Bass leaves after amp warms up?


I don't understand-after my Musical Fidelity M6i amp warms up for about an hour I notice the deep bass & kick drum aren't the same.
They sound less musical with loss of weight/depth.The notes are there but the moving of air have left.Sound is has much less impact and boreing.
I had the same problem with Bryston amp so there is no defect with amps nor with the rest of my equipment/
PSB Synchrony one speakers,AQ cables,Bryston CD Player.
My question has anyone heard similar & is there a plausable reason?
fishing716
Anyone shoot me an email:
tonypoid@aol.com

I will send 2 versions of recorded song with what I feel if different bass output

Thanks
It seems that you have spent a considerable amount of time trying to regain the good sound after it is lost but have you spent anytime trying to lose the good sound. IOW have you done the mute/unmute or switching inputs etc repeatedly before you have lost the good sound to try and create the problem?

If you have some success on causing the problem on purpose it would give us another clue.
Why don't you pick up a couple of very quiet "whisper" fans to keep the amp cool to see if it is truly a warm up thing.
Are you using the "plugs" on the bottom woofer ports? If not you should try them. You may find that with the plugs the bass is lean at first but fills out after the amp is fully warmed up.
IMO, It sounds like you have about the same bass energy in both good and bad recordings. It seems to be the character or quality of the bass that is changing. Tight and defined when amp cool, loser and woolier when warmed up. The Bryston amps I've used in the past had this quality to them. If you do not have the plugs installed in the lower vents I suggest you try them. The speaker will have an overly tight or lean bass until the amp gets warm upon which the bass should take on a more normal "Q".