Originally Posted by AB Hancock
Originally Posted by Bob Pariseau
^ Yes, that would be a natural reaction for these symptoms. HOWEVER, you just reported that the problem STILL exists even with ALL HDMI cables disconnected from the OPPO, right?
This is a critical question. We have to be clear on the answer. No HDMI cables connected to the OPPO -- not Inputs, not Outputs -- none. But the problem still exists on the Analog audio outs, right? If so, it can't be HDMI related.
Does your prior Denon player have a 3-prong power plug?
Bob you are the best and I am totally embarrassed. I pulled the coaxial cable from the cable box and the hum vanished. Perfect silence. I can't believe I didn't think of the cable box as being the source of the problem. Repair arriving in the a.m.
THANK YOU THANK YOU THANK YOU!!!!!
Now a SUPER satisfied Oppo owner!
Cool! Or as I sometimes say, "Suddenly! As if by logic!"
Just so you understand what's going on here, the cable TV feed is a shielded cable. The shield sheaths the cable and is supposed to keep outside interference from screwing up the real cable signal. But that sheath is a conductor in its own right and so it will carry whatever external garbage it picks up looking for a path back to ground to dump it. Cable lines typically are run on power poles, and so one of the main sources of garbage is the interference radiated by the power lines.
Now, what's SUPPOSED to happen is that where the cable feed enters your house there should be a good ground connection from the exterior attachment box to "real" ground. I mean well into the dirt or a clean connection to something metal that goes well into the dirt. This is the thing that's usually screwed up. The ground connection either doesn't exist, or is connected to a pipe that turns into PVC plastic before it goes into the dirt, or the connections are loose or corroded.
A secondary problem can happen inside the walls of your house. The cable shield can pick up interference along its run from the outside box to your set top box -- perhaps from power lines inside the walls. Now this will typically be smaller amounts of interference, but still stuff you don't want. What's supposed to happen is that the shield of the in-wall cable carries that stuff back to the outside attachment box, and thence to ground through its ground wire. But those cables in the walls are often installed by contractors who come from the school of shoddy. The raw wire run through the walls needs to have the little metal plugs attached at each end, and if the contractor rushes the job the installed plug-end doesn't actually make electrical contact with the cable shield. So the shield of that in-wall cable is "floating" -- not connected to ground. If it finds a path to ground through your equipment then interference picked up in-wall will be dumped out that way. The real fix is to cut off and re-attach the plugs, but typically for in-wall problems the repair guy will take the much quicker step of installing a "hum blocker".
A hum-blocker is a cheap, cylindrical adapter that gets attached in-line on that cable feed -- usually right before it screws into your set top box. It is a zero gain transformer with no electrical connection between the cable shield on either side. The cable TV signal passes through the transformer, but garbage on the shield of the cable can't get past it. Voila!
The problem is that because these are CHEAP transformers, and because the cable TV signal covers such a wide range of frequencies, installing one of these may result in weakening of signal for some your your channels. Depending on whether any of your channels were weak to begin with, you might even lose some channels. That still may be better than getting to the plug ends of the in-wall cable!
With that background, the thing to understand is that the typical cable guy will reach for a "hum blocker" as the *FIRST* thing to try. And that's not good. Although it will "work" -- i.e., your noise will go away -- you do have that problem of weakening some channels.
But more important, if the exterior cable feed is not properly grounded to begin with, a "hum blocker" won't fix that. And that ground connection is not just to keep noise from getting into your system. It also is needed to keep surges from entering your house on the shield of that cable feed!
Bottom line: Insist that the repair guy check and correct the grounding of the external feed *FIRST*. Use of a "hum blocker" should be the fix of last choice -- i.e., after you learn that fixing the external ground doesn't completely eliminate the problem.
NOTE: Make sure your cable plugs are screwed down tight. A loosely screwed cable plug will also not have as good a ground connection to the shield of the cable.