DISCLAIMER: I am probably the person Saxo is referring to in this thread. Apologies to those who find my involvement inappropriate.
I am personally a fan of OTL amplification in the right circumstance.
In my long and winding audio road, the road of tube amplification has struck me as more musical than other options. Eventually, upon the advice of a great friend here on Audiogon, relaying the feelings of himself, Israel Blume, and Arthur Salvatore, I gave OTL a shot. True to his tremendous insight, the OTL wing of tube amplifiers struck me even more deeply. To the extent where the amplification in my main system is now OTL, the Atma Sphere M60 monoblocks.
The benefit which I hear most profoundly is that is simply sounds more like music than most anything else I have come across. A trumpet sounds like a trumpet, a piano sounds like a piano, and a voice sounds like a voice. There is a sense of, if not realness, getting as close to the master tape as I can get. OTL may not be the amp for most audiophiles, but I have to say I have found they strike a very deep chord in a musician. While my many musician friends have always admired the sound of my system's incarnations over the years, their interest jumped quantum levels with the OTL sound.
I am not one to profess something sounds "live" without great reservation. Let's face it, the illusion we all pursue, live music, is something that is experienced very rarely in audio systems. No matter the cost.
At least to the extent I have experienced OTL amplification in the systems of me and several friends, a great many of the concerns I have of solid state and transformer coupled tube amplifiers are ameliorated. The speed/pace of the music just seems much faster than with transformer couple tube amplifiers. It's actually quite astonishing at times. There is also a clarity and sense of hearing into the recording that defies description. I have thought that I have previously heard things get as clear and focused as they could. OTL proved I still had a lot more to hear and learn. I am sure, I still do... In these matters, the sound is what the VERY best of solid state always aspires to. However, there is a sense of soul and living to the sound that solid state just plain does not accomplish. Use all the overused descriptions we have in this hobby: musical, liquid, smooth, natural, alive, fast, clear, detailed, refined, natural, real, whatever. They apply.
About the best analogy I can make is to light. Solid state might be flourescent. Transformer coupled tube amplification might be incandescent. OTL seems more to me like sunlight.
On the downside, OTL is not perfect by any stretch of the imagination. But then, is any amplifier?
My biggest complaint is the amount of heat generated. This past summer, the coke furnace at full throttle heat of the amps combined with a brutal heatwave, drove me to try other amplifiers in my system. I tried some highly regarded products that just did not measure up to what I was trying to replace. Secondly, the electricity usage is atronomical. Credit the necessity of all those output tubes, in pure Class A triode operation. Usually, the number of tubes is a source of complaint, but not in my case. New output tubes are $12(Sovtek) or $20(Svetlana), and I have bought vintage NOS tubes at much lower rates. Try 4 NOS RCA 6AS7G for $9.99, and that price is available most of the time. At 8 tubes/amp X 2, that's only $40. I also bought 6 NOS British made Sylvanias for $17.99. Contrast this with Western Electric 300B, and it looks dirt cheap. Sonically, OTL does not grab the woofer's voice coil by the throat and totally blow me back the way I have seen other amps, including tube amps, do with my Coincident subwoofers. On the other hand, a lot of people feel that the bass in my system is more than generous. And, I have to allow that the bass is as tight and believable as I have come across in my system. Still, I have to call them as I see them, and I see the bass as not the strong suit. Although not the case in my system, OTL is incompatible with a great many loudspeakers. In fact, with my Frieds, the sound just never came alive. A marriage akin Princess Diana and Rob Schneider.
Normally, my first priority is the interaction between listening room and loudspeaker. After that, comes loudspeaker and power amplifier. Given that once someone decides to make a committment to OTL, the loudspeaker - amplifier pairing takes steps upward in terms of level of importance. Fortunately, my current room and loudspeakers provided me with a lot of good luck. My speakers simply love my room and work quite well with OTL amplification. Others will have to look elsewhere. There is no getting around that.
I would like to mention something about the use of autoformers between OTL amplification and the loudspeaker. Yes, they do improve the compatibility of the two via impedence multiplication. No question. The load the amplifier sees, in terms of impedence will increase anywhere from 2X - 16X, depending on how you configure the autoformers. Bass response will certainly improve, most specifically becoming tighter. Distortion will also get a bit better. BUT, and this is the big but, the magic of the OTL somehow vanishes to whatever degree. It is system dependent. The sound becomes whiter, more antiseptic, less warm, less alive, less real. More like a solid state amplifier sound. My opinions on this were mirrored by two other audiophiles trying them in their systems as well.
And, like everything in audio and life. Just because someone feels the that something is good, doesn't mean it is so. You may very well be on the opposite end of the spectrum. In fact, I myself(others here concurred) have twice found the Atma Sphere/Class Audio Reproductions demo to be about as horrendously bad sound as I have EVER come across, HiFi, lowfi, or no fi. Others have praised the combination lavishly. We all have our opinions.
