Expanding the Class D Conversation: How Would You Characterize Their Differences?

@hilde45 - For additional context, my primary system includes: 

QLN prestige 3 speakers: Known for a somewhat laid back and musical sound  signature.  
AGD Audion mkiii monoblocks 
Linear Tube Audio level 2 preamp: Has proven to be an ideal pairing with the AGD amps. Spacious and imparts a tube tone but with solid state speed and dynamics. 
SoulNote D2 Dac: Lively, lots of leading edge energy, brings density to the sound. 
Innuos Pulsar Streamer

Cardas Clear speaker cables and interconnects

Mad Scientist Prime USB cable
Mix of LessLoss, Cardas and Kubala Sosna Emotion power cables 

Puritan 156 with the Puritan Ultimate cable 

@bluethinker Great system. Thanks for the context.

I wonder if anyone has an opinion about SMSL. Here's a review of a newer model:

https://www.youtube.com/watch?v=SS6Xp_m6KwE

These reviews on YouTube get dismissed. I understand the skepticism. But there are claims made here worth considering – and then if there's reason, they can be dismissed.

Jay claims that this is a real competitor to  AGD and Orchard Audio. Those brands justify their higher cost through (he says) superior build quality, componentry, and (he says) marginally greater refinement—particularly in high-frequency neutrality and overall sonic polish.  For example, he says that AGD Audion is the "most neutral" and "most refined," while Orchard offers similar high-frequency refinement.  

However, he does say he prefers SMSL's sonic character to Orchard's, finding it more transparent with better high-frequency refinement and less edge. He also prefers its overall build quality. 

I'm trying to either take this video seriously or eliminate its claims by reasoning. Because given the modest performance gap described, it makes some of us hesitate. After all, we're talking about a gap between a $419 SMSL and amplifiers costing $2,500-$8,000+.

It's a puzzle how viewers can weight the descriptors used—"refinement," "neutrality," "build quality"—to determine whether amplifiers 10x or more expensive are actually worth the investment? What threshold of difference in these qualities justifies that price multiplier?

The obvious answer is always, "You have to try things for yourself." So I just might. 

But you can see the bind reports or reviews like this can put people in. While those who need a budget GaN amp can just try this one out, others who might be willing to spend a lot more are left wondering – am I about to be a sucker if I pay 10x more?

You asked if I had actually compared the Atma-Sphere Class D amps to the AGD.  No, I only have Ralph's amps here, but everything I've read about the AGD amps tells me they are equal to, or possibly superior.  Maybe I'll get the chance to hear them at some point.  Concerning the SMSL question, based on my experience with two different SMSL DAC's, I'd say they definitely have the engineering chops to compete in this arena.  

Like @doni above, I have not been able to compare my Atma-Sphere GanFET Class D monoblocks to any of the AGD amps. I have also not had the pleasure of listening to any of the Orchard amps. Fortunately, I am very happy with my Atma-Sphere amps, so I'm not actively searching for any demo days.

When I first started reading about the latest versions of Class D amps, several European makers of Class D modules were saying that faster-switching FETs (like GanFETs) were not needed to achieve optimal Class D performance. However, several U.S. amp designers (like Ralph Karsten, Alberto Guerra, and Leo Ayzenshtat) saw clear advantages in going the GanFET route. The reviews of modern Class D amps (whether using GanFET designs or not) seemed to emphasize that these amps were clear, neutral, honest, and great at saving you money. While all those nice things could be true, this description sounded more like what you might look for in a banker rather than in an amp that helps you establish an emotional connection to music. 

So I began looking for a GanFET amp that was not only clear and transparent, but which also had richness, fullness of tone, and natural warmth coming directly from the music. I wanted the music to be engaging and "real," too, like there were real musicians playing/singing in the room. Of course, I couldn't judge these characteristics without listening to several amps in my home system. But I didn't want to go to the expense and hassle of buying three or four amps to demo at home, so I made an educated guess and chose the Atma-Sphere monoblocks based on online reviews and respect for the career of Ralph Karsten as an amp designer.

Two design issues helped sway my decision on the Atma-Sphere amps: (1) use of a linear power supply with a toroid; (2) having a distortion profile that minimizes harshness or hardness. Both AGD and Orchard offer toroidal power supplies, but only on their most expensive models. AGD offers a LPS on the Solo at $24K (per pair) and Orchard offers the Starkrimson Mono Ultra Premium LPS at $7K (per pair). I can't confirm that the solid foundation of the Atma-Sphere amps is related to its LPS, but it's a distinct possibility.

With regard to distortion profiles, Ralph makes a strong argument that his amps have a non-fatiguing profile that minimizes harshness in the sound. AGD and Orchard do not discuss this issue. When Ralph speaks, I tend to listen.

These are just a few of the issues I considered before I decided to invest in the Atma-Sphere Class D monoblocks. I've been very happy with my choice.  

I think Class D can be implemented to sound very good.  I have yet to hear a Class D version that can make you feel the music like an A or A/B can.  Also, I've yet to hear a Class D that doesn't fatigue me fairly quickly.