Is dirty power the culprit?

I have experienced the same problem and yes it is power related. Do a little research on EMI/RFI rejection and implementing a "Star Ground" system circuit. I no longer have the seesaw effect.

I would guess both power and the human factors cited above are likely culprits.

It could also be you just don't like your present system. I've had similar feelings about systems over the years, I'm finally at the point where I like my system all the time. While I may not enjoy it to the same level at each listening session, I never end my sessions feeling something is fundamentally wrong with the system, now chalk it up solely to mood/disposition variables.

well, for what it's worth, i live in boston as well and have experienced similar differences with my systems that i attribute to the power.

oddly, the evenings in boston seem to be the worst times for power. often things sound pretty good to me in the morning and early afternoon, but get noticeably worse in the evenings -- until 1am or so.

and it does seem that some days are worse/better than others.

oh well. i just deal with it by listening to better-recorded material or by just watching tv. flight of the conchords sounds funny with bad power or good...

one day the system sounds so wonderful you are convinced you do not need to change a thing in your system and are set for life. Then the following day or a couple of days later the system sounds like a collection of items purchased at toys are us.
Montepilot (Threads | Answers)

Montepeliot, what you describe are *extreme* swings in your evaluation of your system's performance, not marginal ones. Don't allow anyone to suggest to you this is some psycho- acoustic phenomenon, tied to your mood or emotions, or state of mind at the time. These swings in performance are tied to the AC. Other than dedicated lines, which you cannot do where you live, I really don't know of a conditioner or regenerator to recommend. My attempts with the PS Premier were a failure (it did more harm to the sonics than good in my setup) I did try the APS Purepower regenerator and I'd like to try it again. For me it beat the Premier. I'd still have it if not for a glitch with the backup batterty. If only we could isolate our equipment from the power grid altogether and have pure clean power! Then we could hear what the gear is really capable of. That would be ideal!

These swings in performance are tied to the AC.

I always admire the way that vague symptoms in a nine line post (sounds "wonderful" versus "collection of items purchased at toys are us") can be diagnosed by others with such unquestioning certitude even though they haven't seen, much less heard, the system themselves.

It would like phoning a doctor who has never seen you, complaining of generic symptoms, and getting a precise diagnosis.

Power line issues can cause problems but it is hardly the only cause. Several avenues of investigation have been suggested to the OP. I hope he finds one - or a combination of them - helps with his problem.