Hi Bill, Just FWIW, our amps, other than being OTLs, are nothing like the Futterman amps. When I went into business making OTLs back in 1977, I rapidly found out that 'OTL' was equated with unreliable. At the time I knew very little about the Futterman. What I have sorted out over the years was that Julias seemed to know what he was doing- his amps seemed to hold up. The later versions sold by NYAL didn't fare so well- that is where the reputation that we have been fighting ever since seemed to come from.
We sidestepped the reliability issue by employing an output circuit called a Circlotron. We did it in a way that had not been done prior and got a patent. The amps proved very reliable, so much so that we even built guitar amps using the circuit, which can be heavily overdriven all day long, something that would cause the prior art to go into oscillation. Apparently we were the first to make class A OTLs as well and for many years the MA-2 was not only the biggest OTL in production, but also the biggest triode amp and the biggest class A amplifier.
Since the amps were fully balanced and differential, we wound up offering the first balanced-line products to the high end audio market (the original MA-1, 1987) and followed with the 2nd balanced line high end audio product, the MP-1 in 1989. The preamps use the same circuit as the amps to bypass the use of an output coupling cap.
There have been several other OTL manufacturers that have come and gone- Prodigy (Futterman variant, and IMO the best Futterman execution anyone ever did), Counterpoint (Futterman variant developed by Roger Modjesky if memory serves), Silvaweld (Korean Futterman) and Sans Pariel (Futterman variant developed by Charlie Kittleson for San Pariel). I am missing a few names here- its funny when you look back on all this stuff and realize how many there were!
Non-Futterman amps include Graaf, Tenor, Naked Truth Audio and Joule Electra. Of those only Joule had staying power. There was a Hungarian OTL manufacturer and I believe another in Italy that is still in business.
There is that whole thing about OTLs being load-sensitive. This is true but I find transistor amps to be just as load-sensitive but there are more speakers for transistors :) This whole conversation lead me to look at how negative feedback can or cannot help an amp to drive a speaker- its possible to make OTLs with very high damping factors and very low output impedances, but running the same amount of feedback as a transistor amp. What I found though is that there is no point. You run that much feedback and the amp can be unstable, and for sure it will never sound right- to make it sound like music you have to run zero feedback (and **that** is where the choice of speaker is important). My philosophy is that if the speaker needs the amp to have feedback, that speaker will never sound like real music, so why bother? There is no question that this has limited sales potential, but in high end sound is what should be paramount IMO.
Thanks for the bit of history.
We sidestepped the reliability issue by employing an output circuit called a Circlotron. We did it in a way that had not been done prior and got a patent. The amps proved very reliable, so much so that we even built guitar amps using the circuit, which can be heavily overdriven all day long, something that would cause the prior art to go into oscillation. Apparently we were the first to make class A OTLs as well and for many years the MA-2 was not only the biggest OTL in production, but also the biggest triode amp and the biggest class A amplifier.
Since the amps were fully balanced and differential, we wound up offering the first balanced-line products to the high end audio market (the original MA-1, 1987) and followed with the 2nd balanced line high end audio product, the MP-1 in 1989. The preamps use the same circuit as the amps to bypass the use of an output coupling cap.
There have been several other OTL manufacturers that have come and gone- Prodigy (Futterman variant, and IMO the best Futterman execution anyone ever did), Counterpoint (Futterman variant developed by Roger Modjesky if memory serves), Silvaweld (Korean Futterman) and Sans Pariel (Futterman variant developed by Charlie Kittleson for San Pariel). I am missing a few names here- its funny when you look back on all this stuff and realize how many there were!
Non-Futterman amps include Graaf, Tenor, Naked Truth Audio and Joule Electra. Of those only Joule had staying power. There was a Hungarian OTL manufacturer and I believe another in Italy that is still in business.
There is that whole thing about OTLs being load-sensitive. This is true but I find transistor amps to be just as load-sensitive but there are more speakers for transistors :) This whole conversation lead me to look at how negative feedback can or cannot help an amp to drive a speaker- its possible to make OTLs with very high damping factors and very low output impedances, but running the same amount of feedback as a transistor amp. What I found though is that there is no point. You run that much feedback and the amp can be unstable, and for sure it will never sound right- to make it sound like music you have to run zero feedback (and **that** is where the choice of speaker is important). My philosophy is that if the speaker needs the amp to have feedback, that speaker will never sound like real music, so why bother? There is no question that this has limited sales potential, but in high end sound is what should be paramount IMO.
Thanks for the bit of history.