With two phases feeding two sets of windings, is there any fear of issues with each being on opposed phase of the A/C?
J!m, your thought process is valid, and it could be a valid concern, especially when we start cross-connecting (2) different 220v amps with 2 different AC feeds to a common pre-amp running off of 110v. (We can stop worrying at the preamp, assuming that all the music source boxes are being fed from
a common power strip.)
Back when I looked into all this, I learned that on a given
residential street, only (1) of the (3) phases coming from the power plant is being distributed. (And for load-balancing, the next street over has the 2nd phase, and the third street has the third phase, and this repeats...)
Anyway, at the transformer out on the pole feeding your house, it takes this single phase, and by running it through a center-tapped transformer, our house is fed with (2) equal-yet-opposite 'opposing 110v' 60hz sine wave power. (Apologies to those that already know all this - just trying to illustrate the point. Anyway, if you trace out the power flow inside your circuit-breaker panel, you will see these (2) separate 110v feeds are physically alternated. Ergo, a single breaker = 110v -- double breaker = 220v.)
OK, given this I *think* that depending upon where you have your 220v circuit breaker physically located (ie: left vs. right stack in your breaker box) you could end up where if you were to scope/trigger the 'A' channel on the 'hot' wire feeding the LEFT amp you would see the power peak positive, while simultaneously if you were to put the 'B' channel of the scope on the RIGHT amp you would end up with the 'hot' wire showing the peak negative at the same moment in time. (And the 110v line level boxes would be in a 'power phase sync' with one amp or the other, but not both.
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The solution would be to avoid putting your system into that kind of power quandry. If it was my listening room, I would first figure out where do I physically locate the (2) 220v circuit breakers so that they are 'in phase' with each other. This would be easy to verify using a 2-channel o-scope.
Voila! And then for bonus points you could try the 110v circuit breaker on each leg & go with whichever brings your system the most tranquil baseline.
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I don't know if I did justice to all of the above...and please, any electrician out there who can make this a better explanation don't hesitate to accuratize my attempted description. (I *do* know that one time I went through all my 2-prong boxes and (those that had identical-width non-polarized plugs) I would flip one power connector both ways, measuring the 2 resulting voltage differentials between the 2 box chassis under test, and went with the lowest reading between the 2. (And then marked each plug with a red nail polish dot so that I could keep it right after unplugging/replugging stuff. (And yes, I could hear the difference in lower background hum in the overall system. (!)
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Getting back to your question -- 1) Your concern is valid, but 2) we should be able to get both amps fed power 'in phase', and 3) we can prove it with a dual-trace scope.
Does this makes it clearer, or further muddy the waters?
FWIW -