How far have ss amps really come in the last twenty years?

I have owned and enjoyed my Jeff Rowland model 8 ( recently modded and upgraded by Jeff to the last version) for many years. I recently had the opportunity of comparing it ( after mods) to a few of the current ss models from Gamut, D'Agostino, YBA, Parasound, Sim audio, CH precision, Constellation,PS audio,Pass Labs  and Musical Fidelity. The results were very interesting, because to my ears and in the systems that we did the comparison, the Rowland held its own against all but the most expensive D'Ag and CH amps. Even those were only very slightly outclassing the Rowland in the areas of top end resolution...and a tad in the bottom end resolution. Now the thing is that the last revision to the Rowland 8 was designed by Jeff over ten years ago! 
So, my question for those more technically inclined than myself far has the design of ss amps come in the last ten...or even twenty years? 
I have owned and enjoyed my Jeff Rowland model 8 for many years ... I recently had the opportunity of comparing it ( after mods) to a few of the current ss models ... the Rowland held its own
... how far has the design of ss amps come in the last ten...or even twenty years?
It looks like you've answered your own question.
..don't know much about electronics, but I think that parts (caps, resistors, etc) have gotten better through the years rather than amp design.
If you are not hearing distinct differences in the amps you listed, I would suspect your system is not the best it could be.

@don_c55 Actually I don’t think so. I heard the comparisons in various systems, so unless they are all sub-par, your theory isn’t applicable.

@ cleeds. While that may be the case, it seems to me that if that is the case, it doesn’t explain the technical reasons as to why.
@stringreen That’s the thing, and my question, why hasn’t ss amp design progressed through the years? Although, it would appear that to some it has...yet my listening tests seemed to indicate that the improvements are very small.
@stringreen +1  Within the last year I sent my Steve McCormack modified DNA-1 back to him for a 20th anniversary upgrade.  Steve and the guys at SMc Audio really did an extensive refit on the amp.  Steve explained that he has had some deep pocket customers asking him to build them ne-plus ultra amps with absolutely first rate parts and circuit layout schemes.  He has taken much of what he learned from those experiences and trickled it down to his more monetarily modest upgrades.
As @stringreen mentioned, much of the improvements have been in improved parts quality.  I hope to listen to my current amp till time ends my listening altogether.
@hifiman5  Your point seems to be that the parts are definitely improved, but the overall circuit designs are about the same; which is why I was questioning those with more technical expertise as to why this seems to be the case. 
There's three different aspects to this question: design, implementation, and results. From a design point of view there may be nothing better since the Distributed Node Amplifier. I don't know, it just seems that way.

In terms of how the exact details of how that or any other design is implemented, well that is a whole other story. Because as stringreen and others notice its not just the design but the parts that go into them. Then on top of that you have to factor in the way those parts are used. Not only where in a circuit but the physical circuit itself. People over time just get better at shielding, the physical location of a circuit, vibration control, all the little details. No doubt this has gotten better. 

And then, results. What I think you're asking- how much better do they sound today? To which I would ask: Do they?

There's another aspect that comes into play which I think is perhaps the biggest advance - price for performance on an inflation-adjusted basis you get way more today.
Are saying most all expensive amps made in the last 20 years sound similar?

Very hard to believe!

Do they all have the same flavor?

Or do you have no preference of one over another?

If so, there is no best or better or worse.
On paper the best possible circuits have already been designed, now it's just a matter of implementation and personal preference.
How far have ss amps really come in the last twenty years?

Quite a bit, just to pick one area, global feedback was used too much to get distortion down 20 or more years ago, these days the good ones do it without too much feedback, and with the use sometimes of just local feedback, but that takes a bit more matching ect to do right but the rewards are exponential.

Cheers George 
SS amplification reached sonic equivalence decades ago! If you think that amplifier A sounds better than amplifier B, remember it is only in your mind - not in Reality! Expectation bias is the ruling factor here when trying to ascertain amplifier "quality"!
All today's SS amplifiers measure exceedingly well in all parameters! Sonic neutrality is the order of the day! To say that amplifier A sounds "better" or "blows away" amplifier B is to be guilty of delusional thinking! Measurements rule - not "my golden ears" told me it is so!
If you want to hear an amplifier sound "different" get a tube amp with an output impedance of several ohms! Ohm's Law rules here! A frequency response that will follow the varying impedance of the typical speaker.
Hogwash. All amplifiers have a sound, and are distinctly different from one another. Which you prefer has many factors, such as the speakers being driven, with their sensitivity and impedance. Amps can change a little from the output source impedance driving them. Circuit designs, parts used, size and regulation of the power supplies, all matter. What is your flavor ? The best sounding ( smoothest ) to me are Class A designs. To answer the question as to what is new in 20 years, I would say Class D output stages. For those who do not hear differences in amplification, I would not outwardly admit it. I am sorry for you, because there is much to be discovered. Enjoy ! MrD.
@mrdecibel : I probably have more amps (both SS and tube) on hand (along with speakers) than you do! So I can speak with some experience! And I agree with you that Class D is an interesting development - though I was aware of it long ago with Infinity's ill-fated attempt at it! 
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In an interview with Steve Guttenberg Dan D'Agostino commented that one of the best sounding amps he ever produced was the KSA 50. I have a KSA 300S and I have wondered how it would compare to today's high end SS amps. I have personally heard a direct comparison between Bryston 28B3 monos and 2 different high end Class D amps which shall go unnamed. The difference was striking and obvious within the first 5 seconds. The Brystons incorporating a traditional design were far superior in every respect to the more "modern" Class D amps. So, addressing the original question, it's clear to me that newer circuit designs are not necessarily better. 

Please give us a list of all of your equipment. Also your age would be nice. I am seeing a distinct pattern.
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The OP and some others are missing the most important consideration of amplifier design here.  Namely, that good, well thought out design techniques have been known since the mid sixties.  That is a long time, even for a senior like me.  What has changed is the advent of more available and more affordable high quality parts to choose from.  So, it is easier ( and cheaper in inflation adjusted terms ) to make high quality amps than it used to be, but none of that matters if your intent is to "design to market"  instead of producing the best equipment you can for a given amount of dollars.  This difference is closely comparable to the difference between GM and Toyota in auto manufacturing.  One tries to make the most profit for a given class of cars, while the other tries to make the best car they can at a given price point and still make money.  The same issues are true in audio manufacturing and always will be.  The other side of this "human" issue can also, be compared to autos.  For example, those people who feel the need to spend more than others can in order to say that they have "the best" of whatever.  No one needs to spend $150K+ for the highest quality auto and no one needs to spend $150K+ for the best audio gear either --BUT SOME DO.
I think, there is no definitive answer.
On one side, the business lives from the impression that the latest design is better than the model before.
On the other side, you buy/bought brain. With some luck you own a unit done right. From design, layout or parts.
Even when you go to a more modern unit from the same designer, there is no guarantee that it will sound better. Different? Yes. But better?
After all my years with High End I think, most have done something outstanding on pure luck. They made something and it was a 10 out of 10.
The majority of Audiophiles want to invest money after some time. They want to change. And to justify the investment or to be King somewhere, they tell and think, yes, it is better than my former unit. And when it is more expensive, it has to be better. That’s the rule of the High End game.
Audiophiles, who go for a cheaper unit because it is better and talk about that, are rare.
But probably they know it better what is going on.
When i go to High End Shows the last 15 years, my impression was, 80% is for - expensive - ear cancer, 20% is good.
When everything will become better, this percentage should vary. But it doesn’t.
A couple of weeks ago, I had my Ayre amp looked at for a "noise" - "resonance" that I heard in my left speaker.  Ayre told me that the amp was performing well with no noise that they could detect.....I asked them to look further and do anything that they thought would improve the piece. I got the amp back after they replaced a number of capacitors, and other improved parts.  They also applied a tape to the heat sinks....the result was a better sounding amp...but the circuit itself wasn't changed.  (I doubt if the resonance tape on the heat sinks did THAT much). (the original "noise" prevails.)
I was wondering how long it would take for the "all cables sound the same" camp to chime in with the "all amps sound the same" nonsense.
Talk about an agenda.
@stringreen How old is your Ayre? I am surprised that the company couldn’t detect the ’noise’ on the left channel!! It is definitely something that they should have picked up, because IMO ’IF’ you can hear it, it should be something that can be picked up as a functional/technical problem.

@syntax Nice post! I think that in my case, Jeff brought out a model at the time that he didn’t skimp on..and that factor allows it to be so very competitive even today ( particularly after the mods were recently done).
Nonetheless, aside from Class D ( which I also feel was, and continues to be, a step backwards ( except for the lower weight and heat issuance) ) it seems there really hasn’t been any true advances in the ss amp realm.
Heat sinks are very resonant, in most designs. And, every transformer has an amount of physical vibration. Isolating both of these issues display an increase in sq. Roberjerman, you are a character. I am sure, at this moment, you do have more equipment than I, but I doubt very much you have owned more than I, or have been exposed to more equipment than I. You stated you were in a band, so I believe your ears are shot, and unfortunately, you probably did not use ear protection. You have a tendency showing up everywhere here, claiming a system you have " currently hooked up in another room " is as good as anything today. Examples are Quad 57s, DCM Time Windows, GAS Son of Ampzilla, etc. I know from my own ownership how enjoyable these were at the time, but to say they compete with todays products, well, I am sure there would be a handful of people to agree with you, especially with the Quad 57s. Older ss amplifiers sound brash, or dark, because of the parts used in the day, or some other characteristics of design. And, the constant trolling you seem to enjoy so much, on the power cord threads, stating they make no difference, making a joke of yourself, because I do not know of one piece of audio gear in your " collection " that has an IEC inlet. I am inviting people here, to read up on many of your posts, to show the pattern, and some of us already know. So with this I wish you the best. Enjoy ! MrD.

Just to be clear...I am CERTAINLY NOT saying that there is no difference in SQ between ss amps. I have heard many ss amps that are strident and non-resolving, among many other issues that they have. OTOH, I am questioning whether there is that much difference between some of the top flite ss amps of today- and the top flite one's from as far back as twenty years ago.
I think that the improvements in SS amps exceeds those made with tube amps. Years ago there werent many SS designs that I could enjoy. Now there are many, mostly from Europe and very expensive. 
Hi Davey.... I've been searching for this noise for over a year.  It sounds like a I banged on everything in the room - nothing loose/vibrating.  The sound is there on CD and Vinyl, so I thought it might be the speaker - Vandersteen 5A.  I reached out to Richard who suggested it sounds like the support cones are loose....checked - nope.  I removed the tweeter and sent it to Vandersteen.....fine.  When I got the driver back into the cabinet, I removed the midrange and sent it back to Vandersteen - fine.  I then removed the high pass filters from both speakers, the integral amps, and the crossovers thinking the factory would replace the batteries while checking for the noise (which they did)... but they also told me there was nothing wrong with the components I sent to them.  The noise is not coming from the preamp, because I have a dedicated amp for the earphones, and - no noise.  This is very interesting, and a real project.   I'm off to the audiologist for inspection....we'll see....(hear)
All I can say is; I once owned a fully refurbished, by Krell, KSA-250 amp and to my ears it sounded wonderful. Even my wife and children commented on the superior sound quality. Tight deep bass and superb transient response. It seemed to take a firm grip of my speakers (B&W N801 at the time) and made them do what it wanted to do. Seven years ago I sold the Krell and have regretted the decision ever since. So yes, if in top notch condition, some older SS amps can sound wonderful. The key words here are; CONDITION and SOME.

This is what Robert Harley said about the Krell KSA-250 27 years ago: . 
mgatt, you should have heard the Krell’s replacement ( whatever you purchased to replace it ), in your system before you sold it. Live an learn. Enjoy ! MrD.
@mgattmch   I would bet that your old Krell KSA 250 would give most ss amps today a very tough run for their money! 

@stringreen  What you describe must be a bit infuriating! If it is just in the left channel, have you tried simple things like swapping all the cables..left to right etc. 
A resonance sound could be coming from the furniture in the room as well. That is what I have noticed when I have had issues like that, and they can be difficult to suss out!
Frustrating is right Dave..... Tried left/right cable swap and remained in the left...I even tried entirely different brand of luck. Moved the chairs/sofa to another room....same.
"mrdecibel" and "daveyf", I stupidly did. The Krell KSA-250 was part of a 5.1 HT set-up that doubled as a stereo system. I used the Krell for front L/R and two Pioneer Elite M91 amps for rear L/R and one for the center channel. Sure looked nice. But, the whole system was heating up my HT room dramatically in the summer (I lived near Houston at the time). So I replaced all three SS amps with a Krell TAS. Heating problem solved. But, it was obvious the Krell TAS was not in the same league as the KSA-250. Like I said, I have regretted the decision to sell the KSA-250 ever since. Probably my single most stupid HiFi decision in close on 50 years with this wonderful hobby! But then again, probably best not to talk about the Wharfedale E90 speakers.

The nice thing about the Krell TAS versus the KSA-250 is reliability. The KSA-250 runs so hot it is obvious a re-capping will be required at sometime or something will fail due to the extreme heat. Not so with the TAS, the Krell service department tell me this is an extremely reliable amp and very rarely needs repair. Ah well, peace of mind is worth something in this instance.
@stringreen   Wow, strange. I think that there could still be a room node that you are hearing. Do you have any acoustical damping in your room/system?

@mgattmch  That is one of the issues that I think has gotten significantly better with many ss amps over the years....far less heat production. Although, the Class D amps, which run cool, leave a lot to be desired IME. Personally, a heat engine for an amp, isn't going to be on my radar anymore. 
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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.

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.
stringreen, I have to ask, as I might have missed something, so sorry...have you tried using another amp during this time, and have you completely reversed the left and right channels of the system, into the speakers ? In other words, the left speaker was receiving all of the right information, and the right receiving the left. Also, did you exchange the left and right speakers during this time ( physically ), to see ( hear ) if anything has changed. You also mention it cannot be coming from the preamp, based on your dedicated headphone amp not showing the problem. I would try and eliminate the preamp, if you can, and drive the amp only with a source, such as a cd player. If you do not have another volume control anywhere, you can take a cd, that has an extremely low passage, just to listen, for that moment. It is possible your preamp is picking up rf, or something else. I would not count out the preamp as being the source of the issue. Simply trying to help. Always, MrD. 
@mrdecibel : I have never been in a rock band and my hearing is still good! Right in front of me to my left is a Richard Brown Electronics Lab BEL 1001 amp (serial no. 0001). A favorite of Harry Pearson's from 1980. This requires an IEC cord - for which I bought a $99 Pangea from Audio Advisor. My TOTL Toshiba DVD player (2003) needs the same. So there, at least two pieces using IEC outlets!

I will put that BEL 1001 amp (first production one!) up against any of today's pricey gear! For too long audiophiles have been conned into the belief "spend more, get more"! So a $10K amp has to be sonically much better than a $1K amp? And a $50K amp better than the $10K amp? Not necessarily true! With electronic gear diminishing returns sets in quite quickly! 
roberjerman, I obviously have been mistaken, so I apologize. So you do believe, good amplifiers, sound different from one another, and that some, such as your Bel, sound superior. Great, we are getting somewhere. And, you purchased a Pangea cord, and, did not return it. Another great ! See, was that so hard. BTW, the MK V was a great version of your amp; the original you have, good potential, and would sound good with my pair of AR3a, giving them some zip in the high end, and lots of control in the low end. The Bel I owned, for about a year ( version 3 I believe ), drove a pair of Janis W1s for a while, which I replaced with an Electron Kinetics Eagle 2A, and sold the Bel. A good amp, yes, but lost out big to my Krell KSA 50, which to my ears, was in another league. When I sold the Bel, I had no regrets, and still don't. Enjoy ! MrD.
If you want to hear an amplifier sound "different" get a tube amp with an output impedance of several ohms! Ohm's Law rules here! A frequency response that will follow the varying impedance of the typical speaker.
There is far more to it than that!

Distortion plays a major role in the sound of any amplifier due to how the ear/brain system treats distortion, which is to say it treats it as a tonality. We've known this fact since the 1930s (see Radioton Designer's Handbook, 3rd edition).

Most solid state amps are designed to have minimal distortion and is why so many of them sound the same, which is to say, harsh and bright especially at higher volume levels. Now tube amps actually make more distortion, but because they have lower ordered harmonics in greater percentage quantities than solid state, the ear's masking principle allows the lower orders to mask the presence of the higher orders. This is why they sound smoother. The odd bit is that the presence of the 2nd or 3rd harmonic (both of which are treated the same by the human ear) causes a greater sense of detail and soundstage definition! This is why tubes are generally more detailed and have more depth.

Now if we could eliminate distortion entirely that would be great. But we can't, so it appears that an injection of a 2nd or 3rd harmonic is beneficial to solid state designs. This is recognized by several prominent solid state designers in high end (John Curl and Nelson Pass come to mind) and it should be no surprise that they have turned out some of the more highly lauded solid state amps as a result.

It is this bit of understanding about how the human ear works that is one thing that's changed in the last 20 years and it is perhaps the most significant- parts and topology notwithstanding. Its our ability to take advantage of how the ear works through engineering that yields the most progress. We're only just now starting to crack that nut.
I am sorry, but neither Pass nor Curl can compete at the top level. Perhaps they are doing something wrong.
That's right, I will win anytime because I am unbiased. Ralph's amps work very well with a very limited number of speakers, by the way, this includes Classic Audio and Sound Labs, of course. So that you know.
 @atmasphere  Distortion is an interesting term. Distortion compared to what? You mention that the human ear treats 2nd and 3rd harmonic distortion favorably. Therefore, one needs to question whether these distortions are distortions at all. Since we, as humans are using our ear/brain to determine what is considered as a true  and pure signal, wouldn’t it make more sense to label a signal that doesn’t include these 2nd and 3rd harmonics as the signal that is actually distorted...?
@stringreen, I would closely watch the temperature of your amp for overheating after the heatsinks were taped up. To function properly, they need to have maximum surface area exposed to air, and to allow air to move by convection through them. 
Thanks  for your caution....  In fact, the amp only gets warm - never hot to the touch.  ...and too, the tape was put on by the factory.  It covers only about 15% or so of the fins, and only in the horizontal plane...the fins are vertical.  Thanks again - I'll be vigilant.