Amplifier technology reached maturity in the seventies, when output transformers were abandoned in solid state amps. Ever since, well designed amplifiers used within their specifications have exceeded human hearing acuity. Since then, measurements have still improved somewhat, but I am not convinced this has improved sound quality (there is no point in being more perfect than audibly perfect). Already in the seventies Quad commissioned an independent research to compare Peter Walker’s three famous amplifier designs, and the test showed no audible differences: http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1978/Valves%20versus%20Transistor.... I personally participated in one of these blind demonstrations, and was surprised at the time, but convinced by the science. I appreciate there are people here who believe differently, but they never subject their subjective impresions to rigorous scientific scrutiny.
Of course there have been engineering advances. Manufacturing technology has changed, with cheaper and more reliable products as the main benefits. At the moment we are witnessing the more and more common inclusion of digital inputs. In the near future I expect that energy saving of the power stage will become more and more important for environmental reasons, leading to more class D designs. In Europe, we already have mandatory power consumption regulations for many domestic appliances, including televisions. I am convinced this trend will soon extend to audio equipment.
Of course there have been engineering advances. Manufacturing technology has changed, with cheaper and more reliable products as the main benefits. At the moment we are witnessing the more and more common inclusion of digital inputs. In the near future I expect that energy saving of the power stage will become more and more important for environmental reasons, leading to more class D designs. In Europe, we already have mandatory power consumption regulations for many domestic appliances, including televisions. I am convinced this trend will soon extend to audio equipment.