is McIntosh known for good dynamics?

@atmasphere I've never encountered a discussion about dynamics that was "really" about distortion. Certainly my discussion here is not. So I have no idea what your point of posting on their thread was.

What I am discussing, and you haven't responded to my prior post on this topic, is that by good dynamics I'm referring to an accurate/transparent presentation or subjective effect of dynamics. Sudden louds should have startle factor, sudden quiets should have a compelling quality and not lose focus, and small dynamic changes should be evident and have musical impact. (By the way my reference is classical, acoustic music. Subjectively good dynamics may be described differently in rock or other kinds of music.)

Yes, the amp can affect the subjective presentation of dynamics. The signal can be getting louder and softer, of course, but that doesn't mean it will have the proper musical impact. What's going on inside the amp? I don't know. I suspect that the ability of the power supply to supply instantaneous current spikes has something to do with it. 

 I’ve never encountered a discussion about dynamics that was "really" about distortion.

@magon  Such conversations can be quite insidious so it might be that was the case without you being aware of it.

What I am discussing, and you haven’t responded to my prior post on this topic

Actually I did, in my first post on this thread, when I said

Actual musical dynamic contrast comes from the signal itself. The amp should have nothing to do with it. 

Yes, the amp can affect the subjective presentation of dynamics.

But this bit suggests my comments about distortion is relevant.

To avoid the problem of the term ’dynamics’ (which is often plural when distortion is a strong possibility in the conversation) I instead use the phrase ’dynamic impact’.

The power supply in a class A amp that won’t make much difference to this since the draw on the supply is constant, but in all other classes of operation the power supply must be beefy enough to have reserve energy on tap when big power drains occur. If not, current will be constrained at higher power levels. The more feedback the amp has, the less effect this will have but it still makes a difference. We see this in class D amps a lot; an insufficient power supply can result in the class D amp sounding ’boring’.

The bottom line is the best amps will have their ducks in a row with respect to all these factors: beefy supply and not generating higher ordered harmonics.

@atmasphere While I understand what you're saying, that distortion will make the contrast between loud and soft greater, I don't think that is likely to result in realistic dynamics.

In live music, microdynamics are particularly evident, and sudden changes are evocative. This is a perfectly accurate presentation, by which I mean the live event is the reference. 

Among my audiophile friends, we generally like live classical music, so that is our reference. When an amp can portray high dynamic resolution and startle factor, I think it makes sense that that amp is doing something right.

Maybe there are a few audiophiles somewhere who get fooled by distortion. Maybe they don't have a live reference, or they are listening to studio recorded music, maybe even highly processed music. I haven't run into them.

You seem to have something against SETs. I have listened to some good SET  headphone amps, and they had great microdynamic resolution. I didn't listen long enough to get a sense of the macrodynamics.

I think it can be a fallacy to blame "euphonic distortion." That is, someone says amp XYZ is realistic (or vinyl is realistic, digital is not, etc.) and the engineer can't explain it. All they know is that some types (some types) of distortion are higher in amp XYZ, so with no other explanation available to the engineer, they say that it's "euphonic distortion." What I think is that distortion can't explain realism. 

While I understand what you're saying, that distortion will make the contrast between loud and soft greater, I don't think that is likely to result in realistic dynamics.

I have listened to some good SET  headphone amps, and they had great microdynamic resolution.

@magon  Your comments here describe exactly what I'm talking about, in particular your comment about SETs. This is literally one of the things I have against them! (The other thing about SETs (not so much headphone amps) is they have real problems playing bass, but that's a discussion for another thread.)

Now to understand how this works you have to understand how the ear differentiates sound pressure levels. It does this through the detection of higher ordered harmonics.

This is very easy to demonstrate using simple test equipment: 

sine/squarewave generator, 

amplifier

a speaker and a VU meter. 

You start by connecting the VU meter in such a way (perhaps at the output of the amp) that it can read easily across its entire scale. Then  you put a sine wave through the setup, set the gain to read zero VU on the meter (near the top of its scale). Get a good idea of how loud that sounds to you. Then you turn the volume all the way down, cover up the VU meter, switch the generator to square wave and turn up the volume until it sounds as loud as before. Then uncover the VU meter and you'll see what this is all about.

Square waves are composed entirely of higher ordered harmonics.

If you don't understand that the ear uses higher ordered harmonics to sense sound pressure, then what I've been telling you would make no sense.

so with no other explanation available to the engineer, they say that it's "euphonic distortion."

Actually the explanation has been available to the engineer for nearly 100 years (I refer you to the Radiotron Designer's Handbook, 3rd edition, published in the 1930s). Here it is: 'Euphonic distortion' is lower ordered harmonics, the 2nd and 3rd.  They are innocuous to the ear in that they are close to the fundamental tone and musically related (the octave above and the 5th above that). So they are unobjectionable and simply contribute to that quality audiophiles refer to as 'warmth' or 'bloom'.

@atmasphere 

You don't seem to have gotten my point. TLDR; distortion can't explain realism.

Longer explanation: what I call good dynamics are also realistic dynamics when comparing the sound with live classical music, which has the greatest micro and macro dynamics of all. 

Second point: any reproduction system (including photographs, video, painting, whatever) has distortion and also can be realistic to a varying degree at the same time. We're pretty good at ignoring certain kinds of distortion. For example second harmonic distortion might be largely ignorable or have no impact on the musical presentation. Any system can also be accurate in some respects at the same time it has distortion. For instance, system A might have a non-flat frequency response and system B might be flat as a ruler, but system A might have more realistic transient reproduction. 

I find good vinyl to be more realistic than most digital. The engineer might say "vinyl has more distortion, therefore you actually are liking the distortion." But I didn't say I like vinyl, I said it's more realistic. The engineer has no explanation for that. Therefore they fall back on the euphonic distortion theory. I don't think the engineer is interested in finding out what vinyl does more realistically. Maybe its transient reproduction is more realistic. 

I found the SET amps to have realistic microdynamics. My belief is that to the extent these SETs had distortion, it's largely ignorable or doesn't affect the music. By the way I'm not making a claim about all SETs as I'm sure there are some with higher distortion, bad design, or plain don't sound good.