Class A or Class D solid-state amplifiers (modern designs)

@petaluman As you might expect I have read Nelson's article before.

He addresses the issue of poles in the amplifier caused by adding more stages of gain and how that adversely affects the use of feedback. I addressed that issue in my first post to this thread.

A class D amp only has one stage of gain FWIW. Nelson does not address the solutions class D offers to the issues described in his article.

Clearly articdeth is out of touch with how good class D has gotten in the last few years. Most recently, GaN tech is about to sweep the floor with any class under 500 watts

@atmasphere 

My comment was about amp history.  I don't know when the cascode amp paper was written, but the Threshold CAS-1 & CAS-2 amps date from the early 80s.  I don't know the history of class D amps, but am not surprised a paper likely written ~40 years ago about audio amplification didn't include class D.

I do have a question for you, if you don't mind my asking.  As we all get older, we're discovering that parts inside our stereos age (and worse) as well.  What have you been able to glean about the long term reliability of class D amps, what goes wrong, and what is the result?  I know it's probably a lot of the same parts, but they're being used differently.

What have you been able to glean about the long term reliability of class D amps, what goes wrong, and what is the result? 

Electrolytic caps last longer if they have a charge on them and they are not subjected to heat. WRT the other parts used, surface mount has been around for several decades and reliability seems to be at or better then the level of reliability of thru-hole parts. I expect class D amps will hold up very well.

IMO and IME, well built high pulse draw systems do indeed hold up very well. To the point, IIRC, that they are extensively used (if not entirely ubiquitous) in the satellite business.

However, the minds that execute a given class D amplifier circuit, or whom chose it’s parts values and it’s layout, tracing sizes, mass, interactions (placement, length, etc), and what have you..may not all be on that level of ’a deep history in milspec and beyond’ of knowledge and skills applied.

Where the end users buy by price being a major factor. Which, when it comes to peaks and pinnacles can be a rather foolish position, but also..sometimes.. prudent. It's tricky.

Our end effect, as we cascade down that path of logic and reality... is to have the market filled with class D amplifiers that individually sound different, with wide spectrums of distortion products that allow them to differentiate themselves from others. With quite a few designs that don’t (operationally) last very long, compared to their older amplifier brethren of non class D nature.. With a difficult path to refurbishment or repair, in many cases, re general knowledge in technical types to deal with repair efforts.

If the past is any guide, I expect that class D will finally surpass the desires of most of even the high end audio crowd, re sound qualities heard, but not yet..not yet...

I’m well familiar with this effect of even the high end crowd finally being swayed, as I come from the ’CRT projector is king’ high end projection market. Where I was making some of those ’pinnacle’ CRT units myself. Then digital projectors came along and dominated the bottom of the market, and then slowly became better and better and dominated the meat of the middle of the market... and then slowly crept into the high end market.

Where analog projection has to fight to beat out the best in digital projection technology and the battle...- is over. Digital projection wins, even at the very peak, in almost every way possible. I saw the writing on the wall in 2003, and began switching form working on modifying the peak of analog projection to working on digital projection technology, to improve it.

In that, in the last while...I purchased a 2014 DLP projector and even a 2018 4k DLP engine/hardware design package, and analyzed both. I found that the innovations I came up with in 2005-2006, where I had stopped working on DLP engines, all that work was still viable and not anywhere near being included in any DLP engines that I was aware of. So their upward trend in qualities was and is moving quite slow, and my design change works were still valid and useful to improving modern DLP projection. After all that time. sheesh. Either I’m quick or they are slow.

I nearly ended up working with Delta (approx 65% of the DLP projectors on the market are made by them), but I was being treated in the usual way that the inventive type are treated by, by the given major corporation. That I was just the simple vessel for the message that was intended for them. Not looking for self aggrandizement but just a simple fair deal. But..no. Typical corporate systems, is what most innovators will run into. A given boardroom of ass-wipes who are paid for how aggressively they can steal from and malign any innovator who is foolish enough to get close to them.

It’s kinda like what was said in the film ’Pi":

Rabbi Cohen: Who do you think you are? You are only a vessel from our God. You are carrying a delivery that was meant for us.
Maximillian Cohen: It was given to me.

And they don’t care, they are selling projectors regardless. and, the more technology they can own, or if not.. push to it’s death into a ditch, is all, well...just fine. This is what inventors find out when they approach corporations.

Class D amplification might take the same sort of path of not being as good as it could be and not innovating as quickly as it might. Accordingly.. it’s not quite there yet as (observed/heard sonic qualities) pinnacles may go. Never say never.

I spent two years constantly working on class D amplifiers cleaning up their ’flaws’ and I have no place to put those innovations as it’s the same problem that all inventive types that don’t work for corporations - run into. Not whining in public here - - that’s the way it is....