2. pc-audio
  3. 1150170453

any words of wisdom for usb noise problems?

i thought usb connections would be trouble-free after placing waveterminal u24 between my desktop pc and the dac in my panasonic reciever (office system). itunes runs dead quiet there. i am trying to implement a pc feed into my levinson preamp in main system. when the usb cable makes contact between my laptop pc and the u24 running into the preamp i get substantial noise, which is substantially worse when a usb hard drive is also attached.i googled "usb noise" and saw references to some midi users' and photo printer issues and some filter products (argh!- hope to avoid this step). also mention of computer screens as possible culprits any suggestions or similar experiences?
wkraft
slothman
311 posts
 
My prevoius post may have been premature... here is an interesting product I stumbled upon as well. It's basically a 5V battery pack built in the middle of USB cable. I can't seem to find the power requirements for the U24 in the manual but this product looks like it may work with the Waveterminal. I may bite and report back with my results. The battery powered hub that I came across but may not be powerful enough.
vfoostdijka929
3 posts
 
I found the solution for the noise problem and it is amazingly simple and totally free, at least in my case, but I think also for a lot of other users of external soundcards in general.

The problem was not the quality of the power supply.
The digital noise was created by a ground loop between my laptop, the U24 and my audiomixer. All noises disappeared instantly by plugging the laptop's power adapter in an unearthed AC outlet. Bye bye ground loop, bye bye noise!

If you don't want to leave your laptop (or computer) without an earth connection, the other solution is to add a line level DI-box in your analog audio in/out lines.

Best regards,

Vincent
vfoostdijka929
3 posts
 
Or, instead of a DI-box, an inexpensive ground loop isolator:-)
hagtech
173 posts
 
The problem is likely a solid connection between PC ground and audio system ground. This is an issue with many USB DACs. A lot of them do NOT offer galvanic isolation, hence, much of the noise from one system enters the other.

This is EXACTLY why I use s/pdif transformer isolation in my USB dacs and converters. You won't need to unplug your PC wall-wart.

jh
audioengr
3,282 posts
 
As long as we are all advertising here, I'll pipe in too.

This is precisely why I use pulse transformers to galvanically isolate the PC from the Audio System.

Steve N.
Empirical Audio
Manufacturer
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