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
