Basic electrical questions.

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.

Shadorne and Jea48 -- I went through the Bill Whitlock paper and presentation you linked to -- really super!!! He's absolutely right when he says these issues are not adequately addressed (or addressed at all) in EE curricula, and even EE's often don't know the difference between a ground loop and a fruit loop. :)

Shadorne -- thanks very much for the compliments. As someone with a digital design background, and who builds his own pc's, I agree 1000% that pc's are particularly proficient noise generators, due primarily to the fast edge speeds (rise and fall times) that are present on the innumerable digital signals running around in them, as well as to the large currents that can be change value very quickly as a result of fluctuating demands on the cpu and other devices.

Whitlock very persuasively supports what you said about high impedance shields, in single-ended interconnects, saying that they are typically one of the most major contributors to noise problems. He makes the point that ground offsets and resulting noise are inevitable (although they can be minimized), but it is the resistance of the shields of single-ended interconnects where that noise typically gets introduced into the signal path to the greatest extent. Therefore single-ended interconnects should be as short as possible, and selected for the lowest possible shield resistance.

Blindjim -- Re signal attenuation per unit length of cables, you are probably thinking of video or rf transmission lines, where both the cable impedance and the signal frequencies are well defined and controlled. I don't think that the attenuation is determinable in a meaningful way for noise components that are present at many unknown frequencies and are being conducted through power wiring that has poorly defined and controlled high frequency characteristics. But see page 4 of the reference below (one of those that Shadorne and Jea48 provided) for some rough indications of the impedance of typical power wiring.

For those who don't have time to go through the 140 pages or so of these two references, I'd suggest at least looking at the following pages of this link:

http://www.jensen-transformers.com/an/generic%20seminar.pdf

Page 12: "how the noise gets in"

P. 14: "solutions"

P. 20: "choosing cables"

P. 21: "a checklist" -- especially good!

P. 27: "always ground shield at driver (at least)"

P. 28: "unbalanced to balanced interfaces" (if applicable)

P. 40: "Many of the benefits often ascribed to power treatment schemes are simply due to plugging all system equipment into the same power strip or dedicated branch circuit. For obvious reasons, this is always a good idea"

P. 40: "surge suppressor cautions" (they can do much more harm than good if used improperly)

Thanks again,
-- Al

Jea48,
I have read Hansen's article, and he does a good job of explaining the sources of disturbances on a household AC line. One has to appreciate well designed audio equipment that operates successfully in such a harsh environment. I do have some issues with his statements on Filters and Fixes (Part 2, pg. 7).

A dedicated line from your service panel to your audio equipment (I call it "star sourcing," similar to star grounding) can do wonders to keep noise and harmonic currents out of your audio equipment. With a dedicated supply, your amplification need only endure the noise from its system mates, rather than the hash from the washer, garage door opener, and furnace.

He recognizes the benefit of multiple dedicated lines with star grounding to reduce ground loops. And he recognizes that multiple dedicated lines by themselves do not prevent noise from one line getting on another. But then he contradicts himself by asserting that dedicated lines to a garage door opener and furnace will not pass their hash over to the dedicated audio line. As long as they are all connected in parallel on a common phase at the service panel, they will all share the same voltage disturbances. You can't have it both ways. I do agree that the length of the connection can attenuate conducted EMI and to that extent some of the crosstalk is reduced, but for short runs it would be minor.

This is why I advocate an iso on the audio subpannel and either a second iso on noisy lines or some conditioning at the componant. In my case the subpanel is adjacent to the audio room and less than 50 ft. from the service panel.

PS, thanks again for your excellent counsel when I designed and implemented this a couple of years ago.

Almarg,
The question of whether to tie the ground to common at the subpanel is an interesting one. I chose to do that and not let the audio system float. There are codes which apply to this question and I will let Jea48 address them if he so chooses.