First, it would be great to compile a list vendors selling both kits and assembled products. My attempt below, please add.

1) Transcendent Sound
2) Atma-Sphere
3) Graff
4) Joule Electra - ?

Also, for the DIYers, it would be great to put a list together of known schematics.

List of Schematics

1)
2)
3)

Thanks
Hakn Sr.

 Re: OTL Vendors - Bernt 14:52:07 11/26/04 (0)
 Re: OTL Vendors - Brian Walsh 17:27:20 10/19/04 (0)
 Re: OTL Vendors - Passive Chappy 11:04:10 10/18/04 (0)

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Show full thread outline!

 Re: OTL Vendors - Bernt 14:52:07 11/26/04 (0)
 Re: OTL Vendors - Brian Walsh 17:27:20 10/19/04 (0)
 Re: OTL Vendors - Passive Chappy 11:04:10 10/18/04 (0)
 Re: OTL Vendors - Duke 08:26:52 10/18/04 (6)
 Re: OTL Vendors...Futterman - AJ 15:20:07 10/18/04 (5)
 Re: OTL Vendors...Futterman - Duke 16:33:10 10/18/04 (4)
 Re: OTL Vendors...Futterman - Mike Mount 21:39:52 10/18/04 (3)
 Re: OTL Vendors...Futterman - AJ 18:31:17 10/19/04 (2)
 Re: Hit nail on the head with Futterman - Mike Mount 20:26:08 10/21/04 (1)
 Re: Hit nail on the head with Futterman - heidi 16:29:25 11/23/04 (0)
 Re: Joule... - Rich Brkich 07:23:05 10/18/04 (33)
 Re: Joule... - ABhagan 10:45:00 10/18/04 (32)
 Re: Joule... - Rich Brkich 15:29:05 10/18/04 (31)
 Re: Joule... - ABhagan 20:51:03 10/18/04 (21)
 I think we could agree to say... - Rich Brkich 13:36:48 10/19/04 (20)
 Re: I think we could agree to say... - ABhagan 17:53:49 10/19/04 (19)
 Why do you care? - Lew 13:31:54 10/20/04 (4)
 Re: Why do you care? - ABhagan 16:34:47 10/20/04 (2)
 I'm all for Berning enthusiasts being a part of this group myself (nt) - Wellfed 17:11:02 10/20/04 (1)
 I agree! (nt) - Rushton 17:33:55 10/20/04 (0)
 Re: Why do you care? - joneill 15:02:26 10/20/04 (0)
 Re: I think we could agree to say... - Rich Brkich 20:30:24 10/19/04 (13)
 Re: I think we could agree to say... - ABhagan 08:23:01 10/20/04 (12)
 Re: I think we could agree to say... - Lew 07:29:51 10/21/04 (0)
 I have never meant to make the design to sound like a compromise... - Rich Brkich 19:21:44 10/20/04 (7)
 Re: I have never meant to make the design to sound like a compromise... - ABhagan 20:42:34 10/20/04 (6)
 Re: I have never meant to make the design to sound like a compromise... - Rich Brkich 07:51:10 10/21/04 (5)
 Re: I have never meant to make the design to sound like a compromise... - ABhagan 09:16:21 10/21/04 (4)
 So, A guy walks into his local car dealership.... - Rich Brkich 15:15:12 10/22/04 (3)
 Re: So, A guy walks into his local car dealership.... - ABhagan 18:00:00 10/22/04 (2)
 Re: So, A guy walks into his local car dealership.... - Rich Brkich 07:43:45 10/27/04 (1)
 Re: So, A guy walks into his local car dealership.... - ABhagan 18:01:10 10/27/04 (0)
 OK Allen, that's enough advertising for now ;-) [nt] - Wellfed 17:16:45 10/20/04 (2)
 Re: OK Allen, that's enough advertising for now ;-) [nt] - ABhagan 17:27:27 10/20/04 (1)
 I hear you and I have always admired your enthusiasm... - Wellfed 17:32:01 10/20/04 (0)
 Another recent exchange between David and Ralph... - Rushton 16:51:47 10/18/04 (8)
 Re: Another recent exchange between David and Ralph... - twl 06:11:47 10/21/04 (7)
 Good to see you could drop by Tom... - Wellfed 12:20:13 10/21/04 (6)
 Re: Good to see you could drop by Tom... - twl 09:44:40 10/22/04 (2)
 I know the feeling... - Wellfed 10:27:12 10/22/04 (1)
 Re: I know the feeling... - twl 11:28:02 10/22/04 (0)
 Re: Good to see you could drop by Tom... - twl 09:43:25 10/22/04 (2)
 I'd like to take a road trip and come see you... - Wellfed 10:42:13 10/22/04 (1)
 Re: I'd like to take a road trip and come see you... - twl 11:31:19 10/22/04 (0)
 Re: OTL Vendors - fourprof 03:59:09 10/18/04 (0)

IMHO as a EE - I would not consider the Berning amp a OTL nor do I beleive David Berning refers to it directly as one (I have read through much of the technical info on this amps design - which is brilliant BTW). What David Berning has done is to design a different and very good type of output transformer device (i.e. a very clever circuit that emulates the current and voltage multiplying/dividing capabilities of a conventional transformer without the hysterises distortions that a coventional magnetic circuit transfomers exhibits).

Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

VDN from Croatia is (or was) an OTL manufacturer; their 100-watt amp was imported for a while by Sound Lab (speaker manufacturer).

I know of several people using Fourier amplifiers, though I think the company's been out of business for about eight or ten years.

I believe that Acoustat made a dedicated OTL amp for one of their speakers, and I think Beveridge once did the same thing.

Anybody out there running a Futterman?

http://www.davidberning.com/hansen_on_zh270.htm

this pretty well tells the story, this amp in every respect performs as an OTL and better in the respect of speaker impedance matching, the technology that allows this to happen is very, very complicated indeed and transcends normal audio circuitry and therefore it's stereotyping, this is where I think the confusion comes from, this amp is trying to be "labeled" into a simple category.

I have seen well respected manufactures call this amp a digital amp, a hybrid amp with a solid state output, then to a aircore transformer coupled amp.
What it is, is something that is very hard to understand in normal audio terms and is nowhere close to any of the above.

I may also add that the term Zero Hysteresis may be a confusing terminology, as it misleads one into thinking that it's a transformer, people are under the impression that Dave has invented some miraculous transformer.

If you read Hansen, and understand it, you'll see that the reason for the comparison to Audio transformers is that the amp is doing what Audio transformers do, without a audio transformer, so the relationship is for comparison only.

The RF Impedance matching device is not a transformer but a complete circuitry that employs several transformers, of non of which are Output transformers or any of which are in the audio signal path.

Charles Hansen is a Modern Transfer technology engineer, and he even calls the ZH-270 Complex.

It's all confusing I know, but because this technology is misunderstood or hard to understand, it's misleading not to call it an OTL and it's also wrong just to call it an OTL, it's best to say, I dunno what it is, you figure it out :)

P.S One Stereophile reviewer called it, Output transformer less Amp ( but not OTL )

Allan
Berning Co.

• http://www.davidberning.com/hansen_on_zh270.htm

Don't know if vintage counts...but I run a restored Futteman H-3 into single and stacked quad esl's.... running it for 3years now with no problems. Very articulate with the electrostatics...sounds as good as the the similarily powered new competition.

AJ

You see it all depends on what you call a "transformer"... in traditional circles/thought it is considered a hunk of metal with coils of wire that is used to TRANSFORM current and voltage via some (turns) ratio. Now, if that is what your defintion of what a "transformer" is... then the Berning is a OTL. However, isn't a device/circuit that transforms current and voltage via some ratio by nature a transform-er (whether or not magnetic circuit is used to accomplish the task)? I think it is reasonable to say so, hence I do not think of the Berning amps as OTLs.

Then we get into the concepts of what people (the audiophile public/consumer) think when certain terms are used to describe a product. For example, it is possible to build a solid state class AB amplifer and have the amp "technically" be single ended (i.e. just a ground and B+ power suplies)! Now, when we say single ended in this trade, what folks think of low efficency, single ended class A operation (solid state or tube wtich a max efficency of 20% to 25%). So, is it really valid to call the amp I describe above to the consuming public as "single ended".... personally I think the answer is no becuase, in a way, the company would be mis-representing what they are making given the way terminology is understood by the audiophile. Moving on to what folks think in this trade as what is meant by "OTL" ... I think we can all agree that folks think of this as a tube amp that drives the speakers directly (i.e tube(s) -> speakers just as in the same way conventional solid state amps are Transistor(s) -> Speaker and are "OTL"s too!). We should not think of the Berning in this manner becuase as it is decribed like this: tube(s) -> impedanance transforming device/circuit - > speaker. Just read Hansens article were he discusses the "Impedance Convertor" in the Berning amp's. If you want to put an acronym to all this, call it ZHIC (Zero Hysteresis Impedance Convertor).

P.S. FWIW The Late Harvey Rosenburg called the Berning amps an OTL in Positive Feedback Magazine several years ago... which lead to a long back and forth of letters in the magazine between Harvey and Raplh Karsten about what is an OTL.

Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

• http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1089043298

What people think in the trade as a OTL, is limited to what they know and was the only way to do OTL's for 50 years, this is a new way, a different way, unprecedented reliability, efficient, cool running, light weight, long tube life, compact and most importantly, proper speaker impedance matching, all with the performance and spec's of what people think of as a conventional OTL.

I see Rushton has posted the Thread at audiogon, here is the direct link to Dave comments below.

As for the tube-> converter->speaker description, again it's much more complicated than that, if we are simply talking audio frequency, as you are, the converter is not in the signal path and therefore not an issue, so it should be like this.

(250KH)
Converter
|
Tube->speaker

Allan
David Berning Co.

• http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1089043298&openflup&19&4#19

This period of sound is still pretty amazing. I (a Super-IT and) have a pair of NYAL Futterman OTL 3 with ESL57s and\or Rogers LS3\5as - sweet pair! Use mostly on - Special Occaisions.

But, M60s still sound better . . .

Duke is in the south and I am in the north (Chicago) where are you?

Hmmm now maybe I should tell Jud to call his amps "direct output coupled OTLs" instead of just "OTLs"... :-) :-) :-)

Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

Add Naked Truth Audio to the list of OTL manufacturers, although I don't know of their status.

Acoustat and Beveridge, mentioned below, made direct drive servo amps for their electrostatic loudspeakers. The Acoustat amps can work with any of their full range ESLs such as 2+2s, even though Acoustat never sold them that way.

Yes, or course traditional OTL's do not use RF impedance converters, traditional OTL amps were designed long before modern power conversion technology, maybe the best way to describe it all is in two categories.

Traditional OTL (TOTL)
Modern OTL (MOTL)

To say the Berning design is not a OTL is misleading, it's just not traditional OTL.

As for this statement
"while the output tubes of the Berning amplfier are coupled to the speaker through a Impedance Converter".

The answer is, not in the signal path, nor at audio frequencies, so why is it relevant, when there are OTL makers with a capacitive coupled design and that's not?

No doubt the the Atmas are nice. I spent alot of time with the s-30..The vintage Futterman with the 6FW5's at $3.00 a piece held its own against the s-30, in other words I would not trade to forsake the vintage Futt... a real piece of history.Now don't get me wrong I recognize the limitations of the Futterman BUT it still smokes out the detail beyond the capabilities of many highly regarded amps run through my system and I consider my front end to be capable. I have no experience with the big Atmaspheres MA-1 etc... but for the price$ they should be great. Besides I'm a bit of a vintage nut.

I more intrigued by the design of the Joule...although I doubt I'll ever see one in my neck of the woods.... The Tenors are nice and for me are almost locally manufactured....I'm near Toronto Canada.

A cap on the output of an simple amplifer is used to block DC from getting to the speaker... it provides no other function. From an audio signal point of view... the speaker sees the output impedance of the active device (tube or transistor) and the amplifing device see the impedance of the speaker. The capacitor in this case is not an impedance matching or "transforming" device. Inductors are often used on the output of power amplifers (tube and solid state) in such a manner to block high frequency (ultrasonic) info from boucing around through amp (generally through the feedback loop) and driving the amp into oscilation. Again, another reactive device (i.e a inductor or capacitor) that does not effect how the speaker or the amplifing device see each other.

Again, a output transformer at its core purpose in a audio amplifier is a impedance matching device (in the case of tube amplifer - take high voltage low current tube power and transform it to low voltage high current power that is best suited to drive the low impedance speaker load). Look at the Hansen article you pointed me to ... figure 10. As you can see there is something there between the amplifing device and the load.... it is even defined as a impedance matching apparatus in David' patent. The only direct path between the ouput device here and the speaker is a common ground. If there was nothing but a peice of wire a one or two passive parts between the tube and the load, why would there be something worth patenting here????

I'm getting tired and rambling... Alan it is hard for me get into this becuase I get so easily fustrated. Our audio world is not perfect... and full a various terms and terminologies which have certain implied meanings and ond connatations... single ended, push-pull, SE, SET, OTL, etc. If an OTL tube amp is a Orange, and a conventional hunk of iron output tranformer coupled tube amp is an Grapefruit, then the Berning amp is Tangerine. While it may be a relative of both fruits, it should certainly not be confused as one of the other fruits.

OK... now that I've really gone off the deep... Icall it quits for today.

G'nigh all.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

It is obvious that the ZH-270 is not a typical OTL, but just by the fact that it does not have a output transformer, simply makes it a OTL by default, now what it is other than that should be another debate.

The reason there is something worth patenting here is that there are different ways of doing the same thing or getting the same results, Dave is able to get the same results of a conventional OTL while matching speaker impedances and a whole lot of other benefits, simply matching speaker impedance is not patentable, doing it in a OTL fashion is.

You make it sound like this design is a compromise, while in fact it's a true innovation in amplifier design, Hansen even made that comment.

Yes, in the Audio industry today, there are many Mars dust, voodoo spells, nonmetallic metal drawn from the breath of god, invisible sound force fields type products out there and it's getting damn hard to discriminate between magic and science.

Let me spell it out as I see it, because there is so much bunk out there and the Berning is so complicated and way over the wall in design, it seems more comfortable for the Status quo to put it into the "magic" realm to try and discredit it.
In fact they should really be glad a product like this came along, it shows that new technology can be put to a sound design like OTL's, bringing the OTL into the future, giving it life and excitement, the ZH-270 does not compete with the VZN-100's or the MA-2 but does compete with Solid State amps, someone buying a ZH-270 becomes a future potential buyer of a VZN-100 or a MA-2.

The ZH-270 is a easy amp to transcend the SS to tube move, it's light, cool and reliable, once the consumer has made the move to OTL in this manner, it's hard to move anywhere else but up the chain, and at $4995.00, there are plenty of options to move up to and at this time non being a Berning, a VZN-100 and MA-2 heaven.

Allan
David Berning Co

I agree. Who really cares. I never bought into the hype of "is it or isn't it" really an OTL. As a former ZH270 owner for three years, I found it to be one damn fine sounding amp. If I could have swung the bucks to keep it and the JE VZN, I would have.

For me, it's a large tent and there is plenty of room for ZOTL folk IMHO.

Jim

Allan
Berning Co.

BTW, I very much agree that the Berning design topology is a great high end step into the world of tube amps for those who have stuck with high end solid state amps over the years. In many ways it is the ultimate no muss, no fuss tube amp. If I do have criticisms, it has more to do with more pratical things (like the crowded rear panel layout of the ZH-270, the lack of a single input no volume control version, and I would like less gain) which I think would make the amp more universally appealing (though given the backorder situation, I doubt these are a concern! :-) )
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

• Some Pictures of the 1998 Philly Triode Society Meet

I know, it's because I think it's portrayed or described in a simplistic manner, as I said before, the converter is really only part of a number of transformers that make up a circuit, an is no way configured or coupled like a output transformer to the circuit and the converter operates at a fixed frequency of 250Kh, and cannot operate at audio frequencies, there is just no way of mistaking this thing for a output transformer.
It's a perfect something but not a output transformer :)

Yeah, you missed one, it's also very plain looking ( that's polite English for kinda ugly )
This is not an amp someone buys on impulse :)

Allan
David Berning Co

I own a custom ZOTL that Dave made for me last year.
It is a SET-ZOTL which uses Type 45 output tubes driven by 6SN7 tubes, choke loading, 12v battery power only. The chokes were hand-wound by Dave, and the entire unit is hand-wired point-to-point and is considered a "prototype unit". I use Sylvania 6SN7GT tubes and Emmission Labs 45 mesh plate tubes.The output is rated at 2 watts into 8 ohms.

I find the discussion about the ZOTL being an "OTL" or not, to be something that has come up numerous times since Dave invented the ZOTL. I feel he intended to make some distinction between the two, because he used the name ZOTL instead of OTL. Whether any particular individual wishes to apply the moniker "OTL" to it, or not, is rather immaterial. Rather, this circuit truly is a unique design, which actually exceeds the capabilities of both output transformers and traditional OTL, so I would classify it as a "new generation" of circuit.The ZOTL provides the impedance matching as good or better than output transformers, without the drawbacks, and provides the sonic attributes as good or better than traditional OTL, without the drawbacks. This combination of superior impedance matching and lack of output transformer, provides some things that have never been available before. For example, my SET ZOTL has only one output tube per channel, and no output transformers. This is impossible to do with traditional OTL circuits, due to the inability to match the high impedance of the tube to the low output impedance needed to drive the speakers(unless a gang of output tubes is employed).

Regarding the presence of certain transformers in the output stage, they are not output transformers, and only perform impedance matching functions at the 250kHz level(out of the audio range), and pass the signal within the audio range. This is a unique method used in audio, and derives its origins from industrial power-transfer technology. It is obvious to see that these transformers could never be output transformers, from a cursory inspection.

Understanding the details of the circuit is one thing... but you are missing conceptually what the very clever David Berning impedance convertor circuit does. While is does not use conventional output transformer technology (i.e a core of magenetic material wraped with coils, with a primary and secondary winding that has a speaker connected on one end and output tubes on the other side), it essentially emulates what a conventional output transformer does, but in a *much* better manner.

A OTL (in the spirit of the term that is most well understood by audio geeks) has no such impedance converting device between the output tubes and the speakers... i.e. what are more specifically called direct coupled OTLs... the tubes directly drive the load. Thing is though, you will very rarely ever see a audiophile use the term direct coupled OTL becuase is is essentailly assumed by defiention that what he/she means. I think calling other types of amplifer designs OTLs does a diservice to the audiophile public becuase they MAY very well think they are getting/seeing/reading about a direct coupled OTL when they are not.

So, what we are disagreeing here is a matter of a definition which I guess we will just have to agree to disagree on.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

the speaker “sees” the tube transfer characteristics and the tubes “see” the speaker’s dynamic characteristics.

Just at it would in any direct coupled OTL.

No amount of emulation of any output transformer can do that :)

"I think calling other types of amplifer designs OTLs does a diservice to the audiophile public becuase they MAY very well think they are getting/seeing/reading about a direct coupled OTL when they are not."

Are all production cars internal combustion, with either a automatic or manual transmission, are all TV's vacuum tube, you need to be blasted into space by big rockets? At one time or another, the answers to all these questions would have been yes but not anymore.

Electric powered cars are not cars?
Plasma TV's are not TV's
Flying a plane into space is not space travel?

By not letting the audiophile public know that they have choices over what was conventional with the same results, is really the disservice.

Allan
Berning Co.

My (older) WATT IIs do not do well with any of my OTLs!

Have not used Quad ESL57s in a while - with much mention of them recently - I pulled mine out and am getting ready to vacume them down good, charge em'up and listen this weekend mostly with AS M60s (maybe tubes pulled to lower p to p), I may have to pull OTL3s out too and visit the past . . . will post more.

Silverline SR17s reign supreme with everything (Levinson 336) SS or OTL tubed . . . freaking fabulous sounds with this speaker.

I am still trying to get the house finished, so my fiancee can move in. I expect that by the end of the year it will be habitable. Maybe not great, but habitable.

It constantly amazes me, every time I use it.

I sold my Atma-Sphere 208 table and am going to miss it. I have aspirations to become a dealer in the near future and need a TT that is more readily available for customers.

I am considering one of the Teres trio. Any input you can give me on the subject would be appreciated.

Salesman comes up and say "Can I help you"

Customer says, "Yeah, I'm looking to ge one of these SUVs. This one here has a gas engine in it right? I'm not looking for a deisel."

Saleman says "Yep, got a V6 gas engine in there."

The customer thinks, "great< I got a fiar deal here, lets get it!, and makes the deal for the truck there on the lot. He come back next monday, picks up the SUV and drives her home. Being a curious guy (thinks he knows a thing or two about cars & thier design), the guy pops the hood and takes a look at the engine... he aslo takes a look undearneath the car and grumbles out loud "What the *****?" Turns out the customer's new SUV is a hybird Gas electric vehicle.... you don't have to plug in, and runs and drives just like a regular gas SUV... heck, gets even better gas milage.. "its better" the saleman and company says to the upset customer "look how more efficent it... the way the motors and such work you save on brakes, etc etc."... "No matter", the customer says, "you folks decived me becuase you didn't tell me upfront that I wasn't getting the old fashioned gasoline drivetrain that I originally asked for!"

THE END.

Moral of the story, while the gas -electric hybrid vehicle may drive, ride, brake, handle just like a old fashioned gasoline engine vehicle, it does not make it one.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

We should have a vote on which scenario is most likely :)

Man, where would the rest of the world be if it was not for newer ways of doing things, still be watching black and white TV's, driving undependable gas guzzlers?

For god sake don't tell me you watch a black and white TV and drive a 1966 dodge ;) Then I see where yah coming from :)

You are of course, correct and indirectly make my point. Since this is different tehcnology, call it and market it as something different.... the interaction could have been:

Customer: "So is this one of those newfangled gasoline electric hybrids???"

Salesman: Yep! The best that technology currenty has to offer... the performance like that of a gasoline engine with better enconomy and better for the environment... you see the gas engine provides extra power for the batteries and the electric drive motors when needed... works seemlessly and drives and rides like a regular SUV. Now if you want, we also have the old fashioned gasoline engine driven SUVs as well..."

So now the customer can make an informed desicsion... maybe he is an old fashioned guy, likes to work on his own cars and just wants an old fashioned gasoline engine SUV. OR, maybe he is a guy excited by this new technology and a SUV that gives him the utlility of such a vehicle with better economy/efficency.
Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

Yes, you are kind of right, but I don't see a New amp technology forum and it would be kind of boring for the Berning guys anyway :)!

The real big problem is the CIRCUS that high end audio has become, a audiophile cannot tell between magic and science anymore, fundamentally what is correct, is getting grayer and grayer.

It is now very difficult to differentiate yourself with a break true technology to some voodoo spell hybrid lie and because people cannot understand the ZH technology, it's just easy for us to say OTL.

I can go on about this industry but I a sure you know what I mean.