Basic electrical questions.

In my own system, I have installed an isolation transformer feeding the subpanel, with separate dedicated lines to each component. To address the issue above, I have put a second isolation transformer on the CD dedicated line to keep its digital hash from contaminating the other components.

This has proved very effective for me, as there is now no difference in the background noise level between the CD player while off, and the CD player playing while muted. If you are contemplating multiple dedicated lines off a single subpanel, I suggest you consider this approach.
12-10-08: Zargon

Zargon,
I was burning the midnight oil last night when I responded to your post. I forgot to address your comments in regards to the use of good isolation transformers.

The application of iso xfmrs as you have is a great way to go. Especially using iso xfmrs on your digital equipment.

Al,

You are correct about ground loops - usually ground and neutral are connected at the electrical panel. If you have different equipment plugged in to different locations and then chained together for audio purposes there is indeed a greater risk of a ground loop. Provided house wiring is correct then the major culprits are high impedance shields on interconnects, imbalanced RCA consumer gear and power supply leakage from components.

The digital issue is I believe related to the use of switched mode power supplies - which is common these days as they are cheap. These can create noise on AC power which can affect some equipment with less than perfectly designed power supplies. I have not seen any proof of this but my experience suggests that PC's are particularly nasty/noisy - they also vary in demand as a function of processor requirements - simply look at a Playstation - how hot it runs and the tiny size for all the current it takes....

As for RF/EMI - never been a problem for me - so I'd agree with Eldartford that this is a much rarer problem.

Here is a useful resource. Enjoy! BTW - it is great to see some well thought out posts on these subjects - I read your thoughtful posts with interest.

One point of interest here is what was said about the actual length of the ckts themselves. I read somewhere there is a formula for figuring out the db per feet in loss. I don’t recall it now, but I know it happens. This effect occurs using dedicated lines as an added benefit, though it’s seldom if ever expressed as such.
12-11-08: Blindjim

I have read that also.... I looked last night and could not find the article. I know it is out there.
>>

In regards to ground loop hum.....
.

That's exactly how I work it:
Sep/exclusive circuit for Amp and Sub. 20amp, PS Audio Soloist outlet.
And since I am not wealthy enough to rewire the entire house with yet more new circuits, the rest of plugged into a good power conditioner off an existing house circuit. The digital stuff IS plugged thru an Iso transformer which provides additional benefits.
If I were starting from a Clean Sheet of Paper, I'd have hi power and low power dedicated lines and a whole house arrestor installed. I think a major limit yet unaddressed here is that, for example, I have only a 100amp service to my house. The TRUE addict would have double panels, maybe a 200amp total service with one panel dedicated to the HT/Sound system.

Maybe you are not familiar with Charles Hansen

Or maybe I am. I have read the work of, met in person, and/or had close working relationships with many brilliant people . . . most of whom I disagree with on one thing or another . . . in spite of the fact that I hold them and their work in high regard. This is why the concept of peer review is a cornerstone of so many disciplines, and the proper citation of multiple sources is a requirement for any scholarly paper.

Again, I encourage those interested in these subjects to get their information from multiple sources, and give at least a quick glance to bibliographies and sources.