Discussing digital and class A amps

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Peter Daniel said:
Single ended nature of air is described on page 6 of this manual.
http://www.passlabs.com/pdf/aleph/a0man.pdf


I am not sure I would buy Nelson's argument there. When you "push" air, say with a diaphragm, you are neccessarily "pulling" air on the other side of the diaphragm: air being sucked into "space" left by the diaphragm.

his argument seems to be based on Fig1 where pushing the same amount of air caused higher increase in pressure (than pulling the same amount of air).

However, if we had a "ficticious" gas that followed V*P1.4=Constant, we would have a situation whereby "pushing" the same amount of air caused lower increase in pressure. and this "ficticious" gas would generate primarily 2nd order harmonics, just like air.

I would agree with his argument on cross-over distortion, but I am not sure if characterizing air as SE, and linking that SE-characteristics of air with amp topology make much sense to me.

so maybe Nelson can shade some light on this.
 
I don't have much experience with digital amps, and really none with class-A's, but I just felt like throwing in my two cents anyway. I think that it is/will be possible to make digital amps that sound incredibly good with extremely low distortion and noise and an overall pleasing sound. I doubt that they'll ever sound exactly the same as class-a's, but whether they sound better or worse will be a matter of individual preference. I haven't ever listened to any of the high-end digital amps, so I'll go by something within my frame of reference. This is (don't laugh) the BASH digital hybrid amp in my Klipsch promedia 5.1 ultra computer speakers. The amp compares quite well to the "high-end" of the typical consumer audio market, i.e. what you can buy at circuit city or best buy. Compared to my capacitance-starved pioneer receiver, it has a much cleaner, more realistic sound throughout the entire frequency range, no hissing even at maximum volume, and recreates vocals with remarkable clarity. The only thing where I hear it lacking is in the soundstage definition, which I believe to be the result of the mids in the satellites being slightly recessed. Overall, however, the sound from my promedia system is much more pleasing than the sound from my (admittedly poorly-built) pioneer receiver, which claims a .01% THD in stereo mode. However, I find that very hard to believe.
 
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one advantage, or "interesting" thing, with digital amp that I have seen noone talking about is the ability to program their clipping behavior.

one can easily map the signals such that above a pre-determined threshold level, the signal is "compressed". this will allow "soft clipping" like a tube amp and enhance headroom, to one's liking.
 
millwood said:



I am not sure I would buy Nelson's argument there. When you "push" air, say with a diaphragm, you are neccessarily "pulling" air on the other side of the diaphragm: air being sucked into "space" left by the diaphragm.



The air is not "sucked" into the vacuum. It is pushed there by air molecules on the the other side of the air molecules closest to the vacuum.

I do not know if this makes a difference in the mathematical argument you make, but vacuums can do no work. They just apear that way to us due to the effect of higger pressure air (further from the vacuum) acting on lower pressure air closer to the vacuum.
 
About Digital:
If you are not very strict you may call some amps digital (like the TacT and the TI). But if you take the meaning of the word digital really serious then there is no such thing like a digital amp, nor will there ever be one !
Let's simply call them what they are, switching amps or class-d amps.

About the future:
The technology is mature enough to be used for most of today's audio applications IMO. But I think the best linear amplifiers will always be a tiny step further regarding quality. So I doubt whether they will RULE high-end audio.

About distortion:
I don't believe that you NEED to have even order distortion at all, in order to achieve good sound. The best would be no distortion of any kind. The reproduction chain should be as transparent as possible. But if there IS distortion, it better be even order than odd order.
Since no part of the reproduction chain is perfect it is advisible to balance some parameters. Therefore it is not advisible to lower harmonic distortion beyond the capabilities of almost any measurement equipment at the cost of other parameters.

About the output filter:
I agree that this is a restriction if you compare it to amps like SonnyA's damnnbloodyfast and superstable amplifier.
But today's most used audio source has a much steeper otput filter with a much lower cutoff-frequency than most class-d amps have.


Regards

Charles
 
Nelson Pass said:


You don't like these ideas? I've got others.....

;)

I do like the these ideas

I like to think of creation as being SE

harmony and balance are present in life when yang, the active principal, and yin, the passive principal are in harmony and balance

How much more SE can you get than that ?

Don't get me wrong I'm not a buddist, the Hindus also have Shiva & Shakti but that's another story...or is it ?....

Nelson, could we hear some more ideas please ?

we're all ears...;)
 
Anybody whos been working with pneumatics would know this as a fact. When compressing air there is no upper limit (well there is, since it turnes liquid at some point, but it mostly dosnt apply to pneumatics...let alone an audio driver), but vaccuum ends at 0 and has a very steep curve from 1 to 0.

SE or not is though not the question here, since it should represent no big problem to make a digi amp run in SE mode.

MAgura
 
Regarding the single-ended nature of air compression:

Is a pressure change of +- 300 pa a large pressure change ? Sure it isn't !!
=> It is approximately +- 0.3 % of the static air pressure.

Does such a pressure-change produce a high SPL ?
Is it loud ? No it isn't !
Is it very loud ? It is neither !
=> It is in fact damnbloodyloud at 142 dB (re 20 pa) !!!!!!!

What does anyone expect the air's nonlinearity to be at normal listening levels ? I think not much, not even when the nearfield pressure-change in front of a driver (which is significantly higher than in the far-field) is considered. One pressuere change that IS indeed more significant is the one INSIDE the box.
But without knowing the driver's exact behaviour it wouldn't be possible to make a conclusion in what direction the amps linearity has to be "bent" in order to compensate for this.

Regards

Charles
 
Reference SPL (0 dB) corresponds to 0.00002 Pa of pressure (RMS). The atmospheric pressure is about 100,000 Pa. Therefore, 110 dB SPL corresponds to about 6.3 Pa, or a whopping 0.0063% of air pressure. At this point our P^1.4 curve deviates from a straight line by about 0.00000011%. I wish I had an amp with this kind of nonlinearity...
 
Im sure your calculations are all correct, but you are calculating the wrong thing. What is the issue is whether the behaviour of air changes when you go from pressure to vaccuum or not, and anybody whos used to work with air as a medium can tell you that it does.

The effect of pressure is obvious. The effect of vaccuum is backflow...a rather uncontrollable unit.

Magura
 
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talking about harmony and yin-yan, I would think push-pull is more accurate and appropriate: like yin-yan, push-pull is all about action and reaction. the law of the universe, :)

I don't think the whole "air is SE or life is SE" argument will get us anywhere. It certainly doesn't help produce a better sounding amp.
 
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Magura said:
The effect of pressure is obvious. The effect of vaccuum is backflow...a rather uncontrollable unit.

Magura


the effect of vaccum is exactly the same as the effect of pressure. except for vaccum, it is the effect of "low" pressure.

what "pressure" does is to create a "pressure" differential between two sides of air moledules so that a force exists to push the molecule one way or the other. If you hold constant air on one side of the molecule, and reduce the pressure on the other side of the air molecule, it will move, in the same fashion and by the same law of physics as if you had increased the pressure, by the same amount, on the otherside of the molecule.

pressure itself doesn't do a whole lot of anything. It is the pressure differential that moves things.
 
millwood said:
talking about harmony and yin-yan, I would think push-pull is more accurate and appropriate: like yin-yan, push-pull is all about action and reaction. the law of the universe, :)

I don't think the whole "air is SE or life is SE" argument will get us anywhere. It certainly doesn't help produce a better sounding amp.

I beg to differ.

Yang, among other qualities, is 'active'
Yin, among other qualities is 'passive'

In PP by definition each device is active one pulling one pushing

In SE the active semiconducor device acts and the load, be it R, CCS or L, just responds or reacts to whaevert the active element to doing.

I think you may find that many experienced and well respected audio engineers have concluded that SE does produce better sounding amps.

John Linsely Hood certainly came to this conclusion and I get the distinct impression that Nelson is of the same opinion.

cheers

mike
 
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mikelm said:
Yang, among other qualities, is 'active'
Yin, among other qualities is 'passive'


"hot vs. cold", "bright vs. dark", "male vs. female", "aggression vs. non-aggression", "act vs. react", etc. are just many facets of yin vs. yan.

mikelm said:
In PP by definition each device is active one pulling one pushing


that's yin vs. yan or yan vs. yin however you want to view it.

mikelm said:
In SE the active semiconducor device acts and the load, be it R, CCS or L, just responds or reacts to whaevert the active element to doing.


In PP the active semiconducor device acts and the load, be it R, CCS or L, just responds or reacts to whaevert the active element to doing.
 
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