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In Reply to: RE:what's wrong with push/pull design? [n.t.a.] posted by pictureguy on April 17, 2015 at 15:57:20
Hi do you mean that musical instruments can cause RAREFACTIONS ?
maybe singers yes ... when they suck air in to sing.
What i meant is that complete silence is the reference level.
You cannot go lower than that level.
Maybe i have not completely understood the explanation of Mr. Pass.
Kind regards,
bg
Follow Ups:
Think about a drum head. It vibrates in both the forward and backwards directions when the membrane moves forward it compresses air and when it moves backwards into the drum body it will pull some air (as the membrane displaces air will move to fill the vacuum). However, it is a single membrane creating the distinct sound and not two separate membrance pieces moving in opposite directions.
A single ended amplifier will amplify both the positive and negative aspects of the waveform without a handoff that invariably creates crossover distortion unless the push/pull amplifier is biased in Class A. Another sideeffect of push/pull is the cancellation of even order harmonics. This is not an effect seen in nature. Natural instruments and sound sources usually have monotonic harmonic structure (2nd, 3rd, 4th harmonic etc. in an exponential decay). A well designed SET amp will have the same monotonic distortion pattern as seen in nature.
A perfect push/pull amp will have NO even order harmonics. In practice though, they will have a 2nd order about the same size as the 3rd harmonic but then the evens will drop off quickly after that.
In nature pretty much everything is single ended push/pull is a purely human conception of how to make an amp more efficient but not really more correct.
That being said, I have heard some extremely good sounding push/pull amps but they lack the coherence of a really great SET, IMO.
.
However an SET amp can not amplify even a simple sine wave correctly. It compresses the negative side of the wave compared to the positive side. So the amp is inherently non symmetrical and therefore non-linear. And this problem is caused by the topology of single ended and therefore not correctable. Fortunately this distortion sounds good to many.
Under clipping conditions you would be likely correct but well below that I think they are symmetrical enough not to cause too high distortion (my JJ amp is about .1% at 1 watt). If it was as bad as you say then it would be several % at all power levels.
That's where the high SET 2nd harmonic distortion comes from.
Yes, many if not all love distortion, clipping is most favored ... :) BTW, the New Pass Amplifiers are considered to sound like an SET with PP power and drive...
Regards..
Edits: 04/21/15
Hi and very interesting indeed and thanks a lot again for the very valuable explanation.
Therefore single ended designs have indeed some very strong points.
Maybe a good compromised would be to keep single ended operations at least to a certain power level and use a push-pull booster for the higher powers.
Like single-ended up to 10W and the last stage push-pull, of course when higher powers are required.
Thanks again.
Kind regards,
bg
Yes, complete silence is a reference level. Just try to ACHIEVE that in practice, however.
It takes special rooms and design to get the SPL down to such levels. ZERO SPL would be roughly the same as absolute Zero. You know it's 'there' but can you get to it?
ALL sound is composed of pressure / rarefaction. If you want just pressure, go under water a few feet. LESS pressure? Go UP in a plane with the door open. Or up a tall montain. The guys that climb the tallest peaks bring OXYGEN cylinders.
I just wonder about how MUCH the difference is in the micro-pressure DURING a sound wave?
Too much is never enough
Hi so you mean that Mr. Pass is wrong in his statement ?
Excuse me but i am really trying to understand here if what he is saying is right or wrong.
The poster was asking what could be wrong in push-pull amps i search and found the Mr. Pass argument in favor of single-ended amps and against push-pull.
Thanks.
Kind regards,
bg
I tend to disagree with Pass. Air is NOT just pressure, but when a sound producing element moves it produces pressure on one side and a rarefaction on the OTHER. 'The wave' of sound.
Do I MISunderstand Pass? Maybe. Where is the rest of the article?
Too much is never enough
Hi and thanks for the explanation
Link to the article attachedOne thing is sure ... he is very convinced on his position.
At the end he states ... " Regardless of the type of gain device, in systems where the utmost in natural reproduction is the goal, simple single-ended Class A circuits are the topologies of choice " ... stilling all doubts about his thinking.
Kind regards,
bg
Edits: 04/18/15 04/18/15
I believe it is possible to agree with Pass on his ELECTRICAL stuff without necessarily buying into his model of sound in air. It is clear that sound reaching your ear is composed of BOTH pressure higher AND lower than 'still air'. Whatever that happens to be on any particular day or time. Sound is NOT like wind blowing where you can measure a static positive pressure.
Too much is never enough
Hi and yes i think so me too.
And honestly i am a little out of my reach here. I am not a scientist.
I mentioned that article because is the only one that i have found about the push-pull vs. single-end approach.
However it is a very interesting topic. Many audiophiles like the single-ended approach especially with tubes.
Thanks again.
Kind regards,
bg
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