Bass leaves after amp warms up?

"The thread that refuses to die! Will it survive to 1,000 responses? What is the record?"

We're in the middle of a "cliff-hanger", hoping to find out what happens in the end. Like "who shot JR?".

I think the record is 10,582 posts on the MM vs MC cartridge thread and it's still climbing.

Is there any correlation for time of day? Maybe there is a difference in the power quality feed into your premise based on something else happening around your local grid? A long shot I know.

Since you have controlled for so many elements, the most likely culprit to suspect is YOU. I would set up a controlled blind test with an audiophile friend so you would listen to the system for 10-minutes on at least 4 separate occasions without knowing if the system was just turned on or if it had been on playing music for an hour or more. If this proves the effect is not imagined then I would sell all my equipment and move.

Certainly any help is appreciated but recordings of the sound differences were sent out and I noticed a difference. I still believe it is somehow related to heat. Either in the amp or the speakers or both. The "bad" sound reminds of an amp that is underpowered or does not have tight control of the bass. My hunch is it is a combination of issues since it never could be replicated consistently.

It is my understanding the OP has moved on.