What is the Single Ended Triode thing?

[Coda II]

Actually two questions:

Subjectively, what are the qualities that are so enticing? (assuming that you like them that is)
But also what is it, objectively, that they are doing that gives rise to those qualities?

My listening sample has so far been restricted to a single unit, the 300B Tron Atlantic. And what it does is to portray music, particularly acoustic music, in the most believable way that I have heard. The sense of instruments and voices in a space isn't something I have encountered to the same degree outside of actual instruments and voices.
But is this an illusion? Obviously yes, but what I mean is: is it adding something that the recording process has taken away. Or is it transparent to such a degree that what is there on the recording is allowed to come through? Is it the purity of signal path; because it is single ended, because it is class A that is the biggest contributory factor? Or is it very well managed distortions that conjure the suspension of disbelief?

As with everything, I am sure that there is no specific, definitive answer, but is there consensus?

 

[Caledon1297]

SNIP

As with everything, I am sure that there is no specific, definitive answer, but is there consensus?

 

[Barrymagrec]

Lots of even order (nice) distortion.

Not hi fi under the meaning of the act though, but who cares if it pleases the listener.

 

[JensenHealey]

SE Class A is a very 'simple' (may be not so simple to do well, but in principle it is an uncomplicated method) circuit. The lack of any crossover artefacts s likely a key to its 'sound' signature - or lack of!

 

[early]

Most like you are hearing low ( or maybe non) NFB and high distortion (relative to SS).

Does sound nice though with the right speakers

 

[Chris81]

IMO this:

...Or is it transparent to such a degree that what is there on the recording is allowed to come through? Is it the purity of signal path; because it is single ended, because it is class A that is the biggest contributory factor?...

 

[Steve 57]

It's nice to see a variety of reasons for set amps sounding lifelike.

I use realitively efficient loudspeakers, so a watt is loud in my room, and as single ended amps distortion rises with volume (rather like real instruments) the distortion is really quite low at the volumes I listen... so that to me rules out 2nd harmonic distortion as the reason for the ' lifelikeness'
in any case 2nd harmonic distortion is very difficult to hear until its at higher levels (>5%)
And as 2nd harmonic is the tune being played again, sort of like an echo I'm sure it can soon spoil the sound.. and it does once you get over that 5%

I read an interesting view point a few years ago where some had done tests that proved to him that the process of reducing the rather high distortions in most amplifiers, by the use of push pull and feed back actually also cancels the 2nd harmonics in the recording too.. now how much truth is in that I'm not qualified to say... but it would explain the lack of realism in some amplifiers?

 

[Zombie]

I'd like to try but ESL-988s are an obstacle

 

[gustavm]

It's nice to see a variety of reasons for set amps sounding lifelike.

I read an interesting view point a few years ago where some had done tests that proved to him that the process of reducing the rather high distortions in most amplifiers, by the use of push pull and feed back actually also cancels the 2nd harmonics in the recording too.. now how much truth is in that I'm not qualified to say... but it would explain the lack of realism in some amplifiers?

The current lack of objective measures to understand subjective quality is an interesting topic, but the above sounds rather nonsensical to me, at least as a general conclusion. What you describe should certainly be obvious objectively given more complex test signals than a sine-wave, but it seems very unlikely to me that improving linearity (with feedback or a more linear topology) could result in selective harmonic removal.

 

[Mike Reed]

I'd like to try but ESL-988s are an obstacle

Yes, I have 2905s and whereas the original ESLs (57s) only needed the Quad II's (?) 15 watts or so, I do think these more modern ESLS need a fair amount of welly. Not at all sure that most SET amps would really do then justice. However, like you, I'm interested in the possibility.

 

[Steve 57]

but it seems very unlikely to me that improving linearity (with feedback or a more linear topology) could result in selective harmonic removal.

You may have a point there. You'd think the amplifier would know the difference between 2nd and higher harmonics in the recording and the same as a result as amplifier distortion that its designed to cancel..
But if I remember correctly that was they guys point in what I read

 

[Coda II]

Picking up on some of what's been said above I think it interesting how we view and describe the same thing differently depending on whether we hear it as positive or not.

All instruments produce harmonics; it is why an A on a violin sounds different to the same A on a cello. They may both be playing a note at 440 Hz but each will have its own harmonics which is what makes the same notes sound different. We don't however talk about a violin and cello as being more or less distorted than each other. We may say that a flute has less colouration or is a purer sound, but not that everything else is distorted in comparison.

And if distortion in audio is defined as anything that is apparent on playback that wasn't apparent in the recording then shouldn't we consider a lack of harmonic richness as just as much of a distortion as additional harmonic richness? (not saying one is right and the other wrong, just two sides of the same coin). Do we think that removing words from a Shakespeare play is better than adding them (aside from whether we consider that there may be too many in the first place)?
Depending on preference we may choose enhanced richness over diminished richness - as long as that richness is in keeping with what we expect to hear, ie. it isn't spurious or 'noise' in any way.
Ideally we have all of the harmonic information that was present at the recording, so is this where the simple as possible signal path comes in?
It won't ever be perfect, but is the SET amp designer saying 'I will keep the signal as pure as possible, with as little interference and adjustment from the circuit as possible but will possibly allow an amount of enhancement of the harmonic content' ?

 

[Helen Bach]

yep, coda, like what you say. Harmonic richness is what helps us identify the timbre of instruments. For what it is worth, I analysed the sound from my flute, which is usually thought of as 'a pure tone'. I saw 12 harmonics! And a saxophone showed 32 harmonics. (Neither instrument 'over-blown!'). I really don't understand what Steve57 has written. :?)

 

[Coda II]

yep, coda, like what you say. Harmonic richness is what helps us identify the timbre of instruments. For what it is worth, I analysed the sound from my flute, which is usually thought of as 'a pure tone'. I saw 12 harmonics! And a saxophone showed 32 harmonics. (Neither instrument 'over-blown!'). I really don't understand what Steve57 has written. :?)

I think the point @Steve 57 is making is that where negative feedback is employed in the amplifier (where a fraction of its output is subtracted from its input) with the intention of reducing distortion, it could also be reducing the original harmonic content as well.

 

[davidsrsb]

it could also be reducing the original harmonic content as well.

It cannot/doesn't

 

[Coda II]

It cannot/doesn't

Good to know.

 

[adamdea]

I'm sure that @davidrsb is right
As for the rest- this is all a bit vague. The harmonic signature of an instrument consists of specific levels and proportions of different harmonics and resonances. The harmonic signature of the amp is going to be consistent though. It will therefore not necessarily serve to enhance the distinctness of each instrument- it's pouring a sauce over the top: you may like it; you may not.

 

[Coda II]

I'm sure that @davidrsb is right
As for the rest- this is all a bit vague. The harmonic signature of an instrument consists of specific levels and proportions of different harmonics and resonances. The harmonic signature of the amp is going to be consistent though. It will therefore not necessarily serve to enhance the distinctness of each instrument- it's pouring a sauce over the top: you may like it; you may not.

Is the harmonic signature of an amplifier actually consistent irrespective of the frequency or amplitude of the input? (Don't actually know, but curious).

 

[eastone]

From the user manual to Nelson Pass’s First Watt F8, regarding a scope image of the amplifier’s distortion:

‘You can see that it is a nearly pure second harmonic and that its phase alignment is “negative” at both peaks of the fundamental waveform. No spikes or weird looking stuff. And if you don't like that - well, it's only at 0.012%...

10 years ago when I began working with SIT circuits, I discovered that there was a consistent preference for this sort of characteristic in amplifiers over a range of distortion levels from about .01% to 1%. Somewhere below that, it was not usually heard - and above that it could be excessive. Not only was second harmonic preferred over other harmonic content, but its phase seems to matter.
I used blind evaluations for the SIT-1, the First Watt amplifier, and on the front panel there was a knob that allowed adjustment of this characteristic in distortion amplitude and phase. I found that listeners tended to cluster on the same setting, which was made the center of the adjustment meter. The F8 has this same characteristic, but down at the lower edge of audibility.’

 

[adamdea]

Is the harmonic signature of an amplifier actually consistent irrespective of the frequency or amplitude of the input? (Don't actually know, but curious).

I'm not sure you can give a definitive answer. I would expect it to be largely consistent up to clipping. But there are other issues like output impedance which might introduce other frequency dependent issues
But this is is the wrong question- what I meant was that if the amp is reproducing a signal corresponding with A-440 Hz at a given level - will it know whether it is being produced by a tuba or a flute? It's going to produce the same harmonic spuriae either way (and further distortions of the instrument's harmonics in the signal which will be indistinguishable from the higher harmonics of the instrument embedded in the signal.)