Very interesting comments on the different effect of second harmonic distortion on positive and negative phase of the signal - I would love to hear from other designers concerning this aspect.
Except that nothing really new, but again he clearly refers to audiophile preference:
In the end, the subjective experience is what our customer is looking for. Our taste in sound may not appeal to everyone, but it's what we have to work with, and we only need a small segment of the market to be successful.
I don't think he's pointing to no developments. Perhaps the issue of amplifier development is like traveling by plane across the US. Getting there in one piece is a settled thing. Amplfication is handled with audio much as staying airborne in a plane is handled. But that doesn't mean the trip can't be more comfortable, quieter and faster.
I suspect that Nelson is refering to the seeming truth that equipment performance advancements, both objective and subjective, are becoming more and more slight. In mathematics there is concept known as an asymptote. An asymptote is a line that approaches another line an progressively decreasingly manner, so that the two lines never actually meet. Speaking for myself, this seems to be occuring in audio equipment performance. Performance improvements appear to be in the realm of rapidly diminishing returns, increasingly minute in magnitude - while increasingly large in cost, by the way.
The bigger question is how close are we to achieving convincingly live sounding reproduction? In other words, if, as Nelson seems to be suggesting, we are nearing an audio equipment performance asymptote (which is a product of present technology), is that approaching asymptote near or relatively still far from the objective of convincingly live sounding reproduction? If it is relatively still far, one conclusion is that convincingly live reproduction will require an paradigm shift in technology, or technical approach, giving a new advancement line who's asymptote comes much nearer to the goal of convincingly live reproduction.
I once tried to ask how close people think we are with reproduced music. Some thought 5% like the real thing, others closer to 80-90%. It is all over the map and totally subjective. Would anyone blindfolded ever be able to confuse reproduced music with live music? If the answer is "no", does that mean that there is a huge gap in the difference, or that they sound very much alike, just slightly different enough to know which is which.
It is sort of like watching a good TV. Never do I think I am looking at real explosions or small actual people talking in front of me in my TV room. However, it is very easy for me to get lost into what I am watching, forget that it is all artificial, and simply immerse myself in the story telling experience and visual spectacle. It is the same with good music reproduced on a good system.
For either of these experiences to become more convincing and at the point of being indistinguishable from the real thing, on a subjective level, a real paradigm shift in technology will have to occur.
I once tried to ask how close people think we are with reproduced music. Some thought 5% like the real thing, others closer to 80-90%. It is all over the map and totally subjective.........................................................
I think he's right. All the best basic topologies have been out for decades. Everyone is just tweaking, adding their own special sauce....save for Class D which I suppose is relatively new compared to SE, Push/Pull class A and Class AB switching amps.
I read it as meaning the science of amplifying a signal is understood. Maybe there are tweaks that can be done to a circuit to make the end result even more accurate, but what we have now is pretty darn close to perfect. I agree with previous statements that speakers and digital are where we will continue to see improvements over time.
Well, sadly, Pass is in the camp of starring at voltage distortion all day.
In that sense yes the objective requirements are beyond any "need". But there are a lot of things I would say he hasn't explored.
On a very different note if you look at the work of Bruno who designs all the Hypex stuff you should note he has proven different types of amplifiers don't even work on the same principles as what, say, Pass builds. His classD designs almost defy physics with how different it works.
It seems to me to be a sort of acknowledgement that there has been no advancement in the devices themselves. They are just as non-linear as they have been over the last 90+ years since the first triode, which is still the most linear amplification device, was invented. Without a truly linear amplification devices, all amplifiers are trying to patch over that inherent non-linearity and many of the ways devised actually degrade the sound more than the core (low order) distortion...it is why the renaissance of triodes and SET in particular could even dream of making a comeback. Nelsons SE(Transistor) amps and simpistic designs is an admission that simpler is better than the sophisticated ways of making amps "linear".