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In Reply to: RE: with the data going over the SATA cable to RAM posted by Ugly on July 11, 2014 at 18:18:56
It doesn't take activity on the SATA bus for the SATA cables to act as antennas to re-radiate the common mode energy
Thanks for your comments. The one above more or less echoes the point I was trying to make. I say "more or less" mindful that I should have made it clear that the HDD/SSD in a Fit-PC2 connects direct to the mobo - see pic.
My powering the drive separately involved moving it out of the case and connecting it with a modified Slimline adapter (data cable to the mobo, power cable to an external PSU). In this case, SQ improved despite adding a SATA lead. IOW, though I accept your general point, it's not altogether relevant in this case.
I'm not disputing the benefits of shielding cables and am baffled as to why anyone should see fmak's point as controversial. What I was disputing was TL's suggestion that "[With data in RAM,] the SATA cable is not carrying any signal. It seems unlikely that it is creating any noise just sitting there and doing nothing.", "The SATA cable is involved only when the data is loaded into RAM. That could have happened the night before, but usually it as a minute or two before I start playing the music" and more besides. [Emphasis added]
For reasons including those you outline, I'd have thought it inevitable that SATA cables radiate noise all the time and that HDDs/SSDs continuously generate it regardless of whether they are performing RW operations.
Follow Ups:
Wow, that internal mounting is pathological. It's bound to shuffle the EMI environment around even if unplugged. True, the compulab boards tend to have pretty tight current loops but still... No matter what you do there are gotcha's, packing stuff in is usually good for radiation but not so hot for crosstalk.
Watching the Scottish open, but it's in unreal time.
Regards, Rick
Cool little computer there.For me the controversial part is spending money on something which may or may not help. Details about what was done seem important but hard to get in this case.
For example an improperly applied shield might not help a common mode problem at all. Common mode problems can be tricky that way, ie is your shield ground actually ground or is it some resonating pseudo ground which causes your "shield" to become part of the problem? Usually addressing the source, beads, or some other form of filtering are easier than creating a proper shield when faced with a cable radiating common mode energy.
The details of the nature of the shielding seem especially important to me in the case of situations where noise problems are occurring during periods of little to no sata bus activity as it does sound like a common mode problem.
Edit: deleted text from here.
Edits: 07/12/14 07/12/14
Why and how would you assume that a shielded sata cable may have an improperly applied shield? It's in the cable specification and shielding noisy signal pairs is standard in electronics.!
Seems to me that you have the time to argue for the sake of it and it would be much easier for you to try a shielded v unshielded cable in your system to see if there are any changes. Then you can postulate about common mode effects to your heart's content.
There is no reason to think that motherboard ground planes, component specification, and trace location satisfy the criteria you postulate about.
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.
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
I should never post before drinking my coffee. My second reading of your post made me realize this statement I made above."In summary, based on what I've heard so far I'd be more inclined to try some cable beads than a shielded cable in your situation. Of course it's damn near impossible to make a good armchair assessment on this kind of thing so I'd definitely take my words for what they are worth...not very much. "
does not make much sense to say to a someone who is saying adding a cabled setup reduces system noise. Not that beads wouldn't help but I'd be less inclined to suggest they might in light of my new found comprehension of your post.
Sorry for confusing the topic. I'll edit the previous post accordingly to remove this unneeded comment.
Edit: by the way I definitely concur with rickm's statement about crosstalk above. There is only so much in layout which can be accomplished to prevent the near field coupling due to high di/dt current loops, and high dv/dt hot nodes. Presumably the biggest culprit would be the current loops in low voltage computers like this but those edge rates can be very extreme. In cases where layout is optimized there is not much left to do to it than shielding which would be tough/expensive to pull off well in those close confines and so proximity to the fields is your enemy.
Edits: 07/12/14 07/12/14 07/12/14
If there is no data going over the SATA cables (as in my case) and the signal drivers for these cables are not enabled (as per the SATA specification) then changing the SATA cables is akin to changing any other wire in the box that is not directly carrying a digital signal. It will probably make less difference than changing a power wire, including a SATA power wire to a device that has active digital processing (e.g. a SSD or spinner, both of which have a microprocessor inside).
The problem is that this is all speculation. Unless some method can be devised to give rapid, repeated and reliable measurements that can be correlated to long term listening results, making progress by trial and error listening tests is going to be slow, akin to searching for one's car keys in a dark room without a flashlight.
IMO effort would be better spent on simple devices to provide analog digital separation using a narrow interface between the DAC and the computer. The narrowest possible interface today is the IIS interface with clock at the slave end or the DSD equivalent. Here one is concerned with the operation of a few hundred transistors and the necessary ground and power wiring, not billions of transistors doing unknown functions according to impenetrable software. If a USB DAC is used it must have this isolation built in, since the USB attachment in the DAC is itself a computer due to the complexity of the USB protocol.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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