How is the OTL sound like?

I use Atma-Sphere, the M-60 Mk II.2. These are a revelation. Their reproduction of dynamics, high frequencies, timbre, timing, bass, control is amazing. These are easily the most fluid, grain-free tube amps I ever heard. Super fast, clean and clear, natural and balanced for the whole spectrum, they are superb. I believe, I had a mesmerized look in my face, when I first listened to them. There is everything I hear from my Pass amps AND MORE. They give me every detail with lots of air, combined with brutal power in the bottom without being euphonic linked with stunning speed and transparency. In any case, the sound these amps produce is almost frighteningly real - clean, open, "air", wide soundstage, unbelievable detail - it's all there and then some. And : there is NO "warmth" or other tube-related anomalies - just clean, accurate musical amplification.

Thomasheisig is spot on. OTL's are simply more pure and natural but need to be matched with the right speakers to get the best out of them, and extend their tube life. Sensitivity is less critical than the ohm load they produce over the frequency spectrum. Look for speakers of at least 6-8 ohms with minimal phase angles. The higher the Ohms, the more dynamic and powerful will your amps sound.

Ditto to what's been posted above. When I first heard my Atma-Sphere M-60's (I bought them used, without an audition) I literally had that same warm/fuzzy feeling I had when I was courting my wife.

Thomas, did you first hear the M-60's paired with the Köchel's? If so, I can imagine how intensely profound your experience was. It is profound even when listening to this combination on a daily basis.

I have owned the Atma-Sphere MA1 and M60. I have also had the MA2 in my system and OTL is the way to go IMHO. Now I haven't heard other OTL designs so this might just be an Atma-Sphere thing but these are the best amps I have heard or had in my system. The only drawback is they run hot. Now I don't know too many Class A amps that don't run hot. You do need to listen to OTL designs.

I've owned 2 OTL amps and I liked the sound of both of them very much. I still have one of them, and expect to keep it for a long time. It is very hard to go back to traditional output transformer amps after hearing a good OTL amp.

I agree with most of the above comments, especially the one about using speakers that have 8 ohm loads or more. The output impedance of OTL amps is usually higher than transformer coupled amps, and the higher speaker load gives them a better match.