What could I expect to hear from a Class A amp?

Class A is the opposite of what A-B and Class D type equipment needs.. So Class A and Tubes need "LITTLE" time to warm up and sound there best... My Class A gear gets to good hot and excellent sounding idle in less than a Half hour.. Same with most tubes.

Class A-B and Class D designs do benefit from being turned on for hours or even a Day before critical listening, but that process can even be sped up by playing a music signal thru it and leaving the room.

In general I have tested several times and found that Class A gear and most tubes 40 minuets after start are pretty much 99% the same sounding as if you come back leaving them on for a day or three... Thats why many think Tubes and Class A sound better than some standard solid state gear which is the hidden potential, its simply Class A and tubes do in fact warm up and sound musically enhanced faster. This is from my experience, and some A-B stuff does sound nearly as good after a few more hours of music signal and warm up.

Class A turn it on a half hour prior, and turn it off when your done. A-B will take some experimentation to see if you find differences leaving them on all week.

"It seems I have to continue putting up with listen to music late at night after giving the system most of the evening to warm up."

Spatine - Can you hear it improving over time. Would you know if amplifier was ON for one or three hours? If you cannot tell then don't listen to somebody's recommendations.

You made excellent point about power outage and surge. I use surge protector but still turn off the switch while not at home and unplug my gear during thunderstorm or long absence. Surge protector works for small spikes but is useless for direct lightning hit. My insurance agent told me that stereo equipment is always insured independently of value (One doesn't need special insurance) but it's a little hard to believe.

My amp is class D and uses about 10W idling but I still turn it OFF - I don't see (should I say "hear") reason not to. In case of class A amps electric bills should be one more argument - unless one can really hear big difference over time and is willing to pay for it.

How about blind test - you come home from work and find your gear ON. You have to guess how many hours it was ON. This would perhaps tell us what is real and what is placebo effect.

Kirjanki, during that 4-5 hour warm up, sound quality fluctuation is serious. It can sound pretty good almost at start up, then sound hemped in again a few minutes later. Of course it still sounds better than the previous amp. despite the fact; however, that's not the point here. As to placebo effect, my hearing capability definitely changes from moment to moment. But this 4-5 hour waiting period has been going on for some time now. This definitely isn't so before I got the XA60.5, and behaves as such immediately right after I start using the XA60.5.

Spatine - why do you call it waiting period? Your gear most likely plays at 99% of quality and you can still enjoy music.

On my system it takes short time probably half an hour and it might be related to tweeters warming up.

If I can toss monkey wrench here: Is your time of 4-5 hours same at different hours of the day? I suspect that minuscule improvement might be caused by drop in radio interference at about 6PM since radio stations have to lower their power (FCC rules). I hope that Bearotti doesn't mind that we sidetracked his thread a little.

Class A would be most evident at low power operation (less higher harmonic distortion from zero-crossing effects).

If you use highly efficient speakers that barely use one watt then I'd definitely consider Class A. If you use something a little inefficient say only 91 db SPL for 1 watt at 1 meter then you could go for a design that runs Class A up to a certain point (this kind of topology exists and is well documented - sliding bias if you will). If you are driving something very inefficient like 85 db spl then I'd probably say it is not worth it and stick to Class AB or you favortie Class D etc., as running Class A will be like adding a furnace to your house...

On the warmup issues I think one needs to be careful about making too many assumptions. Firstly a Class A amp will actually begin to cool down when you first start running it (yep, it will run cooler when you have a load). This then opens up the question what kind of load or what kind of RMS power is running through your amp during different tracks and passages of music...all to say that temperature equilibrium doesn't actually exist - it will be changing all the time (so good design is what matters most - agood design will also give the product a longer life as heat generally causes components to fail more quickly). A warm up of 5 to 10 minutes with some heavy music will actually get the major components warm pretty quick (even if the cabinet or heat sinks does not yet show it - at the component level things are already well on the way to approaching design operating temperatures).

Finally, is anyone even aware of the 150+ degree temperatures in the voice coils of your speakers? Did you know that this tempertaure is constantly varying depending on the type of music (quiet and loud passages). Ever play a song that sounds real loud at the beginning - great bass slam and then it seems to lose its punch???....well that would be thermal compressiono in your speakers and it happens in mere seconds from hot voice coils...

All to say that there are big differences in sound in the majority of speakers becuase many are not designed specifically to eliminate thermal compression (by using humongous voice coils for example - this is expensive and not immediately obvious so manufacturers do not often focus on this aspect - given that a better cabinet or better price point will be more appreciated by consumers). Not only will this affect dynamics but it will affect how well the crossover behaves, as the impedance of the individual speaker drivers drift with increasing/decreasing temperature.

If you prepared to worry about your CD/amp warm up - then you should be much more worried about your speakers!!! Ask a simple question - do they have pro drivers with large diameter voice coils? (large diameter increases surface area, which increases heat dissipation and reduces thermal compression effects)