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 agree with Trelja that finding an OTL friendly speaker is the optimal way to go, but I did have exceptional results with the ZEROs and a previous set of speakers that, on paper anyway, were a good match for OTL amps (nominal 8 ohms that never dip below 6.5 ohms). I obtained these results by using an alternative 2X configuration that I understand involves using less of the windings in the autoformer. Using this configuration, I was able to retain the refinement of the Atma-Sphere M-60s, in the process though bass performance suffered. I then put a second pair of ZEROs, using standard 2X configuration, on the woofer binding posts and the overall performance of the system went through the roof. The whole spectrum was improved, bass performance was phenomenal, and the mids and highs benefited in major way as well. The resolution of the system improved enormously. I had strong expectations that by using the second pair of ZEROs I would get the bass performance back that was lost when switching to the alternative 2X setting. I ended up with performance that vastly exceeded the sum of the parts - making me a wildly enthusiastic believer in the ZEROs. I now use a pair of speakers that are rated at a 10 ohm nominal impedance and I achieve better results without the ZEROs.

Wellfed your points are well taken. I however agree with Trelja in my experience with the autoformers. I found the 1.37 setting the best. 2X was ok but anything above that the sound became whiter or more solid statish losing much of the natural sweetness intrinsic to the Transcendent amp I used it with. Indeed the bass was improved. It seems this device designed with the Atma-sphere in mind decidedly didn't do what I needed in my system. I liked it at first but found myself over time going back to direct most of the time. What I needed was more OTL power.

I feel the zero autoformer is a very well priced well designed product that will benefit some systems more than others but bear in mind that the character of the sound changes the higher the multiplier.

I have heard reports that OTL's like Tenors have been known to blow out speakers due to the lack of there being a (transformer, buffering factor?) Any truth to this?

Hi!
The Zero Autoformers have another great advantage: they won't alow that amps blow out your speakers. I believe that was one of the idea's when constructing the Zero's.
I agree that results with them vary, but do try them... I'd rather invest in them (because of their universality-they work even with solid state amps!) then in speaker cables of that price. But that's just my five cents...
Cheers!