Electronics > Beginners

Unwanted digital noise (Not the standard noise floor) from studio monitors

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John B:
Other things to note: the 78mV DC offset is also present between the 2 balanced lines (open circuit), and 1.5uA DC of current between the 2i2 and MOTU on each balanced line (when connected). Significance? I'm not sure whether that is something that needs rectifying or not.

magic:
Now open your PC's PSU, unscrew that useless green-yellow wire from the chassis, put it back together and watch the fireworks >:D

Which is to say, I still think a pair of diodes would be a good idea.

John B:
I just tried another solution. I ran a dedicated mains earthing strap directly to the ground shield of the balanced lines. There was about 50mV offset between the signal ground and mains earth ground, and about 50mA DC when shorted.

It did greatly attenuate the noise, but I think I can still hear it there. Certainly enough to be tolerable for generable use, but not really studio grade.

Still impressed by the cap solution. Totally eliminates the noise.

John B:
So, on the scarlett interface, the balanced output grounds are NOT connected to mains earth / PC chassis ground. There's about 500k  \$\Omega\$ between them. That goes towards explaining the high current to mains ground. There's about 80mA, while on the MOTU side it's balanced pair grounds are connected to mains earth and only get about 500uA DC leaking to ground.

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