I have just purchased the latest Sound Lab M1

Will be using Emotive Audio Epifania preamp with primarily analog source[Basis,Vector,Urishi].I am looking for amp recommendations.Open minded.What do you think?Thanks for your time and thoughts!
I purchased a pair of the M1's in Spring 2006, but I no longer have them in my system. If they have the teroidal transformers as mine did, you will need a tremendous amount of power. I purchased the Atma-Sphere M-2's based on Soundlabs recommendation and it was not enough power. Perhaps the VTL 750's would do the job, but I can't say for certain. My understanding is that Soundlab uses the solid state Parasound JC-1s at audio shows. I do not know how the Parasound JC-1s sound or if they actually have enough power. I hope you have a positive experience with your Soundlabs.
All the best,
Although I'm a perennial advocate of tube amps with electrostats (and have sufficient experience with SS amps and stats -- not all bad BTW) there is one SS amp I would like to audition if I had the opportunity -- i.e. if a friend had one, or something easy like that ;-) And that's the amp currently made by Sanders Sound Systems:


Roger designed these amps (300W stereo and 800W monoblock)specifically for electrostats -- BTW he designed the Innersound Eros electrostatic speaker before starting his new company. Go to his website and read the white paper and other info. It's very interesting. I've not heard one as I say, but that would be my first consideration for an SS amp for those great Soundlabs!
Dennis, you are the only person I've heard of saying Atma-Sphere MA-2s not being adequate to drive Sound Labs. There are quite a few happy owners out there using that combination, and for that matter MA-1s with the power supply boost option. You didn't say whether your M-1s did not have the backplate impedance update which is particularly useful when driving the speakers with OTL amplifiers. Additionally, did your speakers have the higher efficiency panels and (gray) high voltage bias power supplies?

Disclaimer: Sound Lab and Atma-Sphere dealer.

Several things here. First, I agree with Brian regarding the Atma-Sphere MA-2s. His questions are valid - are you sure that the speakers have both of these updates? I can answer one of your other questions as well. The JC-1s have more than enough power for SoundLabs. I owned these amps before my present ones, bringing me to my final point on which I can offer an informed opinion. Ayre MX-Rs are, in my opinion, truly outstanding amps and are well suited to the SoundLabs.

Other amps that owners seem very satisfied with - the previously mentioned Atmas, the VTL 750s that you spoke of, Wolcotts, CAT JL-1 and JL-2, and the big Pass amps. I can tell you from experience that the Rogue Zeus sounds great on them but ultimately gives out too early.

I'll chime in here with another view. I own a pair of Soundlab A3's and use BAT VK 55 monoblocks. I never listen above 85 db and these amps have proven to be very capable. In the summer I use an Innersound ESL 300 MKII. I prefer the 55's midrange over the 300's transparency, both have their strengths and weakness, neither lack detail. Once again, your ears are the final judge.
In answer to the questions concerning my M1's. They did have the updated backplates, and they were the latest panels. They came directly from soundlab to me in June 2006. I have the MA-2 MK III's and the speakers clipped at a volume level that was not all that high. I still have the Atma-Spheres and they are functioning flawlessly, so the amps were not in any way defective. I too like the Soundlabs, but I would certainly want a lot of power to drive them.
Best of luck,
I think the pair of mfa 200d's on audiogon would drive the soundlab's fine as I was looking at them for my m2's. I talked with scott franklin in san jose ca to get his opinion and he said they would do a excellant job in controlling the panels.
If you go the OTL route I would invest in a pair of autoformers.
I own older M1's.

I owned a Levinson 336, but simultaneously home auditioned CAT JL-1's, and Parasound JC1's.

I tried the CAT JL-1's first. It would be an understatement to advise that I was astonished by what they were doing.

I then inserted the JC1's. Needless to say they weren't the CAT's. So, I didn't leave them connected for more than a brief period.

Without directly A/B'ing the JC1’s to the Levinson, my sense was that they equaled or even exceeded the Levinson. For less expense, I thought the Parasounds represented a good deal. But the CAT's -- older models and albeit used -- haven't left my listening room.

I've not tried Atma-sphere or Wolcott amps which have been used quite successfully with S/L’s, but based on lots of research (but no personal experience), I believe the former as a power source for the M1’s, would rival the CAT's -- different, but still superlative.
Something else to consider, if you like OTL-type sound, David Berning's new Quadrature Z. It extends the technology used in his ZH270 to much higher power applications--specifically 200 wpc into 8 ohm, 270 wpc into 4, with 'burst' of 300 wpc. Never heard them with Soundlabs, but sure sound awesome with what I have.
Oneprof, FWIW while unquestionably a brilliant design, the Berning isn't an OTL- it has both an output transformer and semiconductors in the output section.
Hi Ralph.

So, let me get this right, it's now a transformer couple Solid state amp :) what ever happen to it being a Digital amp.

Ralph, it's obvious that you don't understand the technology and that's okay man, it's a long way from the 50's type circuits.

We gave you several reasons before why the ZOTL technology cannot be a digital amp or a solid state amp and why none of the over 24 hand made transformers within these amps are audio transformers, now we didn't expect the average public to understand but we thought you might have.

Hi Allan, I think there is some confusion- I've never said
the Berning was 'digital'-ever...

To be an OTL specifically means no transformers at the output of the output tubes. Its a technicality, the point is that calling something that it isn't is misleading, confusing and detracts from what the amplifier actually is.

The abstract from the patent is quoted below. The part where it refers to 'transformer' as opposed to 'transformerLess' and 'dc-dc switching power converters' merits my comments:

A linear audio amplifier includes a push-pull pair of vacuum tubes operating in a linear amplification mode coupled through a pair of dc-dc switching power converters to an external load impedance. Each power converter includes a transformer with one or more secondary windings that drive rectifier circuits, and the resultant dc voltage sources are loaded by their respective tubes. The power input ports of two bridge power converters are connected in a series totem-pole fashion with the minus power input port of the top bridge connected to the plus power input port of the bottom bridge. A center-tapped fixed voltage source is connected across the two-bridge pair such that the positive voltage is connected to the plus power input port of the top bridge, and the negative voltage is connected to the minus power input port of the bottom bridge. One side of an external load impedance is connected through a noise filter to the junction point of the two bridges, and the other side of the external load is connected to the center tap of the fixed voltage source. The output power ports of each converter drive the primaries of their respective converter transformers. The effective turns ratio between primary and secondary windings of these converter transformers determine the voltage/current step-up/step-down relationships between the tubes and the external load impedance.
Hi Ralph,
It looks like it’s time for me to get involved in doing the best I can to explain the ZOTL technology so more people can understand the real issues. It is good that you pasted my patent abstract into your post, and from the complexity of the description, it is easy to see why the ZOTL technology is hard to grasp. In the near future, I hope to write as non-technical an explanation as I can and post it on the Berning web site to help people understand a little better the implications of the patent, and why it works the way it does.

I maintain the term OTL in the description in the patent and in other discussions of the ZOTL because, simply, there is no output transformer in these amplifiers. No such devices are called out in the patent. What are called out in the patent are converter transformers. This is not simply calling one thing by a different name; it really is very different in form and function.

Since it will take me some time to pen an explanation of patent, I will just say for now that the interested person can visit my web site and look for the review of the ZH270 that Chuck Hansen did in Glass Audio some years ago. Chuck is a switching power supply engineer and was able to fully understand the technology and tried to explain it in terms that non-engineers could understand.

But for now, I think that it may be instructive to make some comparisons between your amplifier and my amplifier. When I look at your amplifier, I see that not only is the speaker connected to the tubes, but it is also connected to a pair of floating power supplies. Is it not true that these power supplies have ss rectifiers and transformers in them? Is it fair play now for me to call your transformers output transformers? I would not do that because it is silly. Your transformers operate at a fixed line frequency that has nothing to do with the audio frequency. Likewise, the converter transformers in my ZOTL amplifiers operate at a fixed frequency that has nothing to do with the audio frequency. Remember, also, that the ZOTL amplifiers are dc coupled except for the input stages, where ac coupling may be used to prevent dc from being passed to the speaker. Clearly, this would not be possible if there were output transformers. Likewise, your output and driver sections are dc coupled.

The real difference between your amplifier, Ralph, and my ZOTL is the power supply. You have simple fixed power supplies that are designed to strike the best balance between allowing the tubes to pass enough current to the speaker and not overcooking the tubes too much. On the other hand, the power converters in the ZOTL perform optimum impedance matching between the speakers and the tubes because they can independently furnish the operating power to the output tubes while providing the current to the speaker via an arbitrary tube voltage step-down ratio, which is the same as the speaker current step-up ratio! In other words, the ZOTL frees the amplifier designer from the requirement that the same current that goes through the speaker must go through the tubes. The ZOTL further adds the wonderful feature of isolation between the high voltage of the tubes and the speaker, and this isolation simplifies dc coupling in that there is no requirement that the output tubes be operated at the same dc level as the speaker.

With the ZOTL, the tubes can be operated at their best efficiency. In the ZH270 and the new Quadrature Z, I choose to operate with a dc plate voltage of around 1400 volts. This would be too high for an audio output transformer, as the insulation would fail if required high fidelity tight-coupling winding procedures were followed. Operating the tubes at this voltage brings the efficiency of the tubes up to what would be expected of transistors in a conventional amplifier. This is why the Quadrature Z can boast 200 watts out of only four modest-sized output tubes (33JV6) at 8 ohms. This goes up to 270 watts at 4 ohms continuous without the tubes showing color. Ralph- that’s 270 watts of OTL tube power into 4 ohms!

David Berning
This has turned into quite a great discussion with two luminary amp designers.
Hi David, your numbers are impressive and as I have always made sure to mention in the past, its an impressive design. I was privy to Harvey Rosenburg's plans when he coined the acronym 'ZOTL' back when he was making a deal with you to manufacture and distribute them.

I've not argued the term 'ZOTL', but when people say the amp is an OTL, well, it isn't. If you removed the aircore transformers from your amp it wouldn't work. I get that you choose to call them 'converter transformers' but the term transformer was sufficient as that term already meant what you were trying to say. A person could as easily say that a every transformer-coupled tube amp made has a transformer that converts from high impedance to low impedance with "an arbitrary tube voltage step-down ratio", to use your expression. Either way it sure sounds like a transformer is somehow involved in the matching between the tubes and the loudspeaker. Your text supports this as does the patent abstract. OTL it isn't.

My point is also that in saying you have an OTL, people come away with a very different idea of what your amp is. Why not call it a 'zero hysteresis amplifier' (isn't that the basis of the letters 'ZH' in the ZH270)?

In an email that you once sent to me when I was having a rough time, you said that high end audio needs companies like mine for the diversity they represent. I've always appreciated that, but in fairness the simple fact is that you are right, and your amplifier represents some pretty serious diversity!! -and one that I for one have always appreciated. Let it shine dude!
"If you removed the aircore transformers from your amp it wouldn't work."

This is not true, it will work, but it will have to work like a regular OTL, unable to handle low impedances, as well as power requirements without a zillion smoking hot tubes, as well as the other short comings that Dave mentioned above.

As I have said before, it is a quantum leap in OTL deign or any kind of tube amp design and as much as you want to harp about a transformer, you know it's an impossibility of it being a AUDIO output transformer, which is really what OTL means!

Hey man, you know all we are trying to do here is educate the audiophile a little and old school does not apply here anymore which is everybody doing the same thing but "only different" slightly.

Take it easy there man!
Hi Winston, There are several good amp recommendations here but if you can get a demo with the new Berning Quad Zs, I have no doubt you would be left with a big smile. When the MBL 9011 amps left me cold, I talked/begged David Berning into working his magic with amps that would power the most difficult speakers made, read M1s, Revel Salons and MBLs. The units offer large current delivery, COOL running tubes, slam and finesse. No other high output amp offers this combination that I know of.
Hi Allan, there is a product called the ZERO (see zeroimpedance.com). It allows our smaller amplifiers to drive loads down to 2 ohms. Its an outboard output transformer, but one with a very low turns ratio.

Without it, our smaller amps can't drive really low impedances like 2-3 ohms. You made my point for me: a transformer is in use in the Berning amplifier, which allows it to drive low impedances, i.e. its not an OTL; failing the definition of an OTL in that it has an output transformer (walks like a transformer, quacks like a transformer, its a transformer). So call it it a ZOTL (although I've got no idea what the acronym stands for, Harvey never told me), or make up a more accurate acronym, if it happens to be that you even *need* an acronym.

I don't object to the technology, never have and I've always admired its ingenuity and said so any time I've mentioned it in the past (you can't get better advertising can you?). This is about something else: for example I am sure I would get castigated if I started calling our amplifier a transistor amp when it has no transistors.

Ya know, one of the biggest marketing issues any OTL manufacturer has to overcome is the legacy of the Futterman amplifier. That legacy is that the amp is unreliable, finicky and can't handle difficult loads. I really feel that we changed that over the years, but what puzzles me is that David must *know* this as if he chooses to call his amp an OTL, people will challenge him on these issues as they have Atma-Sphere. What I don't get is why David would take that on when the amp isn't an OTL in the first place.

About 9 or 10 years ago, in a letter to Positive Feedback, David mentioned that he found it difficult to explain how his amp worked to the public, so he told the public it was an OTL, because it was easier. The admission that the amp was not really an OTL was published that long ago.
Hi Winston,

I don't have any amp recommendation for you (I'm in the high efficiency/low power camp), but I thought it was an interesting coincidence that we both have an Epifania, Vector arm and Basis table (I have a Debut Vacuum and a Lyra Titan cartridge). My Epifania has Teflon caps and is equiped with remote control of volume, source selection, balance and mute.

I like the Soundlab M-1s. Looks like you have impeccable taste in gear.
Some would conclude that my description above in many ways describes the characteristics of an audio output transformer, except for the dc-coupling attributes. In fact, the ZOTL can accurately be described as an ideal output transformer emulation circuit. When I claim that it is OTL, I am saying that the ZOTL lacks the physical item known in the audio industry as an audio output transformer. The physical object known as an audio output transformer is made using an iron-based core that is wound with perhaps a kilometer of magnet wire to obtain the required inductance to couple the full range of audio frequencies from a primary winding (tube side) to a secondary winding to which the speaker is normally connected.

The audio output transformer is a good way to couple tubes to speakers, and makes a lot of practical sense. It is the most economical way to make a tube amp, although I think the ZOTL could compete if made on a high-volume scale. For this reason, almost all tube amps ever made use such a transformer.

But let’s face it, the audio output transformer, with its hysteresic iron core and perhaps a kilometer of wire is plagued by parasitics that adversely affect sound reproduction. The first major OTL pioneer, Futterman, and later persons like Ralph of Atmasphere realized the sonic limitations of output transformers and went to great lengths to find a way to use tubes but eliminate the output transformer. (Apparently Futterman developed his earliest amplifiers with the goal of reducing cost, not achieving better sound). It should be noted that not everyone likes the sound of the OTL amp and some prefer the output transformer coupled sound.

For many years I made transformer-coupled amps, and I am very familiar with the sonic issues of these amplifiers. Almost any amplifier will sound good on reasonably well-recorded music of the pop and jazz variety. But I worked very hard to make some of my difficult recordings sound right. These were still well recorded, but the music itself was difficult to reproduce convincingly. One of my test records was Shostakovich String Quartets on L’oiseau-Lyre DSL011. I struggled with this record for years. I could tweek one resistor this way and make one instrument sound right, but another instrument would then sound wrong. The first ZOTL I built was soon put to the test with this record, and suddenly all of the instruments were reproduced correctly. My output transformer based amplifiers were suddenly obsolete in my mind.

The point that I am making with all this is that the audio output transformer is a sonic filter that while some prefers having it, there is a reduction of reproduced transparency particularly at the frequency extremes. Both traditional OTL designers like Ralph and designers like myself who come up with a new way to beat the colorations of the output transformer have the common goal of integrity of the sound reproduction. In my view, an amplifier that eliminates the audio output transformer, both physically and in sprit, falls into a class that is simply known as the OTL amplifier. In other words, either the amplifier has an audio output transformer characterized as described above, or it doesn’t. The sonic attributes of the ZOTL and the traditional OTL amplifiers are far more similar than different, although differences can be expected based on speaker matching.
Yo Ralph.
Dave did say something like that but what was meant was that the least this amp is, is an OTL, the least it is! So that people can get a little grasp, because it's not output transformer coupled, so then what is it???

Having a transformer that does not operate at audio frequency or anywhere near it, is not a audio output transformer, as Dave has pointed out above it would compare to your power transformer, then if that's the case neither of our amps are OTL's !

After all, this technology is to over come all of the OTL's troubles, as noted in your posting, with the Futterman as well as with many other OTL's but with keeping all of the positive sonic attributes of an OTL.

You have to remember Futterman came out with the OTL in 1954 and his primary reason was for cost savings, he eliminated the audio output transformer because they were costly and he had access to tubes so he could load up the thing with a zillion hot tubes, now Dave's invention does away with both the audio output transformer and the Zillion smoking hot power hungry tubes, just because this is so radical, does not make it an output transformer coupled amp, or anything else other than an invention of tube amp technology with responsibility suitable for modern times.
So that people can get a little grasp, because it's not output transformer coupled, so then what is it???

Why don't you call it what it is? An amplifier coupled by an RF transformer, bypassing traditional output transformer problems? Instead of making up stories about how a transformer isn't a transformer- sounds a little like the Emperor's New Clothes after a while.

That children's story is not just for amusement- it was devise to teach to children how a story can be made up merely for purposes of looking good, or failing that, not looking bad. And what happens when you see through the story.
Oh Ralph.

We're not making up stories, we're telling it like it is, our patent is available for all to see on our website.

There are those that understand it and those that don't, simple.
You'll have to sort out which side of that understanding you are on then. So- by you: a transformer is not a transformer and semiconductors are not semiconductors.
A transformer is a transformer, a audio output transformer is something else, As I said before Ralph, there are over 2 dozen transformers in these amps and not one even comes close to being a audio output transformer, if you can't understand that, what else can I say man.
Sure is a interesting thread; for me it is pretty simple on the OTL definition; If the input signal flows only off the output tubes and goes to the speaker output jacks then to me the amp is OTL; if there is a transformer in the path it is not OTL.
Hey Allan, let's not be condescending toward one another. I see this thread going nowhere (and far off topic, by the way) due to differences in perception and arguing semantics. A transformer is a transformer; you contend there are none, at least in the audio frequency band. It's not a matter of understanding, it's a matter of definition.

In the end the only thing that counts is the sound. I hope Winston, the originator of this discussion thread, is able to pursue some of the amplifiers suggested and recommend that he contact the respective retailers to audition the candidates in his system to make an informed purchasing decision.
Well my friend Jocelyn, he's the guy that mod's the Acoustat's in Quebec Canada uses a Plinius S-250MK1V on his Acoustat's Spectra 6600, and it's the best sound i have heard in 40 years and i have heard quite a few, i have been attending the Montreal S.S.I. audio show for over 20 years so i know how a good system sounds.

PS: just google MrAcoustat Flickr you will see pictures of my Acoustat's 1+1s and the Acoustat's Spectra 6600s the small one weighs 200 pounds each the big ones 600 pounds all metal frames.
This was interesting. I think Dave is a genius and Ralph is right there with him. But as a degreed engineer I have to say that Allans assertion that
"A transformer is a transformer, a audio output transformer is something else" is ahem..., how to say... Ridiculous. I don't care what band a transformer is designed to handle; it is a TRANSFORMER. This to me is like saying a car that has a CVT (continuously variable transmission) is direct drive (i.e. A hub motor) because it does not use a standard slosh-box :). Bunk, it has a transmission.

I personally think the Berning amps are ingenious and I like them, but the schematic clearly shows a transformer in the circuit that audio signal passes through via a carrier frequency on its way to the output...that's a transformer hence it is not an OTL. A rose by any other name (rf transformer) is still a rose (transformer).

Now I get what Davis is saying, he is making a distinction between a typical iron/steel core transformer with kilometers of wire vs a very small air core transformer. I also understand Ralph, in the strictest since no matter how you write it, describe it, obfuscate it..., a transformer exists in the output of the Berning amplifiers. My Graaf amplifiers have NO transformer of any type in the output..., hence they are OTL amplifiers.