I have just purchased the latest Sound Lab M1

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.