Bob, my experience w/ isolation transformers is limited to a brief flirtation about 30 years ago. I'm not sure why people use them. And what you say makes sense at least for most frequencies (although I don't think they pass RF) I think they do offer the ultimate in surge/lightening protection at the possible expense of frying the primary side of the transformer!
As for AC line noise, I can't point you to specific documentation but you shouldn't have much trouble finding it on Google, as it certainly exists. Personally, I'm not terribly concerned with that issue either, as I am with ample, accurate power, and here's why: Most noise in a system comes from what the components and ICs pick up in transmitting and/or processing the audio signals and not from the AC line noise. As you say, decent power supply design should take care of most of that, particularly in power amps. As for source stuff which is processing weak signals, yes noisy AC can be a bigger problem, especially for preamps and more so for tube preamps (and then of course there's the RF your digital stuff (can) put back into the line. But my solution to that is to avoid the problem altogether (if one has a problem) by using noise-cancelling balanced power for the front end components.
Jim Aud (of Purist Audio Design) pretty much convinced me that the first thing to cover is the issue of (AC) energy transfer from the reservoir of electrical potential in your wall, to the component. Which is why that last 5 feet of power cord is so important (I know a lot of folks have a hard time wrapping their heads around this ;--) Using minimum 10AWG PCs for amps, power regenerators, and for some weird reason, DACs, seems to me makes the next biggest difference, after dedicated circuits.
As for AC line noise, I can't point you to specific documentation but you shouldn't have much trouble finding it on Google, as it certainly exists. Personally, I'm not terribly concerned with that issue either, as I am with ample, accurate power, and here's why: Most noise in a system comes from what the components and ICs pick up in transmitting and/or processing the audio signals and not from the AC line noise. As you say, decent power supply design should take care of most of that, particularly in power amps. As for source stuff which is processing weak signals, yes noisy AC can be a bigger problem, especially for preamps and more so for tube preamps (and then of course there's the RF your digital stuff (can) put back into the line. But my solution to that is to avoid the problem altogether (if one has a problem) by using noise-cancelling balanced power for the front end components.
Jim Aud (of Purist Audio Design) pretty much convinced me that the first thing to cover is the issue of (AC) energy transfer from the reservoir of electrical potential in your wall, to the component. Which is why that last 5 feet of power cord is so important (I know a lot of folks have a hard time wrapping their heads around this ;--) Using minimum 10AWG PCs for amps, power regenerators, and for some weird reason, DACs, seems to me makes the next biggest difference, after dedicated circuits.