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

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)

Ahhh the wonders of ribbons. It's like running a space heater in a cold breezy outdoors.

Shadorne - I suspect that ferrofluid used in many tweeters changes viscosity with temperature.

Shadorne -- Excellent thoughts, as usual, which are not commonly realized. Thanks!

I'm not sure I understand, though, why Class A would run cooler when outputting signal into a load. It's tempting to think that could result from a portion of the current that would otherwise flow through some of the output transistors (at zero signal conditions), being diverted through the speaker instead. But I don't think that would happen to any significant degree in the typical situation where the amp's output impedance is much less than the speaker's impedance, so that the amp behaves essentially like a voltage source.

In any event, it seems clear that the presence of signal would not raise the operating temperatures significantly above what they are at idle.

Thanks again!

-- Al