Originally Posted by mcandmar
Happy ending so. With the + and - power line disconnected there is still a ground connection via the metal body of the USB plugs / cable shielding, i suspect that was passing through the noise you were still hearing. An isolator should cure that issue if you should still have it, certainly the version of the isolator i used will.
The fact your XLR connection was causing it is interesting, although you have a + and - for the left and right channel, there is also a ground line tied to connector body / cable shielding if applicable so the issue may be an incomplete ground circuit there on either your source or speaker end.
Regarding the new type of noise that started playing with Gnd and 5v disconnected, I found out it was only when the Gnd was disconnected, 5v made no difference, I found Unplugging my speakers from the wall outlet / or powering them on via a switch stops the sine wave noise - Speakers are self powered.
I've switched back and forth with the gnd and 5v connected / disconnected, and each time the tape is on the pins, each instrument in music has its own space (dependent of recording quality of course). Basically much cleaner sound.
One small problem, the Dac sometimes randomly disconnects, and the pc fails to recognise it, happens a couple of times a day, I simply reboot the Dac, I also have to unplug the speakers when I listen via the headphones - otherwise the sine wave noise returns, but imo a small tradeoff for the sound improvement.
If anybody reading this has a Self powered Dac connected to a computer which has a lot of noise, ie gaming machine with a beast of a graphics card installed, try sticking electrical tape over 5v and gnd of your Usb cable and let us know if there is any difference. I bet there will be!
Having an Async Usb connection I really wanted to use Usb over Optical for Music listening, hence why all this bother. Optical is perfectly fine for gaming tho.
If an isolator could do the same job of disconnecting the Gnd and filtering out computer noise without me having to unplug my speakers I'm sold, but at £30+ its a large price to pay if it only does the same as what I've done here using couple pieces of tape.
Even though what I believe to be an improvement I have to admit, it could all be placebo.
Edited by fluidz - 11/10/13 at 9:35am