Get a Bose!
It seems like my system sounds different all the time just subtly, wether it's the stats, the tubes, the enviroment or just my frame of mind I couldn't tell you.
I host a weekly music listening session for a circle of music enthusiasts of several dozen people. Some weeks there are just a few of us, at other times ther may be 12-15 people in the room. Many participants have been coming by for ten years or more and have themselves become avid collectors of outstanding and rare recordings. Some are avid audiophiles, others know a stylus as a needle and only use boomboxes at home.
Most know the sound of my system by now as well as I do. Everyone agrees that there are significant differences in sound from week to week, all things being equal (no new tweaks or equipment changes).
One can always tell when the sound falls in place; no one leaves until all the wine has disappeared or I turn off the power. My wife has been known to play the terminator role at times but sometimes she is as reluctant as the guests to refrain from asking for one more John Cage or Shostakovich sonata before turning off the lights.
At other times people drift away early, even when there is still a nice Cabernet or Sancerre sitting around.
I have never been able to pin down the cause of the discrepancy between listening sessions. I remember Enid Lumley's column in the Absolute Sound of yesteryear (before it became a trade ad rag), claiming that small causes such as that the setting of her water heater influenced the sound and thinking, this can't be true, she must be listening to her own mood rather than to her sound system.
I know that small things matter: don't use lights with dimmers anywhere, don't run fluorescents even the bulb variety, don't run dehumidifiers and turn off the refrigerator. I have even kept a record of barometric pressure and relative humidity but I have never been able to establish a repeatable cause and effect between utterly captivating sound reproduction and just another record.
Invariably the group always seems to know and votes with it's feet. Not wanting to say something like: "get a Bose". There seems always to be a perfect consensus and I have no way of foreseeing how the evening will unfold.
I should say that I use an all tube set-up, 58 tubes in all, from phonostage (Aesthetix) with two separate power supplies, preamp (AR RefII mark II) to AR V140 monoblocks into a pair of Summits. No digits, vinyl only.
So Enid was right after all, but she stopped writing audio and I have no intention of quiting listening; there is always another night.