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In Reply to: RE: an improperly applied shield posted by fmak on July 13, 2014 at 02:25:13
As I explained in that post, if the shield tie point is not actually ground as can be the case with typical common mode problems where the entire chassis, signal ground etc. is changing potential with respect to earth at the resonating frequency then tying your shield to it does no good to solve these common mode problems and maybe even makes things worse by tie-ing in even more conductor and effectively enlarging the antenna.
"There is no reason to think that motherboard ground planes, component specification, and trace location satisfy the criteria you postulate about."
No reason unless you happen to be living on planet earth and are subject to the laws of nature that is. This will be happening in every PC at least to some degree. As I've said before, if this is the most significant noise problem amongst the noise problems attempting to be solved then shielding from the sata bus signalling activity might not even noticeably help. It's just one of many examples I could have used. It just happens to be one which is likely to be a more significant problem to more readers here than sata bus signaling radiation and is most often the result of bad power supply design but can be fairly effectively dealt with in most cases by proper rf grounding of the audio gear,including the PC, as much as possible.
That is why I brought it up by attempting to get more details about your system. Again, I have no way of knowing your system. Even when asked you seem reluctant to share the details.
For an illustration about the pc chassis quietness try using your scope to measure your pc chassis to a another unloaded breaker circuits ground. You will not need the most sensitive ranges of your scope to see signal even in an otherwise quiet rf ambient environment if your pc is typical.
Follow Ups:
you seem to have a lot of time postulating and imagining. CMRR issues are common not only due to grounding but poor CMRR in active components and trace routing. It is not the only issue in computer audio and the issue I posted was that of an unshielded sata cable either radiating or receiving interference.
No need to postulate or imagine.
Fact is you neglected to give proper context to your statements and so I tried digging deeper.
I hope I get the chance to repeat this thing I've stated over and over some more because you seems so great at comprehending it.
It would be too much to expect reports that correlate listening observations with measurements, especially since these reports don't contain detailed particulars of what was listened to. I would not expect measurements from those audiophiles who don't claim to be technical, but those who have already posted pictures of their test equipment and boasted of escapades involving scopes and soldering irons are certainly capabible of such.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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