Why no threads on OTL amps?

Twl, well put, your comments hit the nail right on the head. Why do so many seem resistant to the thought of a more evolved OTL design? That is my question.

Try this -

www.condor-connection.org/slog/

Then goto SLOG on line, view archives, on line archive 1, scroll to roughly the middle of the posts and find "here's the correct image" by Brian Walsh 10/24/01 and click on the thread.

That will take you to the picture.

Chris

OTL amps are sonically amazing, however alot of people are afraid of them because of reliabilty issues, incompatible speaker matching concerns as well as the massive power consumption the bigger OTL's require and of course tube life. Very few OTL's (almost none of them can handle under 2 ohms for long and certainly not at higher spl's) can be used with a wide range of speakers with large impedence swings however, very, very few can do this and most of the ones that can typically require about as much energy as a small power plant when driving full range speakers at reasonable levels and create enough heat to dismiss the use of a furnace during the winter months :)
There are numerous threads about OTL's here at this sight, try a search for any of the manufacturers names of OTL amps, that may provide better search results. In the paragraph above, I attempted to illustrate a brief summary of why alot of people dismiss the use of a typical OTL because of obvious limitations and operating characteristics. There is however a special OTL amp I know of that can easily tolerate difficult impedence swings, does not require massive amounts of power at idle or at peak for that matter and has a tube life of 4 or 5 times that of a conventional OTL is the David Berning ZH-270.
Many have a misunderstanding of what the ZH270 does to accomplish the difficult task of tolerating impedence swings throughout the frequency spectrum so I will attempt to summerize this highly advanced design as simply as possible:

You see, the ZH270 is the first OTL amp that can properly match the high voltage, low current operating conditions of tubes to the low voltage, high current requirements of most dynamic loudspeakers without the need for audio-output transformers. The 270 does not require the use of banks and banks of tubes to achieve a significant amount of power to the loudspeakers. This is done through the use of RF (radio freq.) which allows the voltage-current characteristics of the tubes from their normal impedence plane to one that is ideal for driving dynamic speakers.

Is everyone still with me??, I hope so :)

Ok, the RF re-mapping occurs through the use of a tiny RF transformer at a carrier freq. of 250kHz. As a result, the audio signal gets a care free ride on the HF wave and is therefore not subjected to any parasitic elements that would otherwise be present. The 270 is DC coupled with the exeception of a small high quality DC blocking capacitor at the input of the amp.

Alright, I'll stop with the technical babble unless anyone else is interested in hearing more about this breakthrough OTL design (there is much more that can be said about this special amp, I'm serious) :) Look around for an OTL that weighs 10lbs and can drive anything, your search will lead you to the same little OTL time and time again. It puts out the most powerful 70 watts with the most drive I have ever heard from any amp.

No other amp sounds like a good OTL, neither SS or traditional tube amps can imitate the incredible sonics of an tube amp without transformers. The OTL sound is in a league of its own in many ways. I highly recommend listening to an OTL amplifier, I think then you will understand why OTL owners are so passionate about their sound.

Best Regards,
Chris

Hi Tim, what speakers is your friend using with the Tenors if you don't mind?

Thanks,
Chris

Definitely include the Berning 270 for OTL's which put out little heat, the 270 puts off very little heat, in fact less than any other OTL I can think of. It also does not use much power from the AC - 100W@idle & 300W max. and increases output power into lower impedences which no other OTL does. This is really breakthrough technology for OTL tube amplifiers.

Regards,
Chris

"The Tenors can handle impedence swings as well as any OTL."

Not true actually, the Berning OTL's INCREASE output power into lower impedences. The Tenors cannot do this simply due to the nature of their design. This does not mean they are not great sounding amplifers, it just means they will have to struggle more with more difficult loads than a single ZH270. Lets quickly look at a couple specifications -


Tenor 75wi (monos) - @ 4, 6, 8 ohm - 55, 75, 75W respectively.

Power consumption - 730W (not indicated if this is idle or max.)

Berning 270 (stereo per channel) @ 8 ohm - 70W (84W output at onset of clipping), 4 ohm - 110W at onset of clippin.

Power consumption - 100W @ idle, 300W max.


I doubt the Tenors (or any other OTL) withstand less than 2 ohms or less for very long without losing steam, they were not designed to drive those difficult impedences with any consistancy. A ZH270 I know for a fact will tolerate quite low impedences for extended periods AND can provide much higher ouput power into lower impedences because of its unique ability to match impedence.

For example -

I personally heard the ZH270 drive a pair of Magnepan 3.6QR's LOUD with lots of drive tolerating some huge dynamic swings while playing some crazy techno music. For the kind of headroom we had one would think we were using some big solid state bruiser, but we weren't. We were using a single ZH270 with the difficult to drive Maggies.

Any 70W amp has its limits, true but we are discussing the subject of OTL amps specifically and I would welcome a friendly comparison with the Berning ZH270 and a Tenor Classic 75wi. I am confident a single 270 would do more than hold its own with the Tenors, especially with difficult to drive speakers like the Magnepans and/or ESL's for that matter.

Chris

http://www.condor-connection.org/slog/bbs/messages/422.html

This is an link to an image of a cutting edge, state of the art designed OTL amplifer made by David Berning based on ZH technology used on his current product line up.

As you can see by the internal layout, this is a radical departure from the conventional OTL technology based on Futterman principals some 50 years ago.

This mono block weighs 8 or 9 pounds and puts out 120W into 8 ohms and INCREASES output power into lower impedences.

Just for a minute, think of all the limitations and drawbacks associated with the current OTL amplifiers. Now think about one without these limitations, not possible? Incorrect, it is possible and happening right now.

Jtinn, your comments are appreciated but in my opinion are quite closed minded about this amplifer design which eliminates the need for an audio output transformer, hence "OTL". Sure, not OTL in the sense of the some 50 year old school of though about OTL tube amps but an OTL design nonetheless.

Please keep in mind this is a new kind of OTL amp design which requires the old school thought of conventional OTL designs to be tossed out entirely and a new sophisticated one to be layed out on the board from scratch.

Anyone want to compare the old school OTL with the new school OTL directly? Please come on by, I'd put this 270 against any other 70W OTL on the market today.

Chris

Jtinn, just for the record it is not my goal to invalidate your comments entirely and perhaps my statement of being "quite closed minded" was going a bit far. My intent is not to create personal conflict in this forum, as I do not feel its necessary in order to make a point. Everyone is entitled to their own opinions and interpretation of the design in question. Like many around here often state, "let your own ears decide".

Best Regards,
Chris