Quote:I've got 3 dedicated ground 20Amp circuits going to my setup, one for 2000 watt subwoofer, one for Home Theater Amp, and one for ZMA and Oppo. I've tried a mix of all three, and I get even worse noise when I try to put some of the gear one a different circuit from the new P10.
I played with moving cables and trying to narrow down the issue more. I get definitely get a buzz coming through the speakers when the HDMI from the HTPC is connected to the Oppo. But, the worse part is, as soon as I plug the Oppo into *any* power, I get that same buzz again. If I try it on one of the other circuits, the buzz is actually increased considerably.
I think there is a weird ground loop somewhere. and switching to a different circuit simply make the ground loop bigger by going back to the circuit breaker panel then looping back to the equipment. So different circuits aren't helping.
I'll have to poke at it some more...but now it's seeming like the Oppo is the central source of the noise, not the HTPC (though the HTPC was a source of *some* noise, it can easily be remedied by streaming over CAT6 rather than over HDMI)
LR, when you have completely separate power circuits connected to separate audio components in the same system the chances of ground loops (AC hum) are increased. In your case each of your 3 separate circuits will obviously have their own three conductors Hot, Ground & Earth Ground. First thing to check is that all three circuits have the correct polarity Hot & Ground leads on all three circuits need to be wired to the correct prongs at your wall outlets. If you don't have one pick up a polarity tester at Lowes, it simply plugs into the outlet and gives you indications via LED's if the polarity is correct.
I will assume you have good quality wall sockets that have a good grip on all three prongs of any cord plugged into them. I've seen 50 year old homes with sockets that were completely worn out and could barely hold a cord in place.
Once outlet polarity for all three circuits has been confirmed then we move on to the Earth Ground. Current typically enters your component via the Hot prong and leaves via the Ground prong. The third wire Earth Ground acts as a Safety should the Hot lead short to the chassis of any component. Rather than shocking you when you touch the chassis current flows to Earth Ground via the Earth Ground Lead which typically trips the circuit breaker rendering the short harmless.
Most would assume the Earth Grounds (one each on each separate circuit) would all have Zero volts on them and in a perfect world they would. You can check this with an inexpensive Digital Volt Meter from Radio Shack. Set the meter for "AC Volts". Set the range for something like "20 Volt Range". This should allow you to read 20.00 volts down to 00.01 volts. Touch one test lead from the meter to the Earth Ground on one circuit and Touch the other test lead from the meter to Earth Ground on another circuit (try combinations of all three circuits). You are hoping to see 00.00 volts in each case but may actually get something from a few tenths to a couple Volts.
So lets assume you have 3 components (component A, B & C) each connected to a separate power circuit. Lets say the Earth Ground on component A has 1.00 Volt AC on it while the Earth Grounds on components B & C are at 0.00 Volts. Typically the chassis of each audio component would be connected directly to Earth Ground.
So what we end up with is the chassis of component A at 1.00 Volt and the chassis of components B & C at 0.00 volts. Voltage is like water pressure, water flows from High pressure to Low pressure. Current flows from High voltage to Low voltage. So the 1.00 volt in the chassis of component A will try to find a way to the 0.00 Volts in chassis B & C and typically that is via speaker cables, interconnects, HDMI cables etc. that connect the three audio components in this example. The result is AC Hum.
You can also use your Digital Volt Meter to check for Voltage potential between each component Chassis in your system. If you touch one test lead to the chassis of Component A and the other test lead to the chassis of component B and get any Voltage reading then you have a ground loop. Could be that of your Three separate power circuits (power circuits A, B & C) One of the circuits has the cleanest path to Earth Ground (least resistance). If for example Earth Ground on circuit A is at 0.00 Volts, circuit B at 0.12 Volts and Circuit C at 1.02 Volts then voltage from any component plugged into Circuits B & C will want to flow to the component plugged into Circuit A.
So what do we do. Probably the easiest test would be to connect each piece of gear one at a time to One Power Circuit. This way no matter which circuit you choose each piece of equipment will see the exact same Earth Ground. Even if you choose Circuit C at 1.02 Volts in the above example the ground loop is eliminated. In this case the chassis of each component would be at exactly 1.02 Volts. So if you touch one lead of your Digital Volt Meter to one component and the other lead to another component the reading will be 0.00 Volts. The voltage differential between the two components is 0.00 Volts which means there will be no current flow between the two. It's current flow that causes the Hum and without a voltage differential there is no current flow just as if there is no water pressure there is no water flow. If you have a water hose with 1.02 pounds of pressure at each end there will be no flow of water.
If connecting everything to the same circuit eliminates the AC Hum then I think this would confirm that the Earth Ground on one or more of your 3 separate power circuits has what is called a higher potential to Earth Ground than the others. This is not uncommon and for a number of reasons that we don't have time to discuss here.
You mentioned possibly Lifting the Earth Ground on the Oppo. Lifting the Earth Ground means basically disconnecting the connection from the Oppo chassis to Earth Ground at the wall outlet. This is a bit of a Shot In The Dark and even if it reduces your Hum it may not eliminate it. Not to mention it eliminates the safety feature mentioned earlier.
I had a similar issue once where I was forced to use a separate circuit for a remotely located sub. In that case I had my main audio system connected to a Tripp Lite surge suppressor with metal case and the sub connected to a second Tripp Lite. I ended up connecting a separate ground wire to the metal case of one suppressor and running it under the carpet to the metal case of the other. Since the metal cases of each suppressor were wired to Earth Ground via the wall socket this in effect provided every component access to the Earth Ground with the least resistance to Earth Ground. In this case I suspected current was feeding back from the sub through the line level connection to my Oppo. Attaching a separate wire between the two surge suppressors created an alternative path to earth ground and solved the problem.
So in the end if you use Multiple Power Circuits to power a single audio system it is not uncommon that one circuit will have a more direct path to Earth Ground than the Others. Current follows the path of least resistance and if that means it has to go through speaker cables or interconnects to get there it will.
Sorry this is such a long post LR but ground loops are not necessarily simple to understand or resolve. Hope this gives you some ideas to try when you get back to it.