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Alleged PC power supply etc "noise:" Has it been measured?, Is pc internal "noise" a genuine worry?
Arnold B. Kruege...
post May 7 2014, 15:32
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QUOTE (Thad E Ginathom @ May 6 2014, 15:27) *
QUOTE (Arnold B. Krueger @ May 6 2014, 18:56) *
Let me put it this way. Right after setting up a new computer with a FIIO E5 headphone amp (USB powered) I had this horrible noise. I had been powering the E5 off of one of the USB ports on the computer. I rummaged through my stuff, picked out a generic switchmode USB power supply, powered the E5 with it, and obtained utter silent bliss.

Later on I ran into a similar situation while trying to power an E5 and a Sansa Fuze from two different ports on a portable USB charger. The E5 sounded great if I unplugged it from the charger and ran it on its own battery. I think I'm figureing this out... ;-)


Good. Noise can be transmitted over USB power then.

Is there anything to suggest that it can be transmitted over the power lines of a USB connection to a device which is not USB powered?



Bottom line is that USB is based on a metallic conductive connection between the USB device (power or signal or both) and that makes it a potential participant in ground loops.

That suggests that noise can be transmitted via USB caqbles no matter how you connect them to the PC, or what kind of noise is or is not on the connection itself. The simple existence of the connection indicts it. BTW, the same is true of HDMI. But its not true of LAN connections or optical audio connections.
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AndyH-ha
post May 7 2014, 20:15
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The crucial factor is the design of the USB device itself, whether or not it reject/filters noise adequately. The same is true of internal soundcards, whether built in or PCI/PCIe.
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Thad E Ginathom
post May 8 2014, 11:01
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Again, thank you both.

I guess I am being spoon-fed basics here. I appreciate it that people take the time and trouble to do that. I guess I've said already that I'm trying to get real information rather than audiophile mythology: I hope many other seekers will find and benefit too.


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The most important audio cables are the ones in the brain
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Arnold B. Kruege...
post May 8 2014, 12:35
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QUOTE (Thad E Ginathom @ May 8 2014, 06:01) *
Again, thank you both.

I guess I am being spoon-fed basics here. I appreciate it that people take the time and trouble to do that. I guess I've said already that I'm trying to get real information rather than audiophile mythology: I hope many other seekers will find and benefit too.



The important thing is that a top performing USB device has to hit on all cylinders of which there are at least two: Power and signal.

One irony about my Fiio E5 story is that there is no digital processing within it. It is just a miniature analog power amp. Whatever noise that came from USB comes in via the power terminals. I don't think that shielding or the suual kinds of interference rejection had anything to do with it at all. The noise came in via a power supply ground wire. It was a grounding problem. This shows how USB power is a potential exposure all by itself.

I don't know if I made this clear but the E5 caused no problems with the first PC that it was installed on and ran cleanly for years as a booster for a number of different audio interfaces, both internal and external (USB). But it was problematical with a second PC as well as a portable Li Ion charger. This shows the importance of getting the power part of the equation right, which has nothing to do with shielding or the like.

It seems obvious to me that the E5 was not tested in all possible relevant configurations. Even though there is one spec for USB power, there are many possible implementations and they can make a difference.

The good news to me is that external USB power supplies are usually the fix and they are cheap and readily available. But, its not the cleanliness or absence of noise of the USB power supply that makes a difference. The difference is that the external power supply removes a potential ground loop that might be the fault of some other part of the system, in this case possibly the PC itself.
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