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

I am two weeks in with a Buckeye 8x500 ncore hypex class D and I absolutely love everything about it. It runs cool even after hours of use, if you need to move it you could carry it under one arm, the amount of power is a gamechanger for me because I moved up significantly. My system sounds significantly better to me, and that is all that matters. I also appreciate not paying thousands for a pretty case, I get if you are going to display it in a listening room but for a theater application it is perfect.  The weight and the heat might not matter to most but I appreciate never worrying about the amp running hot. 

@atmasphere "Actually there are a few class D amps that have a better first Watt than a good number of class A amps.” - list of “few” and “good” ones will be helpful! 

Analog output filter question: how output filter is designed, order, phase v frequency., loading considerations (reactive speaker x-over + spkr-dr complex loading), R/L/C components tolerance, frequency dependency, aging / magnetic core inductors nonlinearity? 

@westcoastaudiophile You might try the AGD Audion, one of the Orchard Audio amps or one of ours.

WRT to the analog filter, its job is to remove the switching artifacts that occur at the switching frequency. What is left will be a sine wave called the "residual". This sine wave is at the switching frequency so might be 500KHz. Its amplitude is so low that its of no concern to any loudspeaker driver, whose inductance will block it.

The filter is designed according to normal filter theory; typically second order. Usually its designed with a target load in mind, which might be 4 or 8 Ohms. Increasing the load (speaker) impedance results in a higher Q (Quality) of the filter effect. The load will shift the frequency a bit but usually its well outside of the audio band so that’s not a problem.

The characteristics of the capacitors and inductors involved is critical, since stray inductance (which might be caused by the leads of the capacitors, which extend not just from the circuit board but well into the part itself) can cause parasitics as well as the design of the choke.

It is for this reason its usually not a good idea to replace the caps or inductor in a class D amp in an effort to get better sound since reducing RFI is part of the filter’s task. Parasitic oscillation may be introduced! We found we had to be quite careful about the inductor in our amp, which uses a ferrite core. It was so critical we had to build our own jig to wind the chokes so we could control the inductance without strays. The vendors we tried to have the part custom wound simply didn’t seem to have the ability to get it right. To make the choke work properly we use a Litz wire. 

Of course the filter introduces phase shift as any filter. However, in our case the amplifier is using quite a lot of feedback and so is able to correct phase at high frequencies.

@atmasphere "target load in mind, which might be 4 or 8 Ohms” - in my 40y + sound works I haven’t seen such speaker, with purely resistive load (2/4/6/8/12/16)! In order to design output filter properly, we need to take complex model of loading, including variety of speaker cables, DC protection relay ckt, speaker crossover, spkr driver/s complex, often resonating impedances, which is tremendous engineering task! I’ve used class D amps in PA systems with active x-overs, where spkr was driven directly by the amp with short cable and w/o any x-overs in the path. For home use, I would definitely look for class D amps if I need power efficiency, that’s it.