OTL amplifiers

I really cannot add much to the advantage/disadvantage of OTL amps, except to say that they certainly do possess a magic and realness that is hard to beat.

But, I would like to say something about the Zero autoformers. If they work for you, and you like them, then please just use them and be happy. However, I feel they are not a good solution whatsoever. They steal most of the OTL magic out of the sound, imparting a very white, bleached sound which makes me feel as if I am listening to solid state.

In my experience, the way to do it is to find speakers which present the amp an OTL friendly(that means high impedance) load.

Not to take anything away from Paul Speltz; the man is obviously a genius, when it comes to AtmaSphere amps, and his mods boggle the mind. Using the Zero autoformers will allow people with not the best matching speakers to be able to use OTL amplification. But again, it simply does not sound nearly as good as doing it the right way.

I would like to say that I am sure the recount of Ralph Karsten demoing his amps' ruggedness by shorting the outputs with a coin and having NOTHING happen is 100% accurate.

The reason I say this, and I am not proud in doing so, is one a couple of occasions, I have shorted the amp by moving my loudspeakers around, frantically trying to wrest that one extra bit of performance via speaker positioning. The stiff loudspeaker cables were not as compliant, and the amp was shorted.

What happened? Nothing!

Except for maybe in one bad situation, no sound coming out of the speakers for a second or so, until I realized what I just did. As soon as I unshorted the amp, the music immediately began playing again. Same as it ever did.

I didn't even blow a fuse!

The only times I have blown fuses was when I really wasn't yet adept at biasing the amps, and I had one setting way out of wack. Other than the fuse, nothing else was wrong.

How many amps, tube or solid state, can match this kind of performance???

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.

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.