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

OP- I'm guessing you're right about the reason for the tube.

@sdl4 With regard to distortion profiles, Ralph makes a strong argument that his amps have a non-fatiguing profile 

A key discussion about "distortion profiles", and what amp designers decide to do.

I pay very close attention to amplifier designers who seek a careful balance between so-called "perfect" ultra-low distortion specs, vs. keeping the right amount of distortion around in order to not kill the "music" and for the most enjoyable engagement.

After trying a few pieces of gear with ultra low distortion specs, realizing the real musicality was taken away, boring, un-engaging, I started paying a little less attention to pure engineers and more towards proven amp designers with "great ears" who put the sound of music first. Could I listen to it "all day" is what I look for any more. Cold, sterile, dry sounding amplifiers with great specs are of no interest at all. None, nadda   This is why I keep older Class A SS and tube monoblocks around, for now. This whole thread is interesting to learn which Class-D designers, "get it" about the "music" vs so-called perfect specs. Is a razor sharp camera with the highest resolution in the world the best for producing beautiful photos?  

A reference below, to a well known solid state integrated amp many love the sound of, has this profile. Nowhere near close to a so called perfect low distortion profile.  I wonder if anyone here can guess which integrated amplifier it is, ?. Tip, this amplifier is not made in the USA. 

Key Distortion & Performance Characteristics:

• Class A Operation: Operates in Class A, which eliminates the crossover distortion common in Class AB designs.
• Harmonic Profile: The distortion is generally described as low-order, contributing to a "sweet" and "liquid" midrange without harshness.
• THD Levels: Lab tests indicate distortion levels of 1% THD at 5W/8ohm and 10W/4ohm, rising to 2% at higher dynamic loads (15W/8ohm, 19W/4ohm).

AGD Audion are the only Class D amplifiers I have heard that I could live with- and ENJOY! 

They are the only ones that do not sound dry and mechanical.  Some amps attempt to add a bit of liquid warmth but they seem to take on an opaque quality at the same time.  Not good. 

The GaN Fets are as billed- incredibly fast- but that is  where the good stuff ends.  

Final thoughts are that active speaker installations definitely short circuit much of the perceived Class D sonic biases- at the expense of the drawbacks of an integrated system.  

People that put an emphasis on measurements seem to be the most interested and capable of enjoying them.  

I pay very close attention to amplifier designers who seek a careful balance between so-called "perfect" ultra-low distortion specs, vs. keeping the right amount of distortion around in order to not kill the "music" and for the most enjoyable engagement.

After trying a few pieces of gear with ultra low distortion specs, realizing the real musicality was taken away, boring, un-engaging, I started paying a little less attention to pure engineers and more towards proven amp designers with "great ears" who put the sound of music first.

Obviously, there are those who like the additional "color" of lower level distortion, such as 2nd harmonic. I’m one of them. Still, others take the path of Linn. (See quote below.)

Now, those who want -- or expect -- a certain sonic "seasoning" might not want to go this path. They need the extra seasoning of added (good) distortion.

I imagine Linn’s attitude is more like, "put your seasoning on using other components, but not the amp."

To each his own, but I have a hard time believing that Linn set out to create a boring, unengaging amp or was not putting the "music-first." Indeed, the implication in the above comment seems to be -- maybe I am misreading? -- that adding 2nd harmonic seasoning is *necessary* for putting the "music first."  I cannot imagine that all the amps that don’t add seasoning are, therefore, not putting the music first. Set aside the measurement-chasing-only designers. Are the rest of the designers AWOL about good sound if they don’t season? I cannot think that is what is meant because it is not very defensible.

Take a look at this paragraph interesting; from a review of a Linn amplifier in Stereophile:

"I think probably the biggest performance advance we were aiming for in the Solo 800—the thing we felt makes a huge difference to a power amplifier—was lower distortion," she said. "We went all out to bring distortion down from every source and choose topologies and components that give you the lowest possible distortion. We were really aiming for the purest signal reproduction. While distortion levels in the older Solo 500 are really quite good, there is room for improvement, especially when amps are driven really hard by large, lower-impedance speakers.

"We were able to do more with more modern architectures and more modern components. Previously, we hadn’t really done a lot of the design work necessary to drive difficult speaker loads. Mostly, we’d just aimed at 8 ohm speaker loads rather than at much bigger loudspeakers that sometimes present really difficult loads. We wanted the amp to perform with excellence even when it was working really hard." Many engineers initially focus on measurements as they build prototype after prototype. Once their measurements are the best they can achieve, they turn their attention to sound quality, "tuning" the sound. Roscoe and her team proceeded differently.

"We didn’t really feel we needed to tune the amplifier sonically," she said. "We designed for very, very low distortion levels, very low noise levels, wide bandwidth, and low output impedance, all of which are obviously measurable. Then, when we listened to the design, we felt that it sounded so clear that there didn’t seem to be reason to do more. I don’t know what we would have tuned really. We didn’t feel like we could improve it by listening to it and changing something empirically. Instead, we heard what you would expect from an amplifier that measures as well as the Solo 800 does. It really seemed to pick out music better.

"Ultimately, when ’tuning’ the sound by listening and modifying the design, designers usually select which distortion is least offensive to the ear. However, when there is so little distortion there, this becomes a more meaningless exercise." 

Could it be that people who have listened to music for so long are so used to distortion coming from their systems, home, car etc..that without it music seems lifeless? 
‘The more I think about it, the more I wonder. How many of us have listened to live music without it going through some sort of electronic equipment. Does the music even get distorted at a live show going through electronics? So, how many of us have heard pure music from instruments without it being altered in some sense, even by acoustics in a venue. Perhaps we’ve been trained from years of hearing it one way. To the point of not really appreciating what pure music may be, or as close a class d may be getting to perfect frequency response.