Bass leaves after amp warms up?

The absolute difference is the "good" version has imputus,groove,the kick is firm w/deep bass that moves air.
All these contribute to an effect that stimulates the senses and you are rewarded with a connection to the music.When these attributes are muted the result is sound with no emotional resonance.

All this speculation has failed to resolve one desire:
To have the full dynamics I hear in my system stay without playing hide & seek/
On a positive note my dealer & friend @Audio Salon has agreed to lend a dedicated amp for me to compare.
Musical Fidelity M6 power amp/250 watts

Al, 0.7 db across a spectrum can be quite noticeable to the ear, whereas on a sine wave is undetectable.

You might normalize the two tracks, invert the phase of one and play them simultaneously, then you could hear the 'missing' bass.

Csontos, I used to work at the Allied Radio Shack service department, and put myself through college there and at other consumer electronics service departments. Transistor amps that came in with the bias a mile off was a pet peeve of mine. Funny that nothing has changed in 35 years...

I'd be surprised though if a minor deviation from nominal bias is what is causing this. However I'm not saying that isn't it, just that I would be surprised. IMO/IME it is very telling any way you look at it that turning off the amp for a while does the trick. It really does suggest that heat or 'warmup' has something to do with it, and that whatever it is when it is not warmed is preferable to Fishing. That is what made me think of MOSFETs at the get-go of this thread, as I have experienced that plenty of times with MOSFET amps.

It does sound to me a like a fan is in order!

Update
I have not turned off the amp when the bass has left.
I would return with the amp still on and the bass has returned in 30-60 minutes

Therefore the full dynamics come & go throughout the day

It would be a fabulous experience to get together with you guys:)

04-22-13: Atmasphere
Al, 0.7 db across a spectrum can be quite noticeable to the ear, whereas on a sine wave is undetectable.

Thanks, Ralph. FWIW, though, note that the 0.7 db was between maximum instantaneous values, which might have occurred on as little as one sample out of the many millions of samples in the track. Averaged on an rms basis across the entire track, the difference was 0.4 db (comparing the sub-300 Hz content of the "good-3db" and "bad" waveforms).

You might normalize the two tracks, invert the phase of one and play them simultaneously, then you could hear the 'missing' bass.

Actually, prior to posting my report I spent a good deal of time trying to do exactly that. Inverting one 2-channel signal and summing it together with the other 2-channel signal whose volume had (at least approximately) been equalized. And alternatively, playing them both at the same time. Unfortunately, I couldn't get the software to accomplish that properly, after trying several alternative approaches using two different software programs. Not sure why.

Also, "normalizing" is somewhat ambiguous in this case, because the differences between the "good" and "bad" waveforms are different depending on whether peak or rms values are considered.

Best regards,
-- Al