New vs Used - Significant sonic improvements in preamp/amp design in the last 20 years?

My opinion, is many examples would qualify as an improvement.
Especially in the last five to ten years.
A small change can make a big difference! In any late/early model.
Manufacturers constantly make changes/development for improvement.
A transformer, PCB, a Chip, and making everything work as design will allow.
For example Technics latest iteration implemented as Reference/Grand/
Premium tiers for Sonic Excellence. (my personal bias)
Tube based design does suggest an exception because of parts (tubes)
that are no longer being made. (exceptions on both sides of the question)
The Sonic difference between lower and higher tier models may be less!
Items of note:
Gan - FET high speed device
Toroidal Transformer

Greg

Those are good points.

I would love to hear from folks who have the opportunity to A/B components that were sonically Class A 10-20 years ago against the same class today.  I've recently had a chance to hear a couple of new Class A amps and preamps vs some older designs with great speakers and Class A+ digital front ends. I was surprised at how similar they were.

We developed and patented a means of direct-coupling a balanced output. We use it in our tube preamps, the first of which were built in 1989. It was the world's first balanced line preamp for home use.
You can still find the older ones used but they don't turn up all that often (we can update older units and reactivate the warranty). But recently we had one come through the shop that was the 3rd ever built. With some minor work to deal with the age of the unit (new filter caps and the like) it tested out very well and I would without hesitation put it up against much of today's preamps and not only expect it to keep up but surpass many of them.
Some older designs, like the H/K Citation 1, are so well done that if properly refurbished they easily keep up with many modern designs. That is part of why Citation 1s hold up their value!

One thing that seems to have improved is coupling capacitors. Its a lot easier to get Teflon parts now than it was 25 years ago, and the newer parts measure and perform better. Resistors have seen improvement too on the bottom end- cheap resistors are a lot better now than 25 years ago. Expensive resistors not so much. We option with Caddock resistors (which are custom built for us) and so far have yet to see anything surpass them (please note that Caddock makes a number of different parts that are intended for different applications, so my statement applies to a certain model).

Its easier to find some tubes now than 25 years ago, for example 6SN7s are in production now while 30 years ago they were not. Filter capacitors IME are not as good as they used to be. The proliferation of inexpensive Chinese parts has seen to that. However, good quality Chinese parts can be quite good, but if you want better you still have to get something else.