Power output of tube amps compared to solid states

I'm having a hard time trying to figure out how tube amp power output relates to solid state power output. I've been looking at the classifieds for tube amps and I see lots of tube amps with 50w or 60w output, but nothing close to the 250w output typical of solid state amps.

So I have no idea what type of tube amp is required for my set up, right now I'm using totem forests with a required power rating of 150w-200w at 8ohms. The bass is so powerful on these that I have the sub crossover set to 40hz.

My question is, are tube amps so efficient that 50w from a tube sounds like 150w from a solid state? Or will 50w output from a tube severely limit how loud I can play my speakers? If so, are tubes usually meant to be driving super-high efficiency speakers?

I had previously tried a tube pre-amp with a solid state power amp (both musical fidelity) and didn't like the results because the imaging suffered greatly, even though the music sounded nicer from a distance. Now I want to try a solid state pre-amp (bryston) with a tube power amp (no idea which brand to look at), but I don't know how much power output I need or if it will even be possible with my speakers. Does anyone know what I would require?
I have wondered the same thing as I am looking to replace my 175wpc solid state amp with a tube amp in the 150wpc range. I have been told that tube amps sound a lot more powerful than solid state amps. Why, I don't know.

A tube amp can typically 'sound louder' than it's specified wattage. There is no hard and fast rule on this as it can depend on how 'soft' the power supply is, the output stage topology (PP versus SE, Class A versus Class AB) and how much voltage the driver stage can swing.

An example is the venerable Dynaco Mark III monoblock. Though specified for 60W, it can actually do short bursts of 100W.

Another example - I once had a pair of SE EL156 amplifiers good for maybe 20Ws. Up to really loud volumes, it could keep up with my 250W solid state volume. Then it would start to clip... not in a nasty way, but the bass would get sloppy and the sound would start to gently compress.
I have owned several pairs of Dynaco MKIII monos and I have never heard of a Dynaco MKIII producing 100 watts.

Also, these 20 watt single ended amps that keep up with higher powered amps only do so on efficient speakers when everything is just right, but all it takes is a power hungry crossover and the little amps fall apart.

To be realistic, a 100 watt tube amplifier will drive most any speaker.
While there are no universal absolute rules, a common difference between tube amps and solid state is the manner in which they clip.

Many solid state amps clip harshly. The peaks above max output are flat-topped with a square-wave like edge. This generates a lot of higher order harmonic distortion that sounds harsh, metallic or edgy.

Tube amps generally have softer clipping when over driven. Since this is more pleasant sounding, it gives the impression of more power since you don't hit a brick wall.

Of course, there are a ton of variables to consider. The main ones are how loud you listen and the efficiency of your speakers. While tube amps have a devoted following they are not for everyone. Make sure you can audition an amp in your system before you commit.
tubes have high output impedance so they need transformer to convert its output voltage into current to drive nowdays speakers. hence the power of tube amps become less 'visible' to the lower frequencies due to the transformer limitation. this yields that they sound louder per given power because they do not spend their power onto the subwoofer frequencies as solid states do.
other than that power can't be solid state or tube it's just a product of voltage and current.
Sorry, Marakanetz, that explanation is not correct. First off, not all tube amps have output transformers. Mlsstl put his finger on the issue- odd ordered harmonics.

Smooth clipping is less odd-orders. Music is a very transient sort of waveform- when the transients clip the amp (even though the rest of the waveform does not), this will be a major factor in what separates the tubes from the transistors, **not** low frequency bandwidth. Odd-ordered harmonics are used by the ear/brain system as loudness cues; the transistor amp overloading on transients will be sounding very loud, whereas a tube amp might still seem to be asking you for more, without the associated harshness.

This is why guitar players prefer tubes as well.

BTW the difference between 250 watts and 100 watts in only about 4 db- not that much to the human ear.
The why rather than the how:

1) instantaneous power as it relates to distortion. In a very short increment of time, tubes can put out a lot more power than transistors or FETs for a given distortion level. This has mainly to do with electron mobility being a zillion times higher in a vacuum than in doped silicon, not to mention asymmetrical drift velocity issues in silicon. But I'll digress here. This is why 'soft clipping' is possible.

2) overload recovery of tubes is much better than solid-state. This is a follow-on to #1. After a transient, there is no reactive impedance to charge recovery in a vacuum like there is in semiconductors. This prevents frequency domain disruptions in tubes (the messing up of harmonics). This is the main point Lavardin has tried to resolve with their own solid-state devices.

There are other more-minor factors mired in the nitty gritty of device physics but these two are the most important, as I see it.

When it comes to steady-state signals, the power levels ARE the same if the Watts are the same. But music is most definitely NOT a steady-state signal. Nearly all measurements and graphs you will see on the performance of an amplifier are based on steady-state. These cannot be used to accurately explain transient phenomena. They can give an overall indication of performance ability, but nothing more. This is why many people believe measurements do not describe how a component actually sounds.

Getting back to the post, efficiency is a separate issue from power output. For Forests, a 50 or 60W tube amp will be great. We had a 55W Cayin on a pair for a long time and it was wonderful. Their impedance is high so they do not demand lots of current, making tube amps the way to go with Forests IMO.

my due respect to your OTLs, they are money-no-object electronics for whoever can afford to spend extra $$$ for nearly twice larger amount of tubes per channel for the same desired output power vs. an amp with output transformer.

speaking of power compare in plain English, 100Wpc amp wouldn't 'reach' to 12" woofer... you wouldn't even see it's moving unless you crank the volume levels high; while 250Wpc amp would move the 12" woofer at the same sound pressure levels... so 4db also has diversified meaning towards full range.
Marakanetz, not to be on your case or anything but while we do go for as much performance as possible at the same time we take advantage of the vintage look to keep the overall cost down, making our amps affordable against similarly-powered tube amps.

The idea that larger woofers are harder to control is pure mythology and a common one at that. My speakers at home have dual 15" woofers per side and our little S-30 can put plenty of excursion on them.

The amount of excursion a speaker has can be extremely variable as all speakers have different damping requirements. IOW it is not the case that the higher the damping factor the better- in fact there are no known examples of any speaker needed more than a damping factor of 20:1, yet there are cases of speakers that need damping factors as little as 0.1:1 (usually these are designs intended for open baffle).

If the amplifier under-damps the speaker, you actually get excessive excursion rather than too little, and vice versa if the the speaker is over-damped.
Rrog -

I was talking 'peak' power, not steady state.


see the above for some measured performance.
I was talking 'peak' power, not steady state.
Unfortunately I don't believe this term has a standard definition or measurement protocol. As such, the measurement varies widely between those manufacturers who even bother to publish a figure.

What's the duration of the "peak" - is it 1 millisecond, 100 ms, 1 second, 10 or something else? What's the distortion level permitted? What frequency (frequencies?) are used for measurement, or is pink or white noise used?

Depending on the games that are played, "peak power" can be 30% or 40% higher than RMS or it can appear as a multiple of even 5 or 6 times the steady-state power.

Given all of those variables, many people believe the only value a "peak power" measurement has is for the advertising and marketing department.
I remember hear a 30 watt tube amp "versus" a 250 watt SS amp at a Stereophile show, simply to see if people coult tell which was playing in an A/B demo. I don't think the speakers were particularly high efficiency, but the difference in power was not in the least bit noticeable at fairly loud show room conditions - and yes, it was fairly easy to pick the tube amp.
Here's an interesting tale, at least to me:

I have a pair of Apogee Cepheus 6 ribbon hybrid speakers that I recently unpacked from the audio archive (aka the garage). While these speakers are not amp killers like the older Apogee full range planars, conventional wisdom has always been 100W minimum and 200W or more is better. I had been powering them with either a Krell KAV-250 or a Songraphe SA-400 - both worked well.

Just for giggles I hooked up my CJ Premier 11A tube amp @ 70 Wpc. Sounded great; sweeter than either of the SS amps, and to my surprise, better bass. Much better - bass was deeper and much better controlled than with either SS amp. Volume was very good; about the same as the SS amps.

OK, so why not push my luck? I then hooked up a GTA SE-40 40(or so) Wpc, and SET to boot. Well, it sounded pretty darned good as well. Sweeter even than the CJ, although not nearly as much bass. Volume was adequate but not hopping loud.

I would love to test these speakers with an Atma-Sphere M60. Ralph???
Br3098, try it, you never know- for sure it will work with a pair of ZEROs...
Ralph, I just might do that. It's a smallish room - I don't imagine that you have a quietized water cooling system perfected yet?
Acrossley; Just to chime in, power is power period. and power is defined as IxIxR or VxV/R or VxI. In any case, power is related to resistance only. But speaker loads are not only made up by resistance only but what is called impedance that includes resistive loads and inductive loads and capacitive loads. So, when you see an amp spec'd at 50 wpc into 8 ohms, the manufacturer is stating clearly that this amp will produce 50 wpc from a particular input voltage (input sensitivity) into an 8 ohm resistive load. If they wanted to be clearer they would tell you what the power output is into an impedance (R+L+C) load at particular frequencies. but they will not do that. So, basically, what is on the amp specs is not what is really happening because your speakers are not resistive loads. So you are comparing apples to oranges. another example would be to take two 50 wpc into 8 ohm amps. One tubed and one ss. They both have a particular input sensitivity which will drive an 8 ohm resistive load at 50 wpc and typically that is measured with an input signal of 1khz. But, make that load a reactive (resistive, inductive and capacitive) load at 1khz at the same input signal level and you have an entirely different story. Or lower or increase the frequency with the same input signal level and no way will you see 50 wpc, unless you have a very well designed and built amp and let me tell you, you will pay a lot for that amp. Because it was designed and built correctly. I hope I didn't glaze your eyes. but every 50 wpc rated amp cannot drive the same loads the same because they were not designed to. The specs presented do not tell you everything. But, my point (long as it is) is that 50 wpc into 8 ohms resistive is the same, no matter what amp we are talking about. But the real loads your amps see are definitely not resistive and therefore the 50 wpc into 8 ohm spec goes out the window.

Br3098, I appreciate the humor but seriously, the heat of our amps is quite manageable. Up here in Minnesota we see the highest dewpoints recorded anywhere worldwide and our amps are easy to live with even in the summer. However the heat comes from being class A, not the number of tubes. You can run the amp in Standby all day and at the end of the day, put your hand on the tubes without fear of burns. But from stone cold, within a minute the tubes are way too hot to touch because they are conducting.

IOW a solid state amp of the same power that is also class A will heat up your room in much the same way- it will make about 85% of the same heat. The real issue is, what do you want the system to sound like? Real music? If so, you are going to have to go class A- all other classes of operation are performance compromises.

Now it may be that you can find nice-sounding amps that are not class A, in fact they abound. But the very best, the ones that stand apart- they will be class A.
sorry for confusing, but i'm not speaking in terms of chaotic woofer movement. i'm speaking in terms of amount of pushed air from the woofer which is nothing else but sound.
I also absolutely agree and even sure that larger drivers are easier to control since they don't need to be moved excessively by the voice coil to have the same SPL, but would they 'dive down' to its designed lowest frequency with 30W is a pure question of speaker design and type of driver.
My friend received Wyred4Sound ST1000 instead of traded-in Quicksilver M60 and the lower end difference, overall control and sound delivery is 100% towards Wyred4Sound driving Aerial 10T. This 'gentle giant' really pushes the air from Aerials!
If anybody wants to challenge S30 next to Wyred4Sound on the true full range speaker such as Aerial 10t drop me a note. I'll be more than happy to A/B it with anybody local or currently local to NYC.
Arthur (Aball), I'd like to both thank and congratulate you on one of the most enlightening and informative posts I've encountered in my 10+ years here.

!!!! *** BRAVO *** !!!!

Perhaps Bud Fried's (a man who claimed he was born 25 years too early - I believe the true number was far higher) favorite anecdote was the one about the ship's captain who set both sail and his watch (at promptly 12PM) by the clock tower in the town square, and let everyone know the clock tower was the ultimate reference. One day the keeper of the clock tower was asked what method he used to keep the clock in time, only to answer, "Well, every day, day in and day out, precisely at noon, there's a ship whose captain sets sail at that very moment..." and I'm sure you can figure out the rest of the story.

Long ago, I came to the conclusion that the mantra "watts is watts" represented a most (among, if not, the most in audio) fundamentally flawed proposition. Though I've not invested the requisite time, effort, or thought into why, the fact that music is nothing like the steady state test tones that measurements are should make obvious how far off the path the numbers can lead us. It's simply the difference separating arithmetic/algebra from calculus, and I believe we're missing that point.

Most everyone in this field can (and does) measure the things that conflict with the ear, then go on to regurgitate what they read or were taught (yet do not understand) why we are mistaken because the numbers say so. Very few prove the ability to transcend all of that, as you have here, and can as I like to say, "question the answers and answer the questions" en route to actually UNDERSTANDING the topic at hand. That is the difference between a technician and a scientist/enginneer. Regardless of the job title, in my life, I've met precious few scientists/engineers.

Thank you again!
Hey Joe - thanks! I knew only a few would care but I wasn't expecting a full realization. I could have gone on for 10 pages. Your anecdotes and thoughts are right on! It really is the difference between algebra and calculus.

Arthur are you trying to say that at certain moment of time tube can throw let's say 1kw of transient power into the load??
Do you have any source that would graphically show measurements of the tube output transient response?
I have an access to the oscilloscope equipment and would be glad to be directed to test family of a transient responses of let's say popular EL34 tube.
Oh Marakanetz. I'm not sure I can help. Believe it or not, I have several oscilloscopes. I also have impedance analyzers, spectrum analyzers and electronic loads. I work in a state-of-the-art electronics laboratory. The reason I said what I did is because I realize these measurement devices are so we can observe simplifications of the real thing. I know it all too well.

To think that a human can build something that would have the capability of human hearing is an ego trip that no one should succumb to. In my opinion. The day measurements can beat the human brain, our demise, and our goal, will have been reached.

1kW of power from a tube as you imagine it, has no physical foundations. Heat generation alone would preclude that possibility. I was talking about what are called "time scales." We have many scales, as much in engineering as in philosophy, ultimately, but all of them fall short of truly representing what we can witness because time effects extend ad infinitum in both directions and thus there is no end to splitting them up into comprehensible slices. Algebraic formulas and measurements occupy only a small part, but calculus covers them all. This was the point Joe so succinctly and eloquently outlined above. One of the tools available to see the remaining parts is called "frequency domain analysis;" the repercussions of which are called "harmonics," which also extend ad infinitum. There is no end to the formulas in the frequency domain. The day I realized all this was mentally liberating.

Classical formulas exist so that we can comprehend what is going on. This is done by throwing out all variables that we deem "unnescessary" because we would otherwise be overwhelmed. The Taylor Series Expansion in calculus points it out very clearly. But are those variables we throw out truly unnecessary? Would they exist if they weren't? Of course not. That is the crux between art and science.

You are free to believe as you like. If your definition of power has no total derivative, then you win. Otherwise, consider power as subject to time scales and you will know what I am talking about. If you would like to understand the mechanisms I speak of in lots more detail, I very-highly recommend Papoulis' book, aptly called "Signal Analysis."

Honestly, Arthur, these two you have submitted are among THE all time posts here on Audiogon. For my money, quite possibly, in fact, the best. I'd be more than interested and appreciative if you laid out as much of what you've concluded as you desire, be it here or offline, irrespective of length, depth, or breadth.

As you can see my coming to the thread four days late, I came quite close to missing it altogether. And, the laziness of not reading a thread from beginning to end actually caused me to overlook it completely in my first pass. It was only in bubbling up through the thread to get a point of reference for some of the back and forth that was going on was I lucky enough to stumble upon it. I'm surprised it didn't elicit a waterfall of subsequent discussion. Hopefully, it still may; even if calculus, and mathematics in general, is something we fall far short on as a society at large out of our irrational fear of something that should not to be feared, but embraced.

A few simplistic and personal audio examples that I'm sure most of us can relate to:
1) I used to have two integrateds manufactured by the same company, created by the same designer (if that's of any concern). One was a 120 wpc (hybrid - tube preamp/solid state output) solid state amp, the other a measly 11 wpc push-pull 2A3 tube unit. Apart from such characteristics as tone, (which is actually a quantum leap over the so-called "simple" subject at hand - power), the 11 wpc tube amp walked away from the 120 wpc in what I remember to be every loudspeaker I paired the two of them with. In fact, the order of magnitude difference in rated power seemed exactly backwards

2) That same aforementioned 11 wpc 2A3 tube integrated was also available in a 22 wpc 300B version. Again, obviously, the tale of the tape seemed to make it plain as to who was who. Again, the 2A3 amplifier readily eclipsed the supposedly more powerful 300B model. Any reasonable and average person who didn't read the product spec sheets and relied solely on their own personal being when asked to match amps and numbers in order to assign the power ratings would have chosen the exact opposite of what the paperwork stated

3) A week ago, my buddy and I visited a local dealer to listen to a pair of loudspeakers he was interested in. One of the amplifiers we used in the demo was the Manley Stingray. Initially, we listened in tetrode mode, which provides 40 wpc. As an adamant fan of triode tube operation, I badgered him enough so that at some point, he acquiesced, and we "moved down" to the low rent 20 wpc triode provided. Yet again, in any subjective real world listening test, one would think the ratings would have been the other way around. Triode operation was simply far larger and richer, putting some real meat on the bones and yielding more real world tractable power

4) One question (OK, I lied, this one is neither simple nor clean, and admittedly, maybe I've always missed the boat on this subject...) I've always wrestled with - from the methods we calculate power today, biasing a tube amplifier into Class A operation ALWAYS yields a lower figure than Class A/B operation. Yet this contradicts what would otherwise inherently be obvious (at least, to an admittedly stupid and simple person such as myself) that more current flow through a tube would equate to more (and not less) power. Anyway, my real world example is the Jadis integrateds (again, for those who care, another situation of same company/same designer). The Orchestra Reference is 52 wpc (published specs are usually 40 wpc, but taken from the smaller Orchestra figures) Class A/B, the DA30 30 wpc Class A - both amps using 2 output tubes per side be they EL34/KT77, 6550/KT88/KT90, etc. You know where I'm going here, along the lines of my argument, in my real-world experience with the two, the DA30 is readily the stronger amplifier

Continuing again with the arithmetic/algebra - calculus theme, attempts to correlate the steady state conditions that are the very nature of the measurements of amplifiers heretofore with the dynamic and instantaneously changing phenomena that music (and, the reactive load the partnering loudspeaker presents to an amplifier - something curiously ignored in these measurements) is has, and will continue to, create(d) more problems and confusion than solutions. Along those lines, we often become slaves to such measurements and the machines we have built to implement and execute them which your statement, "To think that a human can build something that would have the capability of human hearing is an ego trip that no one should succumb to. In my opinion. The day measurements can beat the human brain, our demise, and our goal, will have been reached." captures so well.

Then again, living in a world where "watts is watts" and "watts - more is better" is so much less difficult than asking the tough questions that you have, and provides for the quick and easy compartmentalization and subsequent rankings/judgements desired by the customer, salesperson, and (most unfortunately) even, the scientist/engineer/teacher.

My overall point is this subject is far more complex (which we should embrace as a challenge/something fun, and not run away because we feel it's hard work, too dificult/esoteric to understand or just plain scary) than plugging in parameters like Watts, Volts, and Amps into a simple algebraic equation, solving for the one unknown of the three, then going home for the day because we think we're finished. In no way am I saying here that Ohm's Law is any less beautiful, valid, or even appropriate. However, the numbers that we're inserting into the formula when dealing in relationship of amplifier, music, and loudspeaker relationship clearly are.

Thanks for your response. I am seriously considering giving one an M-60 pair a try. In your opinion, do the Zeros (or other auto transformers) change the sound much?
Great post there Joe. About your comment that Class A operation reveals lower-power figures that expected: You are absolutely correct that theoretically Class A should be able to yield higher power because there is no zero crossing. There are three main aspects, as I see it, as to why in reality it doesn't work out that way - and also how they impact tone because your comments about differences in tone between single-ended and push-pull are actually related.

1) Accurate low frequency reproduction is more challenging in tube circuits that slide into Class B because the power continuity gets broken when no tube is operating. This particularly impacts the low frequencies because they are the ones that need the most power. And they are the ones that mainly have to do with tone.

If I may use an automotive analogy, it is like comparing a manual transmission with a dual-clutch transmission, such as the ones in the latest Audis and BMWs. There is no interruption of power in the dual-clutch setups since there is always a set of plates that are transmitting full power. This is like Class A. But in the other case, you have to put the clutch in and the RPMs drop like a rock as you disconnect the engine (amp) form the transmission (speakers). This is like Class B. The end result is that tone (mainly bass) is much more easily conveyed in Class A operation since the power is always on tap. There is no denying in the world of automobiles that constant power leads to higher performance. Guess which mode of transmission is used in race cars.

2) The actual power ratings are lower than Class AB because of physical power dissipation limits. To operate with a constant bias requires high heat dissipation from the tube's plate. This would be fine except that the cooling medium inside a tube is vacuum, which is as bad as it gets! A vacuum is a terrific thermal insulator since there can be no convection cooling and thus all the cooling is due to "black body raditiation." I have better stop there before I get into the Second Law of Thermodynamics! lol. So yeah, to keep the tube from overheating you have to cut back on the output power. Basically you trade power for bias, which has of course its known merits in addition to this inconvenience.

3) The output transformers in a Class B amp are not designed the same as in a Class A amp. If the amp is Class AB, I am sorry to break the news to some of you but that means it is a Class B amp as far as circuit design goes. Many people feel it is better to say AB rather than B but as far as the electrical design is concerned, there is Class A and then there is Class B.

In a Class A amp, the output transformers have to have an air gap. This means that the core is not made of one continuous piece like it is in a Class B amp. This is due to the fact in Class A you have constant positive DC current in the primaries of the output transformers that should be equal to half the peak output current. In order to prevent the core from "overloading," technically called "saturation," you have to literally cut a slit into the core somewhere so that the excess magnetic field (that goes above and beyond satisfying the core's inherent magentic self-inductance which is what allows it to work in the first place) gets trapped in the air gap. Since air doesn't magnetically saturate, it is a stabilization method for the core.

In addition, this means that a transformer for a Class A amp must be a lot larger than a Class B one because you can't maximize the use of the core since the polarity is always positive, and, the air gap adds its own detriment to the performance of the core.

In a Class B (aka Push-Pull), you don't have to worry about these problems because of what I pointed out in 1) above: the net DC current in the output transformer is essentially zero because the tubes each turn off at the end of their respective cycles. They aren't "on" all the time like they are in Class A.

I feel certain that all these differences account for the changes in sound and tone between a Class A amp and a Class B amp, in addition to the differences in circuit topology of course. If you can live with reduced output power, higher temperatures, higher cost, and higher weight, then Class A has definite advantages. :)

I have two push-pull amps now and I am dying to get a Class A SET because I finally have speakers that can live with their downsides. I’m still in the process of figuring out which one to get. As far as differences between different push-pull amps, that lays in the gray area of performance overlap between designs. Which is better will depend on the type of tube, the power supply design, circuit design, personal preferences, speakers, and room.

As I said before, the sonic results of all these technical details can only be adequately assessed if there is an experienced human in the feedback loop. Only then are all the requisite variables fully taken into account.


I just switched from a Class-B (push-pull) tube amp to a Class-A (single-ended) tube amp. My speakers are Rogers Studio 7s (90dbW sensitivity).

Your understanding of the physics of Class-A and Class-B are far beyond mine, but here are my subjective observations.

The Class-A (single-ended) tube amp heats up the room much better than the regular room heater (which I have had to turn off). It gets HOT! I don't know what I am going to do during the summer.

The other thing I have discovered is that my electric bill has doubled (I just got it today)!

Yet it seems to be worth it. The Class-A (single-ended) sounds dramatically more like live music than the Class-B amp does. Everything sounds so much smoother, so much more like what I experience sitting in front of a live string quintet or a live orchestra. It's a dramatic leap up in quality. I have no idea why this is so.

Subjectively, the Class-A amp sounds significantly louder than the Class-B amp even though it has half the wattage. Moreover, the dynamic range seems greater with the Class-A amp. On more than one occasion, I have turned the volume up during a quiet passage only to be blasted out of the sofa during a loud passage. The difference between high and low seem much greater with the Class-A amp, whereas with the Class-B amp dynamic range seems more constricted.

It's hard to cut up the audioband into bass, mid-range, and treble with the Class-A amp. I just hear music. Seemless music. Every note (from high to low) sounds realistic.

Transients seem much more bold and much more dramatic. I dive for cover now during the cannon shots of the 1812.

The class-A amp does not sound soft or romantic in the way that I was expecting. It sounds as sharp, crystalline or as velvety as the music demands. It does not seem to obscure music with an omni-present coloration of its own. It sounds significantly more accurate than my push-pull amp (which gives a slightly rose tinted patina to everything).

Going from Class-B to Class-A has been nothing short of a sonic revelation. I can deal with the heat for the dramatic increase in the beauty and realness of my music.
Arthur, thank you for the insight, I appreciate it. There's a lot to think about there.

I believe the transmission analogy is a good one. Even if for me, accepting the inherent performance superiority of dual clutch transmission, nothing can replace the joy a clutch pedal provides. I'm also glad you touched on Black Body Radiation.

One point of contention is that Class A is not the exclusive condition of the single ended topology. And, conversely, push pull does not need to be Class A/B or Class B; plenty of PP amps operate in Class A.
Arther, I quite enjoyed your post as well (and previous) but was also a bit confused as to which of your comments apply to SE topology and which to class A bias. Seems to me it was actually mostly the former.
Oh yes, sorry for the confusion, Paul is right. I had SE Class A in mind. That's the type of amp I've been on the prowl for so that's what I've been thinking about lately.

My comments still apply for Class A push-pull however because they have the same ungapped core design as Class B push-pull since the two halves of each channel remain in opposite polarity and similarly sum in the secondaries. Hence my generalization from the circuit design point-of-view.

There is a scientific explanation as to why Class-A amps sound better than Class-B,but there is no scientific explanation as to why tube sounds as loud as solid state when the tube is less powerful.
Power output I believe, regardless of amp technology used, translates essentially only to how loud things should go, all other factors aside.

This does not say anything about how optimally an amp drives a particular speaker design. By optimally I mean that all frequencies are delivered essentially on equal ground even as the load impedance varies by frequency from the nominal, generalized overall rating.

Distortion will be lower when an amp drives a speaker with higher input impedance in general I believe, all other factors aside.

In general SS amps are better able to drive speakers with lower input impedance more optimally and with lower distortion for properly balanced sound than tube amps (in general).

That is my general understanding. Please correct me if I am off base here.

My point is that power output alone ma determine the quantity of sound (volume/spl) that can be produced, but not the quality, even at lower volumes. Other factors come into play there.
Orpheus10 and Mapman, the reason tubes seem more powerful has to do with the way we perceive sound and the different ways that tubes and transistors make distortion. I would look at some of Arthur's comments above- they are right on the money.

I think I also had some of this explained above too- if I need to clarify it just let me know.

No further clarification needed on my behalf. Transients are key. Its pretty clear to me that its mostly about details relating to distortion and how different factors contribute to that, as you say.
I am going to jump into this "tower of babel" with all four feet and state my qualifications for doing so.
Before I became an Audiophile, I was an electronics technician who knew all the electronics formulas. "If you can not measure it, you can not hear it" was my slogan.
After I became an Audiophile, I laid my meters to rest. I can hear things that no meter can measure.
"Is this dog better than that dog"? Unfortunately, no one can answer this question but you. This is not a scientific arena, this is a very subjective audio arena.
I have to believe science plays a role here, there is still good design and bad design and I believe is governed by understanding electrical principles. If that is not sound, no pun intended, you are not going to get good equipment. Now as to the seasoning that a knowing chef wishes to use, that is more subjective, and the art in audio engineering IMHO.
I think it is useful to differentiate between matters of opinion and matters that do involve empirical differences but differences that we may not currently be able to accurately measure.

We do not currently measure amplifiers playing actual music and so do not really look at harmonic, IM, and other types of distortion products amplifiers actually produce making *music*. Furthermore, and much more importantly, we know only a very little bit of how to "weight" the results because we know rather little about how the ear/brain system actually works - what sorts of distortions make music unpleasant or unrealistic and what sorts really just don't matter all that much. (Of course we do know some of that, as Atmasphere & others have mentioned.)

Why some audio amplifier designs tend to sound better or more realistic may not be easy to describe empirically but it is at least not entirely a matter of opinion. Preference for dogs is. :)

(Ok, if you establish certain criteria, such a strength or cuteness, one could of course rate dogs quantitatively as well...)
I found very interesting work that was done by a group of Russians a while back. I am pretty sure I printed it out but I originally found it online. I'll have to see if I can find it again to post a link to it here, but at any rate, they had actually done measurement studies of how different amplifiers amplify Gaussian white noise (much closer to music than a sine wave is). I believe they may have also used music too.

They did Fourier analysis of the outputs of each amplifier and compared them. They found very real differences in the low-frequency reproduction, not much difference in the midrange, and once again some differences in the treble. Then they repeated the tests using the "best" amp of the group with various cables hooked up to its output. I think they used like 10 meter long cables to magnify the effects. Once again, the responses were different with different cables.

I'll see if i can find it again. Last time I looked for it I wasn't able to. But I found it extremely interesting and have not seen anything like it since. Maybe I'll just take some amps to the lab and redo the experiments myself! That's what I should do if I can find the time.

*PS* I just did a search to see if I could find it and ran across this paper. I haven't read it yet but it looks interesting. Too bad the input signals are still sine waves though....


>>03-16-10: Paulfolbrecht
Furthermore, and much more importantly, we know only a very little bit of how to "weight" the results because we know rather little about how the ear/brain system actually works - what sorts of distortions make music unpleasant or unrealistic and what sorts really just don't matter all that much.<<

May I suggest "This is Your Brain on Music" by Dr. Daniel J. Levitin for greater insight.

Given to me as a gift last Father's Day, I'm reading it for the second time as we speak.

Fascinating to say the least.
Orpheus10, the reason it seems subjective is only because the industry as a whole really does not want to talk about the science. For that I point you to the writings of Norman Crowhurst regarding feedback and its effects, also to

and if you have the time, I recommend reading 'Chaos' by James Gleick. Inside that book (a good primer for Chaos Theory) you will see some interesting waveforms, some of which you have seen before if you have spent any time around audio gear. BTW, Norman Crowhurst actually has charts of the strange attactors that govern the behavior of audio amplifiers using loop negative feedback, although he had no idea at the time that years later those charts would be associated with strange attactors.

General Electric also proved some fundamental rules of human hearing the mid-60s, which for the most part was totally ignored by the audio industry (how we perceive volume through the presence of 5th,7th and 9th harmonics). This work has been extended in the 21st century by Dr. Herbert Melcher, a noted neuro-chemist, who has discovered that as an audio reproduction system violates human hearing rules (too much of the wrong distortions, too slow, stuff like that) that the processing of sound moves from the human limbic system to the cerebral cortex- and for this he actually has hard numbers!

IOW there is plenty of science, much of it on-going, to support why tube power seems more powerful; like I mentioned before, its not about the power, its about how the technologies distort.
I don't have the scientific background that many here obviously have, and perhaps I'm missing something but, I haven't seen anything here that would appear to qualify as evidence, never mind proof of the claims that tubes are more powerful than ss. In some cases there appears to be contradictions from previous arguments making the same claim, and an absence of perhaps other considerations. It would appear that some references might potentially support the other point of view. There's a big difference between coincidence, correlation and causation. Still a very good read and I encourage further contributions. Very interesting.
My understanding from the experts is not that tubes are more powerful, rather they distort in a less offensive way that makes them able to go louder before the listener takes offense.
Post removed 

That is true.

I suppose that could be one reason perhaps why many are tube fans yet many are not.
Unsound, what is meant by offense is not really a matter of taste. Back in the 1960s, GE did a test where they played music and test tones for people and gauged the response.

What they did was to introduce two types of distortion- even lower orders, and higher odd orders, in two tests. What they found was that people will tolerate without objection up to about 30% distortion if its all lower orders, but tiny amounts of odd orders, less than 0.1% was highly objectionable!

IOW, what they found out was that the human ear listens for the 5th, 7th and 9th harmonics in order to determine the volume of a sound and that we are sensitive to distortions as low as 0.001%, where we really don't care about lower orders (the 2nd,3rd and 4th).

This is also the difference between tubes and transistors as far as distortion goes. I myself do not like what many have come to call the 'tube coloration' and I have found that with careful design there is no reason to have to tolerate it either. Nor do I like transistor coloration, but its a lot harder to design transistor amps that lack it; all of them that I have heard that lack transistor coloration are all also zero feedback class A designs, I think not out of coincidence.

I don't fault anyone for disdaining the typical distortions that are easily heard in a lot of gear- I feel the same way.
Atmasphere, your points are well taken but, I'm doubt that these findings were experienced by 100% of the people tested. Just as in other areas of audio, for what ever reason some people seem to be more or less sensitive to some aspects more or less than others. There are other considerations that need to be considered; budget, heat, space, compatibility with connected gear, etc.. When the entire equation is put forth, new sources of "offense" can be introduced. In certain circumstances the benefits of one technology are over ridden by the exposure or introduction of new flaws.