Solid state design options...

All the discussion points to one thing. Trade-offs for the typical audiophile amps. They were all optimized for a few particular things but not everything and they can't be due to cost consideration.

It's possible to design and build a 1000W/ch amp class A, balanced, zero-global feedback, balanced and high current delivery, but it will probably cost a quarter of a million dollars per channel and the size of a sofa.

So all these compromises designer made will basically force the marketing to emphasize specific strength which usually make all these terms unimportant and impossible to compare one on one.

If you are amp buyer, don't take these terms too seriously. If you are an amp designer, that's a complete different story.

BTW, if you can't tell yet, I am by training an eletrical engineer.

I am very picky. I own Krell.
I have no idea about any of these designs as they relate to any of the Krell amps that I now own or have owned in the past.

Buy a good amp from a good company.
Actually I bought great amps from a great company.

Just my 2 cents.

Richard

1, 4 and 5 are bare minimums for a nice amp. 2 is cool if you can balance the entire signal chain. 3 is nice if you can live with the heat and the electric bill. If you dig spec'ing out solid-state amps, compare the number of output devices/channel and the amounts of distortion and noise. After a while you'll get a feel for where the corners were cut.

I usually take a peek at the slew rate. To me it says something about how careful the amp design is; if the amp sounds good to boot, then somebody did his homework. Higher is better but if the topology is sloppy, a high SR can mean instablity, distortion, and noise - especially with more output devices. IMO, this parameter gives the amp its speed (pace), adds to the illusion of realism by presenting transients closer to real time, and presents quieter silences. Of course, it doesn't pull everything together - there are many other factors (I wouldn't call them "marketing gimmicks", they are just specs, which show performance, which in turn only hints at the sound).

I was reading on the VAC website a while back about damping factor, and it caused me to rethink it a bit. Their point is that amps with high DF are essentially using back-emf as feedback to the amp, thus modifying the current delivery from the amp in real time. They then go on to make the points that (1) the voice coil is a lousy sensor, as it wasn't designed for this, and (2) the back-emf almost always passes back through a crossover network, which further changes its amplitude and phase characteristics. Interesting points for those who think high DF is the way to go. It may not necessarily be so. It may actually be better to have a zero-feedback output stage and simply reduce the output impedance as much as possible. Then it's up to the speaker to accurately reproduce the waveform being sent to it. Just some food for thought; I personally don't know which is better.