OTL amplifiers

Some thoughts about reliability and feeding tubes to an OTL faster than spark plugs to a Hemi...

I would be out of line to speak about amplifiers other than the AtmaSphere M60, but I can tell you I have nothing but the utmost respect for what Ralph Karsten has designed.

I have to say that when he says his amps are all but bulletproof, BELIEVE HIM! The literature states that pretty much no matter what goes on, it will not take the amp or your speakers out. That's a fact. It may cost you a couple of fuses while you are learning about biasing, "zero offset", or not shorting the amp, but that's about the worst of it.

As to tube longevity, the prototype of the AtmaSphere M60 is supposedly still running its original set of tubes - 20 years later! I kind of stupidly used one suspect tube(thanks Sovtek...). It was fine for a while, just had a permanent bolt of lightning out to the glass, and pulsated strongly with the music. But, when I ran another pair of amps for 2 months, and put them back into service, that tube just didn't feel like being social. It did all kinds of misbehaving, time after time. And despite some really awful pops and bangs, true to Ralph's word, the tube's pyrotechnics didn't harm my amp or loudspeakr in the slightest - try that with a Futterman. Other than seeing this kind of once in a while Soviet QA, the 6AS7G tubes last a long, long time.

Thanks everyone for your input. The discussion went well beyond what I was looking for, but that's not a bad thing. My feeling right now is that these things are far too fussy for my liking. I am willing to work for my audio heaven, but I do not want it to rule my life. Changing tubes frequently, searching the ends of the earth for the proper speaker, blowing speakers, etc. is not my idea of nirvana. Thanks again, all, for the insights.
Dave

Dfrigovt, I think you have received a lot of misinformation about OTL's that has confused the issues.

Like Trelja, I can only speak about my experience in relation to Atma-Sphere M-60 amps. I have used my M-60's for over 3 years without one problem arising. Yes, the M-60's do require the right speaker, but that can be said about just about every amp out there (too small, too large, etc.) You can pair the Atma-Sphere M-60 and the smaller S-30 successfully with just about any speaker with a nominal impedance of 8 ohms or higher, this is not a small number of speakers by any means. With the ZERO autoformers you can pair them with any speaker that is efficient enough to be driven by 30 watt and 60 watt amplifiers.

With the Atma-Sphere's you will not have to retube frequently, you will not have to worry about blowing your speakers or amps, you will not have any difficulty finding speakers that sound good with these OTL's. I have no knowledge by which to assess other OTL designs, but it is obvious that Tenor, Joule, Transcendant and Graaf are other OTL designs that people are using successfully as well.

OTL amps are obviously not the only amplifier type that will bring nirvana, but the special qualities they possess just might be nirvana for you personally. As you mentioned in your initial request, you are a tube fan, there is no practical consideration that should prohibit you from auditioning these aside from, perhaps, geography.

There is nothing about using Atma-Sphere amps that will rule anything in your life other than a simple 5 minute biasing procedure that should be done every 6 months. It would be a shame if you missed your nirvana by dismissing OTL's out of hand because of wrong information provided by others. There is nothing pertaining to modern era OTL's that will throw you any curves. I don't know why people keep bringing up issues that don't apply any longer, and haven't for years. This is like saying that it is problematic to fly more than a couple hundred feet because the Wright brothers could do no better.

If you haven't already done so, I encourage you to read the ZERO's Story at ZeroImpedance.com, it elaborates on the effect impedance has on the matching of an amplifier to a speaker. If you don't have the motivation to read all of the document, just read the Technical Sidebar near the bottom. This information is useful whether you end up with OTL's, ZERO's, or none of the above.

Yes, I agree with Wellfed. I think that basically the only challenge in running AtmaSphere amplifiers is finding a loudspeaker with highish impedance.

And, if you don't, there are still two options available. First, you could go with the Zero Autoformers. Although I am not the biggest fan of them, they multiply the impedance of your loudspeaker. So, if you had a 4 Ohm speaker, and ran off the 2X taps, you would have a OTL friendly 8 Ohm load. The 4X multiplier would provide the "ideal" 16 Ohm. Second, you could just buy a bigger AtmaSphere amplifier, with more output tubes. Simple as that.

Again, like Wellfed stated, the AtmaSphere amps are about as low maintenance as things get. Biasing them is a walk in the park compared to my Jadis. The most difficult part I find is waiting the 1 hour for the amp to warm up before I begin the biasing procedures. After that, you can literally do it in less than a minute. Even with an amp with its settings waaaayyyy off, it shouldn't take more than a couple minutes.

And, like Ralph Karsten says, they are all but bulletproof.

I could list the two things I consider as negatives, the awesome amount of heat they throw out and the high amount of power drawn, but nothing like tubes, speakers, reliability, or fuss is anything like a negative.

I would suggest you give them an audition. That would be the determining factor for me, sound.

I have Transcendent 80 watt monoblock OTL's and Berning OTL's (according to some). I know someone who has Atma-sphere M-60's and someone else who has the MA-1's, as well as other Berning owners and people who have extensive experience with Joule OTL's. They are being used with a variety of electronics and speakers, ranging from Merlin VSM to Vandersteen5's. None of us has had any of the problems mentioned above. No blown tubes, no blown speakers, no constant fussing. Maybe we are all lucky, but I don't think so. The Bernings run so that tubes last a LONG time, and are auto-biasing; Transcendents need to be hand-biased, but not every time you turn them on. I forget if someone mentioned this above, but supposedly Ralph at Atma-sphere does a demo where he shorts out the amps with a coin, and....nothing happens. NO boom, nothing.