Okay Napalm, I've done a bit of reading of the papers by Analog Devices but it would seem to me to be more of an issue for the design of, in my case, the Casablanca III HD (which has both analogue and digital components) than a discussion of the BDP-2. What am I missing?
Your observation is correct up to the point that eventually you'll have to connect the BDP to some other box containing a DAC.
What you should note is that:
- digital circuits work by switching; this is what produces signals of extremely large bandwidth, up to RF domain
- once you got into RF noise, and its wavelength is comparable to the length of the conductors/traces on your PCB, it will happily propagate inside your box as EMI without any need for galvanic connections
- the RF noise is proportional to the power drawn by the digital component producing it (you have to check the power consumption of that SSD drive to understand how much noise it could make)
- digital circuits by themselves are pretty tolerant to the above noise
- in a pure digital box you can easily get away with just one power supply and local decoupling / good PCB design no need for multiple sources
- the largest amount of noise is usually generated by the digital components not by the power supply itself (even if it's of the switching type)
- you get into trouble when you need to connect the digital circuit to an analog one
- if you have a DAC / ADC you are forced to have some kind of galvanic connection between the digital part and the analog one (as mentioned by TI note) (remember that a DAC is also a digital component that does a pretty good amount of switching inside the case)
