Is this a ground loop problem? (1 Viewer)

[John DeSantis]

I decided instead of paying for another Cable Box I'd run some cables down to my basement HT setup. (trying to view the upper digital channels ) I ran an RG 59 from the Cable Box Composite out to a Video in source on the RCVR (Kenwood 507 ) pic looked good but I'm getting a pretty good hum from the TV speakers. I thought maybe it was a Video problem so I switched the cable and tried the COAX digital audio output. (which I would have to add for sound anyway ) Same thing. I get the hum. I then split the RF output from the boxe and connected the cable that way to just get the channels. No hum but I won't be able to get the 5.1 sound this way. I tried connecting the power to the TV to another source but that didn't help. I know this kind of thing can be hard to cure but I thought maybe someone might have a quick fix or suggestion. Thanks

 

[Steve T]

I had problems similiar to yours (and one more complex) that were cable T.V. related, but I do not have digital cable. If noone can provide you a solution to your problem here at HTF, I suggest you do a search on Google groups for "ground hum". You can learn much about this subject from newsgroups such as rec.audio, sci.electronics, rec.video.cable-tv, and many others. Here is just one thread that pertains to your situation:
http://groups.google.com/groups?hl=e...D10%2 6sa%3DN
My problem was two-fold; the cable service was causing a circuit breaker to trip whenever the T.V. in our living room was turned on, and there was ground hum present from the audio (when played through the HT from the VCR). Someone from the sci.electronics.basic newsgroup suggested I install 75-ohm to 300-ohm matching transformers back to back on the cable before it entered the converter box. I had these matching transformers laying around the house so I tried it. Guess what? It fixed both problems. I later found out by doing more research via the NG that the circuit the T.V. in the living room is connected to is on a GFCI breaker in the breaker box. Since the T.V. has a 2-wire polarized cord, with no direct ground connection, you connect an earth ground to the system via the shield of the coax. The antenna connector of the set is actually connected to the neutral side of the powerline (probably through a small capacitor). This capacitor has a low enough reactance to pass an AC current from the powerline to ground through the coax. This is exactly what a GFCI is supposed to detect, and it responds by tripping out. The matching transformers basically disconnects the cable ground from the system.
Steve

 

[Wayne A. Pflughaupt]

John,

If you have no problems with the cable box at the initial location, the problem might be that the cable box and downstairs system are on different circuits connected to opposite service legs at the breaker panel. For a test, try plugging everything into the same outlet.

Also, try a different cable – your RG-59 cable might be bad.

Regards,

Wayne A. Pflughaupt

 

[John DeSantis]

Thanks guys. I will try different outlets etc. I had done a little reading a while back relating to ground loop problems but I never had this problem and the material seemed a little complicated. I understand the basics of what they're saying though. ( I think ) Just wondering why connecting to the RF out didn't cause a hum. All the equipment downstairs is on the same line. I have DVD,VCR,CD players connected. None of those cause any problems, Just the A/V inputs to the RCVR. I did discover that If I connect the Composite to the VCR line in then there is no hum. I was just going to go with that but then discovered I had it when I tried connecting the sound.

I think I'll also try connecting the Cable Box to another outlet. We shall see!