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Why aren't OTL tube amps more popular?

98.164.188.3
Posted on December 31, 2021 at 10:16:42
LtMandella
 I don't get it. I had a pair of MC30s and they sounded nice, especially midrange.

But when I put an OTL (Transcendent Sound T8-LN) in my system it gave another level of musicality and realism.

So why aren't OTL tube amps the "standard"? They outperform soncially, they don't require costly, heavy, distortion causing tranny.

Is it simply that futterman design is problematic and Bruce's design is still under patent? I thought patent's were only good for 17 years?


 

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RE: Why aren't OTL tube amps more popular?, posted on January 1, 2022 at 09:43:01
6bq5
Audiophile

Posts: 4393
Location: SF Bay
Joined: August 16, 2001
 I think that there are a few issues that plague OTL amps - some anecdotes from history, and others from different design goals/manufacturer's goals-

OTL Amps typically are happier with higher impendence speakers, which is the to opposite of where speaker designers have been heading to take advantage of SS amps and to get more power for the speaker from SS amps-

There are also some old stories that circulated about run-away amps and amps oscillating - sometimes taking speakers out... Not all of these stories are true- or the fault of the amp-

There is also the issue that an OTL AMP is not as tolerant of poor design or poor execution - There have been some OTL Amps that were more 'approachable' - the Counterpoint SA-4 was probably the the best commercial OTL product in it's day - but it was on the more expensive side of the scale- less than the NYAL Multi-chassis OTL amps - but more than other offerings at similar power...

There is also the issue of the tubes mostly used in the '50s-early '80s for OTLs were TV tubes - Horizontal or Vertical amp tubes - that did not get picked up by the Russians, Yugoslavians or Chinese manufacturers...

Happy Listening

 

several reasons, posted on January 3, 2022 at 11:42:23
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 The biggest complaint we run into is 'all the tubes'.

The second is that a lot of speakers really don't work that well with OTLs. That's true but from a purely subjective point of view my experience was that if the speaker wouldn't work with one of our amps (or other OTL) its chances of actually sounding like real music were extremely limited.

Of course there was a lot of legacy from the Futterman amps- in particular those that were not made by Futterman- claims of blowing up, oscillating, etc. In the 1980s when we found that more than solid state vs tubes or analog vs digital, the audio world was very solidly convinced that if it was an OTL, it was going to blow up.

The fact that our amps didn't do that, that our amps were actually reliable, was nearly a Sisyphean task to convey. These days we rarely run into that issue.

Of course when everything is right they are very difficult to best, price no object.

 

RE: Why aren't OTL tube amps more popular?, posted on January 4, 2022 at 10:19:10
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Counterpoint SA4 was among those OTLs that contributed to the reputation for their unreliability, so far as I know. Didn't the SA4 use a servo mechanism to cancel DC at the output, in lieu of coupling capacitors? And wasn't that the Achilles heel of that design? I am not being rhetorical; that's the impression I gained back in the day, without having ever owned or heard one. I do admire many other Counterpoint products, nevertheless. They later made an amp with tube input stage/SS direct-coupled MOSFET output stage (I think) that did sound great. More damaging to the OTL reputation were KSS and Sans Pareil. Futterman amplifiers built by Futterman were quite reliable in my direct experience.

Isn't the Transcendent circuit basically a modified Futterman? The NYAL amplifiers were Futtermans tweaked by George Hammond, who earlier in his career worked with Futterman. So far as I know.

 

RE: Why aren't OTL tube amps more popular?, posted on January 4, 2022 at 14:36:10
Ralph
Manufacturer

Posts: 4778
Location: Minnesota
Joined: April 24, 2002
 Didn't the SA4 use a servo mechanism to cancel DC at the output, in lieu of coupling capacitors? And wasn't that the Achilles heel of that design?
I heard about that a lot from Albert Porter back in the mid 90s. No idea how much of it was true.

 

RE: Why aren't OTL tube amps more popular?, posted on January 4, 2022 at 21:42:30
airheadair
Audiophile

Posts: 393
Location: California
Joined: October 18, 2010
 I have had direct experience with the Counterpoint SA4 as well as the Futterman NYAL OTL3.
When I first bought my Stax F83's, the dealer recommended the Counterpoint, and came to my house to set it up. We let it warm up overnight, and in the morning found that it was audibly oscillating, with no signal being applied.The dealer was able to make an adjustment to stop the oscillation (I'm not sure what he did), but my wife did not like the sound at all, and we did not keep that amplifier. It is true that it used a server mechanism rather than coupling caps to block DC, but I'm not sure if that was a problem in practice or not. I also remember that Peter Moncrieff in his publication IAR, raved about the Futterman, and had some measurements to justify his opinion (in particular its superfast voltage swings, I think). In his review he mentioned that the SA4 had a similar design but without the coupling caps, which I guess was supposed to be a plus, because he was writing very negative things about capacitors at the time. However he told me privately that the Futterman "blows the SA4 out of the water" sonically.
We tried many other amplifiers with our Stax speakers, including some celebrated solid state designs and the Audio Research 250 (which Moncrieff adored) and didn't like them at all, until we got the OTL3's, which my wife instantly endorsed, and which we did keep.
By the way, Moncrief also likes Ralph's amplifiers, perhaps even more than the OTL3's, but I have never heard them myself. I still use the OTL3's, and I have never heard anything sound as remotely musical as this combination. I should point out that the Stax speakers have a very unusual impedance curve: about 4 ohms at the frequency extremes and about 160 in the midrange, and they are very inefficient. I use subwoofers for the bass (thanks Lew).

 

RE: Isn't the Transcendent circuit basically a modified Futterman? , posted on January 13, 2022 at 11:06:23
LtMandella
 No idea, but Bruce obtained a patent for his T8 design so someone with electrical theory and training should be able to say.

I can tell you I have been running a T8 for 20 years powering all kinds of speakers and it has been rock solid and reliable.

 

RE: Why aren't OTL tube amps more popular?, posted on January 27, 2022 at 17:08:31
clio09
Dealer

Posts: 1153
Location: San Rafael, CA
Joined: January 29, 2006
 The SA-4 was based on a circuit design by Roger Modjeski that was done either right near the end of his time or just after he left Beveridge (HBI). Roger gained a lot of experience from working at HBI, and while many have stated that he designed the Beveridge OTLs/direct drive amps, this was a myth, Roger just tested them as they were built and in operation before he started at Beveridge. Mike Eliot worked with Roger at Beveridge, so that's where the personal connection between the two comes in. When Roger completed the circuit design he was dissatisfied with it and decided to focus on other projects, including building the RAM computer tube tester. Mike Eliot bought the design from Roger and built the SA-4. Not sure how much Mike may have tweaked the design, but Roger always referred to the amp (he serviced a few of them) as a Ferrari. When it ran well it was amazing, but reliability was an issue.

 

RE: Why aren't OTL tube amps more popular?, posted on January 27, 2022 at 21:38:38
airheadair
Audiophile

Posts: 393
Location: California
Joined: October 18, 2010
 I have posted about this before, but I will repeat myself here. The SA4 was the first amplifier we tried with our Stax F83 speakers. It oscillated, until the dealer tweaked it somehow. Although it had a clear open sound, we did not care for it. The NYAL OTL3 sounds much much better in our system.

 

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