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
Hello AL:
I re-recorded the two versions of "Respect youself" with the proper adjustments.
What is your email,I will send them to you.
Or anyone else that would like to hear good/bad bass versions(as they sound to me).
tonypoid@aol.com
Fishing, Have you tried putting a fan on the amplifier?

Based on all that we have discussed, it does seem that heat plays a huge role. The fan should be able to cool the amp's heatsinks.
Or even just with the top cover off. Better yet, two sets of recordings should be done; with and without added cooling. This could end up being a very fruitful case study on due diligence by ss amp manufacturers. No wonder there's separate tube and ss camps. Tubes and mosfets do after all share some similarities.
I Listened to my system all morning and discovered what is changing in addition to the bass is overall dynamics & timing..When the sound changes the music seems to sag and it's hard to get into the music.
Like getting on an escalator and "riding" with the music/The second version blocks or prevents following the music in the same way.
Like being "out of sync"
So Weird