How about this. There is no such thing as perfection, therefore we need to make compromises somewhere that are most in alignment with what we like most. So, having built lots of amps in differing topologies, I've decided that I prefer the compromises inherent in PP amps; most SE's sound like mud to me, but my PP's might sound sterile to you. I listen to what I like, you listen to what you like, no issue there. But to say one topology is "better" in all instances is bollocks, especially when someone hasn't experienced all the topologies under discussion.serengetiplains said:
Fine enough?
Hi,
Well, strange as it may seem but almost any half decent OTL using_horror of horrors_a bunch of paralelled tubes in_other horror_PP excels at portraying the acoustic space.
This had me convinced for many, many years that it was the OPT that was eating the finer ends of the resolution of these micro details.
To a certain extent I'm still convinced that most OPTs are to blame for this.
Using a simple circuit such as used by most SE amps is of course always helpful as the risk of something going wrong is greatly reduced or so it would seem.
I'm also convinced that wide bandwidth designs_that includes the OPT_ have inherently a much better chance at giving this "you are there" listening experience.
Either way I suppose any topology can be good provided it is well excecuted...That's the fine print for you.....
Cheers,
Well, strange as it may seem but almost any half decent OTL using_horror of horrors_a bunch of paralelled tubes in_other horror_PP excels at portraying the acoustic space.
This had me convinced for many, many years that it was the OPT that was eating the finer ends of the resolution of these micro details.
To a certain extent I'm still convinced that most OPTs are to blame for this.
Using a simple circuit such as used by most SE amps is of course always helpful as the risk of something going wrong is greatly reduced or so it would seem.
I'm also convinced that wide bandwidth designs_that includes the OPT_ have inherently a much better chance at giving this "you are there" listening experience.
Either way I suppose any topology can be good provided it is well excecuted...That's the fine print for you.....
Cheers,
fdegrove said:
See how well we're all getting along?
Re bandwidth, am I not wrong to say an OTL preserves high frequency phase relationships better, this as a consequence of an OTL's inherently higher bandwidth, not to mention lack of transformer? I wonder if certain micro-details (micro-micro-details?) are lost when phase is distorted?
Yes, Class A push-pull is really more like two tubes in parallel without the generated even harmonic distortion. Two facts about CLASS A push-pull that are not always understood:
1. The signal is split into two complete signals, one 180 deg. out of phase (or inverted) with the other, amplified by the output tubes, and then added together in the output transformer.
2. Each tube in a Class A push-pull output stage sees the whole primary impedence, plate-to-plate, of the output transformer.
One can see how, in order to maximize perfomance of a Class A push-pull power amplifier, it is imperative that the tubes are matched and the two halves of the primary of the OPT are identical, AC-wise.
The real problem with push-pull compared to single-ended is that, because there is no DC bias on the OPT, the magnetic field of the core of the OPT collapses (or would like to do so) every time the AC signal crosses zero, causing audible low-level weirdness. To minimize this problem, high-mu cores can be used. I sure would like to try a nickel push-pull OPT some day.
John
That's why I prefer to use the term inverter, rather than splitter, though I usually fall back into the habit of using the S word.jlsem said:
No, each tube sees half of the a-a load.
There are methods to force balance, and they make a big difference.
I'd like to try Ni or amorphous cores too one day, but I think the magnetic field issue is more theoretical than practical.
In Class A push-pull, the impedence each tube sees, i.e. the slope of the load line, is more complicated than just looking at the turns ratio. There is an autoformer effect when one tube is conducting and the other isn't, so although the impedence each tube sees varies throughout the cycle, it is essentially the full plate-to-plate impedence at the quiescent operating point. Remember we are talking Class A only here.
John
I do understand. However, how do you reconcile comments such as "There is an autoformer effect when one tube is conducting and the other isn't" and "Class A"?jlsem said:
Still say it's a-a/2, until someone shows a mathematical anaylsis otherwise and it's too damn hot here to be interested in doing it myself.
There was a great series of discussions on this very topic on AA TubeDIY recently. I'm not on my 'puter, so I don't have the URL's saved, but perhaps Douglas (Bandersnatch/Sector 7G) will pop in a comment/post links.
It's not a personal comment. Maybe I didn't word it correctly. I'm talking about operation in the linear region of the tubes' characteristics, the all-important first watt. This is better explained in any number of engineering texts from the 30's and 40's complete with diagrams, equivalent circuits and related equations, so there is no point in arguing it any further here.
It's not a simple case of making blanket statements. The path of operation for each tube is a curved line and the composite path of operation is a straight line. I will repeat what I wrote before: The impedence seen by EACH tube at the quiescent point is approximately the a-a impedence. The path of operation for the COMPOSITE has a slope exactly equal to the inverse of the turns ratio squared multiplied by the inverse of the load resistance or:
1/(N1/N2)*2 x 1/R load
John
From this thread
Posted by Damir on September 12, 2004 at 03:48:19
In Reply to: It's a 9k transformer. posted by Mark Kelly on September 11, 2004
at 23:32:24:
If someone is still confused with those contradictory informations, please see RDH, pages 199-203. Let`s say that our secondary load is 8 Ohms. Then our impedance ratio across whole primary is 9000/8=1125 or turns ratio is 33,54. Turns ratios from both halves of primary to secondary is N2/N1 = N3/N1 = 16,77 where N1 is a number of turns of secondary and N2,N3 number of turns of halves of our primary. From W1=W2+W3 (power in secondary is equal to powers in both halves of our primary) we have formula (4) in RDH:
1/R1 = 1/(R2(N1/N2)^2) + 1/(R3(N1/N3)^2)
R1 is secondary load - 8 Ohms, and R2=R3=reflected loads across halves of our primary. Note that N1/N2 = N1/N3 = 1/16,77 = 0,05963. We have 1/8 = 2/(R2,3 * 0,05963^2)
And our R2=R3 = 4500 Ohms! Or, with both halves of primary loaded (class A) load (that every tube "see") of each half of the CT primary is exactly half of the reflected load across the whole primary.
And, from RDH again, page 201:"If however only one half of the primary is used the transformed load presented is 1/4" (reflected load). In that case (say, class B) we have R2 or R3 = 9000/4=2250 Ohms, this is understandable `cos we transferred the power only across 1/2 of the primary, W1=W2 or W1=W3, see above formula, 1/8 = 1/(R2(N1/N2)^2) = 1/(R3(N1/N3)^2).
I don't have my RDH4 with me, but it jives with all the measurements and simulations I've done over the years.
Posted by Damir on September 12, 2004 at 03:48:19
In Reply to: It's a 9k transformer. posted by Mark Kelly on September 11, 2004
at 23:32:24:
If someone is still confused with those contradictory informations, please see RDH, pages 199-203. Let`s say that our secondary load is 8 Ohms. Then our impedance ratio across whole primary is 9000/8=1125 or turns ratio is 33,54. Turns ratios from both halves of primary to secondary is N2/N1 = N3/N1 = 16,77 where N1 is a number of turns of secondary and N2,N3 number of turns of halves of our primary. From W1=W2+W3 (power in secondary is equal to powers in both halves of our primary) we have formula (4) in RDH:
1/R1 = 1/(R2(N1/N2)^2) + 1/(R3(N1/N3)^2)
R1 is secondary load - 8 Ohms, and R2=R3=reflected loads across halves of our primary. Note that N1/N2 = N1/N3 = 1/16,77 = 0,05963. We have 1/8 = 2/(R2,3 * 0,05963^2)
And our R2=R3 = 4500 Ohms! Or, with both halves of primary loaded (class A) load (that every tube "see") of each half of the CT primary is exactly half of the reflected load across the whole primary.
And, from RDH again, page 201:"If however only one half of the primary is used the transformed load presented is 1/4" (reflected load). In that case (say, class B) we have R2 or R3 = 9000/4=2250 Ohms, this is understandable `cos we transferred the power only across 1/2 of the primary, W1=W2 or W1=W3, see above formula, 1/8 = 1/(R2(N1/N2)^2) = 1/(R3(N1/N3)^2).
I don't have my RDH4 with me, but it jives with all the measurements and simulations I've done over the years.
Your are absolutely correct and I have made a complete fool of myself.
Each tube sees approximately one half the plate-to-plate impedence at the quiescent point. As the grid for one tube swings to its most positive value (while the other tube's grid swings the other way) the impedence it sees approaches the full a-a value. Conversely as it swings toward its most negative value (to 0 volts), the impedence it sees approaches (a-a)/4.
What I can't figure out is how I was able to argue your point 5 years ago on another forum and then come here and say exactly the wrong thing.
John
I owned a kit one in the past, I have heard the guy who designed it, David Wright, wrecked an ongaku which led to him leaving audionote.
Its a very good looking design, with no obivious weakness and attention to detail, nice build and components, but I didn't really like the sound, it was a bit polite, weak, and bright, which was a shame.
ymmv tho' its a good ish price, there is also bottlehead, welborne, and the diyhifi supply one, so plenty of choice.
sowter are great, but pricy due to exchange rate, there is one called silk transformers in thailand, do a search in google, and its sac I think.
Its a very good looking design, with no obivious weakness and attention to detail, nice build and components, but I didn't really like the sound, it was a bit polite, weak, and bright, which was a shame.
ymmv tho' its a good ish price, there is also bottlehead, welborne, and the diyhifi supply one, so plenty of choice.
sowter are great, but pricy due to exchange rate, there is one called silk transformers in thailand, do a search in google, and its sac I think.
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