[Bigfish]

Guys:

My 2 channel system shares the same space as my Direct TV box.  When I turn on my preamp I have a small amount of ground hum coming from the speakers.  Could this be caused or increased by the Direct TV cable/box?  How would you recommend I check it or is there anything I can install in the TV cable to reduce its effect if it is the problem?

Thanks,

Ken

[avahifi]

Your problem is a dirty ground on the cable connection.  You can buy an inexpensive device at Radio Shack that will fix that.

Regards,

Frank Van Alstine

[Wayne1]

The problem is not so much a "dirty" ground but a different ground from your AC line.

The grounding rod for your AC line is in a different place then the grounding rod for your satellite system. When you hook either the TV or Sat box up to your system this will create a ground loop.

The cheap isolation transformers will not work correctly as they totally isolate both the signal and the ground. With cable modems and interactive satellite, you would still need to pass a DC signal through the transformer from the control box.

A bit more expensive version will isolate the grounds and still allow the center conductor to pass DC.

MCM Electronics sells one for $20.00 [Ground Isolation Transformer



A more expensive isolator using a capacitive based design is sold by Jensen Transformers for about $60.00.



Cable Isolator

[richidoo]

I have the Jensen on my FM antenna feed, it works good. Grounding the coax shield to earth rod creates a loop, but it is required for lightning safety.  For my DirecTV feeds I use these lightning arrestors, also grounded to earthrod and dish. I don't have hum problem on the TV system, but I don't think these will stop hum if I did since they are not any kind of isolator, just lightning. The Jensen does stop the very strong hum. It is capacitive coupled, not a transformer like their previous version. I replaced a cheap one from parts express with this one when the cheapo failed. FM sounds much better with the Jensen, so I wouldn't hesitate using it on video, for which it is intended.

Altelicon AL-FFFF (now l-com.com)
http://www.l-com.com/item.aspx?id=20928&cmp=ALSOS

[emac]

Agree with the Jensen.  Ran into problems w/ the cable line and my subwoofer in 2 houses now.  The Jensen did the trick both times. 

[rydenfan]

Before buying anything, the easiest way to check it is to completely unhook all the directv stuff from yuor system. If the hum goes away then you know it is the cause and if not then you know to look somewhere else. Some of those transformers specifically say they are not compatable with Directv so make sure you check the fine print. Also picking up a cheap cheater plug and trying it on various components can be a good way to test where the issue is coming from/through.