Amplification: what are the biggest advances of the last 40 years?

Class D is probably the biggest innovation.

They are close but still does not surpass the best of linear Class-A or A/B designs YET!
I DID SAY YET!!! (before you Class-D junkie’s get your knickers in a knot)

That will come maybe after they take to what Technics did, 3 x higher switching frequency 1.5mhz with the SE-R1 (my last post), one of two of Class-D’s Achilles Heels, too low a "switching frequency" and subsequent low order "output filtering" to get rid of it.
Which still leaves large remnants of it (photo) in the upper mid//high frequency audio band when using around 600-700khz switching frequency as most do today.

The other Achilles Heel is current delivery into very low bass impedances of today many top very hard to drive speakers (which the "better" linear Class-A A/B amps do standing on their heads).
To be able to "almost keep doubling it’s wattage" from 8ohm to 4ohm to 2ohm with independent testing, they never give the 2ohm wattage of class-D when comparing the 8 then 4ohm

Cheers George

 biggest improvement is the GaN transistor and the new amps implementing them.

Only if used to it's fullest, as Technics did in their SE-R1 (maybe in their new SU-R100) with 3 x higher switching frequency (1.5mhz) and 3 x higher output filter for it, so this sort of 10khz square wave oscillation (upper shot) doesn't come of the speaker outputs (gets reduced by 3 x).
Lower shot has Stereophile special external test gear filtering, so it doesn't look bad for the magazine shots to the public.
https://ibb.co/N2HBQH4

Cheers George

bobbydd

Amplification: what are the biggest advances of the last 40 years?

For me I found the biggest advances for musicality/listenability came with giving "global feedback" the big flick.✔
And that came with solid state amps that use highly biased Class-a (for sweetness) but with Bi-Polar (BJT) complimentary (npn/pnp) push pull output stages, but being used without musicality killing "global feedback" surrounding them, instead using a small amount of "local feedback" only around the front amplification stage.

But to do this is properly those complimentary bi-polar output transistors that are to be used without "global feedback" have to be hfe matched, and also their emitter resistors, otherwise instability can occur.
Then you have an amp with an "iron fist" especially into low impedances, yet with the real "speaker disappearing", musicality imagining and depth act.

Cheers George