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Noisy USB Bus. High Frequency content at the USB Data rate. Solutions?

post #1 of 10
Thread Starter 

Hi all.  

 

I have a custom built AMD PC built on an ASUS motherboard.  My DAC is an iFi iDSD Micro, with the iUSB Power and the dual headed Gemini USB cable.  

 

Here is the problem.  I get a slight high frequency noise upon playback.  You have to get within a foot or so of the speakers, but it is there.  The frequency is around 4 khz.   I am guessing it is related to the frequency of the data packets, since it is an even factor of the 12khz USB clock rate. 

 

This noise is only heard using my custom built desktop.  I switch to my laptop, and voila!  It is gone.  

 

But I am quite partial to my desktop PC, and have no desire and really no resources to replace it at this time.  But, I am wondering if going to a PCI USB card would be a solution?  Something basic, or perhaps even something more elaborate, like the Sonore USB card?

 

 

Thanks for any input

 

 

Andrew

post #2 of 10

Well you are in luck, or unlucky, however you want to take it, Schiit audio brought out a USB decrapifier that might suit your needs called the Wyrd which will remove the noise of your USB plug: http://schiit.com/products/wyrd-usb-decrapifier

post #3 of 10

I assume when you are using the laptop, it is placed right next to the speaker as well?

 

I don't really think it has anything to do with dataline noise on the USB. If there is an USB clock problem, as very unlikely as it is, it will not not show up in the analog stage since that will be a digital noise. What it will affect is jitter. I am more incline to think it is either ground noise or magnetic interference.

post #4 of 10

That could be very possible, he should move it away from the speakers.

post #5 of 10
This sounds like rf interference or something along these lines. This might seem ridiculous, but I would put a piece of aluminum foil, making a faraday cage, between the dac and the computer. Also, try putting a ground lift on the dac power supply or plugging it into a outlet on a different circuit.

Trust me, I am an engineer--what could possibly go wrong....
Edited by Dex41 - 8/12/14 at 9:33pm
post #6 of 10
Thread Starter 
Quote:
Originally Posted by ClieOS View Post
 

I assume when you are using the laptop, it is placed right next to the speaker as well?

 

I don't really think it has anything to do with dataline noise on the USB. If there is an USB clock problem, as very unlikely as it is, it will not not show up in the analog stage since that will be a digital noise. What it will affect is jitter. I am more incline to think it is either ground noise or magnetic interference.

 

Yes. laptop right next to speakers.  

 

Whatever the source of the noise is, it is coming down the USB line.  Some kind of emi from my computer.  There is a ton of stuff going on in there with a lot of dirty power.  I agree it is not a clock problem, per se, but there is some kind of noise making its way into the system.  

 

What I am wondering is if these USB PCI solutions, like the one made by Sonore, which has EMI filters on the data line coming into the card, would be the ticket to shield the the audio system from the noise...

post #7 of 10
Thread Starter 
Quote:
Originally Posted by Dex41 View Post

This sounds like rf interference or something along these lines. This might seem ridiculous, but I would put a piece of aluminum foil, making a faraday cage, between the dac and the computer. Also, try putting a ground lift on the dac power supply or plugging it into a outlet on a different circuit.

Trust me, I am an engineer--what could possibly go wrong....

 

 

Actually my DAC power supply, the iUSB power, has a ground lift.  First thing I thought of was to flip it.  Made the noise worse, actually.  Well, not the specific noise, but the overall level of RF noise rose dramatically.  

post #8 of 10
Thread Starter 
Quote:
Originally Posted by TheJosablo View Post
 

Well you are in luck, or unlucky, however you want to take it, Schiit audio brought out a USB decrapifier that might suit your needs called the Wyrd which will remove the noise of your USB plug: http://schiit.com/products/wyrd-usb-decrapifier

 

I already have a similar product(s) from iFi.  The iUSB power, and the iPurifier.  The iPurifier is a low pass filter, but I don't think it is designed to cut noise as low in frequency as what I am describing.  

 

The thing is, these products are mostly dedicated to cleaning up the actual 5v power line.  Problem is, there can still be RF interference that comes down the actual data line, too.  

 

That said, I wonder if the Schitt would make any difference.  My guess is no, but might be worth ordering one just to see....

post #9 of 10
Thread Starter 

Update.

 

I took my iUSB power and iPurifier out of the system, and ran my DAC directly on the USB bus power.  The overall background RF noise got much, much louder, and so did the tone.  Turns out the iFi stuff is really doing an impressive job cleaning up my USB signal.  Wow.  

 

But unforunately, it seems I indeed have a really dirty USB line.  These outboard solutions are helping clean up, but are not solving the problem.  

post #10 of 10
Thread Starter 

final update...

 

was able to pretty much fix it by moving some stuff around on my power circuit.  Lots of switching mode power supplies, etc. down there.  Tedious process of un-grounding some of those switching supplies, changing my iFi iUSB power SPS to a different surge protector, etc. etc...

 

power can be such a nasty thing when it comes to computer audio... so much stuff.

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