.
In some older installations I have seen outlets replaced from the old two wire style to a newer grounded outlet and the ground lug was connected to the conduit.
No actual ground wire run. I would imagine that could cause a difference. How old is the building wiring?

Sounds like your #4 experiment proves the ground is goofy at one outlet. Maybe take the outlet apart and examine ground wire.
It might be interesting to see what the actual voltage is if you have a meter. Measured between the two outlet grounds. Could be some other device plugged in somewhere with a neutral gounded.

I think it is OK to "daisy chain" ground wires but would love to hear from an actual electrician! I don't believe they home run the grounds back to the fuse box.

But I am not an Electician although I do play one on the interwebs.

 

[Jose R.]

Seems weird there is a ground potential difference in what seems to be a short distance. Maybe one outlet is not properly grounded.
In some older installations I have seen outlets replaced from the old two wire style to a newer grounded outlet and the ground lug was connected to the conduit.
No actual ground wire run. I would imagine that could cause a difference. How old is the building wiring?

Sounds like your #4 experiment proves the ground is goofy at one outlet. Maybe take the outlet apart and examine ground wire.
It might be interesting to see what the actual voltage is if you have a meter. Measured between the two outlet grounds. Could be some other device plugged in somewhere with a neutral gounded.

I think it is OK to "daisy chain" ground wires but would love to hear from an actual electrician! I don't believe they home run the grounds back to the fuse box.

But I am not an Electician although I do play one on the interwebs.

Thanks, NoloC... House is from 1971 and grounded via good old fashioned EMT or metal conduit. I have all sorts of meters and test equipment so I can check things out. While that cheapo 3-bulb checker says everything is properly grounded, I'm sure they are not the end-all answer unless you have a completely missing ground. What I may have is a partial ground. My UPS's show good voltage at both locations.

These days, grounds are run with the branch circuit wiring so technically yes, it's a home run back to the panel. Back then, the conduit served as the ground conductor and that obviously goes back to the panel as well. So like you, I don't see the harm in extra grounds as 1. they all end up in the same place anyway and 2. they are only really used when something goes wrong - not part of the actual circuit performance. But hey, correct me if I'm wrong there, I know someone will if so!

When I did my experiment with the extension cord, every single outlet in the house would cause the hum, except for the one the A/V Center is connected to. The BI PC *really* wants to be on the same outlet.

 

[NoloC]

When I did my experiment with the extension cord, every single outlet in the house would cause the hum, except for the one the A/V Center is connected to. The BI PC *really* wants to be on the same outlet.

So I wonder if the A/V center outlet has the ground issue?

I have a similar situation but with a 50 foot hdmi cable, two different AC outlets. No hum. But it doesn't take much potential difference to cause hum.

So is the receiver connected to the tv by analog audio? I assume the hdmi from the PC goes to the TV and then some type of connection from the TV to the receiver? Maybe that could be isolated.

 

[Jose R.]

Aha... The TV to receiver question... It's optical. So I'm completely lost as to how this is getting introduced to the receiver?

BI PC -> HDMI to TV -> Optical to Receiver digital input

Now, there is an HDMI out on the receiver that goes to the TV, but that's a separate HDMI input on the tv. Could the hum be coming in on that cable which is an OUT on the receiver? I'm going to unplug that one and see what happens.

Also note that with EVERYTHING OFF except the receiver, the hum is present. The BI PC nor the tv need to be on.

I'm also going to check the receptacle grounding at both locations.

 

[TonyR]

Because green (earth ground) and white (AC neutral) are at the same potential in the panel where legally tied together, I'd take @NoloC 's advice and open up BOTH outlet boxes and inspect to insure they are wired green wire to green screw and white wire to silver screw of the receptacles, including any feeds from any box to any adjoining outlets.

A 3 bulb outlet checker only knows how to light up it's little neons or indicators with a hot expected on the right hand slot of the outlet and really cannot tell if it's a green or a white on the left slot; in other words, green and white can be swapped in the outlet and the tester can still read "OK".

 

[TonyR]

I'm also going to check the receptacle grounding at both locations.

Good move.

 

[Jose R.]

Because green (earth ground) and white (AC neutral) are at the same potential in the panel where legally tied together, I'd take @NoloC 's advice and open up BOTH outlet boxes and inspect to insure they are wired green wire to green screw and white wire to silver screw, including any feeds from any box to any adjoining outlets.

A 3 bulb outlet checker only knows how to light up it's little neons or indicators with a hot expected on the right hand slot of the outlet and really cannot tell if it's a green on the left or a white; in other words, green and white can be swapped in the outlet and the tester can still read "OK".

That is the plan for tonight however I'm on EMT so I don't have any green wires (except for where romex was used to install a new outlet in the BI closet - which is my doing). I will do continuity checks between the receptacles and their EMT, and also between the grounds between the 2 receptacles in question.

Thanks, all!

 

[TonyR]

I don't believe they home run the grounds back to the fuse box.

Nope, they can go receptacle=>receptacle=>panel

 

[TonyR]

That is the plan for tonight however I'm on EMT so I don't have any green wires (except for where romex was used to install a new outlet in the BI closet - which is my doing). I will do continuity checks between the receptacles and their EMT, and also between the grounds between the 2 receptacles in question.

Thanks, all!

Yikes! I'm sure there's been no change in resistance in those EMT-to-EMT (zinc plated?) mechanical connections in that salty Miami, FL atmosphere over the years.....

I'd still do that inspection (as you said you have planned) but if nothing is found that is blatantly wrong, IMO I'd just run that romex...might save some time AND avoid a recurrence of the same issue elsewhere.

 

[Jose R.]

Yikes! I'm sure there's been no change in resistance in those EMT-to-EMT (zinc plated?) mechanical connections in that salty Miami, FL atmosphere over the years.....

I'd still do that inspection (as you said you have planned) but if nothing is found that is blatantly wrong, IMO I'd just run that romex...might save some time AND avoid a recurrence of the same issue elsewhere.

Yep, it's looking that way... Besides, with the HUGE pita this whole camera installation has turned out to be, this isn't that big a deal in the overall picture.

75% of this project has been adding/modifying existing networking cabling/routers/switches/PC.
15% Electrical modifications.
10% Camera installs and fishing/terminating their cabling - the easiest part.

That backbone is MOFO if you're doing it right...

 

[bp2008]

How has nobody mentioned fiber optic HDMI cables yet? Assuming they don't do something like run a ground wire between the two HDMI connectors, that should solve your problem.

https://amazon.com/s?k=fiber+optic+HDMI&i=electronics&ref=nb_sb_noss_2

 

[bp2008]

How has nobody mentioned fiber optic HDMI cables yet? Assuming they don't do something like run a ground wire between the two HDMI connectors, that should solve your problem.

https://amazon.com/s?k=fiber+optic+HDMI&i=electronics&ref=nb_sb_noss_2

Ok, so I've been looking into this kind of cable and it seems that most if not all of them are actually hybrid fiber optic + conductive wire. They achieve much greater range than standard copper HDMI cables but I'm thinking you can't trust them to not carry an electric current from one end to the other.

 

[bp2008]

I read of some people successfully eliminating their ground loop hum by using HDbaseT equipment. I also came across this pair of adapters which would let you supply your own LC-terminated OM3 fiber: http://amzn.com/B073SRLNCJ Sadly it doesn't support HDMI 2.0 and one of the reviews said it gets very hot.