What are the advantages to a Class A amp & what are the trade offs?

The old school answer of course, was that Class A has lower distortion through the zero volt crossing region.

How audible that is anymore though.... I don't know.

Never buy based on design, etc. Buy based on how it sounds. All this other stuff, heat output, etc, may or may not matter depending on your situation. ie small room, poor ventilation, hot weather, probably not the best place to put a 500 watt heater. Unless maybe it puts out music that is to die for. Which you will only know one way, by listening.

Thanks guys. I knew about the heat and power demands. Wasn't sure what sonic advantages it might have. There is a Canary M70 which has drawn my attention. Its in the power range which I have found to work well with my speakers. Its close to my budget. But i can't find any reviews or much info about it. If i can recoup my $$$ I've been known to take a chance. Sometimes you lose. But sometimes you hit it outta the park. Then too, its may be a  sideways move. I'm kinda itching to pair another amp with my new Preamp (CJ CT5). System sounds Great but I can't seem to leaver it alone.

This question seems to imply that the biggest sonic differences between amps is related to whether it's Class A vs A/B etc.  I don't agree if that's the case.  Maybe I'm reading the OP wrong.

Needless to point out, perhaps, but here goes:

Maybe Class A as a topology term and how it’s actually and truly implemented has become somewhat muddied. We may think to have been confronted with "Class A" sound in some iteration listening to various amps, but it mayn’t have been the case in the true sense of the word.
I’m only trying to suggest that the real benefits of pure Class A could’ve escaped a listener or two when in actuality what has been listened to was a watered down version of the concept as a "high bias" or "Class A up until a few watts" amp, trickery that would seem to sonically fall short of a true, pure Class A implementation.
Come to think of it many may feel the honest power output of a pure Class A amp, certainly as a numeric value, is a limiting factor when most audiophiles use low to moderately sensitive speakers, not that it’s necessarily a giveaway into the real-world capabilities of such a (potentially successful) pairing.

That’s also saying: be realistic with regard to the output power you’ll get from a true Class A amplifier - most likely getting anywhere near 100 watts will mean massive consumption, heat and size, so instead expect going for <50 watts if you intend to stay true to concept, so to speak.
And of course, price. Handling these amounts of heat requires very high quality components, large heatsinks and proper casing/ventilation if many years of trouble free service is to be expected. Then again, being topologically more simple than Class A/B amps and possibly even dispensing with a balanced configuration will save number of components used, with more money that can be allotted to the componentry that are - where it matters most.

... Our industry’s marketing people love to find ways to make products more appealing to consumers, which is why we have seen a never-ending race for higher power. High power is better!! But Class A is a great buzz word too and so you also see this creep into the marketing material. High power and Class A, what could be better? The truth is that high power and Class A are pretty much mutually exclusive. It is reasonably easy to achieve Class A in single chassis designs up to about 100 watts but beyond that it becomes extremely difficult because of the heat.

A number of “tricks” have been used to claim both high power and Pure Class A. While it is perfectly OK to bias an amplifier into partial Class A while allowing additional power for short term transient headroom often this is done without declaring the true operating parameters. Commonly the amplifier is claimed to be “Pure” Class A, and yet only delivers Class A performance up to a percentage of its output power. Other schemes have been invented that cause the amplifier to vary its Class A operation depending on how loud the music is. The idea being that it only runs in Class A to as high a power as needed moment to moment, and thence avoids the heat. This causes the music to modulate the amplifier’s design parameters, and in turn introduces other forms of distortion.

How do you tell determine the truth? Its easy really, just ask what the amplifier’s Class A power consumption is when there is no music playing. Take the number you are given (Watts) and divide by two for a mono amplifier, or four for a stereo amplifier. The number you get is the maximum power that the amplifier could possibly deliver in Pure Class A without some trickery.

http://www.pureaudio.co.nz/?page_id=165