amp tech has stalled in terms of design, although in terms of innovation and advances on some themes, amp builds are being updated with fresh lines of thought on how best to get from input to output.
one example I recall from reading articles on various amp tech is a more limited, or sparse approach in the use of MOS FET devices. presently some makers have reduced the amount of these devices within amps choosing instead of using four, six, eight or mnore to using only a pair per ch in the amp output stage, yet choosing them a lot more carefully with matching them electronically a far higher priority..
otherwise we have to be in agreement that the evolution of the parts themselves has escalated performancewise, and greater attention to isolation and power sup builds has handed us at least SS hybrids, class A, and A/B amps which appear to perform on higher levels with at times fewer parts.
new BK amps from PS Audio for example use this less is more approach. I believe darTZeel was using just one pair of bi polar devices back in '04 or '05 rather than multiples of same as has been the case so very often with sand amps which opt for such device topologies.
although this minimalistic attitude has been ongoing for a while in some maker's amps, it is in fact, 'new' design techniques, so there's that.
more tube amps are now using cathode follower designs for continuous auto biasing rather than mandating owners to self bias each amp and as said, actively engaging a 'continuous' auto bias circuitry, ala vAC's IQ line of amps.
jolita Black Ice INTs partnered with FOSGATE designer to add in a sound enhancing tech to their 18 and 50wpc INT models currently available, or so I've read/heard.
its a tuff act to build an amp whose design is completely unknown, brand new, or not another take on a proven method.
its like reinventing the wheel.
one likely has to hang their hat on the 'less is more' tact, and greater attention to detail in the build's layout as something fresh in amp design, yet its not a totally new 'ground up' blueprint, just different.
i think until someone discovers the 'never before' ways and or means to transmit and develop signals, and does the same for output stage thinking, we will have to be satisfied with innovation and refinement, rather than be unsettled with the SOTA of amplifier philosophies seemingly remaining unchanged.
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I suppose you have switched spkr cables from left to right to see if its not the spkr itself by now, and as such it is a disparaging and interesting concern at the same time.
Much luck to you.