The abbreviation S.E.T. is familiar to all audiophiles. However, when it comes to having any real insights into what amps of that topology can sound like? Many 'philes might as well subscribe to S.E.T.I. scanning the ethers for signs of extraterrestrial intelligence by way of broadcast signals. Believing in the concept is easy, getting hard results isn't. Ditto for the SET concept. It requires plenty of listening to different circuits and output devices to explore the possible permutations and get a handle on what -- if any -- qualities stay consistent regardless of extremes.
All I feel personally comfortable commenting upon at present is that superior examples of the breed I've heard do not at all conform to the stereotype of the "unpredictable tone control and distortion generator" some believe typical of the genre. Further observations that ain't true include curtailed frequency extremes and interpretative dishonesties that contour frequency response for special effects. Yes, there's plenty of evidence to the contrary. The prior phrasing should really read not-necessarily-true observations. "See what's wrong" examples are not at all representative of what single-ended circuits are capable of. They're far more representative of voicing liberties and less than competent design work. They aren't intrinsic rules that force predictable outcomes.
|Neither is it at all conclusive to focus on triodes and overlook pentodes or transistors. Nor does it mean that what I'm about to say about single-ended amps necessarily requires this type of circuit and couldn't be achieved differently. What has struck me and others I've talked to about this is simply that popular notions about SETs -- woolly bass, rolled-off highs, euphonic thickness et al -- are a very poor caricature at best (and character assassination at worst) once you've spent quality time with serious single-ended amps. They can be extremely linear, fast, open and transparent. Pure glass, fresh mountain spring water, a removal rather than insertion of filters - good descriptors all which, when compared to the SET archetype in people's minds, are rather the polar opposite of popular preconceptions.
|Another hang-up that permeates this genre is the fixation on expensive direct-heated triodes like 45s, 2A3s, 300Bs. Inferior examples of 300B SETs have done perhaps more than any other subset of this religion to muddy the waters|
|and envelop the entire genre in an aura of fire-side romance and deep triode allure. Yes, there's plenty of amps that fall into that category. Still, that doesn't define any rules for single-ended amps in general nor rules for 300B single-endeds in particular (as anyone spending time with Wyetech Labs' Sapphire monos for example would already know).
What doesn't help matters further is that by relying on a single output device per channel (though paralleling occurs at times), many SETs seem unduly expensive for the power they deliver. Trying to correlate published and outright embarrassing measurements of a SOTA SET against listening impressions and absolutely ludicrous cost merely puts the final nail in the coffin. The deceased inside the coffin is dressed in utmost finery and described variably as a toy boy; an exclusive indulgence for the super-wealthy; an insult to proper engineering; a prime example for what's wrong with Hi-End audio in the first place; a dunce and impostor; a one-trick pony; a make-everything-sound-pretty lie.
Make no mistake, such walking dead exists and perhaps we could even say, they're in the majority. But insisting that the majority would have the genre pegged is folly. It misses out on its special appeal - a directness that's like lightning and cuts through clouds and atmospheric conditions. Sam Tellig's infamous there's more there there has nearly become a curse for how often it's been used by other writers and likely at least half the time to describe something else. The way I understand it, it combines the sharpness or clarity of the new breed of digital amps and the battery-powered Clari-T with a peculiar dimensional focus that increases contrast without cheating (i.e. without emphasizing transients, playing games in the presence region or inserting a strategic treble lift).
|Plenty of buzzing words have been used to describe this effect. Palpability. Thereness. Immediacy. Directness. If done properly, it never equates to bracing, stark, unduly incisive, hyped, spotlighted or eventually fatiguing. A perhaps useful analogy is the difference between frozen and farm-fresh vegetables. They taste differently. If you prepare an essentially alkaline meal from fresh veggies with just a dose of acidity by way of some lime/lemon juice or the bite of some tangy fruit, there's flavorful nourishing balance with pep and excitement. To me, that's the hallmark of the best SETs and by no means the exclusive providence of tubes.
|A byproduct or co-contributor of this quality is speed expressed as openess, dynamics and jump factor.|
|This is the polar opposite of the euphonic Hashish dreams many people equate with single-ended triodes where everything is rounded-off, a bit lazy and dark and luscious. In fact, the best single-ended amplifiers sound nothing like chocolate. They can be outright tart - speed freaks and utter transparency champs. If they use tubes, they often don't sound like it - or better put, they don't sound like most people have been led to believe tubes do. This has prompted many writers to use variations on the term vintage sound to indicate that yes, there has been -- and continues to be -- a school that fancies those particular attributes. However, there is another school that's apparently far more modern (though older examples like Shindo can be found in the relative past that don't sound vintage by a long shot). Newer proponents of this type of sound are Lamm Industries, Wyetech, Art Audio and Decware. The FirstWatt F2 squarely falls into this category as well - without tubes. There's others but I've only heard so much in person.
All this by way of stressing that if you think S.E.T. and automatically reflect on a particular kind of old-timey sound, chances are it's a lesser example of what's really possible. Superior SETs are far more neutral and linear than that. Their special appeal lies not with prettiness or romance or golden-hued patinas at all. If that's what you still believe about them, you might find it educational to explore the other half of their equation. True, lower power and certain output impedance aspects will generally mandate more care with suitable speaker. But that's not at all a liability. It turns out that the higher efficiencies of such speakers often make for very similar sonic attributes that enhance the special qualities of single-ended amplifiers. In closing, there's a very good reason why brand-new Class D amplifiers of the so-called digital variety pride themselves on having "tube-like" qualities. They're not referring to bloat, fuzziness, prettification or compromised bass and treble after all. No, they hint at directness and superior clarity though they usually lack that special textural/spatial something that has many listeners prefer valves for output devices. So don't be too set against S.E.T.s to forget that what you've heard may only be half the picture and not the whole and nothing but the truth...