Anders,
"If the CD player cannot handle this problem, couldn't it instead be solved by feeding the player with clean AC? Of course I here think of power conditioner and power cable solutions that really remove the RF noise (or a substantial part of it)."
Note that what I've said is theoretical stuff backed up by anecdotal evidence --- I've not performed any good double-blind tests to show what I'm saying is true, but other industries outside of audio do have deal with such issues. With that in mind, RF noise can come from many places within a CD player, and not just the power supply. The sharp edges of the square waves inside a player have high frequencies that could, through capacitance, be injected into other components. Routing problems inside the player of signals can worsen such problems. For example, not directing return currents on the ground plane correctly so that they pass at right angles to sensitive clock signals can induce undesirable changes on the clock. Someone reported once that a Cal Audio player routed some important signal around the perimeter of a circuit board, creating basically a giant antenna so that external magnetic fields could induce currents on that signal.
There have been tests that show a (badly designed) CD player affecting itself very, very dramatically when just playing different CDs. Basically it had an inadequate power supply, and when the disc-reading servos were asked to work extra hard to read a marginal disc, it modulated its efforts into the audio section. No blind tests needed here --- it was very obvious.
RF noise can be injected into DACs through the digital interconnect as well. There could be noise riding on top of the digital signal. Many DACs don't do any common-mode rejection at their inputs --- those that do usually have a pulse transformer at their inputs. Many transport makers are obsessed with making their digital outputs as sharp and fast as possible, possibly to make up for poor timing recovery circuits found in most DACs. This can actually be bad, because high-speed signals tend to have high frequency components that are hard to manage. I have some DACs and transports that put wavey lines onto my cable TV feed. Imagine what else they're putting out.
Here's an interesting web page with technical info and measurements of some of the effects we're talking about:
Marc Heijliger's DAC project
Erland Unruh's DAC
The second one has the most exotic (and quantitatively justifiable) measures I've seen to getting good digital sound. For example, Pete Goudreau's triple-cap bypass networks have basically resistive impedance to over 40 MHz. That is really unheard of.
--Andre
