Any electricians here know about ground loops? Home theater help!

[rage2]

Trying to fix a problem, tying in HD over analog between 2 rooms and running into a ground loop problem.

Upstairs has TV, satellite, receiver, none have grounded plugs but they do plug into a UPS with grounded plug.

Downstairs has TV, satellite, receiver, only satellite has grounded plug. These 3 plug into power bar into wall.

Now, if I tie the 2 together via component, I get what looks to be ground loop interference (slow horizontal green bars in video). If I take an extension cord and plug the downstairs satellite (only device with ground plug) to upstairs UPS, the video interference is gone.

I know upstairs and downstairs ground is different. But the only device with a ground plug is the satellite downstairs, and I didn't think it'd be a ground loop issue. Could it be something is out of phase or something?

Anyways, I don't know this stuff enough. Someone help! :D

[rage2]

bump... come on, someone's gotta know! ;)

[djdante97]

What happens if you move the UPS downstairs, and the power bar upstairs? Is this feasible/desirable with your setup?

[rage2]

Tried it, same effect.

Found kind of a solution... used a "cheater" plug to remove the ground prong. Basically a 3 prong --> 2 prong adapter. Works great because the thing is using chassis ground now for a nice clean ground reference, but apparantly removing the ground prong could fry me if the receiver goes bad.

[Howl]

What kind of UPS?

[Howl]

Sounds like the upstairs has a poor ground....???

[Ben]

basically whats going on is you're running multiple electronics componants on seperate wired grounds which end up at one primary, and because they're each taking seperate routes to get there, you're seeing voltage interference.

You will need all your signal grounds to come to to one common point. If you have 2 grounding points that cannot be avoided, one side must isolate the signal and grounds from the other.

[Ryan@DerdallDesigns]

"LIFT" the ground off of your sat receiver..... Bend over or break off the ground pin....... the receiver does not have to be grounded.... most systems are not. That should solve your issue.

The sat receiver more than likely has a picky Video mod in it, and it is picking up AC noise through the ground in your home.

Worth a shot :thumbsup:

[rage2]

Originally posted by Ryan@DerdallDesigns
"LIFT" the ground off of your sat receiver..... Bend over or break off the ground pin....... the receiver does not have to be grounded.... most systems are not. That should solve your issue.

The sat receiver more than likely has a picky Video mod in it, and it is picking up AC noise through the ground in your home.

Worth a shot :thumbsup:
Yea, that's exactly what I did, well, with a cheater plug, didn't wanna snap off that prong ;).

It's working, clean signal between the 2 sides, just EVERYONE says it's dangerous to kill the ground pin. I don't wanna die over TV lol.

As for UPS, I have some APC Smart-UPS. Huge industrial strength units that can power sat, tv, and audio receivers for 90 mins hehe.

[googe]

monster cable :thumbsup:

[rage2]

Originally posted by googe
monster cable :thumbsup:
haha this has nothing to do with cable quality. It's to do with poor design, the Bell 9200 using AC ground as a ground reference!

I hope you're smart enough not to get suckered by Monster Cable hehe.

[googe]

Originally posted by rage2

haha this has nothing to do with cable quality. It's to do with poor design, the Bell 9200 using AC ground as a ground reference!

I hope you're smart enough not to get suckered by Monster Cable hehe.

haha, i was kidding. you must have seen my anti-monster propaganda before ;)

[rage2]

haha nope, sorry, didn't think u were kidding haha. I'm anti-monster as well.

So does anyone know what the risks are for removing the ground prong?

[legendboy]

instead of removing the ground prong from the cord, kill the breaker that powers that outlet (you don't even need to do that if you wear a glove to hold the receptical when you take it out), pop the outlet cover off, remove the receptical and disconect the green ground wire. tape the end of it up. also, disconect the bare copper ground wire that may be attached to the inside of the receptical box in the wall.

another way (probably easier) would be to find the breaker that controls that plug, pop your breaker box cover off and disconect that particular ground wire from the ground bus bar. this should work ok as long as there are no grounds chained together with other grounds somewhere in that circuit, but easy to figure out.

there are my two 5 minute don't wreck your cord fixes :thumbsup:

[sml]

Rage, can't believe you didn't ask me this... Too late to explain now, I'll be back tomorrow morning with some detail explanation... :zzz:

[Tyler883]

Ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground.

When two or more devices are connected to a common ground through different paths, a ground loop occurs. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum in audio or video equipment.

To prevent ground loops, all signal grounds need to go to one common point. This is ussually accomplished by having all components plugged with 2 prong cords, then making the ground connection by connecting your system to one component that is grounded) or all 2 prong cords and connecting to a wall mounted antena outlet, or a computer, etc. Often, if all components are plugged into the same outlet, multiple ground paths will not matter.

When two grounding points cannot be avoided, one '2 prong component' must isolate the signal and ground from the other signal and ground. This method is can be reached through trial and error, but suffers from limited alternate signal routes from one component to another component.

[Tyler883]

Originally posted by legendboy
instead of removing the ground prong from the cord, kill the breaker that powers that outlet (you don't even need to do that if you wear a glove to hold the receptical when you take it out), pop the outlet cover off, remove the receptical and disconect the green ground wire. tape the end of it up. also, disconect the bare copper ground wire that may be attached to the inside of the receptical box in the wall.



Don't do this.
Something else is bound to get used in that outlet eventually, so you don't want the earth ground permanently compromised.

[Tyler883]

Originally posted by rage2
haha nope, sorry, didn't think u were kidding haha. I'm anti-monster as well.

So does anyone know what the risks are for removing the ground prong?

the third prong protects you from any (rare, sometimes impossible) fault that would apply a dangerous voltage to the chassis of your component. the voltage would be shorted to ground instead of waiting for an unsuspecting person to become the ground. As long as your system maintains a single ground route that everything is still grounded to then you haven't lost this safety feature.

However, there is still a risk, time has a way of oxidizing ground connections, and cause voltage potentials(again asuming that an unlikely fault was to happen) to exist across poor ground connections. But even this is unlikely, because ground loop hums might start as early as a few millivolts, meaning that you will hear or see a problem before it becomes unsafe.

IMO, and it's just my opinion, it's completely safe.:thumbsup:

Edit: At least for typical home electronics. I wouldn't screw around with the thrid prong on power tools, or appliances.

[Zero102]

"LIFT" the ground off of your sat receiver..... Bend over or break off the ground pin....... the receiver does not have to be grounded.... most systems are not. That should solve your issue.

Please never ever do this, or tell ANYBODY to do this.
The problem you have is a couple things.
A lot of AC-DC converters (including what is in a UPS) use the ground pin for a negative on the DC circuit. The end result of this can be a current flowing on the ground of that circuit.
This current flowing will cause a tiny potential difference. This tiny potential difference can be greatly increased by a high-resistance ground. Most likely this is your problem.
For the most part, the potential difference over the ground wire from the furthest plug back to your panel is < 0.1VAC, however when high resistance grounds come in to play, it can be as high as 10VAC or even in extreme cases (broken ground) 120VAC.

To disconnect the ground is to put a band-aid on this solution.
However, the proper solution can be quite time consuming. Most likely, the ground is tied to a neutral somewhere (Since you say you have 2-prong plugs in your house) and what you're really seeing is a high-resistance neutral. Either way, this can pose a serious problem, especially to the electronics in your house.

If in doubt, call a qualified electrician over, he will probably pop open your panel to check how things are bonded (because really only one thing in your house is GROUNDED), as well as most/all plugs on that circuit.

Or, if you wish to dodge this problem (Safely), run an extension cord through with your cables, and run everything off the same circuit.

[Zero102]

The only time it's safe to remove the ground prong is if the appliance/tool bears the double insulated symbol, which is a box inside of another box. Electrical devices so-equipped should not come with a ground pin anyways.

Just an interesting side-note

[sml]

Wow... looks like everyone beat me to the reply! I have to admit there are some people on here who knows what they're talking about! Very impressed!

As stated above, the earth ground pin on an AC cord is for chasis ground. This is a protection for a potential fault which could occur inside your box, ie) A power wire accidentally shorted to the chasis (case of your box) or even an IC gone haywire and short itself out and connect power to the chasis directly. If the chasis was not connected to ground, its potential (voltage) would go up to whatever the fault voltage brings it to. ie) Worst case scenerio would be 120VAC! If the user is not aware of the fault and decides to touch the case of the box, you're going to be in for a nice zap!

Now comes to the part about whether you can or cannot remove the earth ground connection from the cord... It really depends on how the circuit board ICs are connected to signal ground and chasis ground. If somehow the geniuses at Bell decides to connect signal ground to the chasis, then well, you better hope that no fault condition ever occurs! In a normal 2 device closed system, you would ONLY connect chasis ground to pcb ground on the receiver device. Hence the receiver deivce is your ground reference for both receiver and transmitter. If you were to design a sat box, you'd probably do the same thing.... except that when you connect 2 sat boxes on the same power grid, you now have 2 ground connections. BAD!

What I would do is:
a) Go through the circuit, figure out where digital ground is connected to chasis ground and isolate them. Then connect the chasis ground pin on your power cord to the chasis of the box. If you want, you can put a 1M resistor from digital ground to chasis ground to give you that protection and provide you with a chasis ground that's somewhat referenced to your chasis ground.
b) Don't plug in the ground prong just like what you were planning to do. Put the sat box on a piece of glass and DON'T ever touch it before unpluging it from the wall and grounding the case to the ground.

I say go with b), cause you should live life to its fullest!!! No pain, no gain! = )

[Zero102]

Haha, no pain no gain, not the way to go in electrical :P
How about "don't die". :D

[frostyda9]

Originally posted by rage2
Could it be something is out of phase or something?



I would experiment with other outlets if possible. My initial feeling would be that you have devices on both lines of the electrical system, 180 electrical degrees out of phase, which are causing your interference problem. Try to get all your equipment on the same line and I would guess it will disappear.

If you feel comfortable doing it, the best way to do this would be to isolate the circuits feeding the upstairs and downstairs equipment. Once you have done that, switch one of the breakers to the same line (phase) as the other circuit. If you don't have many spots left, just switch it with another circuit and re-label the panel accordingly. Your phases are now aligned and with any luck the problem will no longer persist :thumbsup:

[rage2]

It was definately the stupid bell receiver using the AC ground as signal ground reference :thumbsdow.

Poor design I'm guessing... so after "ungrounding" the bell receiver by using a 3 -> 2 prong adapter, no more noise. But of course, risk of frying myself is something goes wrong!

[Zero102]

frostyda9, it should not matter at all if they are in phase or out of phase.
Especially since for the most part, all of the equipment will use AC-DC rectifiers, with capacitors for buffering, there should be a virtually constant DC supply, which will always be the same, regardless of the phase of the AC supply.
That said, given that Bell used the system ground as the signal ground, anything is possible, and there could be insufficient buffering on the DC side of the rectifier, or other issues, and switching phases is worth a try.
If your panel uses full-size breakers, every second breaker on one side will be on the same phase, and exactly opposite breakers should be on the same phase, so see if you can locate any circuits that are on the same phase as the rest of the equipment, and give it a shot, but don't expect miracles.

[frostyda9]

Well, I'm just 'bench race troubleshooting' here, but that was my shot in the dark after reading about the problem going away when plugged into the same circuit as the other equipment.

Here's my thought for the day: if your upstairs receiver is only a two prong plug (and hence, not grounded), tell me why you should worry about the downstairs one ;)