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In Reply to: RE: Yes, I can see that in a totem pole, posted by Ralph on July 25, 2012 at 10:59:23
That's what I said.
Turning back to the topic of the original post I think that we can agree that OTL amps are not so popular because:
1) they exhibit a larger parts count (i.e. they have a more expensive bill of materials) w.r.t. conventional PP; this limits their interest for DIY people too.
2) in order to get good results (in terms of not only absolute audio performance but also in terms of reliability and durability) there are only a few proven designs, i.e. circlotron/Atma Sphere (non totem pole), Futterman/Trascendent (totem pole).
3) the only nowadays readily available tubes for OTL designs are 6AS7/6080 and 6C33; all other OTL tubes of the past are very difficult to find and/or too expensive.
I think some are using the EL519 too. Neither are particularly expensive.
IME, OTLs are cheaper to build on a DIY basis than a transformer-coupled amp of the same power, once you make the OTL big enough (60 watts or so).
A lot depends on how you build it, where you get your parts, etc.
But I don't think that is what makes them 'unpopular'. IME it has more to do with misconceptions in the field, for example one Futterman variant was so unreliable that it convinced most of the marketplace that if an amp was an OTL it would be unstable and would blow up (I have come to call that the 'Futterman Legacy' as it has been the single biggest marketing problem that we have faced in the last 30 years, and its something that all other OTL manufacturers have had to deal with as well). The 'Futterman Legacy' was so successful at this that in the marketplace there was no debate about it at all, while at the same time the tubes/transistor and analog/digital debates raged on!
So IOW I think it is misconceptions and marketing that are at the roots of the problem.
Perhaps it would be more fair to call it the "Counterpoint SA4 Legacy" or the "KSS Legacy". Not to mention the Sans Pareil products. Futterman's own amps and the conventional derivatives thereof (NYAL, Prodigy, etc) were quite reliable IME.
Still, your basic point is well taken.
I was already dealing with this issue prior to KSS, although they certainly did not help matters...
I always have thought that Prodigy did the best job of any Futterman I've seen.
Never had a single problem with two pairs of monoblocks built for me by Julius, plus one pair of knock-offs built in DC and sanctioned by Julius, over a period of at least 20 years. Then I had Prodigys for a few years. No problems there, either.
Counterpoint SA4, KSS, and Fourier are primarily responsible for the bad rap, IMO.
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