My apology to rejuvenate this thread, but something bother me.
I know someone who get an unexpected hum problem whose origin has been traced to a recent model of Atoll streamer. Nothing can get rid of the hum, which seems to point to a low frequency signal mixed in the output signal inside the Atoll. I acknowledged that this thread is about the DAC200 Signature, but as the current generation of Atoll devices seems more or less built the same way, I tried to get some good pictures of the inside to figure out the internal grounding scheme. At first, I thought that the Atoll has no safety earth despite a three prongs mains inlet socket and the lack of mention of the class of operation on the rear panel, because the three internal mains input terminals are directly soldered on the PCB, which led me to believe that the internal main earth terminal is connected to nothing:
But on a picture of the inside of the DAC300 (the model above the DAC200) I have found on the Internet, we can clearly see a PCB trace going to the solder joint of the mains earth terminal :
This trace goes to this "Earth" point which also corresponds to a mounting point of the PCB :
That trace can also been seen on the second photo on this webpage :
https://vumetre.com/en/tests/manufacturer/atoll/atoll-▻-dac300/
I must say I am rather concerned by the reliability of the connection of the metal chassis to the mains safety earth, for the kind of standoff under the PCB is not visible and the very regular bolts used are obviously black anodized, hence non-conductive.
Except the reduction of the cost of manufacture, I do not see the point of such a configuration. And is the signal ground connected to this "Earth" point ?