Bass leaves after amp warms up?

If changing source impfoves thingx temporarily, its possible the source
selector switch on the amp has a problem. Could be dirty or defective.

Ops comment tnat hs is not listening at hign volume would seem to work
against the amp not being abl to drive the speakers well theory, as well as
swirching sources making a temporary difference. Having tne same
problem with two different amps could point to both being underpowered
and heating up over time and negatively affecting sound.

200 watts,underpowered?

Is this plausible?
1. You bought your PSBs used,
2. Whomever you purchased from blew out the woofers and had them reconed.
3. The new surround is nice and springy when you first start listening but "poops out" when it gets warm,
4. Most amps put out more power after they warm up which contributes to the problem.
Problem solved!

All my equipment is brand new from autuorized dealer

I too experienced bass playing disappearing act with my Audio research VT120 mono amps. It happened that when the amp is cold, the bass is not as extended but concentrated more in the mid bass so it sounded more punchy, when it is warmed up and gets lower, the mid bass hum is smoothed out and sounded like it has lose its dynamics, instead, it is more smoothed out and gets lower. My dealer told me I will hear this if the amp does not have enough current to drive the speaker. I later got a more efficient speaker and all the dynamics are back!