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

It depends on the Class A and whether it is tube based or transistor based but couple things are universally true.  

They are horribly inefficient and run very hot.  Due to that heat, they tend to require large heat sinks.  They tend to be very heavy and power consumption is very high.  Because they are so inefficient, they tend not to be that high power.  

Sound profile is a varied as there are amp companies.  I have heard Class A amps that are dark and warm and others that are bright and shrill.  Tube amps vary as much as transistor amps and careful pairing with your speakers is still required along with plenty of ventilation.  

@verdantaudio I’m glad Gryphon integrated two chimneys in the Colosseum, haha. The amp actually runs pretty cool on low bias, 30w Class A, because of the huge heatsinks, but it runs very hot at 165w Class A. Yes, I can hear a difference between the two.


 @mijostyn I will try that coffee. How much is it a pound? For those who wonder about my math to get to fifty five cents a cup it was $25/454g*10. I only use ten grams a day, that’s my dose.

@larrykell41, we used to have a nice Pasquini espresso machine and grinder in the office which was used on a $1 suggested contribution model. It worked well, providing artisan roasted beans, organic whole milk, and the occasional necessary parts. We were using double shots of 18-20 g per drink. The $1 didn’t account for energy use.
The espresso bar definitely made the office a better place and improved the barista skills, and coffee appreciation of many.

Perhaps a good stereo in an office space, for break time, would revitalize the love of good music reproduction?

A big advantage of Class A amps is that by the standards of any AB amp they have a hugely overbuilt power supply and they can drive low impedance loads without faltering.

One of my systems has a pair of Class A monoblocs that put out 45 watts a channel in stereo configuration, but 500 watts bridged into a 1 ohm load.  Hard for AB amps to match that.  They are also large and heavy, if that matters to you - mine are over 100 lbs. each.

If you don't run difficult loads, then the choice comes down to sound vs. power usage and heat production.  I really like the sound and still own 4 Class A amps, but I use an AB tube amp to run my main system which has quite efficient speakers.(92dB)

@viridian4, The Krell KSA amps are true Class A. They have a feature called "Sustained Plateau Biasing." where they have a sliding bias feature that anticipates the loudest signal and then biases the amp into more Class A wattage before the signal is amplified. There are 4 bias levels and when a higher bias level is triggered it stays at that bias level as long as the signal strength justifies it. All the signal going through the unit is amplified in true Class A but if you are playing quiet music it only uses the lowest bias level. This is why the amp runs hotter when it's played loud. But it's important to note that at no time does the amp run in Class A/B.

Some amps run in pure Class a for a few watts then switch to Class B. The Krell does not do this - it only runs in Class A.

There are a couple other companies that use a similar Class A biasing feature in their modern Class A amps. They, like the Krell series, only run in Class A but don't consume their full power unless demanded by the input signal.