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
I guess that transistors don't have enough heat sink and go hotter than supposed to be in normal operational state.
The noiseless fan can probably rectify your situation
It's your ears, not the equipment. If you were to take a measurement, I'd bet you there'd be no change.

I frequently find, within the first 5-10 minutes, that I increase the volume about 3 dB. That's at an average level between 80-85 dB. It's a bit like your eyes; they adjust to brightness—your ears to sound pressure.
Nah,I'm a professional musican and know what I'm saying.
Besides significant other hears the same thing as myself