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And I mean purely sonic listening experience only.
Don't forget the newer class D
And let's take that one step further, how about between class A and tubes
Follow Ups:
It just depends. I use to sell Krell and Stax when I was a dealer and both were class a. I now have a CJ 350 and Gamut 200 which are the best two amps I have had. They are both AB
Hearing IS believing... either way... words are simply Hot air.
OK, I guess I'll bite on the original topic. I know this thread has wound up in east bumfukt Egypt somewhere but maybe ...
There is no discussion of single ended here because class A is the only way. So it is push pull.
What class A means is more bias. Some amps are only in class A up to a certain output. For true class A you need bias even at clipping. That means the amp will get hotter than if you ran it continuously on a sine wave at one third power. Why can't the new class A power amps do that ? Because they're not really class A. A class A amp dissipates the same power at idle as at full power.
Most of your amp is already class A. Biasing higher does eliminate some distortion, and provides better speaker cone damping, but that does not always make a huge difference.
I agree with (I forgot who) said about shifting the harmonic distortion to the higher octaves. The ear is alot more sensitive, that is why you can hear a piccolo in an orchestra with over 100 other instruments.
Having a high distortion design with alot of feedback to get rid of it can do just that. Because the gain is higher the feedback it higher. But then the feedback has to be limited somehow by frequency so the feedback cannot always be flat response. Flat enough, but not perfect.
The global feedback is not always capped off. Sometimes they use more Miller caps (or capacity) in the voltage stages. this reduces the open loop gain and the feedback is less because of it. This would also tend to shift the harmonic distortion to the higher ranges.
But power transistors usually have a terrible Hfe curve. And in push pull this causes odd order distortion. Biasing them harder helps. Just look at the datasheet for a... ... nevermind I would have to find two, one acceptable and one not ant it is late. Suffice it to say is that no transistor or tube is completely linear.
And you can build a tube amp with good damping, you just need the gain and know how to keep it stable using the output transformer. About a year or so later I am sorry I sold the pair of Chicago BO-15s. They had response into the subsonic. I could have built a hybrid to set the world on its ass.
And speaking of bias, at my last job (I could go back but the dude pissed me off ad I got a gig even closer to home now) I noticed some tube amps need bias adjusted or tampered with somehow. They were redplating. Some are old and people like them, but they say "110V" on them. Nominal voltage in the US is 125 now.
And the lowering bias (current) is not OK in a tube amp because the voltages are too high. It is over the ratings of the tubes, sockets and transformers. Luckily they were overbuilt, made to last. Well they might not now.
Single ended is always class A and favors even order harmonic distortion. the ear finds this more tolerable. One of the reasons is like, musical in a way. When you play one octave up on a musical instrument is sort of harmonizes. It is double the frequency. You play middle C it is 440 Hz. You play the next C up it is 880 Hz. You play them together it is pleasing to the ear. Even if you play a very low C and a very high C it is pleasing to the ear. But it is harmonious.
But if you play 3, 5, 7, 9, 11, and so forth, harmonics of the original note, that is not harmonious.
I think that is behind the allure of single ended. There might be a hair more distortion, but it doesn't kill you.
Never pooh pooh shit like this. I knew people who could not stand the LCD TVs. Something wrong with the color and bothered their eyes. Stuck with CRTs or bought plasmas, that is the two choices. Then I run across this old article says that some people can see a slightly wider spectrum. Hmm, whaddya think ? Not proven by any means but possible. Why not ears ? There are people out there who have perfect pitch and can tune a piano by ear. In fact how was the first piano tuned ?
The answer in the end (I wrote a song with that title) is that class A, all other things being equal, will be better. But true class A with the power (not green at all) and the heating of your components, I deem it simply not worth it. Maybe if you have a pair of Quad ESL-63s in perfect condition you might consider it.
Everyone is entitled to my opinion. Take it or leave it, or argue it or shove... no don't do that... LOL
It's not about if class-A is better, it's more about how much Class-A bias does one really need, IMO, this is determined by the speaker load being Driven ...
Regards..
it probably sounds the best.
I prefer Class BS myself!
You can run class A single-ended or push-pull whether tube or transistor.
So there is a lot of ground to cover here.
But to your question- 'yes' is the simple answer, and comes out of keeping distortion as low as possible.
The human ear converts most forms of distortion into tonality, and in addition has a tipping point where the tonality due to distortion can be favored over actual frequency response errors.
So keeping distortion down is pretty important if you want to have transparency, as distortion will obscure transparency due to the ear's masking principle.
You can suppress distortion by adding loop negative feedback, but its been well-known for the last 60 years that a price is paid for doing so! This involves the addition of higher ordered harmonics and IM distortion that did not exist in the amp otherwise. Of course they are at low levels, but the ear is much more sensitive to higher ordered harmonic distortion than even the best test equipment- it converts the higher ordered harmonic distortion into brightness and hardness.
This is why two amps can have flat frequency response but one might sound bright while the other does not.
Class A operation is one tool in the designer's tool box to help keep distortion down. In doing so, it becomes possible to build an amplifier that is more relaxed and more transparent. Of course there are any number of ways of mucking this up so that the class of operation becomes irrelevant. Much depends on the design!
A lot also depends on your goals. If the best reproduction is your goal then class A will be a part of the equation. If low heat is your goal then class D might be preferable, but it will not be the ultimate in reproduction although it might be quite good. So there is a lot to consider!
My opinion on this issue continues to evolve, as time goes forward and becoming more exposed to newer gear available.My current speakers are ATC-SCM19's (with outboard crossovers), along with sub-woofers. I've tried them with many different amp setups, from class A SS mono-blocks, to various class AB SS pre-amps and power amp combos, and high powered tube setups. Each setup has it's own strengths and shortfalls. Based on the aforementioned gear, the tube amps provided the most enjoyment overall with these speakers. The tube gear with the ATC's really brings out many of the best traits of the speaker playback.
About six months ago, auditioned a pair of Class D mono-blocks and the matching pre-amp (Primare A32 preamp and A34.2 power amps). At the same time, picked up a Benchmark DAC-2. I had never been enamored with class D amps overall, but I have to admit, this combination with the ATC/Sub combo is outstanding. Totally changed my previous outlook on class D amps. The difference was VERY noticeable with all types of music, but especially noticeable with complex symphonic music. Dynamic contrasts, ability to hear low level detail cleanly is remarkable. Easily the closest I've been able to come to replicate a live performance. This is extremely difficult to achieve with classical symphonic music, but this setup at least comes somewhat close.
There are a couple of items at work here. One of them is the fact that the ATC speakers need lots of power to sound there best. At 550 watts, clipping is not an issue. I have become a big believer in having lots of power on hand to avoid distortion/clipping. There was article posted some years ago that Bob Carver measured how much power it took to reproduce the sound of scissors, and it took some astronomical amount of power to play it back cleanly.
Another item is the fact that this version of class D (UFPD) sounds very good overall, and gets out of the way to allow the system to reproduce the music. If one just listened to the playback without knowing what the gear was, one would not pick up on the fact that the power amps are class D.
Lastly, there is a synergy with this combo that the sum sounds even better than the parts. The Benchmark DAC-2 is easily one of the best DAC's I've ever heard, and makes the playback sound that much better.
In summary, I think the amp needs to have good synergy with the speakers, regardless of design class.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
Edits: 06/28/16
Its something I've harped on for many years, as you might expect an OTL manufacturer to do :)
Way back in 1974, John Meyer (www.meyersound.com) was working on a high quality high output loudspeaker. In one of our sessions where he'd talk to me about speaker design, we got into speaker/amp matching. He said, and I quote: "It's a SYSTEM!". Truer words were never spoke.
:)
he moved there so he could stay with his girlfriend. He's been with Meyersound for the last 18 years.
This is not *effectively true* unless the amp is able to drive the speakers cleanly. Right?
-
I guess this brings us back to the major issue: Amp/speaker synergy. Every amp manufacturer should provide a list of recommended speakers.
...or the other way - call your speaker manufacturer for a list of recommended amplifiers.
Not practical. Speaker manufacturers just quote power ratings required and are not concerned with different class of amps.IMO You can not beat a well designed class AB amplifier as I have already posted for reliability sonics & cost.
class AB amplifier as I have already posted for reliability sonics & cost
Cost is all over the place...even for Class AB transistor amps (like D'Agostino Momentum for example or darTZeel) so I really think you cannot generalize this point.
Sonicswise, they are also all over the map...from wretched to ok but nothing special.
Cab, From wretched to OK .... LOL ,
I'm sure the same can be said for any genre of amplifiers , many tooby sound Meh to me, only SET's hold corn.
True, many tube amps sound MEH...even some SETs ;-).
You might like some push/pull triode amps though.
Having a GM70 SET built , similar setup to the Lamm ....
Sounds good. What are you using as a driver ? Interstage transformer? What for an output transformer? Silver wire wound? Single output tube or PSE?
I thought your speakers were not really SET friendly? Did you get some horns?
Speakers are similar to Scinnies load wise , but hybrid in the bass, it's a 4 tower setup , pure 2 way ribbon down to 240hz. I'm looking into doing a horn for the first time in 38 yrs something similar to DDK's but smaller in scale.
Amp will be single tube (true SET) trannies were going to be silver via AN, but they would not do a 2 ohm tap , so I'm sourcing from another.
Regards ...
You're gonna have to 'splain to me what "Scinnies" are.
:)
Living in Audio Sin ..... :)
The way that Duke LeJeune of Audiokinesis speakers has tried and highly recommends Ralph's Atma-Sphere OTL amplifiers...
Edits: 06/28/16
"Every amp manufacturer should provide a list of recommended speakers."
I won't argue with that.
If the user is uneducated and doesn't possess the knowledge to determine (for himself) what loads are appropriate and which one's aren't (for a particular amp circuit) then the list would be imperative.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
And, of course, the most helpful list would include speakers that have been evaluated for sound quality as well as electrical compatibility!
The thread post asked about the class of operation.
Asking about speaker compatibility is another matter altogether and one unrelated to class of operation!
However in general, if high fidelity reproduction is your goal, it is to your advantage to look for a speaker that has a higher impedance, regardless of the technology of amplifier (class D solid state or 300b SET).
The reason is that distortion is always lower driving a higher impedance. This can be seen in the specs of all amplifiers made. It is also audible since the ear converts such distortion into tonality. It is true that the difference might look slight on paper, but the ear does not care about the paper and simply hears the difference, and that will be that it will sound less detailed and harsher when driving a lower impedance or more complex load.
Its one thing to know that an amplifier can indeed drive such loads, but that is not the same as that same amplifier sounding its best!
Now if sound pressure is your goal and you have a solid state amp that can behave as a voltage source, a lower impedance will give you a little more output (not a lot; 3db more as the load impedance is halved) but the price paid is that the system becomes increasingly sensitive to the length and quality of the speaker cables.
So in general it can be said that speaker compatibility will be less critical if the speaker impedance is kept at a higher impedance; 8 or even 16 ohms.
Thanks for the comments anyway.
Why doesn't anyone seem to understand(you may just have written it poorly here) but SET is inherently class A. There can not be a class B SET amp.
"Why doesn't anyone seem to understand(you may just have written it poorly here) but SET is inherently class A. There can not be a class B SET amp. "
I, for one, don't understand. But then, I'm not an electronics guy. I'm a sound and acoustics guy. I know just enough about electronics to sometimes spot a good or a not-so-good electronics product, but I couldn't design either one. Only people who know about components and circuit design would understand. The average audiophile who doesn't work in audio only knows what they read in Stereophile or TAS (or on AA).
Ralph's post was very good - science oriented, not the typical "I like..." useless blather.
:)
And that's the problem. You need to know something about how things work and don't work. And the reviewers are like you; they often don't know. Other wise they wouldn't use redundant terms like SET class A or pure class where it's either class A or it isn't. Rich AB is good but it isn't class A. While how things work and measure may not be the whole story they often tell one a lot and are often warnings that what we hear is what we like but it may not be fidelity. In an imperfect world we need data and ears and the experience to use them together, a very rare commodity. A good example is Floyd Toole on speakers.
You mention Floyd Toole. I'll bring it back around to amplifier designers, since that's the topic at hand: John Curl, Charles Hansen, Nelson Pass, et al. These guys know the fundamental characteristics of components and topologies, and can design an amp six ways to Sunday based on the goals and price point. "Design the best damn amp you can!", versus, "Design the best damn amp we can sell for X thousand dollars!" Those are two different things, and even then, the more expensive amp doesn't mean it's the better amp. It'd be nice if they'd chime in to answer the OP's question.Channeling...
:)
Edits: 06/28/16
With regard to replying, John Curl said to me, "No. Why should I?" Ha!I swear, he's one of the most pragmatic people I've ever known. And, he's right.
What difference does it make? Most people have their preferences and/or biases set in stone, and no amount of talking/writing/discussing will change their mind.
:)
Edits: 07/01/16
51, Please don't project your personality on the rest of us. Some humans can respond to facts and evidence with change.
There is no audio Panacea, John , Pass , et al , know this better than most , if there were, everything would be class-A and be done already ..
My personal thinking is that the most attention should be paid to that first 0.1 to 2 watts output, since that's where a lot of systems are working most of the time. As an example, even though I can crank my lowly Dynaudio/Electro-Voice speakers to fill the house, most of the time I play them at a level where people can still talk at a normal conversational level, which means my stereo is basically slackin' it.The real problem with stereo systems, even after all these decades, is still the speakers. Can y'all say "10 percent harmonic distortion"? (Oops, there's another can o' worms!)
:)
Edits: 07/02/16
Agree on the 1st watt being important......
" is still the speakers. Can y'all say "10 percent harmonic distortion"? (Oops, there's another can o' worms!)"
Mostly low order and mostly in the bass where the hearing is far less sensitive. Probably makes the sound "fuller" than one without it.
With speakers it is still the problem with materials creating bending and breakup modes, storage and release of acoustic energy etc. rather than actual harmonic distortion from the driver non-linearities (they have gotten this part pretty good over the years).
Keep in mind that this kind of distortion is not the same type as generated by electronics, which have far more high order content in the distortion.
I once helped a friend by a stereo system. She (yes she) originally wanted a home theater but after we got a nice set of stereo speakers (AudioPlan Kontrast IIIi) she decided to have a good stereo instead. We auditioned many amps and some made the speakers sound truly and fundamentally different...not just a flavor change. The worst was the integrated Denon she already had...perhaps it was broken but the sound came out so flat, hard and aggressive as well as being stuck to the speakers that she was dumbfounded that it could sound so different. In the end she bought a SET (Cary CAD-572se monos) and a tube preamp (Transcendent Sound Grounded Grid, which I built for her) because that simply sounded far better with the same speaker and wires. She went from zero to SET cultist in one step!! She has very good ears (and brain) and it showed during her evaluations.
Distortion of the speaker itself didn't change but the distortion of the signal coming through it certainly did and it was easily (and sometimes painfully) audible. My guess is that the Denon probably measured just fine by objective standards (although I cannot confirm but it was probably 10 years old) but sounded like doodoo.
Quote :"" is still the speakers. Can y'all say "10 percent harmonic distortion"? (Oops, there's another can o' worms!)"
Mostly low order and mostly in the bass where the hearing is far less sensitive. Probably makes the sound "fuller" than one without it."
And that's why bass controls turnover at 100 Hz if you're lucky. They figure if you want more bass you want that tubby tone. Not me. Most rooms cancel out the lowest octave, it is that which needs to be boosted. What's more, a sealed cabinet is much better, even though it will inherently have less bass usually, the low end is not rolling off as fast.
The method of summing the output of the port and the woofer close miced does not give reliable results. They are not in phase. From what I have "heard" even the best of them suffer in a small room because to have to give them room to shake the air.
"With speakers it is still the problem with materials creating bending and breakup modes, storage and release of acoustic energy etc. rather than actual harmonic distortion from the driver non-linearities (they have gotten this part pretty good over the years). "
In other words, rattling. Just not rattling really bad right now. But you are right. Other distortion generated by the motor of the speaker should be pretty much gone now. In the old days they never expected the cone excursion of today. If they wanted bass they had to use a 15" woofer, some of the 8" of today can outdo them on low bass. And I do not mean one note resonant cavities, I mean something like a Boston Acoustics
A-70. And plenty others. I had the chance to audition a pair of Canton 10" three way system. I could not afford them at the time. The Bostons came closer than any other speaker I heard so I got those. Sealed system.Anyway, IIRC the Boston A-150s were 0.7 % THD at 1,000 Hz. Of course that is not the bass region but then any THD spec on a speaker is pretty rare. I do seem to remember that Quad ESL63s are rated very low in distortion and I mean less than alot of amps. I also wonder how the hell they measured it.
Edits: 07/14/16
Amplifier distortion can be measured but to hear it a set of speakers are needed, now you have a system, and the distortion of the system is strictly dependent on speaker distortion which usually are a several orders of magnitude higher than the amplifier.
Also, if you check out the specs of any high end speaker by checking manufacturers website you will notice that most specs exclude the lowest octave simply because those numbers are embarrassing.
Now back to Class A and the low distortion.
Vahe
I don't buy your argument vahe. I'm not sure I see the logic in it. One thing I do know is that millions and millions of audiophiles can hear that Class A sounds better. How do you come to the conclusion that because the speaker has more distortion that feeding it a signal with an increased or decreased distortion level cannot be perceived or isn't important? You are assuming that the level of distortion in the speaker is some kind of limiting factor. Tweaker
Edits: 07/05/16
"strictly dependent on speaker distortion which usually are a several orders of magnitude higher than the amplifier."
Maybe but the type of distortion and the distortion caused by the interaction of the amp and speaker are probably more detrimental to what you are hearing.
Surely you have had the experience of swapping out an amp on a pair of speakers and then it sounds almost like a completely different system? If you have then you are ignoring evidence that invalidates your comment above.
Or has every amp you have tried on a given set of speakers all sounded the same??
THAT is an excellent reply!
:)
And let's take that one step further, how about between class A and tubes
Some tube designs operate in class A while others are AB. Which simply determines the point at which the amp leaves class A. Don't confuse topological design considerations with the type of active device used.
With tubes, however, there are differences between pentode (or tetrode) and triode operation. Tetrode offers higher power output and arguably better response at the frequency extremes while triode offers better inner detail.
My VTL amps are switchable to either mode for optimizing output for different kinds of music.
IMO tubes are antiques, I dislike Class D even with Class A added ,easily best for me , well designed Class AB both sonically,& for reliability, my current amp is now over 20 years old, completely trouble free, same caps, and despite trying many many amps can not find one that sounds better, maybe as good but at rip-off cost especially for over engineered casework.
Edits: 06/27/16
Well designed Class AB amps, particularly the high power ones, are class A at about 10% to 15% power output and that is where most of music is anyway, even if you play it real loud most of the music will not need much power and you are well within Class A sound.
Vahe
That's a misunderstanding of how things work.It is true that in a Class A/B amp both devices are conducting the full 360 degrees at low power but there is more to the operation of Class A than that.
In a Class A design the devices are biased to idle right in the middle of the "sweet spot" (where the device gets real linear) they are then only operated in the sweet spot unless over driven.
With Class A/B each device is biased well below the sweet spot and each device (in turn) only reaches the sweet spot after the other device has turned off.
A Class A/B amplifier operates in Class A/B and a Class A amplifier operates in Class A.
The only thing that is the same between a Class A/B amp running at low power and a Class A amp is the fact that neither device is being cutoff but, as I said, there's more to Class A operation than whether or not the devices are being cutoff.
Many will argue with me about what is and what isn't Class A but a Class A/B amp running low power will not have the low distortion or sweet sound of a Class A amplifier because the devices are not running in the "most linear portion of the dynamic curve" and in a Class A amp the devices will be.
Just because the devices are not being cutoff doesn't mean they are running in the "most linear portion of the dynamic curve" and good practice is to run the devices in a Class A design in the "most linear portion of the dynamic curve".
So I guess a person could say that a Class A/B amp running at low power is running Class A but I don't think anyone could argue that they are running "good practice" Class A.
All the examples in the books that show Class A show the devices running in the "most linear portion of the dynamic curve".
A Class A/B amp DOES NOT DO THAT, ever.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/29/16 06/29/16 06/30/16
Very nice explanation and I am sure is a surprise to many here who believe manufacturers hype about "high bias" Class AB or running Class A for the first Xwatts.
Never get anywhere near the non-linear saturation region and never get anywhere near the non-linear cutoff region.
That's the true meaning of Class A and the examples of Class A given in all the books.
In the sweet spot and only in the sweet spot!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
John Atkinson of Stereophile has said that, at one time, he believed that Class A SS amps sounded better to him than other types of amps. He now says that he no longer believes that this is *necessarily* true and that various implementations in any amplifier design matter more than topology. After auditioning many different types of high-end SS, hybrid, tube, and other types of designs over the years, he changed his mind.FWIW, I suspect that amp/speaker synergy is probably the key to good sound. And since no one has the time and the resources to try every possible combination, we end up going with what we think sounds best after a limited search. Until we find something that sounds "better".
It could also be that, as our hearing and personal preferences evolve over time, we are prone to changes of mind.
Edits: 06/27/16 06/27/16 06/27/16
in 100 words or less.
Excellent!
"Once this was all Black Plasma and Imagination" -Michael McClure
(nt)
entirely on the power amp's design and execution and of course their prices plays a big role as well and will ultimately dictate the component's overall performance.Case in point, I have had McIntosh, Audio Research, Classe, Bryston and Krell to me all of them offer a certain house sound, however, I found that the more money you spend on any one of them the closer you get to the real thing, performance wise. For example, I had the McIntosh 7200 at one time and as good as it was but it didn't fare well against the McIntosh MC2KW power amp that I auditioned. The Classe CA 300 power amp was excellent driving the Theil speakers, but it paled in comparison to the Classe Omega power amp. When I had the Audio Research D90B I thought I was in heaven driving my KEF 105/2 speakers, well that didn't last long when I heard what the Audio Research D-250 could do.
Anyway, last month I was at my local dealership who happens to be a good friend listening to Wilson speakers and Audio Research new offerings. The Wilson Alexia speakers sounded scary real to me driven by Audio Research Ref 250 power amp and Ref 5SE pre amp. During the audition, I kept looking over my shoulder to see if there were any more speakers in the room. BTW, the KEF Blade sounding just as good driven by Devialet 400 monoblocks that my friend had in a 10'X19' medium size room.
I once asked a good friend about his secret of assembling one of the very best sounding stereo system that I've heard. He told me flatly; "there's no secret as all I did was poured money into it"...at least he was being honest.
If a thing's worth doing, it's worth doing well
(Proverb)
Edits: 06/27/16 06/27/16
Go and listen and find out. It took me four minutes listening to SET amp utterly trounce ever SS amp I had ever heard - and I have heard an awful lot of $50,000US+ SS amps. Class A no feedback Single Ended Triode. Since then I still have yet to hear a SS or Class D or tripath or or or that has sounded better. BUT with appropriately easy to drive speakers. All this gets chucked out the window when a tough to drive speaker is applied - that's why it's always a generalized statement within the parameters of the system.
Class A no global feedback SS amplifiers such as the Sugden A21a can certainly sound better than certain class A/B push pull tube amplifiers. The Sugden is one of the only truly nice sounding SS amplifiers available regardless of price. There is a reason it is the longest selling SS amplifier in history and continues to sell 45+ years later - next year I believe marks its 49th or 50th anniversary. But the Sugden is basically a SET amp without tubes. Single Ended "Topology" (SET).
I agree. Given a reasonable load, SET amps will sound lively, harmonically saturated and beautifully natural (no artificial edge to the initial attack of he note), while also being very nimble and "fast" sounding. By comparison, most of the solid state amps I've heard sound lifeless and bland and most also have an unnaturally hard edge to the sound. People talk about grainy quality to solid state, but, with most good solid state amps I am not bothered by grain; I am most bothered with how dead and uninvolving the system sounds unless it is played at higher volume than I feel I need to play tube gear.
I agree that the Sugden amps sound pretty good for solid state. I also heard a Lavardin integrated amp that sounded good for the money. I had a friend's First Watt amp in my system for two weeks and it was a nice, lively sounding amp with only a slight edge to the initial attack.
While I like SET amps a lot (I own an Audio Note Kageki), I also like low-powered pushpull amps. The amp I am currently running is a pushpull 349 amp that is terrific sounding in my system. This weekend, I heard an extraordinary pushpull amp that utilizes the 271 tube (I am lucky, I think, that it is so out of my price range that I am not that tempted). I have also heard fantastic OTL amps.
totally agree with the above posts. used with the right speakers, SET tube amps beat almost everything. sound like real music, not a synthetic hi-fi approximation.
SET ...!!! Cant disagree haven't been disappointed by one yet.....
Hi Airtime,
Vacuum tubes can be operated Class A, AB, or C as well as solid state devices. I would expect that if someone put his mind to it, a vacuum tube Class D amplifier could also be made.
RCA designed a vacuum tube low level modulated Class C AM broadcast transmitter. They called it an Ampi-phase. I think conceptually is is somewhat similar to a class D amp.
Phil
My experience has been that the sonic benefit of (competently designed) tubed circuits over ss is far, far greater than that of class A over other classes.
Jeremy
hasn't McIntosh been class B forever?
That would be a real surprise to me, AFAIK you can't get low distortion in class B, hence class A/B is typical, with A being the most expensive and hence the least popular.
Most amplfiers operate in B , class a/ab means just that , the first few watts in A ( typically 1-5 watts ) then the rest in class B. High bias A would go as high as 25 watts class-A and really serious class-A may go as high as 100watts . The older Krells like the KSA-200 was biased to 200 watts class-a at 8 ohm and it yanked 1400 watts from your wall outlet idling. At the opposite end amps like McIntosh operates in mostly class-B as they are Biased at only a few watts , typically 5 watts of Class-A bias and these pull typically 120 watts idling ..
Now 5 watts class-A may sound small but in domestic rooms and on speakers of avg sensitivity (86db) Most are only using 1-2 watts rms playing music at moderate levels (80-82db avg din) with peaks exceeding 100 watts on music with high crest factors, So its enough to take care of the quite stuff and that important 1st watt . Now increase avg din to 88 db and its all class B with only the really soft and quite stuff getting into class -A ..Hence why the amt of class-A necessary is really dependent on load being driven , if 4 ohm nominal speakers are being used you only have half as much class -A bias as you do at 8 ohm and if 8 ohm high sensitivity speakers (93db up ) you stay in class -A at much higher levels and leave only on peaks ..
Regards
Edits: 10/16/16 10/16/16
I have a rare Mexican made all-analog 5.1 channel preamp operating strictly in class A with no feedback. It is feeding Outlaw M200 monoblocks, which operate in A class up to 70watts, before switching to AB mode. This combination feeds five full range Thiel speakers.
This is the only solid state system I have ever owned (many, as well as many tube systems)that sounds completely nature, and in many was better than an all-Audio Research system that I used to have driving Thiels.
Whether or not the A mode is intrinsically better, a superb implementation of it surely gets us closer to reality than a lot of other configurations.
Harry
NO- they are classed as AB-1, where the output tubes run in class A up to about 25% of rated power then the amp suns in AB-1
Happy Listening
I think the are all class AB.
Dave
...it really depends on the total design and implementation.
Class A, if implemented well, should sound the best.
Some of us believe that feedback is a sonic no-no. A "can of worms".Directly heated tubes have the lowest inherent distortion of any amplifying device.
Class A is the most linear way to run tubes.
So therefore Class A direct heated tubes is the best way to keep the harmonic distortion low in a amplifier without resorting to the use of feedback.
This leaves you with relatively low output power so high efficient speakers must be used.
That's a can of worms.....everything is a can of worms....... :-)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/26/16
Yes indeed Tre'
But it is not just belief it is also strongly pointed to by psychoacoustic data.
Of course there are so many designs out there and many of them poor that this gets lost somewhat in poor execution. A well executed Class A push/pull amp will sound better than a poorly executed SET. But a properly designed SET has a higher potential in sound quality.
Why is SET 'better'? It is certainly less linear than push/pull.
type of distortion (harmonic pattern) is suboptimal with push/pull due to even order cancellation. Additionally, most A/B and A PP tube amps still use negative feedback that further pushes the harmonic distortion pattern further away from an optimal pattern.
So, more distortion, usually, but the pattern is less optimal.
No amplifier is linear so the pattern becomes paramount with regards to audibility.
But SET amps compress the negative half of the signal relative to the positive half. They aren't even symmetrical in their amplification
My 'best' amp for me is a non feedback, triode, push/pull amp and preferably with high power(leaves out SET) to handle even massive peaks. The Berning BA150 comes close to this. If I accept feedback then the Melos amps come into the picture.
I think this is primarily problem when you are pushing close to clipping...
Nevertheless, the ear makes distortion that is monotonic in pattern, starting with 2nd order and decaying exponentially with increasing order. The relative levels of these harmonics fluctuates with SPL but the pattern is always the lowest order harmonic has the highest level (2nd higher than 3rd higher than 4th etc.). This pattern is important for masking and what the ear/brain expects to hear from natural sounds.
Cheever came up with a metric that involves both harmonic distortion level and overall SPL. That metric gives the lowest (i.e. best) score the more closely an amplifier's distortion pattern fits what he calls the "Aural harmonics", meaning the pattern that is self-generated within the ear.
This is similar to what the French journalist/amp designer Jean Hiraga was claiming in the 1980s (I think it was then) about an ideal amp has a monotonic distortion pattern.
This was also tested by audio Journalist, Keith Howard, who actually added distortion digitally to a recording with a piece of software he wrote. He found that the unaltered file always sounded the best but that the one with a monotonic even/odd pattern with exponential decay was the least offensive of the added distortions. An all odd pattern (the ideal for a push/pull amp) was the worst sounding.
That is probably why a lot of the better sounding push/pull amps don't use feedback and don't have such good even order cancellation... because the pattern is important!
Obviously, high order harmonics that are caused when an amp is in Class B and the use of negative feedback resulting in high orders is an issue as well and standout to the ear as unnatural.
The only type of circuit topology that gives a monotonic pattern is single ended. Push/pull by design results in at least some, if not total, even order harmonic cancellation...this is not a pattern found in nature and our ear brain to some degree rejects this. Probably push/pull triodes sound quite good (I used to have a nice sounding VAC 30/30) in Class A because they are linear enough to not need negative feedback and probably the even order cancellation is not absolute.
I guess most acoustic waveforms in nature are also not symmetrical...where compression and rarefaction happen with different intensities.
`This was also tested by audio Journalist, Keith Howard, who actually added distortion digitally to a recording with a piece of software he wrote. He found that the unaltered file always sounded the best`
- Yes of course !
`but that the one with a monotonic even/odd pattern with exponential decay was the least offensive of the added distortions. An all odd pattern (the ideal for a push/pull amp) was the worst sounding. `
-Realizing this few simple facts many known and unknown amp designers was starts practicing the new type of modern art ,
`The Art of the Amplifier Voicing` :)
Regards !
__
"Art which does not have the appearance of art is true art."
- Old Roman saying -
My point here was mainly that those who claim SETs and other amps with a high 2nd order harmonic are "euphonic" are not correct in this claim.
SET's are different from all others, including other tooby's , there are many good SS amps that will match or better PP Toobs, nothing matches a good SET on the right speakers, well for acoustic instruments.If one does not listen to classical music and or acoustic instruments much, then there is no need to look at SET or PP Toobs in general...
Edits: 06/30/16
As long as you keep the amp in a comfortable operating range then the music can be as complex as you like and it doesn't get confused, compressed or glassy. This means you need a sensitive speaker and/or a small room.
If you go with lower sensitivity speakers, say 90db, then a 30 watt SET will work fine for complex music at moderate levels but not realistic concert levels.
I was able to get very good sound from a 30 watt SET on 84db electrostats because the drop to the listening position was only about 1db in my room. So to get in the mid 90s was possible without driving the amp to death, which was loud enough for me to easily enjoy classcial orchestra. Part of this was due to how well the system sounded with the SOFT parts of a symphony. I could set the lower end around 60db and then peaks to 95db were no problem. Most speakers just can't handle soft parts well until you boost them to where the peaks are now driving the amp to clipping. If the speaker can handle quiet passages without losing the sound quality (very few can do this even moderately well) then you don't have peaks of 105db at home, where most systems and rooms tend to be overloaded.
Was it the NAT or Lamm you prefered on Ribbons ...?
I have never heard NAT and LAMM on the exact same set of Apogees so it is not really possible to give a direct comparison.
KR Audio is far better on STudio Grands though than the Lamm M1.1. How an all Lamm would fare I can only guess...maybe the ML1.1 is really good on ribbons. My friend now has a Kronzilla SXi on his Studio Grands and a VA350 on his Acoustats (he liked my sound so much he basically copied the system).
The Lamms drove his Scintillas while he had them...it sounded not bad but not amazing either...Scintillas with a Sphinx Project 16 was significantly better sounding, IMO.
I never heard my NAT Symbiosis SE hybrid on an Apogee but I did try it on a pair of Relco Sinus One ribbon hybrids. That sounded REALLY good! I didn't buy the speakers only because they were too tall and wide and the WAF was maybe negative :). The ribbon was 1.7 meters long and was in a kind of assymmetric waveguide. The bass was on the bottom and integrated suprisingly well and went deep enough. This speaker was everybit as good as most of the Apogees I have heard and the NAT loved it.
I have heard NAT all tube amps on a pair of Apogee Grands. Really good sound overall.
Good one Banat ...:)@Morricab , you should try that Rotel , disbeliever sounds very Serious, i mean , really now everyone knows there's no way antique toobs can deliver ....
Edits: 06/29/16
What makes you think I haven't ;-)??
I have heard some Rotel gear in the past...can't remember what it sounded like...it was that (non) memorable.
Rotel gear sound pretty good for what it is.I'll keep my DIY SET 300b amps. No holds barred LCLC B+ supply for the finals with Electra Print partial silver single secondary OPTs, separate LCLC feeding a CCS into VR tube voltage regulated power supply for the driver tubes, driver tubes CCS plate loaded......line stage is a AVC, the DIY phono pre is no holds barred LCLC B+ feeding a CCS feeding VR tube voltage regulated and the 6sl7 and 5687 are CCS plate loaded, passive RIAA EQ.
The Rotels are OK but please........
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/30/16
No pic ..? Sounds like a beast , will it drive a 1.5 ohm load ...
Edits: 07/01/16
Here's a picture of one output stage. The other is below it. The driver chassis is there to the left. The power supply for the driver stage is not shown.
No, they won't drive a 1.5 ohm load but then again I don't have any 1.5 ohm loads.
They drive my midranges and tweeters in a biamped system using SS to drive the JBL 2231 woofers crossed at 200Hz.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Very nice.
I have a very interesting amplifier at home right now, the Aries Cerat Diana. It is a 110Kg monster that uses the 813 DHT pentode wired in triode. The driver and input tube are both 814 DHT pentods wired in triode. All are liked up through interstage transformers that are amorphous double C cores. No coupling caps. Sound is incredibly smooth and liquid but with stunning inner resolution and texture.
The power supply is using 3 of these 3kg super caps, SS rectification and I think 6 chokes for filtering.
That looks like a very serious amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I wouldn't be surprised if these theories of harmonic distribution have validity. But I believe that dynamic linearity, accurate changes in level from micro to macro may be the most significant factor in sounding 'real' and an amplifier that must compress the negative half of a waveform can hardly be called linear. Add that SET amps are very low power and peaks in the great classical music can easily top 30 dB and that adds more compression.
In deed the Berning BA150(really about 225 watts by the way) sounds best in its highest distortion(no feedback) format because in spit of added distortion that's where it's most linear.
We could go on and on. Obviously all distortion is bad. And with all the variants of amps there are various distortion combinations and to a certain degree we are now in a subjective region to a certain extent. I suspect that we differ in what we concentrate on when listening and the factors that most offend us are the ones we can't ignore and determine the amps(and other gear) we like the least. And that may be what makes this hobby fun, differences of opinion and that all gear is flawed in some way so we never reach audio nirvana which would be the end of our hobby.
"But I believe that dynamic linearity, accurate changes in level from micro to macro may be the most significant factor in sounding 'real' and an amplifier that must compress the negative half of a waveform can hardly be called linear."
While I would agree with you a zero distortion amplifier would be the ideal, no such thing exists. Therefore, you decrying this compression issue on one half of the cycle (and I think this is only an issue as you approach clipping) and claiming this is a worse problem than those generated by other topologies is not completely logical. One has to look at the outcome of what the topologies produce in terms of distortion products and how these affect human hearing.
For sure if you put a SET on a low impedance insensitive speaker you will get gross distortions that are easily audible. But if you let the amp run in its preferred power range then good ones that don't have transformer core saturation (a big problem with SET but also with many PP tube amps) will sound strikingly natural and uncolored. This is because then the distortion products are reasonably low in level but most importantly low in order and largely monotonic (most still have too many higher order components though). It certainly won't sound compressed despite what you think the scope is showing you.
I don't worry about low power as there are plenty of very good high sensitivity speakers on the market. Since there is no stereo system on the planet that I have heard that can truly do a full orchestra justice, I am not so concerned with reproudcing this kind of music at true concert level at home...it just can't be done by any system, anywhere in the world at this time...maybe someday, maybe not.
What I do care about is can it realistically do a jazz ensemble or chamber music. This is possible with a very good system and a SET with a good horn does it just about the best. Some planars with SETs, OTLs or a good push/pull triode amp can also get pretty realistic sound from this kind of music.
I am an analytical chemist, so making measurements is my living and I believe in analyzing data to reach conclusions. What the data is saying up to this point is that for what listeners generally prefer (it is always statistical...there will always be exceptions...such is the nature of humans) will be a pattern that "hides" in the ear/brain distortion and tone masking. This pattern is specific and the closer an amp gets to this pattern the more chance it has of sounding right to the largest number of listeners.
"
In deed the Berning BA150(really about 225 watts by the way) sounds best in its highest distortion(no feedback) format because in spit of added distortion that's where it's most linear."
I have yet to hear an amp actually improve when feedback was added on amps with variable feedback settings. Probably those that have a lot of feedback probably need the feedback just to work properly. In the Cheever thesis, he bypasses the feedback loop in a Hafler DH500 and gets something like 25% THD! With feedback I think it was 0.05%. So for an amp that is grossly non-linear without feedback then perhaps it at least makes the amp listenable. I would imagine a majority of Class AB SS and tube amps fall into this camp.
Funny enough, Nelson Pass shows how it is possible to make quite interesting, extremely simple designs with a few transistors that apparently sound really good. His SIT-1 and SIT-2 are the simplest possible amplifier...just 1 transistor. Very limited in power, but again high sensitivty speakers are now pletniful. I would love to hear this. Distortion is simple and acceptably low.
His white paper is interesting as he explores what happens when you add multiple active elements and then feedback to the distortion components.
Of course we cannot ignore execution of a design. This is where a lot of SETs fall short. Often there the output transformer is inadequate and saturates...this makes audible distortion of the "warm and wooly" kind. Often the driver stage is inadequate and distorts...and so on.
Same though for push/pull. That is why the VAC 30/30 is an intersting amp. It is Class A, makes around 30 watts, uses 300Bs and has variable feedback (0 to 6db). It is quite heavy thanks to the well proportioned output transformers and bass is deep, tight and controlled but well textured (no one note thud here). Mids are smooth and resolving with nice natural tone...same for the highs. However, in head to head competition with a number of SETs it is found wanting in realism...not easy to say why but the word coherence keeps coming up in conversations with friends about it ( I used to own it as an experiment, I sold it to a friend who sold it in favor of a KR Audio and then to another friend who has now relegated it to a second system in favor of 845 SET monos).
We also compared against the Lamm M1.1, which is a Class A push/pull hybrid and considered to be one of the better amps with a transistor output. That also falls short in believability.
I haven't heard the Berning amps but would love to one day.
If you believe Morricab you will spend the rest of your life throwing money away buying different tubes & amplifiers never being satisfied and not enjoying the music.
If you are satisfied with the level of fidelity you have achieved with your system then that is great for you.
I am actually satisfied right now listening to youtube and apple earbuds while at work but that doesn't mean I don't want maximum quality at home.
Morricab : I get maximum fidelity at home with my excellent system a well designed class AB amplifier with THD 0.005% @ 1 kHz , damping factor 200 at 40Hz can be considered blameless. I have been involved with many tests of speakers for comparing Live v recorded sound and the technicians involved would never consider using antique tube amps.
Edits: 06/29/16
I have no idea what you think is maximum fidelity but based on my experience to date all I can say is that I am doubtful of your claim. Very doubtful.
maximum fidelity means closest approach to live sound.
Now I am even more doubtful of your success.
"But SET amps compress the negative half of the signal relative to the positive half"
That's why using the most linear tubes in the most linear way is so important.
It's important in push pull amps also for, what amounts to, the same reason.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
but it's the topology of SET that causes the affect. Tube linearity can't fix it. Nothing can since the topology is set.
No it's the tube that causes the affect. Push pull masks it, but not entirely."Tube linearity can't fix it. "
More correctly stated "tube linearity can't be fixed". That's why it's so important to choose the most linear tube you can get.
If you load a DHT into a high impedance and don't drive it anywhere near the cutoff region or the saturation point you won't have much power but you also won't have much (if any) asymmetry.
All of the examples in the books of Class A operation show this type of operation, just using the "sweet, linear, center cut" of the dynamic curve.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/28/16
Sorry the asymmetry is there inherent in single ended topology. I checked with Nelson Pass who is a single ended fan and he confirmed what I knew. And in an imperfect world he did give the correct reason for using them. He likes the way they sound. I guess I just can't handle knowing that even a simple sine wave gets fouled up.
simple sine waves and all wave forms are always fouled up by amplification unless that amplification has no distortion.
I've never seen an amp without distortion.
and BTW this might just be semantics but the asymmetry is in the tube and SE has no way to hide that. Push pull hides it but not completely.
If you had a tube that could amplify in a truly symmetrical way then the output from a SE amplifier would be symmetrical. BTW a lot of preamp stages and input stages in power amps are SE, even input stages in push pull amps.
In this graph the input swing is symmetrical but the output voltage and current wave forms are not.
If a truly linear tube was used then the output wave forms would be linear (symmetrical).
A 45 or 2a3 or 300b operating only in the sweet spot in the middle (input signal limited) of the most linear operating condition (idle current, plate voltage, load impedance) are very close to being symmetrical.
So again, the tube used is what is causing the asymmetry in the output of a SE amp.
If you look at the output of each tube separately in a push pull amplifier you will see that same asymmetry.
A push pull amplifier combines the two out of phase outputs of the two tubes to form an output that looks symmetrical while at the same time creating other problems.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
This would suggest then that a single ended MOSFET or bipolar transistor would be even less symmetrical than a triode because their curves are actually far less linear than the triode.
If one wants a linear (low distortion) amplifier one has to start with linear parts.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi Tre',
Can you offer any reason why directly heated tubes should have less distortion than indirectly heated tubes?
Phil
DHT tubes being more linear comes from a geometric advantage; less spacing distance between the electrical internals.With an array of separate heater wires, the rigging to hold them, the necessary separation from other elements to avoid shorting, and other tolerances, the tube internals require and are designed to have more separation than the DHT.
The DHT, without the need to maintain additional separation, is designed so that the cathode, grid, and plate are in very closer proximity.
Edits: 10/13/16 10/13/16
Well, no.But the plate curves clearly show that you can find an operating point (or several for tubes like 45, 2a3, 300b, 845, 211, etc...) where the spacing between the grid lines are even, left and right along the load line from the chosen idle point.
I can't find any operating points for a 6as7, triode wired 6l6, 6550, KT88, EL34, etc.... where that would be the case.
The grid line spacing always gets larger going to the left from the idle point along the load line and smaller to the right along the load line with all those tubes.
When the spacing is not even the plate voltage is not moving evenly and the output wave form will not be symmetrical, top half vs. bottom half.
That's the cause of harmonic distortion. (or more properly said, that is harmonic distortion)
With DHTs the spacing is (comparatively speaking) very even.
I'm sure someone can tell you why DHTs are more linear than IDHT/triode wired pentodes, but I can't. I just know that they are.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/26/16 06/26/16 06/26/16
Hi Tre'
I will have to concede that it may be hard to find an indirectly heated power triode with the beautiful curves of a 300b but I doubt that it has much to do with directly heated vs. indirectly heated. A 12AX7 has some very nice curves. Granted it is not a power triode but it is indirectly heated.
I'm guessing that power triodes were largely being displaced by pentodes and beam tetrodes as indirectly heated tubes were getting more common.
Phil
Interestingly the EL 509 and EL 519 tubes when the screens are driven(Berning BA150 and Melos amps)exhibit extremely good triode curves. The Melos amps were rich class AB amps, about 25 watts class A with loop feedback. The Berning was almost pure class B with variable feedback(it sounded best with no feedback). Both companies' amps were excellent sounding.
"A 12AX7 has some very nice curves. Granted it is not a power triode but it is indirectly heated. "
Yup, the 6sn7 at 14ma 200vdc plate is just about as linear as anything gets but none of the indirectly power tubes come close to the DHTs.
Well.......maybe the 6a5. It's build just like a 2a3 with a W filament but in the 6a5 it's a heater with a tiny cathode tube around it.
I think that indirectly heated power tube is just as linear as it's 2a3/6a3/6b4g cousins.
So i guess the answer to the question is, it's in the physical layout of the way that they are made.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Interestingly, the 813 power pentode is VERY linear when strapped as a triode but it is a directly heated pentode...so there is that directly heated thing again.
Perhaps direct heating is more uniform on the filaments and as a result of a greater uniformity of heating the result is greater linearity??
"Perhaps direct heating is more uniform on the filaments and as a result of a greater uniformity of heating the result is greater linearity??"
I understand what you're getting at but.....
The electrons don't go from the cathode/filament to the plate.
They go from the cathode/filament to the electron cloud and then from the cloud to the plate.
So i think that alone means there is uniformity regardless of structure differences but I don't know!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Well, it is not a static system, unless there is no signal applied to the grid, and so I can imagine emission densities higher in areas where the heating is more efficient and uniform and the extraction therefore being smoother and more linear when it is directly heated.
Just trying to think about it mechanistically as if i were an electron being emitted :).
I could see also maybe that a direct heated filament is hotter towards the center of the length of wire and maybe then the electron dispersion is different...there might even be some literature on this somewhere (probably too old to be on the web though). I bet some old East European tube guys have some idea.
OK,
Check out these monsters. I have some of these and some UTC output transformers.
If I can stay on top of the grass long enough, the plan is to make a pair of class A push-pull amps with these tubes.
Phil
Harder to find but the 6337(not 6336) tubes were beautiful, relatively high power triode output tubes also. And they were jus beautiful to look at.
Yeah, those curves aren't bad but still not a match for a 45 or a 2a3.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Nonetheless, the 6C33C can be used to make a VERY good sounding amp. Perhaps the advantage of having far less windings in the output transformer outweighs a bit of non-linearity from the tube itself. Afterall, the output tranny is a big source of non-linearity in many tube amps.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
yeah I recall asking a friend who built PP triode amps how good thee 300B was one day and was surprised when he said he'd give it a B+ saying he preferred the 2A3 a lot.
A big part of the 300B rep I believe came from the Western Electric 300B which was built so well because it was designed to be buried in the ground for long distance amplification and forgotten for 10 years.
I've been down the high efficiency speaker road. A slippery one with many curves.
I like the way class A amps sound the best. I like the sound of tube amps in particular, thus tube amp designs in class A are my favorite so far .
I don't know what it is about ICE amps and Class D etc, etc.. but I just don't like them as much as class A or even AB amp sound. I don't know if this correlates with anything measurable like distortion.
How do you know that it is the output operating class that distinguishes the amps from all of the other aspects of design that sets them apart from each other?
You can't know.
But, everything else being equal (and they never are) the Class A design will have less inherent harmonic distortion and therefore can be run with less (or no) negative feedback.
So I would say if you have a Class A/B design that's really good (the designer really knew what he was doing) then if that same designer took the same care and designed a Class A version, the Class A version should be better.
But in the end you can't know.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
And yet I heard the Berning BA150 with variable feedback and it sounded best with no feedback where the harmonic and IM distortion were highest and the frequency response from the speakers the poorest.
The VAC 30/30 also has variable feedback and it is strongly preferrble to listen to it with that setting on Zero.
That said, as good as it is for a push/pull amp, it gets beat everytime against good SETs.
And yet a good push/pull amp is probably more linear than an SET due to the non-symmetry of SET output into reactive loads like speakers, which is the source of the high second order harmonic distortion in SET amps.
By the way, more for trivia, the BA150 is a class B amp, with about as little class A bias as anything. And it sounds very good(it is a triode hookup of the EL509 tubes).
And yet a good push/pull amp is probably more linear than an SET due to the non-symmetry of SET output into reactive loads like speakers,
Not subjectively and not as long as neither are overdriven into a compatible speaker.
I had one of the better push/pull triode amps, the VAC 30/30, and it was handily outperformed by several good SETs that I and my friends had on hand. I bought to try out the theory that a good push/pull triode amp would be as good or better sounding than a SET but sadly it just wasn't to be and I found the VAC better than just about every other PP amp I have heard, tube, hybrid or otherwise.
That means you like it more, totally valid. which amp is more linear is another question. and, of course, mu comments can apply to me too.
It also depends on how you like sound. I recall Gordon Holt telling me he was bothered by audio people always wanting smooth sweet sound when reproduction wasn't always that way. He hated systems that made brass pretty saying real brass blared at you. I'm not assuming what kind of reproduction you like but this is an example of how much things can vary in audio.
"which amp is more linear is another question. and, of course, mu comments can apply to me too"
Linear with regard to what? An oscilloscope or a listener? The two requirements are not equivalent and it is a fallacy to talk about accuracy with regard to what a meter says without the all relevant correlation to what listeners find more correct.
Absolute numbers are (almost) meaningless unless put into the context of what they MEAN to the listener.
Obviously if 90% of listeners prefer a given sonic pattern over others that means there are still 10% that for whatever reason prefer something else...that is nature of the beast.
"I recall Gordon Holt telling me he was bothered by audio people always wanting smooth sweet sound when reproduction wasn't always that way"
I would more or less agree with him and good SET doesn't sound only smooth and sweet regardless of the recording...there is very good contrast between recordings of different quality. What good SET doesn't do is exaggerate defects on the recordings that often have flaws in the high frequencies, which is right where a lot of so called "detailed" electronics have similar flaws.
"hated systems that made brass pretty saying real brass blared at you"
Depends on how far away the microphone is from the horn actually.
I like a very wide range of recordings from big bombastic classical symphonies to single instruments to driving rock to all types of Jazz and even some electronic music.
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