SET vs OTL

 
When driven from a balanced source, I thought the dual differential Atma-Sphere circuit required no phase splitter?
 

Atmasphere,

regarding your point on fakeness and removing harmonic distortion... I understand that in an OTL / push pull amp, some of the harmonics will cancel-out showing lowered (measured) harmonic distortion. But if it is the even order harmonics that are being cancelled then the odd-ordered ones are left to dominate, the sound will be much worse/less natural even when measured harmonic distortion. Is this not an issue with OTLs?

As for SETs, the problem is (correct me pls) that even order dynamics can be accentuated by the tube's interaction with the transformer, making the sound more lush/"pleasing" but less natural/neutral.

Regarding my speakers they are Asa monitor pros (http://www.asa.fr/productsPages/gd_monitor_pro.php),
The monitors have a very flat impedence curve and are 8 ohms/ 89db.
They come with a pair of active subs that sort of make up on frequencies below 40hz (cut off point) for where my small OTL amp was lacking.
My listening room is not big and I usually listen to jazz.

Limited budgets mean that one usually buys used equipment from overseas, so it is often not possible to audition... (very hard to find used GM20 Graafs, but did see a Navison Audio OTL on Agon recently). Hence my question on whether a good SET (eg the Cary 300SE) would sound more natural than an OTL amp of similar price/quality.

Sorry, the sentence in first paragraph above should read:

"But if it is the even order harmonics that are being cancelled then the odd-ordered ones will be left to dominate, and the sound will be much worse/less natural even when measured harmonic distortion is lower"..

Aarif,

It is true that there are studies indicating that a 'natural spectrum' of harmonics - which includes even-ordered components - sounds better/more natural to our sound processing systems (brains) than the same signal with only the odd-ordered components - despite the fact that THD is obviously higher in the former case.

Re: "As for SETs, the problem is (correct me pls) that even order dynamics can be accentuated by the tube's interaction with the transformer, making the sound more lush/"pleasing" but less natural/neutral." I've never heard that.

I would say that good SETs on the appropriate speakers do *not* sound 'lush' - ever. They sound crystal-clear, just right, completely natural, etc. That's how a 45 sounds, for example. Or a good 211. Other tubes probably do have some intrinsic 'character'.

Of course, good push-pull OTL tube amps sound a lot like that too. They sound even leaner, or 'whitish', as I would describe it.

What's closer to reality might be impossible to say.

The harmonic structure of a good OTL will be the 3rd harmonic, which the only harmonic that the ear considers musical and thus does not object to. SETs have that and the 2nd harmonic.

Paul, what happens with these harmonics is not that they are not audible! It is that they are not **objectionable**. When GE did their experiments in this regard, they found that people will not *object* to nearly 40% of even-ordered content. That is not the same as 'you can't hear it', you certainly can, and audiophiles have terms for the presence of even orders (just like they do for odd orders) in small amounts. From small amounts to larger amounts: Warm, lush, rich, bloom, thick, murky, woolly, muddy. FWIW these terms refer to even ordered harmonics that are in greater supply than the terms that apply to odd ordered harmonics: hard, harsh, brittle, clinical, etc., where the odd-ordered enhancement may well be less than .001%.

With regards to the phase splitter- some OTLs that is an issue, others it is not. In our amps, there is no 'phase splitter' as a stand-alone circuit- that function is integrated into the single gain stage that exists in our amps.

Most SETs have more than one stage of gain- its my contention that if they were able to have only one, they would be a lot closer to the neutrality that our amps routinely express. I've got a 45 SET and a 2A3 SET- they sound great within their dynamic limitations, but they also sound veiled compared even to amps we were making 10 years ago, despite using the best parts available. As far as I have been able to experience, transformers always limit bandwidth, add distortion and rob the music of detail.

Given the example of the speaker above, I would recommend something with more power than the Graaf, or any SET for that matter. The speaker is simply too inefficient for an SET to strut its stuff. You would really need at least 10 more db for that. There are OTLs that can easily drive that load though. IMO 15 watts would not be enough power, unless you listen near-field and at moderate volumes.