OTL or SET? Differences?

Yu11375,

The Atma-Sphere MA-1 and MA-2 amps are far more flexible in handling a wide variety of speaker loads than the lower output Atma-Sphere amps (S-30 and M-60). With the increased number of output tubes, they have much lower output impedance (as well as higher power) making them much more flexible partners. The MA-2 will drive just about any speaker whose minimum impedance doesn't drop materially below 3.5 ohms. With the MA-1, you need to be a bit more careful in speaker matching, but still a broad selection. With either the MA-2 or MA-1 and appropriately matched full-range speakers, you will get bass impact, resolution and agility that is as good or better than you can get from the best solid state amps I've listened to. Plus, you get that magical reproduction of timbre and harmonic overtone structure that only tubes provide.

In contrast, SETs, as mentioned above, deliver a magical quality through the midrange that can be quite addictive. SETs are often described as sweeter and more "musical;" never quite "accurate," but making the music more beautiful than real -- all of which can be a good thing given all the trade-offs we work with. But, a big trade-off for a classical music listener is that I've yet to hear any SET/speaker combination that can begin to deliver on complex orchestral music (like the Mahler 2nd) or large organ. (There may be a combination of SET and horns out there that does this, I just haven't yet heard it.) If your primary listening preference is small ensemble jazz or chamber music or singer songwriter, SET can be a wonderful way to travel. But be prepared to trade-off on more complex music and on music with substantial mid- and low-bass information.

On the flip side, the Atma-Sphere OTLs will be very neutral, very detailed, highly resolving -- in the words of a listening partner here: pristing like a clear glass onto the music. They won't make the music more beautiful, you'll simply get what's coming from your front-end source without editorial.

N.B., I'm an Atma-Sphere MA-2 and Avalon Eidolon owner.
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I owned both the Lamm ML2 (SET) and the Tenor 75wi (OTL) for a while. I compared the amps with many speakers I had ranging from Kharma to Von Schweikert to Horns to Druids. I found the Tenors to be more sensitive to impedance and the Lamms more sensitive to sensitivity. This is by no means a scientific explination, but based on the limited combinations I've listed above. The Lamms could drive just about any speaker full range at reasonable volume levels. Based on the efficiency of the speaker, the Lamm would start to harden at higher volume levels. The Tenor however could play very loud even with inefficient speakers. However, they would loose control of the bass even at moderate volumes with speakers that had impedance dips. In general the distortion with Lamms was a hardening of the overall sound. The distoriton with Tenors was a boomy bass response. I'm not sure if this is OTL vs. SET or just the difference between Lamm and Tenor amps...hope it helps.

Hi Otto,

If I understand correctly, you're driving the Thiel 3.6's with your S-30. The Thiel's impedance is way below what the S-30 is comfortable with. Apparently you tried the Silverline Sonata also but it didn't have enough bass to do justice to Mahler ("Mauler"?).

High efficiency, ultradeep bass is the most expensive commodity in audio, both in money and in real estate (due to box size requirements). I'm sure you've thought of this, but one possibility might be easier-to-drive but bass-limited main speakers plus a subwoofer or two.

Another possibility is for you to keep the Thiels and use an autoformer to make life easier on your Atma-Spheres. Pauls Speltz's "Zero Autoformer" has saved the day for many an Atma-Sphere owner, and I have customers who use it with more conventional transformer-coupled tube amps. In the majority of cases the Zero is a significant net improvement, but not always, so it's best to try before buying if possible. I do think it would be in your case. I just sold my demo pair or else I'd offer to let you try them.

Pardon me now Otto, but since I've mentioned and suggested something I sell, there's a matter that I have to take care of. I have a stalker who sends me threatening e-mails when he perceives my posts as being overly commercial - according to his criteria, rather than Audiogon's. This morning I got one from him because of my first post in this thread, and I'm sure my mentioning the Zeros will cross the line he has drawn.

Stanhifi, I am tired of your threatening e-mails. Please stop sending them. Don't e-mail Otto as you threatened to either. If you have a problem with my conduct on Audiogon, let's get it out in the open. Go public and take your best shot, or leave me alone.

And Otto, if Stan does e-mail you to attack me, I would very much appreciate your letting me know. I'm not trying to hijack your thread so I invite you to let me know via e-mail if you'd rather, but I'll leave that up to you.

Okay getting back to Otto's situation, note that if you do go for a high efficiency, easy-to-drive fullrange speaker that has genuine deep bass you're talking about a very big enclosure. Without an idea of your price ballpark I hesitate to make specific recommendations among new speakers. In used speakers I'd suggest the big Altec Model 19's which show up occasionally for ballpark a grand or so used (more for a pair in very good condition, but still less than new speakers of comparable performance).

Finally, is building your own enclosures a possibility? If so, prhaps I can offer a suggestion or two that would work well with the S-30.

Duke

Hello Otto...Greetings from Australia !!!
I have tried several good Amplifiers on the Horning Alkibiades 99db,which have very deep bass and the appropiate big enclosure...Rushtons ,comments of the Atma-sphere S30 are spot on "On the flip side, the Atma-Sphere OTLs will be very neutral, very detailed, highly resolving -- in the words of a listening partner here: pristing like a clear glass onto the music. They won't make the music more beautiful, you'll simply get what's coming from your front-end source without editorial."
The Tom Evans "Soul S15" SET Cass A falls somewhere in between my current amplifier,the KR Audio Stereo Kronzilla and the Atma-sphere...The "Soul" controlled the bass on the Hornings better and being a KT88 valve,you could tweak the sound a bit...I would say it was a bit more involving,but it needed a active pre-amp ,where the Atm-sphere and KR are happy with a passive...the KR Audio Kronzilla was in another league...also many would argue that it is not a "true" Set amplifier ,as it uses,like the "Soul",a SS front end...the Kronzilla simply was a step above all of the amplifiers I have heard in control,air and musicality...the PRAT is just great...the only amplifier ,I reckon would compete ,would be the VAC or Canary 300B push/pull...hope this helps...
Regards
Helmut

FWIW, one thing that OTLs and SETs have in common is that neither has any hysteresis loss in the output transformer.

SETs do not reverse the magnetic field in the transformer, and OTLs don't by definition.

Removing the transformer also removes the argument against push-pull. You don't have hysteresis loss, so you don't get the attendant loss of detail that is an effect hysteresis loss. This means that push pull need not be a 'sin' as mentioned above.

Of course our stuff is all-triode too.

Hysteresis loss is the property of magnetic devices wherein it takes a little bit of energy to reverse the magnetic field in the device. In the case of output transformers, this energy comes from the signal and is responsible for a loss of low level detail and an attendant increase in low signal distortion.

Duke, sorry to hear you are having worries. So far in the years I've been on this forum, no-one has challenged me in the way you mention. For that matter I've not had any posts that could not be approved (that I remember anyway...), but I try to be really careful not to cross the line. Too much:)