[randog]

I've got a hum coming through my speakers when the TV is on. Everything except for the amps is plugged into my BP 2.5 Ultra.

I thought the BP was supposed to take care of things like that?

I need to do some troubleshooting, like plug the TV into the wall and the amps into the BP to see what's what, but all that isn't as easy as it sounds, so I thought I'd run it by here to see if anyone can help shed some light.

Everything is on one circuit.

Thanks,
Randog

[tkp]

Since everything is plugged in on the secondary side of the transformer inside the BPT, there is no isolation between these devices.  Most likely, the noise from the TV power supply got on the secondary side of the BPT and effect the preamp/receiver.  If you plug the TV directly into the wall outlet then there will be isolation between the TV and the rest of the stuff on the BPT.

[randog]

That would explain it! Thanks.

So... with a BPT, if I understand correctly, all the components are conditioned from the outside, but not from each other. Is that right?

[tkp]

That would explain it! Thanks.

So... with a BPT, if I understand correctly, all the components are conditioned from the outside, but not from each other. Is that right?

Not for differential mode noise.

[randog]

Well, the hum is still there with the TV plugged into the wall, and it's still there with the amp plugged into the BPT. It goes away when the amp is off. What this tells me is noise from the TV can travel back out from the BPT and back through the amp regardless of whether the amp is plugged into the BPT or the wall. And it tells me that the TV can still cause noise when it is plugged into the wall and the amp is plugged into the BPT (in that case I don't think the BPT is doing its job).

[tkp]

Well, the hum is still there with the TV plugged into the wall, and it's still there with the amp plugged into the BPT. It goes away when the amp is off. What this tells me is noise from the TV can travel back out from the BPT and back through the amp regardless of whether the amp is plugged into the BPT or the wall. And it tells me that the TV can still cause noise when it is plugged into the wall and the amp is plugged into the BPT (in that case I don't think the BPT is doing its job).

You need to find out whether this is a ground loop problem or noise from the TV power supply injecting into the secondary side of the BPT.

Is the noise there with the TV off?  If it is then you have a ground loop problem.  

If the noise is only there when the TV is on then noise is injecting into the system some how.

The BPT has filter on its primary side so it is hard for me to see differential mode noise can get in and since the secondary side is balanced power, the common mode noise is eliminated.

[John Casler]

9 times out of 10, it is the cable or Dish feed causing the hum.

Unplug your cable feed at the wall and unplug the "cable or DISH box" from the system and see if it goes away.

If so, do a search for "hum buster" or such.

Generally the BPT won't do the job on that kind of hum.

[StevenACNJ]

Take a look at one of these from Jensen Transformers VRD-1FF - About $60 - Eliminates ground loop hum from CATV cable.

http://www.jensen-transformers.com/press.html

[randog]

Sounds good. Thanks for the tips... I'll nail this bastard yet!

You can't hear it with normal listening... can it do any damage to the speakers?

Thanks again,
Randog

[randog]

OK, I've done some trouble shooting... I had Dish installed a little over a month ago and walked around their installation. First off, they didn't install a ground (which I thought was required by law). So, I've got them coming back to do so before I spend money on fixes from the outlets-in.

The hum does seem to be related to the cable boxes and/or lines. I've got 2 boxes and 3 incoming cable lines and one outgoing... lots of 'stuff' to give noise.