To SET or not to SET

[sfogg]

Dave,

"The next question, then, is WHY do odd order harmonics have the nasty bite, when both the even and odd fall in the normal hearing range?"

This is getting into personal tastes again. Mark's explanation makes sense to me. But again it is entirely possible there is someone out there that loves 7th order (or whatever).

" If the harmonic progression created from the fundamental is a law of physics, then won't a SS and a tube amp create the fundamental(and hence the harmonic progression) in the same fashion?"

I'm assuming you mean the harmonic distortions introduced by the amp, not the harmonics that are recorded in the signal? If so then the harmonic distortions will not always be the same between amps.

For example look at the SE-OTL above, that is when it is getting close to clipping. It has a very smooth progession of the distortions. Every higher order harmonic is at a lower level then the one before it.

Compare that against the Monarchy SM-70 as it is getting close to clipping.

Its distortions are different. The 7th is a lot lower then the 8th and 9th for example.

I don't think this is just from a fundamental difference between tube/SS. That may well be a factor but the actual design of the amp itself will be a factor too of course.

Shawn

[Deang]

Rick/Shawn -- then I get the freaking T-shirt for surviving this thread, which has caused me to break out with some strange rash.

So, it's settled then -- the "best" sound should come from a high powered SET amp.

[neo33]

"So, it's settled then -- the "best" sound should come from a high powered SET amp."

5 watts sound good to me. .

[Daddy Dee]

Boy, I need to adopt an engineer to help me out following this thread! Wait a minute, I'm supporting one in school right now. But she's not really in to audio.

Rick, I wasn't sure I was following what you were saying about the SE OTL. Have you been listening to one? Or observing what Shawn had said? I don't think I was comprehending that, either. What about the harmonics and "bloom"?

Shawn, if you wouldn't mind to chime in here, too, I'd appreciate that.

Apologies and thanks in advance. If you guys could talk (or type on the keyboard) slower, I might be able to catch on to this.

Note to Amy and Trey: we need an additional smilie icon or two. How about one which suggests, slow, confused, not too bright, Gomer Pyle type icons.

[sfogg]

"I don't think I was comprehending that, either. What about the harmonics and "bloom"?"

This is just a theory of mine that I mentioned earlier in this thread. (On page 8 if you want to read it)

But to try to explain it again....

In many reviews/postings about the sound of a SET amp I've seen mention of SETs 'blooming.' Sometimes a person says 'opening up' which I take to mean the same thing.

I've also noticed one of the complaints against PP (or even higher powered SET amps) is that they don't bloom/open up. I've noticed this pattern in many different posts. You also see it regarding say an 845 or 211 vs the 300b. Then again on a 300b vs the 2a3. And yet again on the 2a3 vs 45. They may even be out there for the 45 vs something like a 76 or whatever. You will note in all such cases the lower powered version is prefered to the higher powered version.

It always appears that the proponent of said amplifier thinks/claims the reason for the 'magic' of this amp is because of how well it does 'that first watt.' The common claim being that it has so much less distortion then some other higher powered amp would have if it was run at the same volume level with the same speakers. This is what I'm suggestion is a major assumption based on the audiophile nervousa goal of 'accuracy.' "If I like this amp then it must be because it is more accurate" is perhaps a very serious falacy.

The charts here are showing the levels (and distribution) of harmonic distortion of a variety of different amps. Contrary to popular opinion the higher powered amps (even the PP tube or (shudder) the SS amps) are not putting out a lot of distortion (even order or odd order), they are putting out very little. Which actually makes sense since they aren't working hard at all.... and the designs of some help to reduce distortions.

On the flip side the lower powered SE amps are working harder. They are being run much closer to their power ratings. As such they are distorting more. The lower the power output of the amp the more it will be distorting.

What I'm suggesting is that perhaps the lovers of that 'blooming' are actually loving the additional harmonic distortions caused by running the amp fairly hard relative to its power output.

And as I've said multiple times there is nothing wrong with liking that, it is a persons personal taste after all.

On a related note I also think this might be a little bit of where the critical matching between SET and speaker comes into play. Yes they need to be well matched for a decent FR due to other interactions between the speaker (impedances) and the amp but I'm also wondering if part of this is simply matching the sensitivity to the amp such that the amp is 'blooming' (but not clipping very very badly) at the typical listening levels of the listener. And on the flip side not using too sensitive a speaker such that the amp isn't working hard enough anymore and therefor isn't blooming.

Where the problem comes in is that conditioning for the goal of 'accuracy.' Very few will be able to admit to themselves that perhaps why they enjoy amp xyz is because it has its own 'sound' which is perhaps in part due to the amps inaccuracies in the form of its harmonic distortions.

And as I mentioned earlier if someone is reading this and thinking 'Well *my* amps don't distort like that...' then they need to ask themselves do they really know that for sure? Or are they making an assumption that that is the case because they enjoy them and therefor they must be 'accurate?'

There is a saying that is basically 'If you don't like the first watt you won't like the rest.' Which is typically said meaning if the first watt isn't low distortion why do you need more like that. I think it is more of if you don't like the first watt without some additional colorations/bloom/harmonic distortions you won't like more of the same.

And again since I'm sure this is going to be missed by someone here.... there is absolutely nothing wrong with enjoying this. That is the entire point of having *your* stereo system... to enjoy it.

I'm just curious about what is going on behind the scenes so to speak as I think some of the more common explainations given (PP or SS being all third order distortion for example) aren't accurate.

Shawn

[Daddy Dee]

Shawn,

That makes sense. Thanks for restating that.

[3dzapper]

"Contrary to popular opinion the higher powered amps (even the PP tube or (shudder) the SS amps) are not putting out a lot of distortion (even order or odd order), they are putting out very little."

Shawn, there is considerable distortion in this amp. Very few would run out and put their money down on an amp that claimed >0.6%THD at 1 watt!(That's using your stated measurement of 2nd order of 0.0095v + 3rd + visible artifacts.) THD being the sum of all the distortion products divided by the fundamental.

Edit: Of course that's why tube amps are rated X watts at 1% THD and SS at X THD at X watts full output.

Rick

By the way Dean, If you really want it you can have the tee shirt just for sitting through all this.

[sfogg]

Rick,

"there is considerable distortion in this amp."

Compared against?

How much distortion would there be at 1w with a 300B or a 2A3 based amp running without feedback?

" Very few would run out and put their money down on an amp that claimed >0.6%THD at 1 watt!"

I suspect that is true.

However, that doesn't mean that plenty of others haven't run out and put their money on an amp with that level (or higher) of distortion at 1w.

For example how do you know you haven't?

EDIT: "(That's using your stated measurement of 2nd order of 0.0095v + 3rd + visible artifacts.) THD being the sum of all the distortion products divided by the fundamental."

THD doesn't include any other visible artifacts. THD is total harmonic distortion. With other artifacts, like powerline noise, the rating is THD+N.You may have also noticed many times the S/N or noise rating of an amp is 'A' weighted. Guess why..... 'A' weighting rolls off the bass pretty dramatically.... which would also roll of powerline noise.

Shawn

[3dzapper]

"However, that doesn't mean that plenty of others haven't run out and put their money on an amp with that level (or higher) of distortion at 1w.

For example how do you know you haven't?"

I am sure I have! But, if they truly stated the 1 watt distortion I probably would have balked.

"THD doesn't include any other visible artifacts."

I meant the vestages of fourth, fifth and any sub-harmonics.

[coda]

Perhaps the biggest movement in high-end audio in the 1990s has been the return to the single-ended triode power amplifier. The single-ended triode (SET) amplifier was the first audio amplifier ever developed, dating back to Lee De Forest's patent of the triode vacuum tube in 1907 and his triode amplifier patent of 1912. SET amplifiers typically produce less that 10Wpc. You heard right: Large numbers of audiophiles are flocking to replace their modern power amplifiers with amplifiers based on 90-year-old technology. Have the past 90 years of amplifier development been a complete waste of time? A surprising number of music lovers and audio designers think so.

The triode is the simplest of all vacuum tubes; its glass envelope encloses just three electrical elements rather than the five elements in the more common (and modern) pentode tube. Triodes have much less output power than pentodes, but more benign distortion characteristics. Virtually all modern tubed amplifiers before the SET comeback used pentodes.

In a single-ended triode amplifier, the triode is operated so that it amplifies the entire audio signal. That's what "single-ended" means. Virtually all other power amplifiers are "push-pull," meaning that one tube (or transistor) handles the positive half of the musical waveform and a second tube (or transistor) handles the negative half.

Think of a push-pull amplifier as a two-man saw: one man pushes and the other man alternately pulls the saw. Another way of looking at the way push-pull amplifiers work is a relay race: one tube (or transistor) hands off the signal to the other tube (or transistor), then gets it back, this switching occurring many times a second; in other words, the musical signal is split into two parts, then combined at the output. SET proponents believe that because the triode amplifies the entire waveform, SET amplifiers offer the ultimate in sound quality and musicality. Moreover, SET amplifiers have no need for a circuit called a phase splitter, which makes them even simpler. Note that a single-ended tubed amplifier can use more than one output tube; what makes it single-ended is the operation in which the tube or tubes amplify the entire waveform rather than a portion of it.

Push-pull amplifiers suffer from something called crossover distortion, which is a discontinuity in the musical waveform in which one tube (or transistor) leaves off and the other tube (or transistor) takes over. A SET never hands off the signal between output devices and thus has no crossover distortion.

In addition, SET circuits are extremely simple and often use very little or no negative feedback. Negative feedback is taking some of the amplifier's output signal and feeding it back to the input. Such feedback lowers distortion, but many feel than any feedback is detrimental to amplifier musicality.

On the test bench, SET amplifiers have laughably bad technical performance. They typically produce fewer than 10Wpc of output power, and have extremely high distortion -- as much as 10% Total Harmonic Distortion (THD) at the amplifier's rated output. Although most SET amplifiers use a single triode output tube, additional triodes can be combined to produce more output power. Some SET amplifiers, however, put out just 3Wpc. In fact, there's a kind of cult around SET amplifiers that strives for lower and lower output power. These SET enthusiasts believe that the lower the ouput power, the better the sound. One SET designer told a reviewer, in all seriousness, "If you liked my 9W amplifier, wait until you hear my 3W model."

In addition to low output power and high distortion, SET amplifiers have a very high output impedance as amplifiers go: on the order of 1.5-3 ohms. This is contrasted with the 0.1 ohm ouput impedance of most solid-state amplifiers, and the 0.8 ohms of many push-pull tubed designs. Because a loudspeaker's impedance isn't constant with frequency, the SET amplifier's high ouput impedance reacts with the loudspeaker's impedance variations to produce changes in frequency response. That is, the SET amplifier will have a different frequency response with every loudspeaker it drives. These variations can range from just 0.1dB with some loudspeakers that have a fairly constant impedance, to as much as 5dB with other loudspeakers. The SET amp's sound will therefore be highly dependent on the loudspeaker with which it is matched.

Despite these technical drawbacks, my listening experience with SET amplifers suggest that this ancient technology has many musical merits. SET amps have a certain presence and immediacy of musical communication that's hard to describe. It's as though the musicians aren't as far removed from here-and-now reality as they are with push-pull amplifiers. SET amps also have a wonderful liquidity and purity of timbre that is completely devoid of grain, hardness, and other artifacts of push-pull amplifiers. When I listen to SET amplifiers (with the right loudspeakers), it's as though the musicians have come alive and are playing in the listening room for me. There's a directness of musical expression that's impossible to put into words, but is immediately understood by anyone who has listened for themselves. You must hear a SET firsthand to know what the fuss is about; no description can convey how they sound.

When auditioning a SET amplifier, it's easy to be seduced by the midrange. That's because SET amplifiers work best in the midband, and less well at the frequency extremes of bass and treble. If the SET demo is being run for your benefit, be sure to listen to a wide variety of music, not just small-scale music or unaccompanied voice -- these will accentuate the SET's strengths and hide its weaknesses.

The importance of matching a SET amplifier to the right loudspeaker cannot be overemphasized. With a low-sensitivity speaker, the SET will produce very little sound, have soft bass, and reproduce almost no dynamic contrast. The ideal loudspeaker for a SET amplifier has high sensitivity (higher than 98dB/1W/1m), high impedance (nominal 8 ohms or higher), and no impedance dips (a minimum impedance of 6 ohms or higher). Such a speaker will produce lots of sound for a small amount of input power, and require very little current. (Remember the example earlier of Paul Klipsch's high-sensitivity speaker that produced concert hall levels with 5W?) There's been a resurgence in high-sensitivity speakers that has paralleled the popularity of SET amplifiers. Some loudspeakers designed for SET amplifiers have sensitivities of more than 100dB, which enable them to produce satisfying listening levels with 5Wpc. SET amplifiers are often coupled with horn-loaded loudspeakers, which have extremely high sensitivity but, in my experience, introduce unacceptable levels of coloration.

The popularity and unmistakable sound quality of SET amplifiers pose a serious dilemma: how can an amplifier that performs so poorly by every "objective" measure produce such an involving musical experience? How can 90-year-old technology eclipse, in many ways, amplifiers designed in the 21st century? What aren't we measuring in SET amplifiers that would reflect their musical magic? Why do conventional measurements fail so dismally at quantifying what's right in SET amplifiers? Do SET amplifiers sound so good because of their high distortion, or despite it? As of yet, no one has the answers to these questions.

Robert Harley, The Complete Guide to High End Audio (Third Edition)

[WhoozYoDaddy]

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa *drool drool drool*.....*stare*

[mike stehr]

"They may even be out there for the 45 vs something like a 76 or whatever."

76 is pretty much a driver tube. I would guess the lower wattage brother to the 45 would be the 71A. It's like 800 mils to a watt, nickel plates, I think a 2.5 volt filament.

I think the lower brother to the 71A would be a 205?

I dunno, there is a lot of tubes between those.

Good posts!

It's too bad you didn't have some sort of lower wattage,(2A3, or 300B)single-ended triode circuit with a air-gapped output transformer.

From what I understand, these triodes(and probably others)tend to have more of a positive swing on the waveforms.

I'm too brain-dead to explain what I'm trying to get at, but I'm sure you can gather from it.

Yeah, if like listening to tube amplifiers then I suppose you gotta like distortion.

I know I do. I happen to like the harmonic distortions tube circuits do when they clip, or mildly clipping.

Sure beats that broken glass sound of a SS amp hiked up to clipping.

(But I've never experienced a SS class A amp, other than "seeing" a Krell in a undersized cabinet overheating, so I just don't discredit SS, I just can't afford what I want. Tubes are simple, cheap and fun with the right speakers).

I have a old Montgomery Ward AM/FM phono receiver, SE 6BQ5 pentode connected job, typical cheap tube garb of the late fifties, early sixties.

One time I had a radio station dialed in playing Van Halen's "Eruption", I hiked that little receiver wide open. That was some sweet distortion, I loved it....

[3dzapper]

"That was some sweet distortion, I loved it...."

"And that's the name of that tune....."

Berretta

Rick

[edwinr]

Okay Shawn. Things are falling into place for me.

Rightly or wrongly I now have a picture in my mind. Low powered amplifiers of the SET persuasian (and some low powered tube amplifiers generally?) act like a musical instrument. They accurately reproduce the incoming musical signal. In addition they add some nice sounding harmonics which are pleasing to most human ears. The low powered tube amp virtually functions like the sound boards of certain stringed musical instruments like the guitar, violin, cello, etc. If we plucked a string without a sounding board we would not be rewarded with a rich sounding musical note - only a flacid parroting (sorry Paul) of what was intended by the musician.

Now many solid state amplifiers do not intend for any harmonic distortion to intrude. Manufacturers of such equipment make a virtue of the fact that their product goes from zero to 100Khz without stopping, with virtually zero distortion, and with ruler flat response. The result is an absolutely dreadful sounding piece of equipment - that horrible 'hi-fi' sound that guarantees a tube aficionado would flee in horror.

But the sad thought is, if you haven't heard the real thing (I'm talking about tubes generally, not just SET), how will you know any different?

[sheltie dave]

Edwin, the quick way to know is at what point does the amp drive you out of the room due to nasty acoustics. I have a 25 wpc HK 630(SS) and a set of 60 wpc tube amps. The SS will drive people out at 1 pm, the tubes at 3 pm. I can't tell if the phone is ringing past 11 am with the SS, I can still tell it at 2 pm with the tubes.

I'm beginning to understand the tuned ear is a pretty good judge of good acoustics...

[sfogg]

" If we plucked a string without a sounding board we would not be rewarded with a rich sounding musical note - only a flacid parroting (sorry Paul) of what was intended by the musician."

But remember the recording of that instrument will have also captured those overtones/haromonics that the instrument originally produced.

When they are fed into the amp they become in effect new fundamentals... that started life as harmonics of the original instrument. An amp which 'blooms' will be creating harmonics of what was originally a harmonic. And amp which doesn't will just reproduce the harmonics of the original event which were recorded.

Obviously some like harmonics on top of what were originally harmonics.

Obviously some don't.

Both are the right answer for the person making their choice.

Shawn

[sfogg]

"The SS will drive people out at 1 pm, the tubes at 3 pm. I can't tell if the phone is ringing past 11 am with the SS, I can still tell it at 2 pm with the tubes."

If you are talking about the volume control on the pre-amp feeding the two different amps that honestly doesn't mean much. The gain of the amps are likely different so they would be putting out different amounts of power even at the same volume control setting on your pre-amp.

The volume control is not much of an indicator of how much power an amp is putting out at all. Unless you have a passive pre-amp almost any amp would be *heavily* clipping well before the volume control is turned up all the way.

Shawn

[edwinr]

Good one Dave!

It's interesting I was reading about Copland, a Danish amplifier manufacturer and their designers use both tube and solid state to achieve their design goals. Also another company (British I think) into this low powered stuff is DNM but they use solid state. I wonder if properly designed low powered solid state could acheive this 'bloom' we have been talking about?

By the way I just got called outside. It's snowing and the kids are going beserk. I think I'll just watch the fun from inside my warm house.

[3dzapper]

" If we plucked a string without a sounding board we would not be rewarded with a rich sounding musical note - only a flacid parroting (sorry Paul) of what was intended by the musician."

"But remember the recording of that instrument will have also captured those overtones/haromonics that the instrument originally produced.

'When they are fed into the amp they become in effect new fundamentals... that started life as harmonics of the original instrument. An amp which 'blooms' will be creating harmonics of what was originally a harmonic. And amp which doesn't will just reproduce the harmonics of the original event which were recorded.'"

True Shawn. Also true is every venue has it's own harmonic signature. The "warm, live" nature of tubes might well be the addition of and emphasis on low order harmonics like a warm hall which are much better recieved than a cool "dead" hall.

Witness the original build of Carnege Hall and all the work which had to be done to make it listenable.(The original, as designed, was dead as a fish on land in winter. I don't remember if it was two or three rebuilds that were performed.) (?)

Rick

[BEC]

Shawn,

There is a test I would like to see someone do. Guess I should just do it myself. I would be interested in seeing the following:

Measure the amplitude of the second harmonic produced by an amp driven to 1 watt. Adjust the signal input down to the point that the fundamental output is at the level measured before for the second harmonic. With that output going to a speaker, one should be able to determine if a given amps harmonic products are audible.

Bob