I have mixed feelings on the subject, but in general, I feel there are not many changes or real improvements. We do have Class D now and it has developed into a viable audiophile amplifier. I own an amp that I built with Abletec modules, it is quite good. Class A or A/B .... What has improved is the linearity of parts, better outputs, lower ESR caps, these have offered us better sounding amplifiers.
So what I am saying is the thing that would make a real difference is circuit design. I can see someone coming along with a killer design and creating a incredible amplifier today, but in general, solid state amps are indeed very similar for the past 30+ years.
I had an old Sumo Nine that my old mentor Ed Martin from Marcof modded. He went overboard with the replacing mediocre parts with best parts available plus increased the filter capacitance 3 times. A few years ago this amp took a lightening strike and I lost it, but he has it and is working on using different outputs, but that amp would really sing, I compared to many amps and kept going back to it. On the other hand, I've heard some designs modified and it doesn't matter how many parts upgrades you do, the amp just didn't respond... So, a good design is where its at. I think that there are alot of old amps that could be improved to compete with the best today. I also believe that with the improvements in parts designs that there are plenty of great things still coming.
