Is it just me?

Another overlooked factor is the quality of your system's electric supply. Generally speaking, a system will sound better during low grid demand hours (late evenings) and worse during high grid demand hours ( daytime weekdays).
High temperatures can also decrease a system's sonic performance due to the extra demands on the grid from home and business air conditioning usage. All of the home and business electrical equipment connected to your neighborhood's electrical grid and any noise this equipment introduces, between the power generating plant and your home, does nothing but degrades the quality, and can even fluctuate the quantity, of the electricity supplied to your audio/video equipment.

I notice my system sounds best later in the evening when the weather is temperate. This is not meant to discount the other factors already mentioned thus far.

Tim

It would appear that weather plays a large role, with wet conditions and low pressure systems being quite bad for the sound, the electrical grid most likely being affected. It would also appear early mornings and nighttime are better times for critical listening. It's difficult to prove other than by tracking sun spot activity over at the National Weather Service site, but sun spot activity might influence the sound, I wouldn't be surprised. Not to mention the myriad things we change in the system without paying much attention. What ever happened to keeping a log of changes we make, even seemingly innocuous changes, like arrangements of cabling, absolute level for the turntable or CD transport, etc.?

Mlman,

The electricity going into your components from your home's outlets can vary from day to day in both quantity and quality. Tyypically, audio and video components will perform best during non-peak hours (usually later in the evening) when the electrical demand from households and businesses on your local power grid are at their lowest.

I've never experimented with power filters or regenerators, but I can verify that my system sounds best in the evenings. My comments are not meant to discount the other factors, mentioned previously, that can also affect your subjective impressions.

Tim

Regenerators and power conditioners are a crap shoot. I've had several of both and now go straight to the wall with aftermarket outlets (take your pick). The one thing I will eventually have done is the installation of a dedicated line or two.

This will happen to me in the car the a stock fm radio, so it's not a high quality system here. Depends on my mood and how I'm relating to the tune that particular moment in time.