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I understand the Atma Sphere design is simply a re-worked Futterman design with (arguably) increased reliability at (again arguably) the cost of decreased sonics. My understanding is that both designs run EXTREMELY HOT (read: not usable anywhere in USA these past few weeks). So I am asking: what is the true benefit of theses designs, and can someone tell me why I should not buy the Futterman that just came up on AgoN for 750.00 instead of an (overpriced?) Atma Sphere copy of the exact same amplifier for 10,000??
Follow Ups:
Atma-sphere amps use a circlotron output stage, not the totem pole type of output stage found in Futterman amplifiers and patented by Julius Futterman. Go look up these topologies in an electronics book and you will see how different they are. There is some information on Kevin Covi's website, for example. That's for starters. In addition, Atma-sphere amps are fully balanced from input to output, whereas Futterman amplifiers are single-ended. Atma-sphere amps, being all-triode and mostly class A operation are quite happy with no applied negative feedback (NFB), whereas the Futterman circuit requires heaps of NFB to maintain stable operation. Atma-sphere amps are direct-coupled at the output, whereas the standard Futterman design mandates large electrolytic coupling capacitors at the output. (A few renegade Futterman-type amplifiers are direct-coupled, and most of those are dangerous to speakers.) There's more. To sum it up, the only thing these two types have in common is that they are both said to be "OTL", but remember that Futterman amps need those coupling capacitors in lieu of an output transformer. Having said all of that, I do not wish to be seen as putting down Futterman amplifiers. I owned at least six different pairs of Futterman-type monoblocks over a 25-year period, and I was happy until I discovered Atma-sphere. IMO, the Atma-sphere design sounds better, period. If you should decide in favor of a Futterman-type amplifier, then I would recommend that you consider Transcendent. Some of the inherent problems associated with the Futterman circuit have been solved by Transcendent's designer, Bruce Rozenblitt. And why would you expect to pay $10,000 for a used Atma-sphere amplifier? (Lets assume you can find one on eBay or Audiogon; the price will be way less than that.) Why is the Futterman amplfier only $750? Well, Julius died in 1979, so if it's a true Futterman amp, it's at least 27 years old. may need new caps, etc. I don't think you've done any homework on this and that you just want to be provocative.Oh yeah, you asked what is the "benefit" of either type of amplifier. Answer: good sound. No output transformer. Neither of them pay royalties, as far as I know.
Sam, it's a reasonable question that you ask, but there's no comparison. Other than both being OTLs, the Atma-Sphere is a very different amplifier. There are lots of posts about this in the archives, but here is a quote from the Atma-Sphere FAQ:
3. Are Atma-Sphere products Futterman OTLs?
No! Our gear employs our patented CirclotronicŪ design which is simpler and superior in every way to the Futterman. The problems of the Futterman design are side stepped by this new approach, making OTL technology available for the first time to a much wider audience.
While some may argue Atma-Sphere's comments about "problems of the Futterman design" no one will contest that the Atma-Sphere amps are some of the most reliable, bullet-proof, amps made. And they are superb sonically. (And, there is a current manufacturer supporting the product.)
...and NO coupling transformersin the entire amp. The Futterman types use at least that many PLUS a huge (electrolytic) output-coupling cap.The NYAL OTLs curently available may well be reliable, fine-sounding amps, but as Rushton wrote, they're a ways from the quality of the current A-S designs.
> > and NO coupling transformers in the entire ampI did with Lundahl 1660 (with either single-stage and two-stage drivers); single stage to IT definitely beats the 'normal' cascoded front end with generic resistors, paper caps and crappy soviet 6n8s (I'm talking about a DIY, not commercial amp). Some 'upper air' was probably lost, but otherwise it was cleaner. Plus the reduction of driver power supply.
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