I may not agree with all of the comments here, but the philosophy outlined by Lynn Olsen in this articles certainly conforms well with my own design ideas;
LYNN OLSON:
Shoog
LYNN OLSON:
Shoog
Correct, and as noted, these are zero NFB designs. I had some jitter issues with my source, so the plots do not show the noise floor, but after resolving the jitter, the FFT spectrum was unchanged. Just never bothered to repeat the tests.
I think it's also worthy to note the low hum components with multiple levels of AC heating DHT's. Am currently in process of cleaning up the AC source for even lower hum without the high frequency components.
Do you care to clarify how - after looking at the graphs on the referenced audioasylum page and after reading "The lower harmonics are quite constant with 2nd @ -78dB rel and 3rd at -70db rel. The higher harmonics increase with power." (on the same page) - you came to the conclusion that "These are impressive figures for a zero feedback PP amp - equaling and bettering anything a zero feedback SE can achieve"?
All amps behave in much the same way - even SE amps. The anticpated consequence of PP is that the 2nd, 4th and 6th harmonic are surpressed more than would be expected from an SE amp,which in an SE amp starts to swamp the distortion spectrum as power rises. This is what the FFT plots are showing. This maybe considered a bad thing by those who prefer all their distortion to appear to be 2nd harmonic.
Shoog
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Quite interesting. Lynn Olson - who you swear by - seems to be one of " those who prefer all their distortion to appear to be 2nd harmonic":
"The problem with using THD as a yardstick of quality is the order of the distortion term has a far more audible effect than its absolute magnitude. When you have 3 or more fundamental tones, the number of IM sum-and-difference terms are much worse when you have to contend with a large number of harmonics past the third. This was first discussed by Norman Crowhurst and D.E.L. Shorter of the BBC in the mid-Fifties, so it's hardly a new or radical concept."
(Taken from 'Evolution of THD' Harmonic Distortion over the Decades)
The point you are missing is that the Class A PP amps advocated do not produce significantly more distortion - they produce significantly less - without feedback. Less distortion overall will produce the best overall result.
More 2nd harmonic may not be that objectionable, but it is certainly not better than less overall distortion.
Shoog
More 2nd harmonic may not be that objectionable, but it is certainly not better than less overall distortion.
Shoog
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Really? The page you referenced - http://www.audioasylum.com/forums/tubediy/messages/13/131515.html - the amplifier you hold in high esteem has that kind of distribution of THD at *4* watts and to you that's significantly less? What happens then at 8 watts? 10 watts?
Read Olson's article again. He doesn't think so.
The comparison which is meaningful would be;
-build an a PSE amp with the same valves as a PP amp (ie exactly the same complement of valves). The PP amp should be a back to back version of the SE amp. Measure the distortion of the SE and then the PP. If the distortion of the PP is lower overall then my point is proven.
Until this direct comparison is performed, then we are in the realm of speculation. My contention has always been that SE offers nothing that a PP cannot deliver equally well - but has a range of penalties unique unto itself which leaves me preferring the PP amp.
i don't think you have made your case that SE has some superior performance value.
PS - you are on extremely shaky ground when using Lynn Olsen to make your point - since he implicitly prefers PP because of its performance advantages.
More insight into why Lynn prefers PP;
" Transformer coupling has the interesting advantage that each stage is its own little amplifier, complete with its own independent grounding, and in this case, its own PP cancellation of even-harmonic distortion terms. This means the grid of each 300B is presented with a low-distortion signal coming from a complete fully-balanced amplifier ahead of it, not just the output from a single RC-coupled tube.
In terms of distortion, that's not a small difference; it can mean a tenfold reduction of distortion from the driver stage, as well as much more current available for Class A2 operation. (When one 300B grid goes into conduction, the full power of the preceding PP amplifier is available to it. It also means much more linear current is available to drive the high capacitance of the paired 300B grids.)
This is different than just about any other PP amplifier on the market, which are almost all Williamson derivatives of one sort or another. For reasons that are not clear, the introduction of the Williamson in 1948 erased all other amplifier topologies; it took until 1956 for even minor variations to appear (the Dynaco, Acro, Marantz, etc.), and these variations continue to dominate the vacuum-tube PP-amplifier market of the present day.
I loved the sound of the Ongaku and Reichert (as readers of this magazine know), but I never bought into the whole SE-DHT lifestyle thing. I was pretty sure it was the tubes themselves—direct-heated-triodes—that got the credit, not the much-ballyhooed "simplicity" of the SE circuit."
http://www.positive-feedback.com/Issue20/olsenkarna.htm
Shoog
-build an a PSE amp with the same valves as a PP amp (ie exactly the same complement of valves). The PP amp should be a back to back version of the SE amp. Measure the distortion of the SE and then the PP. If the distortion of the PP is lower overall then my point is proven.
Until this direct comparison is performed, then we are in the realm of speculation. My contention has always been that SE offers nothing that a PP cannot deliver equally well - but has a range of penalties unique unto itself which leaves me preferring the PP amp.
i don't think you have made your case that SE has some superior performance value.
PS - you are on extremely shaky ground when using Lynn Olsen to make your point - since he implicitly prefers PP because of its performance advantages.
More insight into why Lynn prefers PP;
" Transformer coupling has the interesting advantage that each stage is its own little amplifier, complete with its own independent grounding, and in this case, its own PP cancellation of even-harmonic distortion terms. This means the grid of each 300B is presented with a low-distortion signal coming from a complete fully-balanced amplifier ahead of it, not just the output from a single RC-coupled tube.
In terms of distortion, that's not a small difference; it can mean a tenfold reduction of distortion from the driver stage, as well as much more current available for Class A2 operation. (When one 300B grid goes into conduction, the full power of the preceding PP amplifier is available to it. It also means much more linear current is available to drive the high capacitance of the paired 300B grids.)
This is different than just about any other PP amplifier on the market, which are almost all Williamson derivatives of one sort or another. For reasons that are not clear, the introduction of the Williamson in 1948 erased all other amplifier topologies; it took until 1956 for even minor variations to appear (the Dynaco, Acro, Marantz, etc.), and these variations continue to dominate the vacuum-tube PP-amplifier market of the present day.
I loved the sound of the Ongaku and Reichert (as readers of this magazine know), but I never bought into the whole SE-DHT lifestyle thing. I was pretty sure it was the tubes themselves—direct-heated-triodes—that got the credit, not the much-ballyhooed "simplicity" of the SE circuit."
http://www.positive-feedback.com/Issue20/olsenkarna.htm
Shoog
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Fullrange:
This may be easier to discuss if you can post an FFT spectrum of a comparable size SE amp. It would seem reasonable to pick a 300B output tube. Then we can compare apples to apples.
As far as the higher order terms issue, I think the point being made by Olson was that higher order terms really start to muck up IMD, with sum and difference terms nearby the fundamental. It wasn't so much saying "as long as distortion is all 2nd, you're good to go". The more you can reduce 2nd, 3rd, 4th, 5th, 7th, 9th, 11th (which in and of themselves may not be audible if in the right relative quantities), the more you can keep IMD to a minimum (which is likely very audible).
Seriously, look at an SE amp and then compare to the posted PP posts or to mine- you will see very clearly which one has lower distortion. Not saying "mine sounds better than yours", just saying one has less distortion, 2nd, 3rd, 4th, whatever.
This may be easier to discuss if you can post an FFT spectrum of a comparable size SE amp. It would seem reasonable to pick a 300B output tube. Then we can compare apples to apples.
As far as the higher order terms issue, I think the point being made by Olson was that higher order terms really start to muck up IMD, with sum and difference terms nearby the fundamental. It wasn't so much saying "as long as distortion is all 2nd, you're good to go". The more you can reduce 2nd, 3rd, 4th, 5th, 7th, 9th, 11th (which in and of themselves may not be audible if in the right relative quantities), the more you can keep IMD to a minimum (which is likely very audible).
Seriously, look at an SE amp and then compare to the posted PP posts or to mine- you will see very clearly which one has lower distortion. Not saying "mine sounds better than yours", just saying one has less distortion, 2nd, 3rd, 4th, whatever.
You're beating around the bush. And this, again, is why:
"The problem with using THD as a yardstick of quality is the order of the distortion term has a far more audible effect than its absolute magnitude. When you have 3 or more fundamental tones, the number of IM sum-and-difference terms are much worse when you have to contend with a large number of harmonics past the third. This was first discussed by Norman Crowhurst and D.E.L. Shorter of the BBC in the mid-Fifties, so it's hardly a new or radical concept." Lynn Olson
The point is that higher order residuals which are not at levels which are audible are not significant. Take away the 2nd harmonic and the SE amp is still producing similar quantities and magnitudes of the objectionable distortion. If they are audible in the PP then they are audible in the SE as well.
What your quote is saying is not what you think it is saying. It is pointing out that simply having a lot of 2nd harmonic will not hide the higher orders if they are there.
Shoog
No, not just Olson's point. Crowhurst's point as well. Both preferring PP. And both realizing that THD numbers are not the answer. So then, why would you take THD numbers as the main weapon to beat the poor SE?
Its not a case of beating the poor SE, its a case of putting the SE into its proper context - which is not mythical as some believe.
Shoog
2nd order harmonics are relateable to the the fundamental notes, which is why they are much more tolerable to us to listen to. They are integer multiples.
Many of instruments we listen to are oscillators that oscillate at "partial" frequencies.
It is these "partials" that combine to give the fundamental notes we hear.
This is why a little bit of 2nd order sounds "musical". You could actually apply this as a technical term, where less 2nd is more, but is still 2nd order.
You could say that a SE amp is good at singing along with the music, it has "distortion in tune".
Odd order harmonics on the other hand don't mathematically integrate with the fundamental notes. They are out of tune with what you want to hear.
These odd harmonics give the effect similar to a tone deaf kazoo wielding heckler at Alison Krauss show. This is slightly annoying at any level.
Many of instruments we listen to are oscillators that oscillate at "partial" frequencies.
It is these "partials" that combine to give the fundamental notes we hear.
This is why a little bit of 2nd order sounds "musical". You could actually apply this as a technical term, where less 2nd is more, but is still 2nd order.
You could say that a SE amp is good at singing along with the music, it has "distortion in tune".
Odd order harmonics on the other hand don't mathematically integrate with the fundamental notes. They are out of tune with what you want to hear.
These odd harmonics give the effect similar to a tone deaf kazoo wielding heckler at Alison Krauss show. This is slightly annoying at any level.
3rd Harmonic makes it sound like a trumpet. Some 2nd and a little 4th makes it sound like a metal wired guitar. 5th and up, NG.
Can you list some SE amps with such measurements? The measurement comparisons of SET and PP (tube and transistor) amps I've seen disagree with you. But I haven't seen many amp measurements so I may be missing something.
I guess, if you take away 2nd harmonic, then possibly. Uh... how would one take away 2nd harmonic from SE amp's output and play through speaker for comparison?
If it's not too costly, I may try that.What I've read and been told, 2nd harmonic stronger than 3rd, can mask the subsequent harmonics. May be they are written by novice and I've been lied to. 🙁
Let me put this into anecdotal context. I recently built a very pure SET design and placed it up against my best Class A PP design. I had been prepped by my research to expect a certain magic from my new SET amp. When myself and a friend auditioned the two over a long afternoon neither found any significant difference when played within their power range. We both agreed that the PP had a slight edge - but not anything worth worrying about.
This made me skeptical of the claims for SET.
What really makes me skeptical is that almost all of the SET fans have never built or listened to a PP amp to the same standards as they apply to their SET amps. Almost no-one has any first hand experience of a fair and honest comparison of a truly great PP amp with a great SET. Those who have really looked into this, those such as Lynn Olsen, Allen Wright and Gary Pimm and members such as zigzag and myself find that PP can at least match SET in every way. Now thats just an opinion - but certainly one worth investigating.
Shoog
This made me skeptical of the claims for SET.
What really makes me skeptical is that almost all of the SET fans have never built or listened to a PP amp to the same standards as they apply to their SET amps. Almost no-one has any first hand experience of a fair and honest comparison of a truly great PP amp with a great SET. Those who have really looked into this, those such as Lynn Olsen, Allen Wright and Gary Pimm and members such as zigzag and myself find that PP can at least match SET in every way. Now thats just an opinion - but certainly one worth investigating.
Shoog
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