A little deeper on amp power please....

All these years and you still assume I'm typing in the least informed context, @atmasphere , give me a little credit?

I meant to say, being forced to now give an exhaustive/exhausting answer:

Ralph, others have posted here and there with the question "what is meant by musicality?". They do so because the word is vague and not particularly helpful. It connotes something positive and nothing more. When a food critic uses the word "tasty" I cringe and when a person near me claims something he or she is eating is  "tasty" I resist the urge to say "sh*t has taste, but I am pretty sure I don't like it". 

@erik_squires @fsonicsmith These are both valid criticisms!

Erik, I give you the credit, the reason I responded the way I did is because that sort of shorthand promotes confusion with those that aren't in on the shorthand. I see confusion about this topic all the time so its become a bit of a sore spot.

By 'musicality' I mean its easy to listen to all day, plays bass right, isn't harsh or bright, has good detail without being clinical, has an 'organic' presentation, yet is uncolored. Sorry for the shorthand on my part.

As far as 'shutting down'; most class A and AB solid state designs lack the Gain Bandwidth Product to support the feedback they use; in addition the feedback is misapplied so adds higher ordered harmonics (see the writings of Norman Crowhurst and Peter Baxandall on this issue; neither proposed a solution). The exception might be a zero feedback class A amp which can have ruler flat distortion vs frequency measurements.

Regarding your commend about lower end of the cost spectrum, I think one reason class D has fared so poorly has been insufficient power supplies. IME a power supply for a class D amp has to be robust but a lot of designs I've seen don't seem to reflect that.

@8th-note If I can add to that:

The power paradigm

I suspect that a lot of what we think of as the need for power is really the need for high current

@erik_squires Current cannot exist without power and vice versa. So if the amp can make the power into the load, it can also make the current.

There are a variety of issues with feedback. One is that the feedback node (where the feedback is applied in the amplifier design) usually is non-linear, meaning the feedback signal gets distorted prior to doing its job. This usually means additional distortion generated on that account, which is mostly higher ordered harmonics (and so IMD as well).

That is part of why feedback has gotten a bad rap in high end audio, but its not feedback's fault so much as shoddy execution.

The second problem is most amplifier designs lack the gain bandwidth product to support the amount of feedback being used as well as the gain of the amp. The result of this is that above a certain frequency, distortion increases. IME this phenomena is highly audible. Most THD measurements are made at too low a frequency to really show what is going on, but distortion vs frequency shows this problem with ease.

Class D offers a way around both problems. I think that is why there are class D amps now that are shutting down class A solid state designs for sheer musicality.

@soix Got it in one 😁

SETs are where this is most important- they only have about 20% usable power out of whatever they are rated for.

You really don't want any amp to be asked for more than about 50% of full power even on peaks. The harder you work any amplifier, the more distortion you're going to get. That also means that the load for the amp should be benevolent rather than having odd phase angles in the crossover, low impedance or the like that tax amp's capacity. The more distortion, the less musical, since that distortion is likely to be the kind that the ear hears easily!