Jack Arnott

"When the + and - arms have identical ratios, the bridge is "nulled" and zero voltage difference exists between the lines - infinite common-mode rejection. If the impedance ratios of the two arms are imperfectly matched, mode conversion occurs. Some of the ground noise now appears across the line as noise." But this only works if the two signals are out of polarity with each other. (the plus arm, and the minus arm, referenced in the quote from the article.) One is "adding" and the other is "subtracting". Then you get no signal difference. "A good, accurate definition is "A balanced circuit is a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground and to all other conductors. The purpose of balancing is to make the noise pickup equal in both conductors, in which case it will be a common-mode signal which can be made to cancel out in the load." " So to me the important part is impedance matching, instead of voltage matching. Making transformer balancing better than active circuit balancing, at rejecting noise.

So back to your RCAs, does the shield have anything to do with the signal there?

I think that you give a pretty good description by using asymmetric. I have seen really bad internet articles that say it is about current, but that is the job of a circuit breaker, not the ground fault. GFI is about differential in current. EG, a guitar amp plugged into a GFI. The GFI wants the same amount of current in both the hot and neutral, as stated. If any current goes to say, the guitar strings, and then to the microphone through the guitarists lips, this is bad. So if more than the mentioned 30mA goes to the mic/sound system, instead of the guitar amp plug, the GFI will trip. So back to the Foggie post, most hum in systems from bad power comes from a differential, but in voltage, not current. If there is a voltage difference across the hot and neutral, and the hot and ground, that is where the problem comes in, and the GFI will do nothing for it.

Hi Speedskater, which part of my description do you not agree with? Or think needs a better explanation?

XLR, or more to the point, balanced signal is not bonded. There are three wires, one signal, one signal that is a reverse polarity of this, and the shield. When the signal reaches it's destination, the signal that was reversed is re-reversed to match the original signal. Any noise that has been introduced through the cabling during it's run, is now eliminated. (Assuming that equal amounts of noise have been added to both the original signal and the reversed signal.) Usually, this process is done via transformer, so that there is also no direct connection (or loop) via the shield.

No, no, and no. The way to fix poorly grounded power (if you cannot get the ground itself to be correct), is to use balanced power. This is a transformer system, that effectively isolates the power you are using from the infrastructure.