Does the Vivaldi DAC USB 2.0 input need the 5v through the USB cable? I am using a JCat USB card in my computer and can remove some jumpers to achieve a better sound.
Many USB devices use the 5V line to perform a handshake on boot up. So even if the 5V line is not used thereon to provide power its absence on boot up will not guarantee normal working.
There have been double connecting USB cables made ( e.g. by ifi audio) where one with the 5V line in place is used to perform the handshake. It is then removed leaving the one with the 5V line disabled connected for the rest of the listening session.
Hence even if the Vivaldi does not need the 5V for power the device feeding it may require it in order to recognise the Vivaldi.
So, there is not a YES or NO?
I need to know for sure.
Someone from dCS?
The manual of the card:
If a USB DAC/USB DDC does not require 5V via USB ports, it is recommended to remove (pull) jumpers J3 & J4 from the card for best performance.
The USB Card XE will not output 5V via USB ports if the jumpers are removed.
Removing jumpers is usually something that is reversible ( why they use jumpers instead of a soldered connection). If you can check that this is so then you do not need an expert answer. Remove them and if it works then fine. If it does not then put the jumpers back.
After researching this online my expectation is that it will work. I have found a Rossini user with a JCAT USB card who removed J3 and J4 jumpers and it worked fine. My guess is that it will be the same with Vivaldi. However I cannot guarantee this as he also reported that doing the same with a different DAC did not work.
So just ensure first that you can put back the jumpers after removing them. You won’t cause any harm. It will either work or not.
Thanks, I will try it.
It is indeed very much YMMV - your mileage may vary. Many, many DACs feed (some of) the USB circuitry off that 5V input from the source - this is of course especially true for portable USB DACs. But, for example, my old Metrum DAC also used the 5V input to power the M2Tech USB receiver card, so without 5V in: no sound 
Then again, other DACs don’t need it.
I’d say, try with the jumpers removed. If you get sound, then that is absolutely the best solution. No contamination from the source. If not, you’ll have no choice to put the jumpers back, problem solved…
Well, I finally got the JCAT USB CARD XE and mounted it in my fanless computer. As mentioned, I removed the jumpers from the card. When starting Roon I saw it immediately, no USB card, so unfortunately it won’t work. But … still something positive, the new usb card sounds very good. With the old JCat USB card it already sounded similar to the Rossini DAC ethernet input I had back then, but this card sounds much better, so I’m a happy man.