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I will chime in here

Posted by morricab (S) on January 26, 2015 at 01:40:27

In Reply to: OTL vs SET posted by saki70 on January 11, 2015 at 13:48:31:

First, I have owned a couple of different OTL models: Silvaweld OTL refernce monoblocks (4 x 6C33C per mono) and a Transcendent Sound Beast. I have also owned a fair number of SETs: KR Audio VA350i, JJ 322, Cary CAD-572se, NAT Symbiosis SE and had friends with several others that I have heard at length.

A really good SET will have tight clean bass but it still won't sound like solid state bass, or even the bass of a single ended transistor output design (like my NAT). Harmonically, well within its power envelope, it will also be very transparent and sometimes even slightly lean...at least compared to those SETs with compromised iron. Highs will often be a bit soft(ish) as compared to just about any amp with feedback and/or push pull designs and this is regardless of how extended the bandwidth of the output iron is from my experience. If the amp is using a solid state power supply it will be a bit leaner and perhaps faster sounding than one with a tube power supply.

Palpability and 3d imaging as well as soundstage depth will be world class.

A really good OTL will have SHOCKING transparency...something that I have yet to hear with even the best SETs and of a wholly different quality from SS such that all SS sounds grainy and opaque by comparison. Dynamics also are quite lively. Imaging and soundstaging is right up there with the top SETs. Where they fall down, IMO is often in tonal balance and overall coherence. They tend to sound leaner than most SETs and, IMO, than real life. I think this has to do in many cases with the use of negative feedback (My OTLs used around 10db of negative feedback). Not using output iron probably also impacts this.

Those OTLs that don't use negative feedback are somewhat warmer in character but still have that amazing transparency.

Bass (for a circlotron design) is somewhere between SS and SET bass. It is drier and tighter but still not SS sounding. For other types the bass on normal speakers has issues and could contribute to the lean sound.

Where my OTLs fell down ultimately was in coherence...nothing beats a really good SET, IMO, for seamlessness and "continuousness" (to use a classic HP descriptor). A single ended OTL might do it but it seems that they need too much negative feedback or dozens of tubes to be a viable solution.

There is one company, a Cyprus one called Aries Cerat, that makes a zero feedback, single ended OTL, that is massive and with a large number of output tubes...I am dying to hear it.

My NAT is the closest so far that I have heard to marrying the concept of SET and OTL because it is a direct coupled single ended hybrid with ONE big MOSFET on the output per channel. It has NEARLY the transparency of an OTL and NEARLY the tonal character of a top SET but with a SS like bass. It does not quite get there as the ultimate amplifier. After a couple hours of playing it does get pretty hallucinogenic and very close to the ideal, IMO, but not quite. A MOSFET just has not got the same character as a power triode and you can hear that.

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