.
As measurements at around -140dBV are always critical and depend very much on the test setup, I asked my colleague Raimund from the T+A development dept. to double check the DAC200 noise spectrum when connected directly to the source without an external isolator. Here is the result from the T+A lab:
As can be seen, there is some small amount of USB packet noise, but even without an external isolator it is very low at around -135 dBV. This is considerably lower than in Jussi’s measurement.
According to my experience, it can be helpful to connect the chassis of the source device to the DAC200 chassis with a low impedance ground lead. This in some cases will lower the noise by a couple of a few extra-dBs. Just try it out…
DAC200 output spectrum with chassis to chassis ground lead