Hum/Ground Loop issue

[kermit_xc]

greetings - I got my self into trouble now - I somehow introduced a sub-hum/ground loop issue into my system

Setup:
ULW-10 sub + APS BackUp UPS + coax cable box.

It all worked fine until today, same outlet, same cables - and now I get a hum when the sub is on ... hum goes away when incoming coax TVcable is disconnected from the wall plug --- I am close to losing it - not sure how I could have introduced it with new component rack

The only thing that I can think of is a light switch that I changed to be a single outlet/light-switch to power my wall-mounted TV - the outlet checker does not indicate any open grounds etc. --- what is going on ???

does anybody have any ideas, similar experience ?

--kermit

 

[Adam]

Hi, Kermit. It sounds like you rearranged some stuff and put in a new rack. Correct? If so, did you change any connections at all?

Also, you now have the TV plugged into an electrical outlet that you just installed?

I'm just trying to make sure that I understand the situation. Thanks.

 

[kermit_xc]

Hi, Kermit. It sounds like you rearranged some stuff and put in a new rack. Correct? If so, did you change any connections at all?

Also, you now have the TV plugged into an electrical outlet that you just installed?

I'm just trying to make sure that I understand the situation. Thanks.

yes, I did rearrange some things but connectivity wise everything is the same, pretty much new furniture and the TV went on the wall. Now the outlet wasn't quite a new installation - there was a single light switch which I replaced with a combination switch:
http://www.levitonproducts.com/catalog/model_5335.htm?sid=D77D1B3B5C91F4C1FB5DB5FFB7750EEE&pid=1208



--Adam

 

[TLS Guy]

greetings - I got my self into trouble now - I somehow introduced a sub-hum/ground loop issue into my system

Setup:
ULW-10 sub + APS BackUp UPS + coax cable box.

It all worked fine until today, same outlet, same cables - and now I get a hum when the sub is on ... hum goes away when incoming coax TVcable is disconnected from the wall plug --- I am close to losing it - not sure how I could have introduced it with new component rack

The only thing that I can think of is a light switch that I changed to be a single outlet/light-switch to power my wall-mounted TV - the outlet checker does not indicate any open grounds etc. --- what is going on ???

does anybody have any ideas, similar experience ?

--kermit

It is the common classic ground loop. This occurs when there is a potential between grounds. Cable systems are notorious for having grounds at any potential but ground.

You need to break the cable ground with one of these.

 

[Davemcc]

This is the one I used.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=180-075

 

[kermit_xc]

It is the common classic ground loop. This occurs when there is a potential between grounds. Cable systems are notorious for having grounds at any potential but ground.

You need to break the cable ground with one of these.

well - classic or not - why didn't it occur before? - I realize that I introduced it somehow - and the HOW part is intriguing me - figure it out I will!

but at least I learned something about potential cable grounds - haha love it!


--Kermit

 

[kermit_xc]

alright ... as you can imagine, I gave the problem some thought over the past few days -- and finally came to a reasonable conclusion. Turns out that when I was wiring the combination switch on the wall - I actually grounded it ... yeah, it wasn't grounded before - the previous owners that were in charge of this renovation really dropped the ball in some places. Oh well -I have a reasonable explanation why it worked (didn't hum) before and my mind is clean - the same cannot be said about the equipotentiality of my system though...

was thinking that I put it on here for next search generations

--Kermit

 

[TLS Guy]

alright ... as you can imagine, I gave the problem some thought over the past few days -- and finally came to a reasonable conclusion. Turns out that when I was wiring the combination switch on the wall - I actually grounded it ... yeah, it wasn't grounded before - the previous owners that were in charge of this renovation really dropped the ball in some places. Oh well -I have a reasonable explanation why it worked (didn't hum) before and my mind is clean - the same cannot be said about the equipotentiality of my system though...

was thinking that I put it on here for next search generations

--Kermit

I really appreciate the follow up! That is a nice demonstration of the anatomy of a ground loop.

It is a very good teaching case.

 

[Davemcc]

equipotentiality

was thinking that I put it on here for next search generations

--Kermit

I suspect it will be many generations before anybody searches that word.