Gave up my SET----looking for moderate to higher power replacement options

@agdproduction I’m not in the market for new amplifiers, but I’d happily do a home demo and report about my experience! You can see my current equipment on my systems page...

02-04-2021 8:07am@charles1dad As @twoleftears suggests, my bet is on the AGD amplifiers as the most SET sounding class D design (GAN-based). I'd love to hear them.

They certainly want to convince us that they care about SET musical characteristics with the design, and one dealer advertisement states that SET people do like them (https://www.youtube.com/watch?v=2PKSlTODkJ0).

Unfortunately more than double the OP's budget.

Please contact us if you love to hear the AGD The Audion, we can arrange something for you and add some direct experience to this discussion.

I’ve had KT88 tube amps before and really liked them. Maybe you might as well?

Don Sachs makes a really nice one:
http://www.dsachsconsulting.com/custom%20kt88%20tube%20amp.html

CAD$3,750 which works out to under US$3,000.

I have Don’s linestage. Very high build quality and workmanship. 

I got a D-Sonic to replace a Mesa Baron while it is under repair (blew a tube, etc.) and during the worst part of Houston summers (which run from about April through January.)  the D-sonic is very nice, lots of detail, virtually unlimited power, clean bass, truly excellent with movies, but in no way does it have the life and magic of tubes with music.  going from SET to D is like apples to oranges, or steak to vegan.     Even so, tube amps are like sports cars (or vinyl) and need considerably more money and attention than SS, in the normal course of events.  Freedom from heat, maintenance and additional expense is something many tube lovers eventually crave, but it’s a vacation, you wouldn’t want to move there for good.

brianlucey---I picked up my first JAS Array 2.1 for an even trade for a pair of Monarchy Audio SE 160's and then a few yrs later bought a demo JAS for less than $1500 shipped.  Add about $600-700 for tubes and I had great sound for well under $2500.  My Audiozone Amp1 is fairly close ($1100 used) and could probably be modded to get even closer.  And I see reviews stating that some of the First Watt amps are as good as SET or even better.  Granted these are all lower power than I want to go in the future but, you can get that kind of sound for under $3000----it's not absurd :)

rodge827---i was just looking at a used Digital Audio Company Maraschino Cherry STM 60V KING but it sold.  I couldn't find any good reviews of that particular model and can't a take review too seriously if the items they compare to are ...... lower caliber?  So the DAC amps are a contender for a SET replacement?

Crown, Krell or Mark Levinson

@luisma31, 
Thank you, I appreciate your very kind comments. 
Your Atma-Sphere  MA-1 mono blocks will serve you excellently. 
Charles 

If you love the sound that you had you’re not gonna find it by going backwards on SET or A or AB or certainly Class D

and you’re not gonna find it for two or $3000, that’s absurd

Things that sounds THAT great are heavy and hot and take power and that’s just life.

High powered reliable SET is the Allnic Audio A-6000. Much louder than the conservative 60 W per side rating, you should never run out of juice with your rig

I’m an advocate for high quality SET amplifiers

@charles1dad I know you are, I followed all your posts and I know you had / have Coincident? and you tried the Elrog’s in the beginning and every single 300B on earth, I followed your posts because unlike most here in these forums your comments "made sense" and weren’t radical. As a matter of fact your posts partially pushed me to try SET’s just not the "high quality" ones.
And yes I wasn’t trying to detriment SET amps, I just haven’t been able to test / try a proper setup of speakers with these.Thank you for the kind words Charles.

Cal,
Excellent perspective.  The primary issue with those who consider themselves "Objective " is their stubbornness and dismissive attitude toward those who simple trust what they hear. Condescendingly retorts  "It's all in your head" . I firmly believe that humans hear things that at this point in time science is unable to measure.

The belief that if you cannot verify with some "objective" measure then it doesn't exist is very narrow minded. Ironic as science is all about being open minded and exploring uncharted territory. It's about solving the mysterious and incompletely understood phenomena. 
Charles 

@luisma31,
I'm an advocate for high quality SET amplifiers and can relate to @icherepkal and his wonderful listening experiences with his former SET amplifier.  However I have always been clear that proper speaker matching is mandatory to ensure a satisfying outcome. I was able to meet that requirement and as a result experience sonic joy for over 11 years with my 300b SET.

The Atma-Sphere MA-1 is an amplifier that I'm quite familiar with and can thoroughly understand your happiness with it. No question given its 140 watts there's far more flexibility in matching speakers and is simply more universal in application.  I see no reason why you won't enjoy the MA-1 for many years. 
Charles 

My dream post-academic career would be getting involved in such an effort, but unfortunately I haven't been able to figure out how to get in the door... "Hey bro, I'm a former top scientist in my field with research on the evolutionary function of music and world-leading expertise in measuring subjective perception" hasn't worked yet.

@atmasphere No doubt.  If the human ear hears it different, then there somewhere (at some point in time) exists the ability to measure a difference.  The ASR style measurement folks want to claim that human hearing primarily responds to written words and visual bling.  Certainly these things matter, but not like actual differences in sound. 

It takes people like you to educate them in what to measure, but unfortunately many in that crowd seem to care more about mocking subjective perception than truly understanding sound reproduction and measuring the things that predict these subjective differences.  

It does not sound like a set amp. Only set amps sound like set amps. Solid state amps are only going to be an approximation, but leave you lacking.

A push-pull tube amp with a single-ended input will exhibit a prominent 5th harmonic in addition to the 2nd and 3rd. Mathematically, this is the result of this type of amplifier having both a quadratic and cubic non-linearity. So it will tend to favor odd ordered harmonics to a certain degree, and higher ordered harmonics will fall off at a rate similar to that of an SET.


This reinforces the complaints that SET lovers often level at Push-pull amplifiers. Its nice to know that the math and measurements support what the subjective camp (SET lovers) is saying in this case.


However its important to understand that an entirely differential push-pull tube amplifier expresses a cubic non-linearity, which IME is even easier to listen to than SETs. I think this is the bit that the SET crowd misses and its not surprising because I’ve yet to see any designer of SETs talk about a quadratic non-linearity.


What is important here is that the subjective camp, theoretical mathematics and practical mathematics are in agreement about what we experience as audiophiles.


I don’t like to take sides on the objectivist/subjectivist debate. I see it as a bit ignorant; in particular when objectivists talk about ’being measurable’ they usually don’t have a clue about what to measure (although they are otherwise correct). As a result for the last 40-50 years they’ve been pushing amplifiers that have increasing distortion as frequency is increased and so sound bright and harsh, especially when driven to higher output levels (and this due to the simple fact that these amps employ feedback in insufficient amounts). That’s not objective IME; its simply expressing poor taste.

I wanted to experiment with SET amps as my only reference with modern tube amps are my Atmasphere MA-1s, tried the Dennis Had PSET amps and the venerable Almarro 318B, I know these are not the typical definition of SETs like the 300Bs and such, what I found was that even with my 95 dB sensitivity speakers the amps (as Ralph wisely explained) due to their 18W relatively low power were making distortion after 50 percent gain, tried differently tubes to gain every extra watt possible but really nothing to be done so I kept my Atmasphere and sold the amps. I'm sure the results with 100 plus dB sensitive speakers will be different and these amps are very good, both of them, the Dennis Had is really a tube rolling dream. Going back to my point, at least to my inexperienced ears without the reference set by the Atmasphere monos I wouldn't be able to recognize the distortion at higher levels made by the SETs.

Maybe one day I can get higher sensitivity speakers and try SET again but really having an Amp with the "elasticity" of powering a wide range of speakers is paramount to me.

Thank you Ralph for the education on this post, many will say and argue that you don't know what you're taking about and even like the OP said I had to get my glasses to understand maybe 60 percent of what you're saying (and I'm being generous to myself) what you are saying reflects my empirical results.

Check out the Digital Amplifier Company. I have had a number of his amps over the last few years, with the last being a 2-Cherry. They are powerful and clean without any of the negative characteristics attributed to digital amplifiers. The closest sound to SET in a SS amp I’ve ever come across on my 100db horns. There are many former SET guys who are now big DAC fans.

I sold the DAC amp since I was able to score an excellent pair of 300b monos that I had always wanted. Are the 300b amps better? I’ll just say that if I had the funds the DAC amps would still be around and some serious swapping would still be going on.

Reach out to Tommy at DAC he is a great guy to chat with and could make suggestions on which of his creations would suit you best. DAC also has a 30 day no frills return policy, you would only be responsible for shipping cost both ways.

https://www.cherryamp.com/
DAC Forum: https://www.audiocircle.com/index.php?board=174

@icherepkal , you’re a victim of your own good taste 😊. The JAS audio SET established a very high sonic reference point. Tough for many amps to measure up to.
Charles

@audioguy85 Note that the OP was already finding 45W insufficient with his original SET.  That's what makes the change such a tough task... gonna want 90W+ I think.

boomerbillone----what 300B were you using?

boomerbillone---sounds very interesting and what a nice price.  Where did you purchase yours and are you missing any qualities in the new amp vs the Elekit?  Thanks for the recommendation!

speakermaster---with regards to vintage amps, back in the day I had a Krell KSA 100S, Threshold T-200, Threshold SA4e, and Classe 25.  They were all nice in their own way but none were remotely the kind of transparent I'm looking for.  Compared to the JAS, all were rather on the opaque side and, as a result, not as engaging for me.  I can certainly enjoy music from any of those fine amps but that's not what I want.  I connect most with a recording when it sounds real.  Only a highly (for me anyway----financial restrictions at play here) transparent and detailed system really gets and holds my attention.   To each, their own.  That's just my preference.  No right or wrong.  Thanks for your input though.

$3000 you say? Easy, its called the Sugden A21se. 30 watt single ended pure class A @$3250 brand new. Solid state, made for over 50 years by the pioneers of SS class A. She's a beauty!

I myself am running a conrad johnson mv55. El34 in push pull with mallard reissue tubes. It sounds fantastic into my audio nirvana super 15" Alice ported speakers. 

I design and build my own tube amps but the mv55 made me realize that I needed to really step up my game in that arena.

It does not sound like a set amp. Only set amps sound like set amps. Solid state amps are only going to be an approximation, but leave you lacking.

Suggestion is to purchase another set amp using something like the gm70 as the output tube, get a good pp amp like a conrad johnson, or upgrade you speakers to something 98db or better.

When it comes to audio electronics, there is no free lunch between technologies. Set is going to be limited in power in class A but sound very sweet. Run it in AB and you lose a bit of that sweetnes but gain more power. Run a set with a Mongo transmitting tube and you will get more power, but heat your room unbearably during the warm months.

I suggest a GOOD tube PP amp running kt120 for output if your speakers are not that efficient and you don't want to change out your drivers. Steer clear of Chinese amps. Go for a manufacturer that has a LONG proven track record.

Just my 2 cents, thake what I said above if you want.

Hello lcherepkai!  I recently replaced my 300B, 8 wpc, Elekit 8600-RS with a Starke Sound A4-320. Four channels (can be bridged), Class D, absolutely glorious sound - a rival of the Purifi Audio module in the NAD M33 and the LKV power amp. It beats the 300B amp and has extremely tight control of the speakers it feeds. I have two A4-320s and two of the Purifi Audio EVAL1 kits (also Class D) they are simply unbeatable. Read the reviews. The Starke gives you four channels (for bi-amping maybe?) for under $2000 while LKV wants $10k for two. Same super quality sound, no kidding. The secret is very high frequency "swtching" in the class D amp - 600khz. Try it, you will love it

I have heard class d and am not impressed at all i would look for a great vintage amplifier with a solid state ab output stage from a good company in that 2 to 3 k range you will get much better sound than a class d amplifier I have 18 amplifiers of that type and they all sound better than a class d amplifier.

2. Hopefully Ralph will weigh in but unfortunately I suspect @atmasphere is referencing his own Class D amplifier that is currently under development. I'm sure it'll be wonderful, but not yet available and perhaps outside your budget.

We are working on a class D amplifier which has reached beta production. Its intended pricepoint is about 5000.00/pair. Although I think our amp is doing quite well as far as being musical  is concerned, I was not talking about it specifically. I was more talking about how feedback is troublesome if improperly used (which is about 99% of the time). The Benchmark is an example of an amp that does feedback properly. Self oscillating class D amps are another example.


Feedback has gotten a bad rap and deservedly so because if you don't run enough of it (and that's been the case in the last 60 years), it will generate higher ordered harmonics and IMD at the feedback node (unless you are very careful about the latter). This causes harshness and brightness, and this is the main reason transistors are harsh and bright. If you run feedback in tube amps, they get harsher and brighter too (and this will be in spite of the fact that the frequency response is actually **flatter**, because the brightness is caused by distortion, not a frequency response error).

So we've seen designers, including myself, building zero feedback amplifiers to prevent this brightness and harshness. You can think of the use of feedback as being on a bell curve, use a tiny bit and its not bad but doesn't do a lot, use more and the distortion issues increase (all the while suppressing the innate distortion of the circuit, so it will measure well but not sound as good as the specs suggest). But finally you get to the other side of the curve, which is at about 35-40dB (meaning that if the amp had no feedback, it would have to have at least 65-70dB of gain!). At this point there is so much feedback that it allows the amp to compensate for the distortion generated by the feedback, and corrects phase shift too.


One thing I forgot to mention is how distortion can increase at higher frequencies if feedback is insufficient. You really want the distortion to be the same regardless of frequency. Our OTLs can do this, which is part of why they are musical, and the smaller the SET, the more they can do that as well (this is part of why the lower powered SETs are held in such high esteem). To cover up this problem, the distortion specs you see are usually done at 100Hz! If you measure the distortion spectra at 1KHz you get far more meaningful information- look at what the amp is then doing at 7KHz, which is in the area where the ear is most sensitive (birdsong frequencies). The 7th harmonic is unpleasant! If you measure at 100Hz, the 7th harmonic can often appear benign. This is why many solid state amps seem to do bass just fine, because at bass frequencies, they really **are** doing just fine because there's enough feedback. But as frequency is increased, the amp can run out of Gain Bandwidth Product, which is a way of saying that the feedback is being reduced. This is a very common problem!


My experience with monostrapping and bridging amplifiers isn't good. The amps almost always get less musical (higher distortion). Lower impedance loads can be an issue as well because the current expected of the output devices might be exceeded, such as into 2 ohms- that leads to failure and shipping costs...


I miss Al as well. He was a friend, a good egg and always steady on.

Hi cal,
Yes, as we all recall Al was excellent with his (Always) clearly written, detailed yet easy to comprehend technical explanations. Bridging amplifiers is but one of many examples where Al offered  clarification and when necessarily caution. I learned much from him.
Charles

And thanks for channeling @almarg for the technical reminder about why the Benchmarks would struggle when in bridged mono mode.  It makes total technical sense, but is ironic that when configured to deliver the most power, they also lose the ability to deliver the needed current into low Ohm loads.  Unfortunately this is likely the exact kind of case in which one would actually need the additional power.  Watts are cheap... until they aren't.   

@charles1dad As @twoleftears suggests, my bet is on the AGD amplifiers as the most SET sounding class D design (GAN-based).  I'd love to hear them. 

They certainly want to convince us that they care about SET musical characteristics with the design, and one dealer advertisement states that SET people do like them (https://www.youtube.com/watch?v=2PKSlTODkJ0). 

Unfortunately more than double the OP's budget.

I thought Halcro Audio is no longer an active manufacturer and I may be wrong in that regard.
Charles

As the late (And great) Al use to point out , when you bridge an amplifier the speaker impedance load (As seen by the amplifier) is halved. So a 4 ohm load becomes 2 ohms and so on.
Charles

I wouldn’t deny for a nanosecond that there are listeners who would love the Benchmark sonic presentation. Every audio component has a "sound" or individual signature. In the past I recall similar declarations about the defunct Halcro amplifiers. Dead on accuracy and sonic neutrality with breathtaking bench measurements.
Charles

Depends how low the impedance of the speaker is. The Benchmark can do 500 watts bridged into 4 Ohms at .00026% distortion. If the speaker hangs around 2 Ohms they don't reccomend you use them bridged.

The Benchmark AHB2 doesn’t have a "sound" it’s one of the best measuring amps around. If your speakers and ears can take it you can push 120dbspl and the noise floor will still be -10dBSPL below. If there was ever an amp considered neutral it’s the AHB2.

@icherepkal,
I will 2nd your request of Ralph to identify these special SET sounding high NFB  class D amplifiers . I’m "genuinely" interested in who are the manufacturers capable of what I’d consider a very admirable feat. They deserve exposure and recognition. I can’t deny some may exist but I’ve yet to come across any thus far. Obviously I haven't heard every class D amplifier in existence. 
Charles

@lcherepkai 

1. I've also heard that about the Benchmarks. My impression is that they are not capable of handling low impedance loads, and (perhaps surprisingly) it seems this becomes more of an issue if you're running them as monoblocks. If you're thinking about them, I'd just reach out to Benchmark with your speaker specifications and ask about compatibility. From all reports they're great amplifiers. As Charles mentions, the comparison of this high- feedback amplifier typology to your SET experience will be very interesting. There are some used units around and I think you can get some new ones with free home trials, so it might be easy to find out.

2. Hopefully Ralph will weigh in but unfortunately I suspect @atmasphere is referencing his own Class D amplifier that is currently under development. I'm sure it'll be wonderful, but not yet available and perhaps outside your budget. 

Charles---I probably won't (ever) be able to swing the Mola Mola or Soulution amps but am interested in the Benchmark.  I'd be much more likely to seek them out if the used price were lower though.  How did you feel about the Benchmark's sound?  I read a few comments about some incompatibility issues with some speakers?

Mapman---these Focus clones are a fairly good match with 805 based SETs.  The 45w is ample power for the most part.  I just get the itch sometimes to play lounge or dubstep or some brutal bass heavy ambient at un-neighborly levels.  With almost everything else, I never felt I was pushing the JAS hard.  My main listening was jazz and some blues so the volume was usually kept at reasonable levels.  With most other SET amps using other tubes, I would agree with finding the right speakers but I think it less of an issue with 805's.

articdeth---my appreciation of the SET I had was more based on it's pristine sound than tone.  With the right recordings, I was hearing the musicians in the room with me rather than a widow on to  the recording. There was just so much inner detail and (almost) nothing between me and the sound.  Almost every other amp I've used is veiled in comparison.  I'm looking for the transparency and detail I hear about in the best Class D amps without the common shortcomings.   The reviews of some of the First Watt amps sound like what I want, just much more power.

atmasphere---you mention that there are Class D amps you've heard that are very close to the SET sound.  Would you please offer a recommendation or two?  

Many thanks to all.  If I find what I'm looking for, I'll certainly share my experience(s).  

@atmasphere I appreciate your explaination and the educational post Ralph, but I will note that some listeners do find substantial differences between 2nd vs 3rd harmonic dominant designs (e.g., see the "Harmonic Distortion and Sound" section of this article: https://www.passdiy.com/project/articles/audio-distortion-and-feedback).

This even holds when the amplifier typology is otherwise held constant, e.g., when adjusting the front control on the First Watt SIT-1.

Ralph,
I understand that we humans hear the same in regard to neuro-acoustical physiology pathway or msechanism (Using higher order harmonics to gauge sound pressure and detecting harshness and brightness). I should have been more clear as I’m referring to individual taste/preferences IOW the subjective aspect.

You used the term "dry" and that describes how the 3 amplifiers I cited sound to me (Definitely a subjective judgement). Someone else may describe them as accurate and very neutral. This is the hearing/perceptive differences I was referring to.
Charles

I have a Sciit Ragnarok which I like a lot. It is probably class AB and I have not compared it to many others. Around $1.7k.

I’ve heard the Benchmark, Mola Mola and Soulution amplifiers (Examples of High NFB circuits) no SET sonic characteristics in my opinion. I don’t deny that many listeners loves these particular amplifiers and in fact I could be in the minority.

@charles1dad There is a reason that I mentioned the bit about the designer paying attention to human hearing rules (I didn't put it in quite those terms). If he's not careful, and does not permit the lower orders to mask the presence of the higher orders, the amp runs the risk of sounding dry. Now if you get the distortion low enough, this phenomena is reduced, but you have to get really low distortion numbers! 0.0001, that sort of thing. So if for whatever reason you can't get there, then you have to be sure that the lower orders mask the higher orders.

To give you more insight on this, almost any solid state amp has less higher ordered harmonic distortion than almost any SET. But the SET has a huge 2nd order by comparison, which tends to mask those pesky higher orders.


(Here's a fun bit: amps that make the 2nd ordered harmonic as their primary distortion component have what is known mathematically as a Quadratic Non-linearity. Amps that have a 3rd as the primary distortion have what is known as a cubic non-linearity. The difference is, if based on the 2nd the distortion harmonics do not fall off as quickly as they do if the 3rd predominates. Since the 3rd is treated the same by the ear as the 2nd (contributes to warmth and 'bloom') an amp that is based on the 3rd will still have a musical presentation, but otherwise will be perceived as being more neutral since there is less coloration overall (the 3rd will be slightly less than it is in an amp based on the 2nd harmonic) due to distortion. This is why I built entirely differential amplifier circuits, as the simple fact that they cancel even-ordered harmonics in each stage throughout the circuit caused it to have its major distortion component as the 3rd. Since distortion is not compounded from stage to stage, the higher orders fall off at a faster rate as the order is increased.)


Obviously the brightness and harshness of traditional solid state that we've heard over the last 50 years (and why tubes are still around) is a coloration too. I don't agree that we hear all that differently: all humans use the higher ordered harmonics to sense sound pressure and all human's ear/brain systems assign the same values of brightness and harshness to these harmonics when they are distortion. IME people express these differences out of expectations of what a stereo should be, if not sounding real. When you ask for the music to sound real, then (again IME) these differences tend to go away and people start hearing the same things.

Just out of curiosity, I went over to usam and looked at the amps for sale between $2000 & $3000. Not that I think they’re going to sound like a SET, but three I’d be interested in trying if I were in your situation were the Ayre V-X5e (200W), Modwright Instruments KWA100 (100W), and the Carver Crimson 275 (75-90W).

Lots of quality recommendations and educational posts in here. Good luck with the search. I was going to tell you about my efforts in the same regard, but I went from 8W 300b SET monos to a 25W First Watt PP. Moving from 45W to 100W seems like a tall order. My journey was difficult and I think yours will be harder, especially with the budget limitations. Please do post back with updates regarding the journey...

Pretty much any good quality SS amp of any design and modest power capable of handling a varying load would be well suited to drive just a pair of satellites with bass crossed over elsewhere, Class D included.

SET or OTF would not be my first choice in that those typically require easy impedance loads to do their best which may or may not be the case here. Only measurements would tell for sure. Push/pull tube would be a safer bet if you must use tubes. Good SS or class D should have no problems whatsover.

With SET or OTF, it is always a good idea to seek speakers that are specifically designed to work with those well. IT's a different paradigm.  Your choices will be more limited for best performance although subjectively any amp might still produce some good or pleasing results. Just not the best possible.

@icherekpal,
If you have an opportunity to hear amplifiers the subscribe to the high negative feedback (NFB) application as explained by Ralph, would you please share your listening impressions of them?

I’ve heard the Benchmark, Mola Mola and Soulution amplifiers (Examples of High NFB circuits) no SET sonic characteristics in my opinion. I don’t deny that many listeners loves these particular amplifiers and in fact I could be in the minority.

Given your very happy listening experience with the JAS Audio SET I wonder what your take would be. I in no manner dispute Ralph’s technical explanation, rather just relating my listening experiences. There's absolutely no doubt that we all hear things differently. 
Charles

It was just more detailed with subtleties that increased realism beyond anything else.  That's what I'm asking about in a possible Class D replacement.

Speaking from experience, the right class D amp can do that. Class D has as many variations as any other type of amp does, so just because one class D might not bring home the bacon says nothing about another.

If your used to your SET tube sound, no class D will ever match the tone.

Again, speaking from experience, I've not found this to be the case. The main differences we hear in amplifiers are two-fold: what is the distortion signature, and how flat is the frequency response.

SETs generate a lot of distortion. At full power its typically 10%. If you're really serious about using one, your loudspeakers should be efficient enough that the SET is never asked to make more than about 20-25% of full power (this will limit the higher ordered harmonic distortion that causes them to sound 'dynamic'). It should be noted that the dynamic nature of music should come from the recording, not the amplification!

Now the advantage of SET is that as power is decreased to zero, the distortion drops to unmeasurable. This is the source of that 'magical inner detail' that so many talk about. Put simply, its that First Watt that is actually very good (unless you have a type 45-based amp, in which case it will be that first 100th of a watt).


But SETs by no means rule the roost in this regard. Our amps have the same property of linearly decreasing distortion. Our amps are push-pull; that sort of quality in a push-pull amp is rare! But there isn't some sort of pixie dust that allows for it; you simply have to be aware of how amps make distortion, and what distortions are going to be heard by the ear. Any zero feedback tube amplifier that is fully differential from input to output will have this quality.


Let's talk about the lower ordered harmonics for a moment. Its the 2nd order that makes SETs have that ever-lovin' tube sound- it give the amp a rich, warm quality and assists the ear/brain system in winnowing out detail and soundstage (that latter bit is IMO something that could do with more research as to why this is so). To this end, the 2nd harmonic is fairly innocuous. Other than making the amp a bit more euphonic, you don't hear it.


The 3rd harmonic has this same quality- the ear treats it the same way. The presence of the 2nd and 3rd in sufficient quantity can mask the presence of higher ordered harmonics to a certain extent. This is part of why tube amps sound smoother than a lot of solid state. But that isn't the entire picture.

The ear/brain system assigns a tonality to all forms of distortion. The lower orders mostly richness, the higher orders cause harshness and brightness even in tiny amounts. This is because the ear uses them to sense sound pressure and so has to be keenly sensitive to their presence.


This is why many solid state amps have sounded bright- its entirely due to the higher ordered harmonics making themselves known.


The problem has been feedback in amplifiers. If used in insufficient quantity, it will add distortion of its own while suppressing the innate distortion of the circuit in which its used. But- if you use **enough** feedback this will allow the amplifier to compensate for the distortion caused by feedback itself. Nelson Pass comments on this in an article he wrote about distortion. In it he speculates that you'll need more than 70dB of open loop gain (this is how much gain the amp has if there is no feedback). This is a very difficult number to achieve in traditional solid state amps since oscillation is a clear and present danger due to a phenomena known as phase shift. How that works is that at some frequency above the audio band, the phase shift of the amplifier starts to go up. When it passes about 90 degrees, the amp can use the feedback as positive rather than negative- and so oscillation can result. So many designers don't push their luck.

But Luck has nothing to do with it. Sound engineering does, and some designers have succeeded in making amps of this type. The Benchmark is one example.  There is another way to get around this problem. That way is to use a class D amplifier and use so much feedback that the amp goes into oscillation. But in this case, the oscillation is used as the switching frequency of the amplifier, so we're OK with that. Such an amp can have north of 40dB of feedback, allowing it to compensate not only for distortion caused by feedback but also phase shift caused by the output filter of the amp.


Once either of these approaches are achieved, its then up to the designer to understand how the ear senses distortion and how the ear's masking principle works. If he does this right, then he will see to it that despite the resulting low distortion of the amp, the primary distortion components are still the lower orders.


If he does this, the resulting amp will be smooth like tubes and will be extremely detailed at the same time. So you can get that 'magic'. The only downside is that any amplifier that does this will have a hard clipping character, so it will be important to have more than enough power to do the job- IOW you *never* clip the amp!


The flip side of this is to avoid using any feedback at all, relying on other techniques to control distortion. Do there you have it. You can have an SET which has no feedback, or a class D which uses a ton of feedback, and the two can sound surprisingly similar (although IME you'll hear more detail from the class D, and of course it will have more power)!

If your used to your SET tube sound, no class D will ever match the tone.
your better going more powerful tube amp, or a class A SS amp, or a nice class AB amp.

@icherekpal, 
Thank you for the kind comments. 
Charles 

jjss49--The Audiozone Amp1 is (if I understand it correctly) also a Peter Daniel's creation and is pretty much the same amp with dual front mount volume pots and it is really quite nice.  I keep the pots fully open and use the volume on my DAC.  I run into volume limitations occasionally and that's mostly the reason I seek something else.  It falls short of the JAS Array in some regards but I could live with it sonically.  

lalitk--these DIY/Legacy Focus clones are quite sensitive.  When going from the Von Schweikert VR 4 Gen II to these, I was shocked at how much louder these were than the VR 4's with the volume set at its customary setting.  And I'm thinking replacing these would be a huge P.I.T.A .  Getting something as good would be expensive and selling these....oh, easier to keep them!

geof3---i asked about the Pass xa25 vs the Gamut D100/200 recently as was told the Gamuts were quite a bit more transparent and the Pass were a warmer and smoother sounding amp.  No criticism here, I would just prefer the greater transparency.  I'm happy to use cables to adjust the sound as necessary

charles1dad---you're always a gentleman on these forums and offer good advice as well which probably puts you in the minority but I certainly appreciate that.  

brownsfan----still spinning aluminum exclusively so digital it is!  I'll look into the Lyngdorf.   Love it when I get concrete options.  Thanks

purest sounding lowish power ss amps i have heard in my system are jun kimura san’s 47 labs gaincard and related peter daniel audiosector patek se (which i have still kept) ... not sure they will do their magic in your specific application

but you definitely trading something away when you leave SET amplification