I have just purchased the latest Sound Lab M1

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.

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 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 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!

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.

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.