Using a cheater 3-prong to 2-prong adapter

[Jadnashua]

It's not all that uncommon to only connect the shield at one end of a coaxial or similar cable. If you try it, you'd want to cut it close to one of the connectors. ANd, yes, you can get HDMI to fiber optic converters. Some profess transmission as far as 12-miles. Quality ones are not cheap, but may be worth the ease of installation. https://www.amazon.com/StarTech-com-HDMI-Fiber-Extender-Control/dp/B00CM3HULU

 

[Reach4]

https://www.amazon.com/Protector-Lighting-AIMOS-Portable-Supports/dp/B07TYLZS1K/

Because I don't see what else it could be doing other than interrupting the continuity of the shield to keep it from being a current path. But that's may also reflect my lack of training in electronics engineering. : - )

I expect it uses some kind of breakdown diodes or MOV thermistors to shunt the voltage when it gets high. It's not going to be a hum stopper or noise blocker. https://en.wikipedia.org/wiki/Surge_protector

 

[Sponsor]

 

[wwhitney]

I expect it uses some kind of breakdown diodes or MOV thermistors to shunt the voltage when it gets high. It's not going to be a hum stopper or noise blocker. https://en.wikipedia.org/wiki/Surge_protector

That approach works for somewhat elevated voltage on power wiring, you can shunt the voltage to the EGC.

But on an HMDI cable, what's it going to shunt, the data lines to the shield? And it didn't look big enough to have MOVs in it. I think it's just as likely the shield itself will carry an elevated voltage in the first place, which is why I'm speculating it just breaks the shield.

Cheers, Wayne

 

[Stuff]

Still waiting to hear of your results with an extension cord.

 

[uscpsycho]

Is there such a thing as an HDMI isolator? Maybe a device that takes HDMI and converts it to an optical format? Or maybe the HDMI shield only has to be grounded on one end (I'm unclear on when it's enough to ground a cable shield at one end, and when it has to be grounded on both ends), in which case you could just use the equivalent of a "cheater HDMI connector". Much better to break the ground loop at the HDMI cable than at the EGC of the projector.

If you can get an HDMI cable to the remote projector location, why can't you get an extension cord to it? [I don't really like the idea, but it would be enough to run a separate EGC alongside the HDMI cable and connect it to the grounding prong on the cheater. That way all the equipment EGCs come from the common point of receptacle #1.]

There does seem to be an HDMI isolator but I'm not sure if this would work as desired and the price is insane.

I am using ethernet baluns that carry my HDMI signal over Cat 6. I can't run an extension cord along the same path because it's in my walls and was prewired during construction.

The HDMI cable needs to be shielded, but not from both ends. Remove an inch of jacket from one end of the HDMI cable and carefully cut/peel the shield off.

You are saying that removing one inch of shielding will eliminate my ground loop buzz? The cable only runs from the projector to the HDMI balun which is a few inches away

If you think this will work I'll give it a try, does it matter of the unshielded end of the cable connects to the projector or the balun?

I can't tell what it does because of all the marketing speak, but I guess that this protect may do the equivalent, if you want something neater looking and reversible:

https://www.amazon.com/Protector-Lighting-AIMOS-Portable-Supports/dp/B07TYLZS1K/

Because I don't see what else it could be doing other than interrupting the continuity of the shield to keep it from being a current path. But that's may also reflect my lack of training in electronics engineering. : - )

Cheers, Wayne

Not sure if that would do it but it's only HDMI 1.4 which means no 4K or HDR. For $15 I'd be willing to try it if it was up to current spec. Maybe there is something with higher specs.

It's not all that uncommon to only connect the shield at one end of a coaxial or similar cable. If you try it, you'd want to cut it close to one of the connectors.

Connect the shield? Are you referring to one of those $15 HDMI surge protectors mentioned earlier? Or the previous suggestion to remove shielding from one end of the cable?

Still waiting to hear of your results with an extension cord.

I still haven't gone through the hassle of running an extension cord all the way from the amp to the projector but I will tonight.

I did get one of those GFCI wall adapters I mentioned earlier and using it with the cheater plug and I still need to add a surge protector. So until I get this properly resolved (hopefully) this should be safer for me and the projector than the cheater plug alone.

 

[uscpsycho]

I just read the specs on two different HDMI optical isolators and they only handle up to 1080p and that is out of the question. If there are any that handle 4K I suspect they are even more expensive. Yikes.

Nobody responded to my question about electricians. Are ground loop issues like this common enough that any licensed electrician should be able to understand it, troubleshoot it and properly fix it? Or do I need to hunt for someone with specialized experience? If I can't properly fix this with dongles, cables and adapters I should get it fixed properly.

 

[wwhitney]

I am using ethernet baluns that carry my HDMI signal over Cat 6.

So is the Cat 6 shielded? If not, that disproves the shield carrying noise theory. If so, it might be easier to disrupt the shield on the Cat 6 than on the HDMI. [Edit: are these baluns unpowered? If they are line voltage powered, that's another complexity to the ground loop question.]

As to electricians, assuming the extension cord works, the simplest thing to do would be to get an electrician to extend the circuit from #1 to #2. That's totally standard, while diagnosing ground loops is quite specailized.

Cheers, Wayne

 

[uscpsycho]

So is the Cat 6 shielded? If not, that disproves the shield carrying noise theory. If so, it might be easier to disrupt the shield on the Cat 6 than on the HDMI. [Edit: are these baluns unpowered? If they are line voltage powered, that's another complexity to the ground loop question.]

As to electricians, assuming the extension cord works, the simplest thing to do would be to get an electrician to extend the circuit from #1 to #2. That's totally standard, while diagnosing ground loops is quite specailized.

Cheers, Wayne

I have both a shielded and unshielded Cat 6 running between the two locations and I have the same problem when using either one. So I assume un-shielding the HDMI cable will be a waste of time and energy?

The baluns are powered, but they are POE so they are only powered at one end. I tried powering them at the projector side and the receiver side (same outlet as the receiver itself), it did not make a difference. I also tried two different balun models and that didn't make a difference either.

 

[Jadnashua]

Way back when I was in the Army, I worked as a radar repairman on a missile system. It was not uncommon to have some coax cables where the shield was only connected at one end. That kept the grounds separate. That should be fairly easy to check out at not a great cost. The signal lines in the HDMI cable should be twisted pairs, that generally helps cancel out RF noises, but the shielding is important to eliminate some interference. WHen dealing with radar returns, after the receiver, the signal levels can be quite small, so you don't want them lost in the noise. The same philosophy works with video and audio.

You didn't indicate if you checked that the power grounds were solid on all of the connections and that the receptacles weren't worn (the plug fits in easily - it should be tight). That should be your first line of attack. You need to check not only the receptacles, but the power panel as well and maybe even the ground rods for the panel. It might all be fixed by making a connection tight by screwing down the clamp, or fixing a poorly done wire nut connection. Make sure that the ground going to the receptacles are tight, and are bonded to the metal box, if they aren't plastic. While you're at it, make sure that the hot/neutral aren't reversed anywhere.

 

[wwhitney]

I have both a shielded and unshielded Cat 6 running between the two locations and I have the same problem when using either one. So I assume un-shielding the HDMI cable will be a waste of time and energy?

Yeah, if the HMDI shield is not continuous from point #1 to point #2, it's not going to be part of the problem loop. With the shielded Cat 6, it might be continuous (depending on how the shield is terminated, I don't think an RJ-45 exposes the shield), but with an unshielded cable, it obviously can't be.

Do try the extension cord and let us know if that works. It will narrow down the range of possibilities.

You could see if you can get a projector that comes with a two prong plug. Or one that's POE.

Cheers, Wayne

 

[uscpsycho]

Way back when I was in the Army, I worked as a radar repairman on a missile system. It was not uncommon to have some coax cables where the shield was only connected at one end. That kept the grounds separate. That should be fairly easy to check out at not a great cost. The signal lines in the HDMI cable should be twisted pairs, that generally helps cancel out RF noises, but the shielding is important to eliminate some interference. WHen dealing with radar returns, after the receiver, the signal levels can be quite small, so you don't want them lost in the noise. The same philosophy works with video and audio.

I follow you. But I'm not sure if you're saying I should still try to un-shield one end of an HDMI cable or not.

You didn't indicate if you checked that the power grounds were solid on all of the connections and that the receptacles weren't worn (the plug fits in easily - it should be tight). That should be your first line of attack. You need to check not only the receptacles, but the power panel as well and maybe even the ground rods for the panel. It might all be fixed by making a connection tight by screwing down the clamp, or fixing a poorly done wire nut connection. Make sure that the ground going to the receptacles are tight, and are bonded to the metal box, if they aren't plastic. While you're at it, make sure that the hot/neutral aren't reversed anywhere.

I can't check the outlet's wiring so easily because it is above my very large projector which is attached to the ceiling and very carefully aligned with my screen. Getting into that box would require taking down the projector and that would be a major project.

But this is a new outlet and I have a lot of confidence in the electrician who installed it not to leave wires loose. So on the list of things that might be wrong, loose wires is pretty low on the list.

Do try the extension cord and let us know if that works. It will narrow down the range of possibilities.

You could see if you can get a projector that comes with a two prong plug. Or one that's POE.

Cheers, Wayne

I tried the extension cord and can confirm there is no buzz at all when I plug the projector into the same receptacle as the other AV gear.

I can probably find a slide projector that uses two prongs!

 

[Drick]

You are saying that removing one inch of shielding will eliminate my ground loop buzz? The cable only runs from the projector to the HDMI balun which is a few inches away

If you think this will work I'll give it a try, does it matter of the unshielded end of the cable connects to the projector or the balun?

When I wrote this I didn't realize you were sending HDMI over unshielded CAT6. That being said the ground loop is coming from somewhere and I still think its worth a try.

I have one other thought; Is the projector on a different circuit breaker than the A/V equipment? If its on a different circuit breaker are the two circuit breakers on the same phase? ( You want them to be on the same phase.) Generally you can determine this be counting and determining if they are odd or even. Start counting from the top left going down the left side, skipping over the larger 2 pole breakers. Do the same thing on the right side and start your counting over from the number 1. Even numbered breakers will be on one phase and odd numbered breakers will be on the other.

 

[Drick]

But this is a new outlet and I have a lot of confidence in the electrician who installed it not to leave wires loose. So on the list of things that might be wrong, loose wires is pretty low on the list.

While I feel ok saying that the wires are likely tight I have way less confidence in saying that the hot and neutral aren't reversed. I used to do new construction and we would literally install hundreds of outlets a month. The last thing we would do would be walk the house with a plug tester. If I had a dollar for every hot/neutral reversed outlet I found... Just sayin. And I can almost guarantee you if the outlet is in the ceiling nobody checked it. You don't have to move the projector, but use the extension cord to plug it into a different outlet in the same room as the projector to prove that its not a problem with that particular outlet.

I tried the extension cord and can confirm there is no buzz at all when I plug the projector into the same receptacle as the other AV gear.

How about if you use the extension cord to plug the projector into another outlet in the same room? Different rooms? Room with an outlet on a different phase?

 

[wwhitney]

But this is a new outlet

Drick's suggestion of checking if the two circuits are on opposite legs, and moving one of the breakers if so, is a good one. I don't understand why that would lead to a hum, but it's plausible, and the fix would be very easy.

[Edit: I guess moving the breaker would require an electrician, so a test you could yourself is to power the projector from various circuits in the house using the extension cord, and then see what the pattern is. Mostly likely either every circuit other than the primary A/V circuit would cause a hum, or only those circuits on the opposite leg from the A/V circuit will cause the hum.]

Otherwise, since it's a new outlet, then you or the installing electrician should know where the other end of the cable supplying the outlet originates. Which would give you a head start on refeeding that outlet from the primary A/V circuit.

Cheers, Wayne

P.S. A diagram of your A/V system would be helpful.

 

[uscpsycho]

Is the projector on a different circuit breaker than the A/V equipment? If its on a different circuit breaker are the two circuit breakers on the same phase? ( You want them to be on the same phase.) Generally you can determine this be counting and determining if they are odd or even. Start counting from the top left going down the left side, skipping over the larger 2 pole breakers. Do the same thing on the right side and start your counting over from the number 1. Even numbered breakers will be on one phase and odd numbered breakers will be on the other.

They are on different breakers.

Is a 2 pole breaker when there are two switches in the space of one breaker? Or when there are 2+ breakers that have a bar connecting them?

You don't have to move the projector, but use the extension cord to plug it into a different outlet in the same room as the projector to prove that its not a problem with that particular outlet.


How about if you use the extension cord to plug the projector into another outlet in the same room? Different rooms? Room with an outlet on a different phase?

I plugged the projector into another outlet in the same room and I still have buzz. I'll try plugging it into a different phase if you answer my question above so I can figure out how to count the breakers.

Otherwise, since it's a new outlet, then you or the installing electrician should know where the other end of the cable supplying the outlet originates. Which would give you a head start on refeeding that outlet from the primary A/V circuit.

P.S. A diagram of your A/V system would be helpful.

That electrician is long gone. Wouldn't come back just to answer that question and probably wouldn't remember because it's been a while.

The AV for the theater is quite simple.
Outlet #1: AV Receiver
Outlet #1: external amp connected to AVR w/ RCA cables
Outlet #1: DVD Player connected to AVR w/ HDMI (uses 2 prong AC plug)
Outlet #1: Chromecast connected to AVR w/ HDMI (powered via USB using 2 prong AC plug)
Outlet #1: HDMI transmitter balun connected to AVR w/ HDMI (uses 2 prong AC plug)
Outlet #1: Bass transducer transmitter connected to AVR w/ RCA cables (uses 2 prong AC plug)

Outlet #2: Projector

No AC: HDMI receiver balun connected to HDMI transmitter balun over Cat 6 + connected to projector via HDMI

Outlet #3: Subwoofer connected to AVR w/ RCA plugs over coax (uses 2 prong AC plug)

Outlets #2 #3 are in the same room.

As I understand it, only devices plugged into ground can be ground loop culprits and the only ones are the AVR, external amp and projector. Everything else has an ungrounded plug -- but all of those things are plugged into a grounded power strip on outlet #1.

The speakers that buzz are the only two connected to the external amp. The ten speakers connected to the AVR do not buzz. It's a bit odd considering the AVR and external amp are plugged into adjacent plugs on the same power strip, but speakers to the AVR don't buzz.

All this got me thinking there might be an issue with the speakers plugged into the external amp, so I tried different speakers and I still got a buzz. I also tried a different external amp (also plugged into outlet #1) and still had the buzz. I tried a different set of cables between the AVR and the external amp and still had the buzz. And unfortunately this is my second AVR (first one had a malfunction) and I had the buzz with both.

I think doing all of that was a waste of time since I know plugging the projector into Outlet #1 with an extension cord solves the problem so there is some issue with Outlet #2. But at least I have conclusively eliminated any other factor from being the cause.

 

[uscpsycho]

As to electricians, assuming the extension cord works, the simplest thing to do would be to get an electrician to extend the circuit from #1 to #2. That's totally standard, while diagnosing ground loops is quite specailized.

The extension cord works, so what does extending the circuit from #1 to #2 mean?

I have a handyman coming Wednesday morning to add an AC outlet in the AV closet where Outlet #1 is. If this is a standard operation I think he's capable of doing it if I can explain it to him. He's not an electrician and not a native English speaker but he knows his stuff. I think he can do this if I can overcome the slight language barrier and explain what needs to be done.

If we've identified a solution I think I just need to have this guy extend the circuit, or bring in an electrician to do it.

 

[wwhitney]

Is a 2 pole breaker when there are two switches in the space of one breaker? Or when there are 2+ breakers that have a bar connecting them?

A "space" corresponds to one removeable blank in the panel cover. Adjacent spaces are on opposite legs. A 2-pole breaker takes 2 spaces and so has connections to opposite legs. A tandem breaker takes 1 space but is functionally two individual half-size breakers providing 2 circuits on the same leg. A quad is a single unit that takes 2 spaces but is functionally two 2-pole breakers; it looks like a doubled tandem, and the outer 2 and inner 2 half-size breakers comprise the two 2-pole breakers.

The speakers that buzz are the only two connected to the external amp. The ten speakers connected to the AVR do not buzz. It's a bit odd considering the AVR and external amp are plugged into adjacent plugs on the same power strip, but speakers to the AVR don't buzz.

I find that odd too. My only guess is that the AVR has better isolation/filtering than the external amp(s) and so avoids the problem? You could try the cheater on the external amp to see if that make the problem go away. Then if an external amp is available with a 2 prong plug, that would be a work-around.

The extension cord works, so what does extending the circuit from #1 to #2 mean?

Electrically, the same as the extension cord, but with in wall wiring. Add a new receptacle next to the existing #2, but bring power to it from the circuit that supplying receptacle #1. [Bringing power directly from the box supplying receptacle #1 would be safest, but I would think that any box on that circuit would work. Although perhaps it's best to be take the safer route.]

Cheers, Wayne

 

[Reach4]

I would be curious what the AC voltage is between the ground pins on the outlets in question.

I would also be interested in the megohms between the ground pin on each unplugged plug and its neutral (the wider blade).

 

[WorthFlorida]

I just read the specs on two different HDMI optical isolators and they only handle up to 1080p and that is out of the question. If there are any that handle 4K I suspect they are even more expensive. Yikes.

Nobody responded to my question about electricians. Are ground loop issues like this common enough that any licensed electrician should be able to understand it, troubleshoot it and properly fix it? Or do I need to hunt for someone with specialized experience? If I can't properly fix this with dongles, cables and adapters I should get it fixed properly.

1) Most electricians do not understand anything less than 1 amp. They work with high voltage & current and rarely get any electronic training. A rarity is if you find someone that works mainly on hospital electrical systems and equipment where isolated grounds are everywhere, then you have a chance.

2) GFCI will not isolate the ground any kind of AC hum or interference. It only monitors that the current flow between the hot and neutral is less than 5 milliamp difference. Above that it trips.

3) It's hard to read from other posts but it appears that one outlet is on one phase and the other is on the other phase of a two phase system and there is a ground potential difference. Place a voltmeter from the hot to the neutral and from the hot to the ground. Check the voltages. Then do the same with the other outlet. You want the readings to be the same.

4) Lastly, California rarely has lightning storms.

 

[Jadnashua]

Have you tried just changing the Ethernet cable?

Are any of the items a simple, 2-prong, unpolarized plug? If they are, try flipping the plug around.