solderdude
Grand Contributor
When you don't hear it, it also cannot degrade the sound.
Here is another tests that in some cases might help.
Plug in the power supply upside down. With SMPS this usually doesn't do anything though.
To see if the groundloop comes from the wall wart there is another test:
While using the DAC pull its mains plug. Most likely it will still play shortly after you pulled the mains plug.
When this is the case, make it hum (no music) and pull the mains plug again.
When the noises disappear immediately you have proven it comes from the powersupply.
When the hum stays about as long as the music did it is not a powersupply problem.
Here is another tests that in some cases might help.
Plug in the power supply upside down. With SMPS this usually doesn't do anything though.
To see if the groundloop comes from the wall wart there is another test:
While using the DAC pull its mains plug. Most likely it will still play shortly after you pulled the mains plug.
When this is the case, make it hum (no music) and pull the mains plug again.
When the noises disappear immediately you have proven it comes from the powersupply.
When the hum stays about as long as the music did it is not a powersupply problem.