OTL Tube Amps-- are they superior to everything?


A recent conversation I had with an Audiogon member got me interested in OTLs. His opinion is that nothing compares to them for clarity, naturalness and superiority in just about every area. The Atmaspheres are the amps he has, and they are purportedly very stable, unlike most other OTL designs, which many can tell you were a living nightmare.

This is ironic, because some mfrs., like McIntosh, actually put output transformers on their better solid state pieces, claiming they provide superior sonics.

What is the truth here?
saxo
Twl, Berning has had a few amps, preamps go down. But what service! I get the feeling all production stops until repairs are made. I know of only two. He was very upset, these are his babies. Turn around for these two were sent back two day's after Berning Received them. If you buy from Berning and you are I of the very few that has a problem, no need to worry. I get the impression he worries more than the customer. We need more customer service like Mr. Berning delivers.
And yes, there is something very special there.
I would highly recomment that you at least try an Atmasphere so that you can experience the true sound of a pure analog OTL piece of equipment. Does not matter whether you find it better, worse or indifferent. You just need to hear it when it matched up well to a speaker(with or without the auto-transformer).

There is just a gain stage then an output stage with zero feedback. Simple and truthful. No transformers or switchmode trick circuits. I personally think the magical OTL sound could be due to several different reasons. One, maybe distortion. Wegel and Lane(couple audio guru's) in 1930 published a formal paper indicating that, when a fundamental signal included its harmonics of the 2nd (@-22db); 3rd(@-26db)' 4th (@-30db), 5th (@-37db) and the 6th (@-46db) then it is characteristically pure sound. In 1960 Toshiba set out to investigate this and arrived at the same conclusions. Interestingly enough, single ended tube (SETs) and (300B) type amplifiers often display spectral contents very close to these characteristics. OTLs included.

Another reason the OTL may be preferred is due to its characteristic high output impedance. This can lead to speaker matching issues for two reasons. Depending on a given speakers crossover this will have the effect of emphasizing the frequency band around the crossover point (anywhere from 330 to 1.5Khz). Emphasizing this frequency range has the effect of producing a warmer or more robust sound. Bob Carver tries to emulate this by adding resistance in the output of his amplifiers (current output). To some extend this may work however, this will be a constant ohmic value where-as, in the OTL such as an Atmasphere this will be a dynamicly changing output-Z. There will be some interaction differences here.

A possible third reason for the highly revered bloom from an OTL amp is the fact that, since it does have a relatively high output Z(3 to 7 ohms in the Atmasphere series) this causes speakers to be less damped. And, being less damped the speaker may very well become closer to being critically damped, which is generally the most desired condition for a particular driver. Generally, when one reads the response of a speaker driver the manufacturer usually specifies it when "critically damped". However, once installed in a cabinet or frame with associated crossover components we don't know the status of driver damping or the designer's intent with a particular system. So sometimes an amplifier with a higher Z-out will improve the overall percieved performance by more closly providing critical damping to the drivers and, of course it may not be advantagous due to the particular design. Hence speaker matching is imortant. Reportedly electrostatic speakers benefit from the highish output impedance due to damping effects where-as planar speakers such as Magnepans need a very low output Z to properly damp their panels. For the latter the auto-transformer will be needed to effect the low Z-out. And, being an auto-transformer there is not much loss in this device to worry about. It is not hindered by the same issues (leakage inductance, output-Z limitations, interwinding capacitance, etc. that affects push pull transformers. Any audible masking of effects are basically insignificant once the proper ratio is selected.

I hope I did not bore you here. Again I recommend that you try an OTL as, for whatever reason, it sure produces a voluptuously immediate soundstage that reeks of musicality and just might nail you.
Twl and Saxo, this reminds me of another thread. Thank you both for making me feel so at home. I love the passion of these kind of threads. After seeing the same questions asked over and over. Threads like this and a few others remind me of the old day's. I mean there's Tubegroover, Wellfed, Twl, Sean, and one if not my favorite, Trelja, all on the same thread. Ya gotta love it. i am sure we will be hearing some input from Jcbtubes once he gets back Sat.
Saxo, I do not mean this as criticism, but the Berning and Atmasphere are two different animals. At least in sound. I know the Berning and IMO, the Atmasphere ain't no Berning. I can also say the Berning ain't no Atmasphere. Great to see so many of the old regulars, not to mention the newer ones.