Originally Posted by sheltonct
Unfortunately for me, most of this thread is above my head, but I have what I think is an easy hum question...
7.1 setup, Denon 2807, 2 amps (for front & surround), Yamaha DVD. My hum obviously is associated with CATV, because when I unhook the cable for music listening, no more hum.
I believe there are enough plugs on my power conditioner (or whatever it's called) for everything, though I may have the sub plugged separately into same wall outlet. There are also CATV in/outs on the conditioner I recall (I'm not home at the moment).
Can I plug the CATV into the conditioner, and then from there into the TV? Will that do the trick, or am I way off base?
Some power conditioners have surge suppressors for cable (could be antenna, dish, or cable TV). But those do nothing to stop hum. Very few power conditioners include a cable surge suppressor that also "breaks" (interrupts) the ground/shield (the Furman 20i does have isolated ground AND surge suppression, other models of theirs may have the same feature, and other brands might have it too, but if they don't SAY it isolates the ground, it doesn't.
So let's assume you don't have one of the power conditioners that DOES isolate the cable ground... what should you do? There's a company called Jensen Transformers who makes an EXCELLENT quality ground loop breaker. You need a second piece of cable to use it. You plug 1 end of the existing cable into the isolator, then plug the new length of cable into the other end of the isolator and then to wherever you need it to be connected. Now the ground for the cable (the shield) is 'broken' and you have isolated the cable ground from the ground from the rest of your system.
Why does the system hum when you connect the cable now? The place the cable is grounded is different than the place your house wiring is grounded. The cable may be grounded to a bar driven into the ground somewhere outside of your house or possibly to a water pipe inside your house somewhere. If the cable installer had run a ground wire from the cable where it comes into your house to the ground rod for your home's entire electrical system, chances are, that would also stop your hum.
When grounds exist in 2 different physical locations, you end up with a real electrical current flowing between those 2 grounds and THAT current flow produces the hum you hear.
If you have Cable TV (not satellite) you want Jensen's Iso-Max VRD-1FF... $60 MSRP. It doesn't appear that they have a product that will work with a satellite feed which can have the same problem. In that case, trying to relocate the ground for the satellite feed to the home's electrical system ground could stop the problem too. Or perhaps some other company that makes these sort of devices has one that works with satellite systems.
When you have this sort of ground loop (different physical ground locations), you may notice that when the ground is wet, the hum is not quite as bad as when the ground is really dry! The moisture affects the conductivity of the earth/ground and that changes the amount of hum you hear in the system.
You probably CAN'T fix the hum by running a wire between 2 different ground rods. You have to physically disconnect from one ground rod (or water pipe) and ground everything to the home's ground rod (often a crow-bar looking thing sticking out of the basement or slab floor or out of the foundation somewhere, or beside the home somewhere not too far from the electrical panel (ours goes through the slab in the garage and the electrical panel is not far from the ground rod). Some fairly beefy wires will be clamped to that ground rod. You can clamp another wire to that rod (don't disturb the existing ground, get a new clamp and add it to the rod, Lowes and Home Depot have them in the electrical department) and run that wire to where the cable or satellite ground had been located before (sometimes to a splitter or a fitting in the cable with a ground screw and hole coming off one side with a bare wire held into the hole by the screw).
Ground loops are fun! Especially when you fix one!