I have noticed that my system consistantly sounds better after 2 1/2 days of being left on. Sometimes I shut my preamp down at nights because it gets too damn hot. This doesn't seem to affect sound, but complete shut down definitely changes things for the worse. As to improved sound after 20 minutes or so, I would guess that it is your ears "warming up". Just like eyesight, ears can focus on sound, and it gets sharper with attention and effort. Also if you start at a lower to mid volume, and
raise the volume slowly, your ears adjust. If you start out too loud, it tends to "blow your ears out", affecting your ability to hear details.
raise the volume slowly, your ears adjust. If you start out too loud, it tends to "blow your ears out", affecting your ability to hear details.