Has anyone switched from Class AB/A to Class D? Was it better? Was it worse?

There are a few differences:

1. I don't think we really know how long class D amps will last, how they will most likely fail, or whether they can be maintained in the same sense as a conventional amp.  They could last longer.

2. Class D amps use far more complex designs.  Many of the amplifier boards are built as modules and used by multiple amp makers.  That's why a class D amp will often be identified as a Nilai, NCORE, Purifi, PASCAL, etc.  Some (all?) of these companies also build and sell compatible power supply boards.  Add a case, power switch, input buffer. wires & connectors, and you're done!  I don't think all class D amps are built this way, though.

3. The more recent introduction of GAN FETs has made for another family of class D amps.  I don't know if these are also mostly being based on modular sub-assemblies; what makes them distinct is the use of a specific kind of transistor.

None of these are necessarily negatives, just things that occurred to me recently.  Hopefully, @atmasphere will drop by and fill in the blanks (please?)

@tomcarr ya, I was eyeing the Class D PS audio monoblocks. But it really stinks for me to buy them without hearing them. Even with the 30 day return period. Were able to hear them first before buying them? 

I'm not Tom, but I also own the M1200 monoblocks.  A friend has them and I did get the opportunity to hear them a number of times before I bought them.  I needed more power than the class A/B monoblocks I had, which I loved and thought would be hard to beat for the money.

After a speaker change to some very power hungry speakers I decided to try the M1200s in my system.  They sound every bit as good as my previous amps and are able to deliver the power the new speakers wanted.  I have also owned the m700 amps, which were surprisingly good, but not as good as my previous amps or the m1200.  

There's always something "better" or "different" that might suit your tastes more than the m1200s, but they are very neutral, light, quiet, and have none of the negative traits I've experienced with other class D amps. 

As a bonus, you can roll the input tube.  I've tried a number of tubes in mine and like Amperex Orange Globe 6dj8 and Genalex Gold Lions the best.

I can understand the attraction from A/b or even A if current is a problem to a class D amp.  But tubes are not something I hear and can easily go to a class D system unless heat or space is the consideration.  A preference for tubes is in a class by itself.  The differences are easily distinguishable in a blind test.  SS v tubes, if you enjoy tubes; my advice is don’t even bother, over time you will be sorry, have spent more money, just to go back to the sound you like, tubes.  
 

In 10 years, as Ralph says….then maybe? 

 But tubes are not something I hear and can easily go to a class D system unless heat or space is the consideration.  A preference for tubes is in a class by itself.  The differences are easily distinguishable in a blind test.  SS v tubes, if you enjoy tubes; my advice is don’t even bother, over time you will be sorry, have spent more money, just to go back to the sound you like, tubes.

@daytrader I like the sound of tubes a lot as you might surmise. I like the sound of the class D amp in my home system better. Its just as smooth in the mids and highs and seems to delineate information in the rear of the soundstage with more clarity than the best tube amps I’ve heard. I don’t miss having to replace tubes or the heat which is a nice side benefit.

1. I don’t think we really know how long class D amps will last, how they will most likely fail, or whether they can be maintained in the same sense as a conventional amp.  They could last longer.

2. Class D amps use far more complex designs.  Many of the amplifier boards are built as modules and used by multiple amp makers.  That’s why a class D amp will often be identified as a Nilai, NCORE, Purifi, PASCAL, etc.  Some (all?) of these companies also build and sell compatible power supply boards.  Add a case, power switch, input buffer. wires & connectors, and you’re done!  I don’t think all class D amps are built this way, though.

3. The more recent introduction of GAN FETs has made for another family of class D amps.  I don’t know if these are also mostly being based on modular sub-assemblies; what makes them distinct is the use of a specific kind of transistor.

None of these are necessarily negatives, just things that occurred to me recently.  Hopefully, @atmasphere will drop by and fill in the blanks (please?)

Class D amps will last as long as any conventional solid state amp; perhaps longer since the filter caps will have less heat around them. 

Class D amps are not particularly complex except in the case of the formula to determine values in the feedback network of class D amps that are of the variety known as ’self oscillating’. In terms of components used our class D amp is simpler than most class AB solid state amps.

Not everyone uses modules from other companies- we certainly don’t; ours is designed and built by us as are power supplies we use. What we found prototyping our amp is that the power supply is critical and for best results should be designed for the application rather than bought off the shelf. That so many people do the mix and match thing is IMO why class D has had trouble getting traction in the last 20 years. 

If you know what you are doing you can build a class D amp that is in the driver’s seat rather than the back seat WRT any other kind of amplifier technology.