high power tube amps vs ss

Onhwy61,
That amplifier can be tweaked very easily, most don't know.
Removal of the top allows access to (I'm going by memory) five white nylon setting screws. Two of which, will adjust the Gain amount.
CAUTION: Turning up the wrong ones can result in possibly frying the board or such. I
would imagine the information is easily found online.I had adjusted mine at least a few times. Great Crunch!!

Now you did it!! I want another one :)

It was an experiment. Thankfully(I guess). I love consensus though. I also love being a pain in the ass. I have nothing else:) Tubes or ss, it's all the same to me. It only has to sound good. Less maintenance with ss.

I'd first get your speaker selection worked out, then worry about amplification. Speaker-amp matching is so key. And speakers are the most important component in the chain. Settle on them, then start figuring out a good amp to match them.

HEY. you 6550 guys, you need SYLVANIA 6550's not those shrill GE's.
I use Winged C's myself as the last quad I saw of unused Sylvania's was going for $600 and that was a few years back.

If I could make transistors do what I can do with ease with tubes I would make transistor amps.

But I can't and no-one else seems to be able to do so either, although a very few (less than 5) come close.

That thing that tubes do is they don't make odd ordered harmonic distortion the way that transistors do. Most solid state devices have a non-linear capacitive aspect that is inherent in the junctions of the device. This capacitance is multiplied by the amount of current through the device. This is one reason transistors make more odd ordered harmonic distortion than tubes.

The discussion about guitar amps does have relevance here. Guitar players prefer the smoother (lower odd ordered harmonic distortion) sound of tubes, especially when overdriving (clipping) the amplifier.

Because tubes (triodes in particular) are the most linear form of amplification known, it is possible and practical to built a tube amp with no negative feedback that has fairly low distortion. This is really hard to do with transistors, and it is notable that the best transistor amps made (in my book) are all zero-feedback designs. However, 99% or so of transistor amps use feedback, and feedback actually *increases* the odd-ordered harmonic distortion in any circuit.

Since the ear uses odd ordered harmonics to figure out how loud a sound is, by adding trace amounts to the signal the result will be brighter and harsher.

The bottom line is if you want it to sound real instead of just a really good hifi, you have to find a way to get rid of that negative feedback. Usually that means going to tubes, and then finding a speaker that works. BTW:

High efficiency speakers would make life a lot easier, but I thought those type of speakers sounded shrill and thin. It may be because I have only heard them with ss amps.

The last sentence here is the important bit.

My speakers are 98 db 1 watt/1 meter, and go to 20Hz. I can shake the building with a 60 watt amp, without concern of clipping the amp. Most 'high power' systems I hear cannot play with the volume, the impact or the clarity I hear at home. Even at +100 db sound pressures, it still sounds smooth and relaxed. IME most audiophiles won't listen at levels over 90db because their system is too harsh. Real music plays at +100 db levels, if you can't do that at home without discomfort, something is wrong with the system.

GE / SYLVANIA? Last I checked they were pretty similar, if not identical. Unreliability of this tube vintage keeps me looking to new stuff. I do like my 12 AX7 Amperex Bugle Boys and Sylvania and Tung Sol 6 SN 7 tubes, but they are more plentiful. Jallen

Ralph, I tried your experiment of ramping up the gain. I was playing an EMI CD of Tchaikovsky (sp?) Nutcracker. The dynamic range is between 20 and 30 db. I never made it beyond 95db. At that point, external distortion made me turn the gain down. I'm referring to wifey. She threatened to throw a bucket of water on my gear. She introduced at least 90db of negative feedback and the odd ordered harmonics from her screaming really hurt my ears. Any suggestions?

I've owned a LOT of tube guitar amps and a couple of SS and hybrids...tube amps are simply snappier and make people happier. I do use SS bass amps though, as you need extreme power for that. Same with tube hifi amps...60 watts per side with 90db speakers and a SS sub (so sue me) shake my walls if need be, so I bet this sort of thing would shake yours. Also regarding heat...with only 4 KT120s there is not too much more heat than a recent partly class A SS amp I was using, but the tube heat is expected...a Twin Reverb will make the beer on top of it sweat all over the place...just a warning.

Almarg.....I am not sure what solid state amps you are speaking of. Not all ss amps DOUBLE IN POWER OUTPUT when the load changes. My McIntosh MC352,350w per channel Amp does not change in power output for 8,4 or 2 ohm loads. So I am perplexed by your statement. It also seems to me that you are lumping all SS amps together and thats not fair. Nice system and I bet those speakers are 95db sensitivity or better so they work well with the Tube amp. I wish I could hear it.

Jallen I just put in a pair of MAZDA CIFTIES-12AU7's and I really like the top end end on these. Awesome sounding tube made in 1962 for the French Military.

Thanks very much, Matt. Yes, the Daedalus Ulysses, in the configuration I have that was introduced about 3 years ago which includes "all poly" crossover capacitors, is 98 db/1W/1m. It also has a very flat impedance curve, as well as high power handling capability, all of which makes it unusually versatile with respect to amplifier selection.

Regarding your question, what I said was "the power capability of a solid state amp into 4 ohms MAY [emphasis added] be as much as twice its capability into 8 ohms."

As you probably realize, the power capability of MOST solid state amps will be substantially greater into 4 ohms than into 8 ohms, in many cases approaching twice as much, and in some cases equaling twice as much. Two ohms may be a different story, of course, as a lot of amplifiers will not do well dealing with such a heavy load.

As you indicated, though, your McIntosh MC-352 amplifier has the same output rating into 8, 4 and 2 ohm loads. That is essentially a consequence of the unusual autoformer-based design of its output circuits. I am not aware of any non-McIntosh amplifiers that use a similar approach.

As opposed to a tube amplifier utilizing an output transformer, however, the solid state + autoformer approach provides considerably lower output impedance/higher damping factor (damping factor being spec'd at 40). As a consequence of that it WILL, like most solid state amplifiers, to a very close approximation double actual power DELIVERY (as opposed to CAPABILITY) as load impedance is halved, AS LONG AS it is operated within its 350W or so capability, and as long as the impedance of the speaker is a reasonable match for the output tap on the amplifier that the speaker is connected to.

In contrast to most tube amps, that essentially places the MC-352 in what Atmasphere refers to as the voltage paradigm camp, i.e., its output voltage for a given input will be essentially constant regardless of load impedance, as long as the amplifier is operated within its capabilities.

Regards,
-- Al

I will add this to what Al said: It is generally thought to be a good sign when a typical solid-state amp doubles in power as the impedance of the speaker is halved. A sign of a good power supply, IIRC.

And yes, generalizing about amps based solely on the amp being solid-state or tube is certainly problematic. But this doubling-down into lower impedance is something that applies for the majority of solid-state amps. Your amps happen to be an exception to that rule of thumb.

Atmasphere, are you comfortable telling us which in your opinion are the 5 ss amps that come close? Just curious.

Al, does the autoformer lower the output impedance of the amp, or increase the perceived impedance load of the speakers. I appreciate the DF math works the same way, but just wasn't sure what changes.

In other the DF of amp is 20:1 if speaker impedance at the test frequency is 20 ohms and the amp's output impedance is 1 ohm. DF is still 20:1 if speaker impedance is 10 ohms at the test frequency and the amp's output impedance is .5 ohms.

Cheers,

Bruce

Hi Bruce,

I suspect that the specified damping factor of 40 for the MC-352 (actually, it is specified as "greater than 40," but I'll assume 40 for present purposes) represents the output impedance of the amp for a given output tap divided into the speaker impedance that tap is nominally intended to be used with.

If so:

The output impedance of the 8 ohm tap would be 8/40 = 0.2 ohms.

The output impedance of the 4 ohm tap would be 4/40 = 0.1 ohms.

The output impedance of the 2 ohm tap would be 2/40 = 0.05 ohms.

The output transistors would presumably see the same load when an 8 ohm speaker (that is truly 8 ohms) is connected to the 8 ohm tap, compared to when a 4 ohm speaker (that is truly 4 ohms) is connected to the 4 ohm tap, compared to when a 2 ohm speaker (that is truly 2 ohms) is connected to the 2 ohm tap.

BTW, thanks for your kind comment earlier in the thread.

Best,

-- Al

I'm a big fan of Nelson Pass, Ayre and Ridley Audio. That's my short list... I think there are a few other candidates out there but I've not been able to hear them.

Me too regarding Nelson Pass designs. One of the few SS designs that to my ears really get closer to making music sound real other than , to my ears, a tube solution (preferably of the OTL variety) ideally matched with the speaker. It always comes down to synergy when making choices and this is not so easy. There are many speakers with difficult load characteristics that are superb that will not electrically match with tube amplification. There is no simple answer to this complex paradigm. Melding components together in a manner that makes recorded music sound real is not easily achieved by Tube vs. SS discussion, too many factors involved in the equation that is evidenced by the same questions continually being asked, IMHO.

I really appreciate the contributions of Almarg and Atmasphere (Ralph) to my better understanding of these issues.

"My questions is: is there anything to be gained by switching to these higher power tube amps over ss amps?"

Maybe or not. It would all depend on what you specifically are shooting for and how well what you have meets your needs or not.

I do not consider Dynaudio speakers and tube amps to be a natural match by design in general, and would not do that without hearing first but that's not to say you might not find something to like there if you heard it.

I do not consider Dynaudio speakers and tube amps to be a natural match by design in general, and would not do that without hearing first but that's not to say you might not find something to like there if you heard it.

Agreed- in spades!

I would venture to guess that Al, but especially Ralph believe it's not possible to arrive at life-like sound without tubes given some of their prior posts. To that end I would like very much for either/both to cite some tube amps that are as fast as any ss amps they've heard so far. Imo, you can't get there without serious speed in an amp. For me it's 'the' most important factor. I really don't care what else it does well or poorly (within reason). And I don't care about published specs.

Csontos I would venture that the Atma-sphere amps, which I have heard in several unfamiliar systems over the years and in my experience the Berning zh series amps are as fast and transparent as any ss amps I am familiar with. Check out Berning's website for the numerous reviews of these amps to get an idea of their performance characteristics.

I have owned and been listening to the Berning zh270 for 11 years and the comments you have made above regarding tube amps in general are true in many instances but certainly not all. This amplifier rivals any ss amp I've listened to with reference to transient attack, pitch definition and bass control.

05-20-13: Csontos
I would venture to guess that Al, but especially Ralph believe it's not possible to arrive at life-like sound without tubes given some of their prior posts. To that end I would like very much for either/both to cite some tube amps that are as fast as any ss amps they've heard so far. Imo, you can't get there without serious speed in an amp.

Hi Peter,

No, I for one would certainly not make any such claim. In part because my listening experience with solid state amps during the past decade or two has been minimal. Prior experience led me in the direction of tubes, with which I've been very happy, and in recent times I've simply had no interest in high end solid state. And my speaker preferences have always tended to be in the direction of those having impedance characteristics that are benign and tube-friendly.

For examples of tube amps that are "fast," for starters consider Ralph's OTL amps. Although I haven't had the pleasure of hearing any of them, by all accounts I've ever seen they have that characteristic in spades.

And among tube amps having transformer coupled outputs, my VAC Renaissance 70/70 Mk III certainly doesn't disappoint. While I realize that you "don't care about published specs," I'll mention that they are rated as being down only 0.5 db at 90 kHz on a small signal basis, and at 58 kHz at full power. At -3 db those ratings are 103 kHz and 85 kHz, respectively. Not very different than the very highly regarded Pass XA.5 series solid state amps, which are rated to 100 kHz (with no specification of power level or how many db down that is based on).

Yes, I know, a few solid state amps, such as those made by Spectral, go out to 1 or 2 MHz or more, but whether or not that is overkill, and whether or not it may even be sonically counter-productive, are certainly debatable.

As a point of reference, I'll add that I frequently compare listening results between my amp + speakers and my Stax electrostatic headphones + Stax solid state headphone amp. I doubt that anyone would ever accuse the Stax components of being "slow," yet I am not disappointed with the "speed" of the amp + speaker combination.

Tubegroover, thank you most kindly for your expression of appreciation.

Best regards,
-- Al

I understand that speed and other sonic parameters are subjective and individually just personal perceptions. I've found good tube power amplifiers to present a wonderful realistic sense of timimg, pace and musical flow.The presentation is very fluid with well preserved continuity. The two Spectral based systems I heard (if they're considered typical of a"fast" SS amplifier) were not even close as far as retaining the believable and natural musical flow and timing.The sound was mechanical and artificial in character But again, this is just my own observation.
Regards,

Csontos, I think that I might understand where some of the tube skepticism among the solid state crowd comes from. Quite often, tubes are used in applications that are less than ideal. I hear them all the time. That’s not to say that a mistake was made. A person has the right to consider only the elements of music that are important to him, and choose a tube amplifier/speaker combination accordingly. But while this person is satisfied with his tube application, others of us might listen to his system and hear musical compromises that we wouldn’t make for ourselves. What Atmasphere, Almarg and others are trying to tell you, is that many of the shortcomings that you perceive to be inherent to tubes, are more likely to be common application flaws.

Dammit! Al, I would love to spend an evening with you listening and drinking. Here's my question Al. I have never tried tube amps and I am fearful that I would miss some SLAM and Impact of the presentation. Does your system belt it out pretty loud and non fatiguing? OR does it seem to be very detailed and airy, but when you turn it up loud, can you listen for long periods? (I guess loud would be above the 35w range)I would love to hear some good tube amps with a different speaker that works well with tubes. There are no stores I can visit nearby. My Dynaudio Contour 3.0s are really great.But they are 86-87db and require a lot of power to open up. My MC352 can drive them over 350w easily and the speakers are rated at 200w. I was thinking of switching to a pair of 70w monoblock tube amps. but I really dont think my dynaudios would like that. of course I have nothing to support this really.what do you think AL. Am I missing out on goosebump city,or is my hybrid system the best I can hope for with these speakers.

Hi Matt,

I have no experience with Dynaudio speakers, but my instinct would be to proceed with caution before going to tube amplification with them. In addition to the comments by Ralph and Mapman just above, I would emphasize that high quality high powered tube amplification tends to be quite expensive. And you clearly need lots of watts.

Based on the impedance curve of your speakers, shown in Stereophile's review here, I would consider their 86 db/2.83V/1m sensitivity to be roughly equivalent to 84 db/1Watt/1m. At typical listening distances (say 10 to 12 feet or so) that would mean that 70 watts into both speakers would produce a maximum SPL of around 96 db or so. While that is adequate for most listeners when listening to highly compressed rock music, I suspect it would be very disappointing with a lot of material having wide dynamic range (i.e., a wide difference in volume between the loudest and the softest notes).

My listening is about 90% classical (including a lot of wide dynamic range symphonic material), 5% rock, and 5% miscellaneous. I've measured some of the classical material I listen to as reaching 105 db at my listening position, which my 98 db/1W/1m speakers and 70W amp handle comfortably.

Although I haven't heard them, if you do want to consider tube amplification you may want to look into the higher powered models from Rogue Audio. Some of them provide close to 200 watts, at relatively reasonable prices, and seem to receive generally favorable user comments.

Best regards,
-- Al

"Does your system belt it out pretty loud and non fatiguing? OR does it seem to be very detailed and airy, but when you turn it up loud, can you listen for long periods?”

Matt, I haven’t heard Al’s Ulysses but I’ve heard the model just under them - the Argos; so I’m very confident that Al’s system would knock your socks off. But additionally, if you ever have the chance to hear a pair of Volti Vittora speakers, I would highly recommend that you take the opportunity; just to finally put to rest, any reservations you might have left, of what a few tube Watts can accomplish with the right speaker.

Al,
Wow, you really listen at very high SPLs.A few days ago a friend and I visited a local jazz club and his phone has an application for SPL measurements. Average volume was roughly 87-92 with drum kit peaks 100-105 (we were very close to the stage) but it was loud (unamplified that night, thakfully).I'd fear for my hearing with those levels at home on a regular basis. Most of my jazz CDs have a range of 25-35 db, but my average listening level is likely noticeably less than yours. I'm very familiar with your VAC REN 70/70 amplifier and it is a classic in my opinion (so is the 30/30 version).There's just something unique and special musically with DHT output tubes, in both SET and push pull mode.
Regards,

Al,
On relatively rare occasions when I crank up the volume it did remain controlled, clear and unstrained in character(95-103 peaks) but I just want to maintain good hearing as long as I can . I'm not getting any younger that's for sure, but my hearing is still quite good.
Charles,

Hearing issues come from sustained high levels, and unlike something like a gunshot next to your head, a short musical burst (from classical music for example) isn't going to hurt you usually...sitting next to a loud drummer might not be a good idea though...I know from what I speak. Also, the "speed" term makes no sense to me when applied to electrical signals flowing through an amp...I wonder if you even CAN measure the speed of a signal from input to output...I want to know if my tube amp is getting musical notes to me in a timely fashion!

Well Wolf, "speed" is another of those audio terms that is hard to define other than to say you certainly recognize it when you hear it. Much of it to my ears is MOST readily recognized in large scale acoustic and choral music with wide and varying dynamic shadings and tones. A "fast" amp seemingly resolves the leading edges of instruments without softening or rounding off, an effect I hear primarily with OTL tube amps, a greater transparency and resolution of all the musical information on the recording. The ability to resolve dynamic shadings without the sound congealing or dynamics compressing. Now as noted by Charles1dad there are amps that are considered "fast" in this manner but miss the subleties of tone and true and accurate pitch of instruments which can, to my ears, lead to fatigue. When the pitch of instruments sounds natural and more like what you hear live and the subtle dynamic shadings and sense of space is preserved, it just sounds more real.

A good test is listening to large scale music at lower volumes and hearing all the information, including bass, preserved as it is at higher volumes. This is definitely an area where "fast" OTL tube amps excel over most if not all transformer coupled tube amps and SS.

Thank you Tubegroover and Al. I didn't mean to challenge you as I expected a relatively immediate response. But I do think you two are most precise in defining speed as I put it. Judging from your responses it's fairly clear that it is in fact a technically quantified attribute and therefore realizing it is not subjective at all. The reason I don't care much about specs is because amps don't necessarily live up to them. But I am aware of which ones they are. As you stated, Tubegroover, 'you know it when you hear it'. Why someone would hear it but not prefer it is beyond me. I'm willing to wager there's not a high end amp out there without this quality, without which a lot of other attributes are down the toilet.

Hi Tubegroover,
Yes you certainly understand the point I was trying to express.Components that emphasize the attack, "lighting fast trsnsients" but fail to maitain note substain and decay sound artificial. This type of presentation is incomplete and therefore less convincing and falls short in realism.As you said that type of sound(speed?) causes fatigue and soon boredom follows.The sign of an exceptional component is one that preserves the timbre,pitch,tone and harmonic overtones that naturally exist in music.This would reflect correct timing and music`s instrinsic speed and flow.
Regards,

Beauty is in the eye of the beholder. Science is not an absolute either. Did the scientists of a thousand years ago believe what the scientists do today? How about a thousand years from now? How is this so and do we know what we are actually measuring? Talk to a physicist. Everything is subjective and always will be. Best, real, accurate, etc. only have meaning between our ears. I prefer to try to think in terms of different and pleasing or not in regards to music. The best ss amps are often described as having tubelike qualities and visa versa. There's that word best again. Says more about the way we think than anything else.

Good tube amp setups I have heard are excellent at both "attack" or sudden transients and "decay", especially with acoustic music.

Same true of SS.

The lesser setups, both SS and tubes, are of course less successful, though the tube amps probably have a better chance of retaining interest musically still when things are not going so right.

Excellent comments by all, IMO. Charles, re the volume levels I listen at, Wolf's comment that:

05-21-13: Wolf_garcia
Hearing issues come from sustained high levels, and unlike something like a gunshot next to your head, a short musical burst (from classical music for example) isn't going to hurt you usually

is exactly applicable. My average listening level on most classical music is probably in the mid-70's. But I have, for example, a great many of the Telarc digitally mastered vinyl releases from the 1980's, which employed zero compression of dynamic range. Many of their symphonic recordings were notorious for their very loud bass drum beats, which can easily exceed 100 db at my listening position with the volume control set such that average levels are completely safe.

Also, as I mentioned in a previous thread here:

One of the widest dynamic range recordings in my collection (although there are many others that are close) is the Sheffield Labs recording of Prokofiev's "Romeo and Juliet," conducted by Erich Leinsdorf. Out of curiosity, a while back I examined its waveforms on a computer, using an audio editing program. The difference in volume between the loudest notes and the softest notes was around 55 db!

On that recording, and quite a few other classical symphonic pieces I have on high quality labels that tend to use minimal or no compression, I frequently measure brief peaks at my listening position in the 100 to 105 db area, using a Radio Shack digital SPL meter, although the average level is by no means particularly loud.

Those peaks are not nearly as loud, btw, as those I heard when I once listened from the very front row at Tanglewood to the Boston Symphony Orchestra performing that same Prokofiev work. My guess is that the peaks easily reached 115 db.

Regarding the definition of "speed," many good comments have been made. If I were to summarize my understanding of the term in just a few words, I would say it means that fast musical transients are reproduced ACCURATELY.

05-21-13: Csontos
Judging from your responses it's fairly clear that it is in fact a technically quantified attribute and therefore realizing it is not subjective at all. The reason I don't care much about specs is because amps don't necessarily live up to them. But I am aware of which ones they are.

I wouldn't go as far as to say that "speed" is technically quantifiable. The bandwidth specs I referred to earlier of course tell just a small part of the story. Bandwidth extending several-fold beyond the limits of our hearing is necessary to maintain phase relationships between harmonics that are at frequencies in the upper treble region, and lower frequencies that will be present in the same musical notes. But that and other speed-related technical parameters, such as slew rate, certainly don't tell the whole story IMO.

For instance, it is well established that excessive use of feedback is conducive to Transient Intermodulation Distortion (TIM), which as its name implies will, if present to a significant degree, result in inaccurate and sloppy reproduction of fast transients. As far as I am aware, TIM is never specified, and I'm not sure that standards defining how it should be measured even exist.

How to minimize or eliminate TIM? Design an amplifier that doesn't need much or any feedback, such as many tube amps and some (but relatively few) solid state amps.

Best regards,
-- Al

Al,
Our "average" listening levels are in the same range(I say mine is roughly mid 70s-low 80s db).Al does your amp allow NFB settings other than zero feedback to match different speakers? Although I`ve heard this amp numerous times I don`t know its feature/control options.
Regards,

Hi Charles,

Yes, the VAC Renaissance 70/70 Mk III has a six-position switch for each channel which, according to the manual, allows the amount of feedback to be selected between 0, 3.5, 4.5, 5.5, 6.5, and 7.5 db (the markings on the panel omit the fractional amounts).

I've been sufficiently happy with the results provided by the 0 db setting, though, that I've never even tried the other positions. If the impedance curve of my speakers were not as flat as it is, however, and if their impedance characteristics were less benign in any other way, I certainly would have felt motivated to experiment with the other settings.

Best regards,
-- Al

Al, I am surprised that curiosity hasn't gotten the better of you.

I suppose then that the fact that my tube amp, although a simple ultralinear design, has very little feedback and thus sounds crisp and accurate...transient impact and overall tonal accuracy seem spot on so I have no complaints. It doesn't hurt that my mid woofer speakers are very small and light magnesium/aluminum things that don't take much to get going, and the REL sub keeps up fine. I know this news is a relief for those who worry about my having a satisfying hifi rig, and that caring and compassionate wave of real love is palpable. Thanks....really...

Petepappp,
Audio and musical enjoyment is overwhelmingly subjective, people listen and either accept or reject.We just like what we like.This is why choices abound in all component catagories,something for everyone.
Regards,

Wolf, I love you man! You always make me smile with your posts.

Somehow I just can't imagine an Almarg thread titled "Best Setting for 70/70 Feedback Control?"

"In theory, theory and practice are the same. In practice, they are not." -- Albert Einstein

Al, kinda curious about the variable negative feedback switch you mentioned. Out of curiosity, if you were driving a speaker with a bumpy impedance curve, how much "smoothing" would be achieved if you used NF?? For example, if your speaker had a 20 ohm bump at 2K Hz, what would happen if you used the maximum amount of NF?

Another question out of curiosity. What is considered a large amount of NF? For example, my amp puts out a pretty typical 26db or so of gain, and uses about 12 db of NF. What does that mean in terms of magnitude, output smoothing of speakers with bumpy impedance loads and the introduction of TIM?

Thanks as usual.

Bruce

To that end I would like very much for either/both to cite some tube amps that are as fast as any ss amps they've heard so far. Imo, you can't get there without serious speed in an amp.

One way to measure speed is rise time, the voltage you can reach in a given amount of time (one microsecond). This is a test that is done with square waves as an input. How does 600V/usec sound? That is faster than most transistor amplifiers, but in this case we are talking about a tube amp.

With rise time there is also usually bandwidth as well. We get full power to about 200KHz and only down about 2 db at 300KHz- this with no feedback. The bandwidth is cut off above that- the output section has bandwidth to about 60MHz or so... Once I used modified version of the amp as a booster amplifier for a CB radio transmitter, years ago, just to prove that we could do it.

So yes, they are fast.

I have never tried tube amps and I am fearful that I would miss some SLAM and Impact of the presentation. Does your system belt it out pretty loud and non fatiguing?

When I put transistor amps in my system I find myself turning up the volume in order to try to get some slam out of the amp. They just don't have it compared to the (usually) much lower powered (tube) amps that I normally run. But keep in mind these amps do have full power right down to 2 Hz.

Its funny, I've heard for years that OTLs are supposed to be wimpy amps, but in practice I find that to be more true of transistor amps, by quite a stretch, at least as far as bass is concerned. That was part of the reason I began investigating what the implications of the amp/speaker interface was really all about. I'm old enough that I remember older audio products from the 50s and 60s, and I have collected texts from the old days too. I noticed that these days things are not done the way they did them in those older textbooks, but it was not because the books were so old the math was wrong. It was because of that Paradigm thing I've been harping on. Quite literally the Voltage Paradigm has its own set of charged terms- 'output impedance' is a good example, meaning something entirely different from what it means in most fields of electronic endeavor. The result is a whole lot of confusion, but we audiophiles are quite used to it (because this has been going on for decades) and so our solution is to take it home and listen to it, regardless of what preferences we might have.

That, IMO, is not very efficient, but until the industry talks openly about these paradigms or models, whatever you want to call them, that's the way its going to be.

Now there's an impressive response. Thank you Ralph for catering to my very limited knowledge and set of sensibilities. Regardless, I do like my sugar sweet. Problem is I can't put my finger on it. I'm only able to get a glimpse. Your prior post has me seriously considering a paradigm shift of my own. I'm already hearing it in my head.

But Ralph, I think you may have mentioned yourself that if a "pure" Power Paradigm tube amp that doesn't use negative feedback and that has a somewhat high output impedance is matched up with a speaker having a "bumpy" impedance curve, there could be coloration of the acoustic presentation. Ergo, the need and importance of matching this type of amp with a speaker having a relatively benign impedance curve. The problem, I think, is that those types of speakers are in the minority of what's out there in the market. As I may have mentioned, some of the "big name" speakers like Magico and the Revel Ultima Salon 2 have impedance curves that would make a "pure" Power Paradigm amp dizzy. Or am I missing something . . . again as usual??

05-21-13: Bifwynne
Al, kinda curious about the variable negative feedback switch you mentioned. Out of curiosity, if you were driving a speaker with a bumpy impedance curve, how much "smoothing" would be achieved if you used NF?? For example, if your speaker had a 20 ohm bump at 2K Hz, what would happen if you used the maximum amount of NF?

Hi Bruce,

I don't know. It would depend on the particular amplifier, and what its output impedance is with and without that amount of feedback. Also, keep in mind that while what would be smoothed as feedback is increased is the variation of output voltage as a function of variations in speaker impedance over the frequency range, the variation of how much power is delivered to the speaker as a function of speaker impedance variation would probably be worsened. And the net sonic effects of all of that would be dependent on the design of the particular speaker.

Another question out of curiosity. What is considered a large amount of NF? For example, my amp puts out a pretty typical 26db or so of gain, and uses about 12 db of NF. What does that mean in terms of magnitude, output smoothing of speakers with bumpy impedance loads and the introduction of TIM?

Ralph would most likely have a better quantitative feel for that than I do. But my general impression is that 12 db of feedback is probably a bit more than average for a high-end tube amp.

Re TIM, variables other than the amount of feedback, such as propagation delay through the particular amplifier (i.e., how much time is required for an input signal to be propagated to the output, which is a parameter that is rarely if ever specified) will have major effects on the answer.

Best,
-- Al