Bass leaves after amp warms up?

Krell man, I take it you 'are' no more:) Those are some serious reviews.

Krellman, Well said. FWIW, I agree with I with you on all three points.

One of the reasons I recommended the SPL meter was for the OP to see for himself that his problem was not with absolute volume level of the bass. He just likes his system's sound when it is cold and the HF's dominate the sound and the sense of speed that can impart to the bass. Most of us, I think, would not consider this to be a balanced sound, but he does and that is why most folks couldn't really figure out his problem or how to solve it, we just don't listen to things with his ears nor his preferences. We have just assumed that he listens with our ears and priorities.

As someone suggested, if that is a sound he really wants, he needs to evaluate his components after they have warmed up and select components that will give him the overall sound he is seeking. A daunting task I suspect.

If you read Atmasphere's and my posts, you will discover that with this school of thought, a warmed up amp is in fact detrimental to optimal sound in that the outputs are then operating with reduced current. It does perform better when cold. But only because factory settings are deliberately conservative in an effort to allay future warranty issues. As I stated, most people don't care about this even if they notice. Factory settings are typically lower than optimal even when cold. Published specs have nothing to do with this issue so the manufacturers just cover their ass. In a class A/B amp for bi-polar devices, about 150ma per ch. is optimal regardless how many outputs there are. Mosfets are a different story. Typically between 200 and 300 ma per ch. Bottom line is heat is the killer so whether they're bi-polar or mosfet, if the temperature of the heat sinks at idle is around 120F, that amp is going to sound great for a long time. I don't believe this is an issue with class A amps, however.

Csontos, you may have missed the post where Al found out that all three amps have bipolar output devices.

My understanding of bipolars is that the hotter they get, the more current they pass- which leads to more heat. This is why they have to have large heatsinks and some sort of bias feedback circuit to control temperature, else they go into thermal runaway.

I think it might be interesting nonetheless to try a set of ZEROs on the system and see how it behaves. http://www.zeroimpedance.com

Then we could put the whole 'system overheating' idea to bed once and for all.

Right now I am thinking that Fishing does not like the sound of the system warmed up. Right now if it were me I would run the system for at least one hour and see how it sounds, and then see how it sounds 3 hours later, after it has warmed up for all that time. I've seen some amps that you don't want to turn off because they need 24 hours to sound right...

I listened to the two recordings on my main system, via both speakers and headphones, after transferring them to CD-R. I also performed various analyses of their waveforms using Sony Sound Forge 9, a professional caliber audio editing program.

By far the most notable difference was in the volume levels. Would I be correct in assuming that you created both recordings with the same setting of the volume control on the amp, and the same setting of the recorder's level control? And would I be correct in assuming that if the recorder provides AGC (automatic gain control) and/or peak limiter functions, that you disabled them?

Before doing any analysis, I cut out dead times at the beginning and end of each recording, because those dead times were slightly different between the two recordings, and that difference might have introduced a small bias in the waveform analyses, in one direction or the other.

With 0 db representing digital full scale (the maximum possible instantaneous volume), I found that the maximum instantaneous volume that was present on the "good" recording was 0.0 db, and the rms average value across the entire recording was about -18.6 db (the two channels being slightly different, but both very close to that number).

On the "bad" recording, the maximum instantaneous volume was about -1.9 db (slightly different between the two channels), with the rms average value across the entire recording being about -21.7 db (again, the two channels being slightly different).

I then produced a CD-R containing (1)the "good" recording, (2)the "bad" recording, and (3)the "good" recording with a 3 db level reduction. The volume difference between (1) and the others was, of course, completely obvious. My wife commented on it immediately from another room in the house. (2) and (3) had some subtle differences, but nothing that I would remotely characterize as missing bass, or even a fundamental change in the character of the bass. And the differences between (2) and (3) were small enough that I suspect they might have disappeared if I had done enough trials to more precisely optimize the 3 db level reduction.

I also used the software to do waveform analyses after applying brickwall (essentially instantaneous cutoff) 300 Hz high pass and low pass filters to the "good -3db" and the "bad" recordings. The high passed content of those signals showed almost no difference in instantaneous peak level (0.2 db, with the "bad" recording being lower), and zero difference in rms level. The low passed content of those signals showed slightly greater but still small differences, about 0.7 and 0.4 db lower on the bad recording in peak and rms levels respectively.

I would agree, btw, with DRubin's characterization of the sound quality of the recording. Parts of the treble region are boosted excessively.

The bottom line: All of the differences, if any, were slight, except for the difference in volume, which on an rms basis across the entire track was about 3 db.

Regards,
-- Al