jea48 In most cases where the building electrical branch circuit wiring is the cause of ground loop hum it is due to the type of wiring used and or the type of wiring method that was used.
I have two 20 amp branch circuits ... My audio system is dead quiet ... No difference of potential, voltage, between the two equipment grounds measured at the wall duplex outlets.
I’ve had similar experience. My system is complex and biamplified, so it uses a bunch of dedicated 20A lines. Each amp is on its own line, plus there are separate lines for digital and analog sources. There are no ground loops.
millercarbon plug all your gear into one circuit. Voila! No ground differential. No hum. Geez how hard was that?
It’s not that simple, because you can get ground loops even if everything is running on the same circuit. That’s because ground can also flow through interconnects and if they are different types, or have different lengths or impedance, you can have different potentials in the grounds, which results in hum. In some instances, you may need to use a grounding block to eliminate the noise,
such as this. But as jea48 noted, the real cause is often the building wiring scheme itself.
Another key element to good AC is the use of tight, clean connections, from the receptacle all the way back to the service panel. I have also seen breakers with bad or corroded contacts - replacing them can not only reduce noise, but can also reduce their internal resistance and improve current delivery.
The two rows of breakers in the box, each row connects to one of the hot legs.
No, this is also mistaken. Typically, the legs alternate within each row. That’s how a 240VAC circuit is wired.
Whichever leg you use, make sure all your system components connect to that leg.
This is common advice, but it’s debatable. I have my digital gear connected to a different leg than everything else in the system. It seems to sound better that way, but I wouldn’t want to have to prove that to anyone.
I’ve experimented with putting each of my amplifiers on different legs, but couldn’t detect any difference.
