OTL Tube Amps-- are they superior to everything?

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.

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 :)

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.