06-22-14: KernelbobThat's interesting. Not to be argumentative, when I had PSA PWD-MkII, I heard no noticeable changes after ~50 hours.
@Jwm, My PSA PWD-MkII took a month to fully break-in. Now, I wasn't feeding it digital input 24/7, but it was powered on for the duration. After two weeks it was at its nadir. At the end of a month it had blossomed and pretty much reached it's performance plateau. So that's around 720 hours. Had it maxed out at the two week point, I would have sent it back. My ARC REF-3 also took a month to settle in.
In general, I agree with Grannying ... my system sounds different depending on my mood, alertness ...