OTL Tube Amps-- are they superior to everything?

A recent conversation I had with an Audiogon member got me interested in OTLs. His opinion is that nothing compares to them for clarity, naturalness and superiority in just about every area. The Atmaspheres are the amps he has, and they are purportedly very stable, unlike most other OTL designs, which many can tell you were a living nightmare.

This is ironic, because some mfrs., like McIntosh, actually put output transformers on their better solid state pieces, claiming they provide superior sonics.

What is the truth here?
The only "truth" is that OTL amps are a compromise, like everything else in audio. They are generally expensive, consume a LOT of power, are comprised of expensive tubes (many tubes) and can very finicky about which speakers they decide to work with. No free lunch, but if you can live with them, the rewards are definitely there.
Apparently, you have not heard of the David Berning ZH 270. Uses only 4 output tubes, idles at 100 watts, weighs 10 lbs. And will drive any speaker you throw at it(power actually increases, as Ohms decrease). It does not suffer from the traditional "comprimises" as the other OTL's out there, yet retains all of the qualities that make an OTL great. Saxo, I highly recommend you check out the Berning website. It is an incredible product.
"Gs5556" is pretty much on the money. You have to be careful with what, and how they are mated with speakers. But, when they are matched correctly they exhibit a most voluptuous, detailed, delicate and dynamic soundstage. In short it has that "reach out and touch me" sound that is so real. Not strident or harsh at all. The bass is not as tight as the solid state kings but, the overall sound just washes away what minor weaknesses it has. They are superb sounding to say the least.

I have used the Atmasphere MA-1 with the Music "Z" transformer on both my Maggie 1.6 and 3.6 speakers. The auto-transformer is needed, actually it is a must for these speakers but, once set correctly for the impedance transformation it produced a most enjoyable sound. My favorite so far. I believe bi-amping would be the best way to go on the Maggies. Solid state on the low end and OTL on mid panel and ribbon.

I have also heard the Atmashpere at length on Sound Lab electrostatic speakers. No auto-transformer is needed here as the SLs exhibit a higher impedance. Spectacular sound here as well. Perhaps this type speaker is the best match of all for an OTL. Quality solid state amps sound very clean but just a little steril and maybe a touch less dynamic by comparison.

Check out the "OTL Online" forum. Lots of good information here. No problems with tubes on the Atmasphere. The design is mature and extremely stable. And, it is peaked in performance. You will not need to think about tweakes. The amplifier is designed as they all should be, right.


The truth is that the amps and speakers must perform together as a "unit". I would generalize to say that if your speakers drop below 8 ohms anywhere you will miss out on something sonically with almost any OTL amp. Several years ago I had Martin-Logan CLS'es and a pair of Fourier Panthere (200W) OTL's...these just didn't cut it despite the conventional wisdom of mating OTL's with stators. More recently I auditioned Atma MA-1 MkII's on my Wilson Sophias. Again, the music's foundation was sorely lacking with this pairing. In contrast, I am using Nagra VPA's which have output transformers but are rated at about one-third the output power of the Atma's. These give up nothing to the Atma's in terms of clarity, naturalness and soundspace and in addition they control the bottom end like a Krell. So while it may sound esoteric to say your amps are OTL's, or pure Class A, or single-ended etc. it's their match with your speakers rather than the design parameters that matter. I would go further to generalize that amps that work well with a wider variety of speakers are better designs than ones that have matching limitations.
While i haven't heard a ton of different OTL's, i do know that the Atma's sound very nice. As Gs mentions above, any design is a compromise of sorts and OTL's are no different.

Having said that, i know that Brian, who is the President of the Chicago Audio Society, recently switched from Atma-Sphere's to the new Parasound JC-1's. He's using these to drive his Sound Lab's. From the brief communications that i've had with him about this, he said that the JC-1 delivers all of the air, liquidity and finesse of the Atma's with the bass impact and slam that one expects from a "kick ass" SS amp. I know that both he and Bob Crump were pleasantly surprised with the results of this side by side comparison. Sean
As stated above, optimal matching of the speaker and amplifier is a must. I don't think this is terribly difficult. There is a product called the ZERO autoformer (www.zeroimpedance.com) that will allow for more speaker choices, and is anything but a compromise in practical terms.

BTW, I am using Atma-Sphere M-60 amps with Köchel K300 horns. In my setup the XLO Signature Shotgun speaker cables I use are vastly superior to the ZEROs.

I believe I am achieving superior results, to each his own though I guess.
Short answer is no.

I agree that all designs are a compromise. You have to decide what compromises are right for you. I have a 20 watt OTL and speakers with low impedences do not work well with it at all. This does not mean that it will sound good with all high impedence speakers either. But, as a general rule, with high impedence or flat 8 ohm speakers, the OTL will sound more transparent and fast than other amp designs.

Most OTL amp designers contend that the Berning is not a true OTL. With all the wires and circuitry in there it is amazing that it even works. It is more amazing when you hear the thing play- with all types of speakers. I believe that Mr. Berning is a genius who just happens to design amps. He is so far ahead of other designers (most of which use basic amplifier circuits created in the 50s- not entirely bad) that the only thing they can do is ignore him. I almost bought one, but........ The only drawback is that it is so unconventional that if it ever breaks you better pray that Mr. Berning is around to fix it (and have parts for it).
It sounds to me like you need to commit to an OTL amp, and then choose a speaker that works well with it. This is a big step, and I'm not sure if I'm ready for such a commitment. I also read quite a few reviews on the otlamp.com website. Although every reviewer liked them very much, Todd Warnke of Sound Stage seemed to zero in on the flaws they do have. So, I guess they don't do everything perfect, but then nothing does.

Sean, since I'm in Chicago, perhaps you could drop me a line, and maybe we could talk...
It sounds to me like you need to commit to an OTL amp, and then choose a speaker that works well with it. This is a big step, and I'm not sure if I'm ready for such a commitment. I also read quite a few reviews on the otlamp.com website. Although every reviewer liked them very much, Todd Warnke of Sound Stage seemed to zero in on the flaws they do have. So, I guess they don't do everything perfect, but then nothing does.

Sean, since I'm in Chicago, perhaps you could drop me a line, and maybe we could talk...
I personally haven't heard any amp design that offers what OTL's do when matched with an optimal load. The traditional design will however exibit problems if not properly matched to a stable high impedance speaker load. The ideal being 16 ohms. Not too many dynamic speakers exibit such a load therefore the zeroformer is used. This thing DOES affect the sound of the amp. The higher the multiplier, the dryer the sound becomes losing some of the characteristic OTL "sound", in my mind a compromise. The plus side with this device is maintaining the clarity at the frequency extremes.

The Berning zh270 really isn't a true OTL which by definition means nothing but wire between the plate and speaker terminal. The Berning uses a patented high frequency impedace converter which is essentially a transformer without the effects of iron, the signal is unaffected. What you get is a pure signal with the pluses of OTL's PLUS the ability to drive low impedance loads at full power. This design is also high bandwidth and doesn't have the limitations of traditional output transformers. I expect some of the more expensive modern tube designs have limited some of the problems associated in the past with transformers.

Ultrakatz's reservations about owning such a product was also a concern of mine. What happens if the designer isn't around to fix the amp if there is a problem down the road? Berning's track record for reliability of his products is legendary, he personally assembles his own amps. I guess at some point you have to take the leap of faith and not worry too much about it. Listening is believing, this amp is quite special as well as offering flexibility beyond a typical basic amplifier.
Had a chance to spend a few hours with the new JC-1s. Very
nice amps. Nice design and nice sound. Nothing even close
to earth shattering, however. Certainly wouldn't swap my
D-400mkIIs for them. I'm surprised an OTL/tube guy would
make the jump to SS because of these amps.
I agree that a Berning ZOTL differs from a normal OTL amp. The ZOTL has all the advantages, and none of the limitations of "normal" OTL.

As many of you already know, I feel that the ZOTL is the premier audio design in history, thus far. That being said, if I heard a better sounding amp that I could afford, I'd buy it tomorrow. Don't think that's too likely, and not because I didn't have the money.

Agree that there are speaker limitations with just about any amplifier, even high power SS ones. Nothing matches with everything perfectly.

To answer your question directly, I feel that tube amps do music better than SS, and OTL gives a clearer faster insight into the music, with the right speakers. ZOTL does that even better, and can do some things a nomal OTL could never do, such as allow true SET configuration, without the use or limitation of traditional audio output transformers.

This is all my humble opinion, and is not meant to disparage any other type of amp, or its manufacturer, or owner. I use the ZOTL product, and know its capabilities.
IMO, Tubegroover and Twl opinions are right on. Must use common since in speaker choice, but you may be amazed at how many speaker options are open to you. Take a listen, you may never want to hear another SS amp again.
Marakanetz: High impedance loads is where OTL's will really shine, especially if they are basically resistive in nature.

Meisterkleef: Only reporting what i've been told, so i don't know. As mentioned before though, i've also been told of another party that had $40K mono-blocks that dumped them and switched to the JC-1's. Obviously, they must be capable of some type of magic. Like anything else though, i would imagine that it was system specific and up to personal preference. Sean
DISCLAIMER: I am probably the person Saxo is referring to in this thread. Apologies to those who find my involvement inappropriate.

I am personally a fan of OTL amplification in the right circumstance.

In my long and winding audio road, the road of tube amplification has struck me as more musical than other options. Eventually, upon the advice of a great friend here on Audiogon, relaying the feelings of himself, Israel Blume, and Arthur Salvatore, I gave OTL a shot. True to his tremendous insight, the OTL wing of tube amplifiers struck me even more deeply. To the extent where the amplification in my main system is now OTL, the Atma Sphere M60 monoblocks.

The benefit which I hear most profoundly is that is simply sounds more like music than most anything else I have come across. A trumpet sounds like a trumpet, a piano sounds like a piano, and a voice sounds like a voice. There is a sense of, if not realness, getting as close to the master tape as I can get. OTL may not be the amp for most audiophiles, but I have to say I have found they strike a very deep chord in a musician. While my many musician friends have always admired the sound of my system's incarnations over the years, their interest jumped quantum levels with the OTL sound.

I am not one to profess something sounds "live" without great reservation. Let's face it, the illusion we all pursue, live music, is something that is experienced very rarely in audio systems. No matter the cost.

At least to the extent I have experienced OTL amplification in the systems of me and several friends, a great many of the concerns I have of solid state and transformer coupled tube amplifiers are ameliorated. The speed/pace of the music just seems much faster than with transformer couple tube amplifiers. It's actually quite astonishing at times. There is also a clarity and sense of hearing into the recording that defies description. I have thought that I have previously heard things get as clear and focused as they could. OTL proved I still had a lot more to hear and learn. I am sure, I still do... In these matters, the sound is what the VERY best of solid state always aspires to. However, there is a sense of soul and living to the sound that solid state just plain does not accomplish. Use all the overused descriptions we have in this hobby: musical, liquid, smooth, natural, alive, fast, clear, detailed, refined, natural, real, whatever. They apply.

About the best analogy I can make is to light. Solid state might be flourescent. Transformer coupled tube amplification might be incandescent. OTL seems more to me like sunlight.

On the downside, OTL is not perfect by any stretch of the imagination. But then, is any amplifier?

My biggest complaint is the amount of heat generated. This past summer, the coke furnace at full throttle heat of the amps combined with a brutal heatwave, drove me to try other amplifiers in my system. I tried some highly regarded products that just did not measure up to what I was trying to replace. Secondly, the electricity usage is atronomical. Credit the necessity of all those output tubes, in pure Class A triode operation. Usually, the number of tubes is a source of complaint, but not in my case. New output tubes are $12(Sovtek) or $20(Svetlana), and I have bought vintage NOS tubes at much lower rates. Try 4 NOS RCA 6AS7G for $9.99, and that price is available most of the time. At 8 tubes/amp X 2, that's only $40. I also bought 6 NOS British made Sylvanias for $17.99. Contrast this with Western Electric 300B, and it looks dirt cheap. Sonically, OTL does not grab the woofer's voice coil by the throat and totally blow me back the way I have seen other amps, including tube amps, do with my Coincident subwoofers. On the other hand, a lot of people feel that the bass in my system is more than generous. And, I have to allow that the bass is as tight and believable as I have come across in my system. Still, I have to call them as I see them, and I see the bass as not the strong suit. Although not the case in my system, OTL is incompatible with a great many loudspeakers. In fact, with my Frieds, the sound just never came alive. A marriage akin Princess Diana and Rob Schneider.

Normally, my first priority is the interaction between listening room and loudspeaker. After that, comes loudspeaker and power amplifier. Given that once someone decides to make a committment to OTL, the loudspeaker - amplifier pairing takes steps upward in terms of level of importance. Fortunately, my current room and loudspeakers provided me with a lot of good luck. My speakers simply love my room and work quite well with OTL amplification. Others will have to look elsewhere. There is no getting around that.

I would like to mention something about the use of autoformers between OTL amplification and the loudspeaker. Yes, they do improve the compatibility of the two via impedence multiplication. No question. The load the amplifier sees, in terms of impedence will increase anywhere from 2X - 16X, depending on how you configure the autoformers. Bass response will certainly improve, most specifically becoming tighter. Distortion will also get a bit better. BUT, and this is the big but, the magic of the OTL somehow vanishes to whatever degree. It is system dependent. The sound becomes whiter, more antiseptic, less warm, less alive, less real. More like a solid state amplifier sound. My opinions on this were mirrored by two other audiophiles trying them in their systems as well.

And, like everything in audio and life. Just because someone feels the that something is good, doesn't mean it is so. You may very well be on the opposite end of the spectrum. In fact, I myself(others here concurred) have twice found the Atma Sphere/Class Audio Reproductions demo to be about as horrendously bad sound as I have EVER come across, HiFi, lowfi, or no fi. Others have praised the combination lavishly. We all have our opinions.
One thing I forgot to say in all of my BS is that sometimes, I prefer the sound of my Jadis amp over the Atma Spheres. It all depends...
Trelja, you did mention OTL to me and I know that you own OTL, and you did provide me with some food for thought there. But you were not the Audiogoner I was referring to. You don't own Atma-spheres, which at the start of this thread, I mentioned were the amps this Audiogoner owned.

This is just a clarification, not meant to take away from your appreciated and insightful comments. Thanks again for the generous sharing of your experience and knowledge.

The Berning sounds very interesting, although I would be concerned about the complexity of the design and its execution, plus the fact that I believe Berning disappears and reemerges periodically. Correct me if I'm wrong.
Saxo, as a multiple Berning owner, I can only agree with what tubegroover and TWL said regarding its abilities and advantages.
However, I'm not quite sure what you mean by the amp 'appearing and disappearing'. If you mean availability of the amp to buy used here on Audiogon, they certainly are less commonly available used than more mainstream products, but that does not mean that there is something 'wrong' with them. There was one available a week or so ago here; it isn't there now, but that's probably because when they come up, they sell fairly quickly. Actually, I was thinking of buying it myself to compare a 'solo' 270 to my monoblocked ones, but common sense reared its ugly head. Both of my Bernings were bought through ads I first saw here on Audiogon, in fact.
Trelja, are you referring to Paul Speltz ZERO autoformers? If so have you ever tried the alternative 2X configuration? I found this configuration was more nuanced than the standard configuration. There was a slight drop off in bass output though. I then used two pairs, alternative 2X on the high frequencies, and standard 2X on the low frequencies. This yielded absolutely phenomenal results on the N.E.A.R. 50Me II speakers I was using at the time. I would love to hear about your results if you happen to try this.
OTL, means output transformer-less device, does not mean "nothing between the plate and speaker terminal", then it would be NPST or something like that, some OTL designs may use caps or resistors in between the plate and terminal, in fact some highly regarded units may do so.

The ZH-270 is an "OTL" amp in every respect of other "OTL" amps, just that it does it in a very high technology way, or different than anyone else.
Ok Allan, but it seems we have had this discussion before. But I ask you this, if an inpedance converter is not a transformer of sorts, what exactly is it? Also true that some OTL's have a cap or resistor between plate and terminal but none have an impedance convertor or transformer, agreed? ;)

Tubegroover, Yes, the RF conversion transformer, is a transformer but Dude, again, like before, it's not in the signal path. So the signal is that of a direct plate to speaker output but this is achieved in the most absolutely ingenious and mind boggling way.
If you really study the design, you'll see that in fact it's superior to a regular OTL.
So maybe the best way to describe the ZH-270 is to say, it's like no other OTL, or there is no other OTL like it :)
Tubegroover, according to David's discussions, the ZOTL circuit is a transformer emulator circuit. It provides the impedance matching without the turns-ratio limitations and saturation limitations of traditional output transfomers. The circuit emulates the "perfect transformer" and doesn't suffer from the sonic limitations of these transformers. Therefore, the audio signal is not subjected to the performance limiting factors associated with output transformers. But the impedance matching is done in a much more efficient way than is possible with a transformer, without degrading signal integrity. This allows virtually vertical rise times in square wave response well beyond the audio range, and this is exhibited by the incredible speed of this amplifier. No audio output transformer can deliver this type of performance.

As far as comparing the ZOTL method to traditional OTL methods of impedance matching, the traditional OTL circuits use multiple sets of tubes in parallel to reduce the output impedance of the amp to a level which could be practical for driving a speaker. Due to the fact that they don't get the output impedance very low, they do better into higher impedance speaker loads. The ZOTL circuit gets the output impedance down to 1.8 ohms, and provides better damping factor into normal speaker impedances. And it does so with fewer tubes in the signal path.

To take this one step further, the Single-Ended ZOTL amps have only 2 tubes per channel(1 driver and 1 output triode). No traditional OTL can do that. The coherency provided by using one output triode in OTL, instead of a multiplicity of output tubes, is something that has never been heard, outside of the Berning circuit amps. So this goes beyond just impedance matching. There has never been a true single-ended triode OTL before this. That, in itself, is a major breakthrough, and is worthy of accolades for allowing closer insight into the music.
Wow!!! TWL, you've been doing some reading :) but it's still even more complicated than that, if you can believe it :)
I do agree Allan and don't pretend to understand how this high frequency converter "carries" the signal and increases the turns ratio to 64-1 and matches impedance to the speakers, it is indeed mind boggling! My point is that a converter/transformer, regardless of how radical and different the approach, is used to achieve what this amp does. Explaining HOW it works would be informative to those wanting to understand this innovative design although I don't think it would be readily understood.

Saxo, if a man designs, builds and puts his name on a product and those products have stood the test of time and along the way have added really innovative approaches to solving some of the real world problems in getting the signal to is purest form, I would be less concerned about the complexity and maybe investigate further whether it is something that might work for you. Due to its features (auto-biasing, 3 feedback settings, 2 inputs for line source components), light weight (10 lbs), low heat output (100 watts idle, 300 watts full power) and most importantly sound reproduction I feel quite certain that I will keep it forever. It is just too cool in more ways than one!
Saxo, I apologize. However, I do own a pair of Atma Sphere M60 monoblocks.

Wellfed, yes it was the Paul Speltz Zero Autoformers I tried in my system. For about 1.5 months, on loan from a good friend, whose testimonial is on the website. Beginning with the 2X setting, and also with some higher multiplication configurations.

I do not deny that in your situation, the Zeroes made an improvement. I think that for the majority of loudspeakers, they will not only make that kind of difference, they are required. However, as I noted, there is a significant loss in the OTL magic. My opinion is that if someone were to go down the OTL path, a better option is to choose a high impedence loudspeaker from the get go. That way, none of the life of the OTL amplification is compromised whatsoever.
Yes, Allan, I studied this quite a bit before getting into Berning's amps. I also know about the RF carrier, and the "bus stop" get-on, and get-off routine. But I felt it was of no use to get into that here, because nobody has understood it previously, and I doubt anybody is going to get it now.

By the way, you should hear this battery powered, choke loaded 45 SE ZOTL. It's the cat's ass. I really would like to get an ear on those direct drive 270 amps you have too. I forgot what speakers you are matching them to. What are they?
*** His opinion is that nothing compares to them for clarity, naturalness and superiority in just about every area.

They do have some very specific and very limited qualities that are attractive but mostly the “attractive qualities" get overwhelmed by a large amount of the very critical fundamental imperfections… There is a LOT of more to it but it will be obviously out of scope of the typical Audiogon member’s aptitude. If you looking for serious information but not for the casual audiophile BS then look somewhere alse.

*** The Atmaspheres are the amps he has, and they are purportedly very stable, unlike most other OTL designs, which many can tell you were a living nightmare.

Atmaspheres actually are very poor electroniks and I sincerely feel that to make any conclusions about topology base on the evaluation of a specifically-badly-implemented brand is a wrong thing to do.

*** What is the truth here?

Look for the answers somewhere else.
Twl, I would love to hear those amps of yours, I'll even make a effort to come and hear it, where ever you are :)

My amps are 6JN6 based but not a 270, they are direct drives, directly driving Sound labs, I have over twice the rail voltage of a regular 270 but a lot of the design is similar, this alone is a testament to the reliability and rock steady stability of the design, it's capable of producing 6000v peak to peak, yeah it only weighs 8lbs each, so not only am I OTL amp but I am transformerless on the electrostatic panels as well.
There is an open invitation to anyone to come and hear this, as talk is cheap
Verybigamp obviously has some very strong feelings on these amps. I don't think I'll have to ask for others to react to this.

About the Berning, after seeing how it looks like someone made it in their garage, perhaps that explains the stingy two-year warranty. At $4,200 for a 10 pound amp, I think I'll pass. Mr. Berning obviously feels he would be paid well for his design abilities.
Someone has emailed me privately to express his opinion of the Atma-Sphere M60. He owned them, and found that the input stage creates distortion that you can hear, although they are transparent and real sounding. He claims most owners have modified the input stages of these amps.

What's all this about?
Saxo, you have alot to learn. Is the poundage of heat sinks or the glitziness of a face plate the measure of an amplifier, in your opinion?

Do you buy your amps by the pound?

FYI, Berning has about the best reliability reputation over the last 25 years, of any manufacturer there is. The stuff never breaks. So much for the "stingy 2 year warranty" that you'll never need.

As far as being built in his garage, no, it's hand assembled by him. He actually builds each one of these himself, and you get an amp that is hand made by the most talented audio designer, probably in history.

Apparently, not only does he feel he should be paid well for his designs, so do the many customers who are WAITING IN LINE to get these amps. And when they do come up on the used market, they sell for about 85% of the new price, and are snapped up in the first few hours on the classified. Quite different than the 200 pound amps you seem to desire, which bring 40-50% of new, on the used market, and languish for days or weeks on the ad boards.

But the biggest thing you will miss is the sound that will destroy anything else you listen to in this price range. Perhaps you should look in the archives, where the Berning amps are repeatedly compared to amps costing $20k.

Don't get me wrong, you are entitled to your opinion about these amps. It was just so glaringly apparent that your opinion is poorly founded, that I had to make a comment.If you have a pre-concieved notion that you don't like OTLs, that's fine, but don't complain about the lack of weight when the whole purpose of OTL design is based on eliminating the heaviest part of a tube amp, which are the output transformers. Your comments show gross ignorance.
Twl, your comments show gross rudeness. Your adolescent, condescending comments should be kept to the high school playground.

You assert that the elimination of the output transformer accounts for an amp that weighs 10 pounds. Transistor amps don't have output transformers, but they have heavy power supply transformers, just as tube amplifiers have, either with or without output transformers. Your comment regarding this shows gross ignorance.

As far as opinions comparing them to 20K amps, there are many opinions comparing X, Y or Z amp to a costly counterpart. Berning has no corner on the market for such praises.
The Berning amp uses a high-speed switching supply instead of a normal power transformer. This was discovered to be superior about 20 years ago. So much for that argument.

You don't have to like the amp. But judge it on its merits, and not its weight. Weight has nothing to do with anything. As far as being ugly, ugly is as ugly does.
Berning lovers, including myself, it's not worth arguing with him, who apparently doesn't care for the sound.
Oh boy, let's keep it to the topic, everyone is entitled to their opinion, that's for sure.
I think Saxo might not fully understand what a Berning designed amp is and maybe rightfully so, as this industry is full of BS an BS'rs, so if I was an outsider, I too would be skeptical of such a claim, so Saxo may be reacting just as I might, if I did not get to know this design first hand or at least still trying to get to know it, WOW!

Just a note, there is a number of highly regarded speaker companies that use the ZH-270 as reference amps, one being an Italian company, that makes some of the most beautifully finished speakers in the world, yet they chose this ugly duckling.
OK, OK......Maybe I don't fully know what type of design innovation Berning has devised, that no transformers are needed. I won't say anything more against it. I will admit that it is considered in high acclaim, so there must be something special there.
Twl, Berning has had a few amps, preamps go down. But what service! I get the feeling all production stops until repairs are made. I know of only two. He was very upset, these are his babies. Turn around for these two were sent back two day's after Berning Received them. If you buy from Berning and you are I of the very few that has a problem, no need to worry. I get the impression he worries more than the customer. We need more customer service like Mr. Berning delivers.
And yes, there is something very special there.
I would highly recomment that you at least try an Atmasphere so that you can experience the true sound of a pure analog OTL piece of equipment. Does not matter whether you find it better, worse or indifferent. You just need to hear it when it matched up well to a speaker(with or without the auto-transformer).

There is just a gain stage then an output stage with zero feedback. Simple and truthful. No transformers or switchmode trick circuits. I personally think the magical OTL sound could be due to several different reasons. One, maybe distortion. Wegel and Lane(couple audio guru's) in 1930 published a formal paper indicating that, when a fundamental signal included its harmonics of the 2nd (@-22db); 3rd(@-26db)' 4th (@-30db), 5th (@-37db) and the 6th (@-46db) then it is characteristically pure sound. In 1960 Toshiba set out to investigate this and arrived at the same conclusions. Interestingly enough, single ended tube (SETs) and (300B) type amplifiers often display spectral contents very close to these characteristics. OTLs included.

Another reason the OTL may be preferred is due to its characteristic high output impedance. This can lead to speaker matching issues for two reasons. Depending on a given speakers crossover this will have the effect of emphasizing the frequency band around the crossover point (anywhere from 330 to 1.5Khz). Emphasizing this frequency range has the effect of producing a warmer or more robust sound. Bob Carver tries to emulate this by adding resistance in the output of his amplifiers (current output). To some extend this may work however, this will be a constant ohmic value where-as, in the OTL such as an Atmasphere this will be a dynamicly changing output-Z. There will be some interaction differences here.

A possible third reason for the highly revered bloom from an OTL amp is the fact that, since it does have a relatively high output Z(3 to 7 ohms in the Atmasphere series) this causes speakers to be less damped. And, being less damped the speaker may very well become closer to being critically damped, which is generally the most desired condition for a particular driver. Generally, when one reads the response of a speaker driver the manufacturer usually specifies it when "critically damped". However, once installed in a cabinet or frame with associated crossover components we don't know the status of driver damping or the designer's intent with a particular system. So sometimes an amplifier with a higher Z-out will improve the overall percieved performance by more closly providing critical damping to the drivers and, of course it may not be advantagous due to the particular design. Hence speaker matching is imortant. Reportedly electrostatic speakers benefit from the highish output impedance due to damping effects where-as planar speakers such as Magnepans need a very low output Z to properly damp their panels. For the latter the auto-transformer will be needed to effect the low Z-out. And, being an auto-transformer there is not much loss in this device to worry about. It is not hindered by the same issues (leakage inductance, output-Z limitations, interwinding capacitance, etc. that affects push pull transformers. Any audible masking of effects are basically insignificant once the proper ratio is selected.

I hope I did not bore you here. Again I recommend that you try an OTL as, for whatever reason, it sure produces a voluptuously immediate soundstage that reeks of musicality and just might nail you.
Twl and Saxo, this reminds me of another thread. Thank you both for making me feel so at home. I love the passion of these kind of threads. After seeing the same questions asked over and over. Threads like this and a few others remind me of the old day's. I mean there's Tubegroover, Wellfed, Twl, Sean, and one if not my favorite, Trelja, all on the same thread. Ya gotta love it. i am sure we will be hearing some input from Jcbtubes once he gets back Sat.
Saxo, I do not mean this as criticism, but the Berning and Atmasphere are two different animals. At least in sound. I know the Berning and IMO, the Atmasphere ain't no Berning. I can also say the Berning ain't no Atmasphere. Great to see so many of the old regulars, not to mention the newer ones.
I guess I have to apologize, too. I am not so regular here as I don't have as much experience or knowledge as many of you. But I can say that Berning is a terrific amp, regardless of the definition of "OTL", with respect to cost, performance, reliability and sound. Then again, YMMV, and this is just a different animal from other brands. Different people has different taste.
Saxo, or anyone else, if you live in NY city, I am enjohing my system with Italian speakers which Allan just mentioned, and would be more than happy to bring my Berning with HAND (not with car nor cart!) to your place. That I could contribute to those with passion for this wonderful hobby.

Enjoy and happy hunting! Ken
Yeah Brulee, I also love the passion and feel it very keenly for this product.

The thing that many philes will overlook with the zotl amps is that they are as small and lightweight as they are and will never be in the running in the beauty queen sweepstakes. There really isn't any marketing so they are word of mouth products. The one thing indisputable regardless of who will attempt to dispute it with me is that this is a cutting edge design sonically and technically, a real tour de force product. I would love to do a blind test with this amp and anything within its power range for a head to head and leave the bs at the door and THEN see what the results might be without visual, price, and other prejudicial impressions muddying up the waters.

I have read comments from others that it was a good performer in its price range, I say balderdash, it is a great performer in any price range within the limits of its power and the requirements of the speakers it might be used with. I just want to set the record straight on that and tell all what I REALLY think. This is not to disparage any other amplifier out there including Atmas-phere, Joule, Tenor, Lamms etc. but to say the Berning in the right system is in this league of component if not the best choice in a particular application.

Yes, I have heard all the above products I mention although admittedly not in a familiar system, I can only use my own as a benchmark.

PS and Romy, if there is any thing of importance that you would add you are welcome but if you just want to disparage (Atmas-phere and others) who have only been in business for over 20 years making great products, just check it at the door and tell us what you DO like, no one gives a damn what you don't.
Saxo, if you're in Chicago, I know someone that can drop over with a ZH-270 for you to hear?? How about that, would that be cool with you :)
Just so that you can hear one, I would be very interested in seeing what you think.
Ya gotta lotta class Saxo. Please don't feel alone. i have been there many times and i suppose i will be there many more times. I have no problem when i make an apology when one is due. I have no problem not to apologize just for the sake of an apology. Twl IMO, deserved your apology (like i should talk) I would take my hat off to you Saxo if i owned one. Hope to see you around more often.
allanbhaganinfo, what a warm gesture. It's people like you that show with action rather than words, a man who deserves respect. You sure got mine!
Thanks for the kind words, Brulee. You're a class act yourself. Yes, Allanb & his friend amazed me in being so generous. I will be in contact with the gentleman and see if a listen can be arranged.
Saxo I am happy for you in this respect, you will get an opportunity to listen to this product on its own terms without being subject to any further influence. Sometimes it does take making strong statements to get across the value of unassuming products that are much more than they appear to be on the surface. I believe you are going to be pleasantly surprised. The best to you, your demeanor reflects the fact you are a real gentleman.