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Old 14th June 2003, 01:41 AM   #51
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by ALW


There's not a single article in the public domain that deals with this issue correctly, that I've seen. Almost all received wisdom is wrong, and derived from other flawed work.
That's a valid opinion.

Quote:
Originally posted by ALW


The differences between A and AB are primarily down to poor design in the AB variants.

Hardly. I really hate to give away some of the real secrets, but simply plot the current variation through output devices in Class A (and we ARE talking ture, scalding hot running Class A) and in Class AB. Then plot the compound output stages Beta/GM/Yfs vs. current in the device.

It is elementary Watson. It even holds absolutely true for the oh so linear "triodes".

Sayonara
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Old 14th June 2003, 02:00 AM   #52
ALW is offline ALW  United Kingdom
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Quote:
Hardly. I really hate to give away some of the real secrets, but simply plot the current variation through output devices in Class A (and we ARE talking ture, scalding hot running Class A) and in Class AB. Then plot the compound output stages Beta/GM/Yfs vs. current in the device.
The design of a class AB amp requires attention to details that are not necessary in class A designs - failing to deal with these issues results in crossover distortion.

In the same way that feedback is blamed for other effects like TIM etc. all of which are failures to get the design, as a whole, right.

Andy.
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Old 14th June 2003, 02:14 AM   #53
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Koinichiwa,

Quote:
Originally posted by ALW


The design of a class AB amp requires attention to details that are not necessary in class A designs - failing to deal with these issues results in crossover distortion.

Okay, I go with that. Except, you need transistors (or Valves or FET's) in the output stage that are almost not manufacturerd and the stuff Semlab made in the earlier days for Naim was as bad as anything (to keep a topical glimpse).

So, with reasonably available devices class AB invariably leads to problems. Of course, a sufficient devotion to the worship of a given manufacturer can make such minor inconveniences go away easily, to the mind of the believer.

I will agree that in pure, unapplied theory Class A and Class AB can be made to perform identically. But once we deal with real components - sorry no such luck buddy.

Quote:
Originally posted by ALW


In the same way that feedback is blamed for other effects like TIM etc. all of which are failures to get the design, as a whole, right.

Hmm. A REAL limited bandwidth Amplifier with looped feedback around the multiple stages will ney MUST be subject to those effects. I would not directly blame "feedback", but in the end, the fundamental toplology gives rise to certain problems. Adding an input bandwidth limiting filter can help of course, so in practical terms for bothy TIM and AB Crossover distortion workqrounds exist that limit the damage done by the problem, yet it still strikes me as bolting the stable doors after the horses are gone.

If we do talk about in effect "cost no objecive" designs, then why accept such compromises and mererly work on the fringes to contain the damage?

Sayonara
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Old 14th June 2003, 08:29 AM   #54
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Default ...Takes deep breath & steps into the fray

I have to give a definite NAY to the original question, I don't believe we're close but I think we're trying to turn an omlette back into raw eggs.

The best system I've ever heard still sounded exactly like a system, not like the real thing. I used to live in a unit on a busy street and when a trumpet player 4 doors down was doing his practice, even over the road noise I knew instinctively that what I was hearing was a real instrument and not a reproduced recording. If we can't do solo trumpet yet, what hope have we got with something as complex as a string quartet, let alone an orchestra or a piano?

To be sure, from time to time we get things "more right" if you will. I love the sound of some of the mid/late 60's Verve recordings done by Norman Granz. To me (remember that bit, it's important), the sound seams more real.
Don't know if this is from tube gear, ribbon mikes, less compression, shorter simpler signal paths or what, I just know that I prefer it.

Sound is a very subjective thing: I know for a fact that my wife and I both find the sound of a couple of speakers I built using Audax HM100ZO HDA midrange drivers to be the sweetest and fastest and most detailed without being fatiguing midrange that we've yet listened to. I also know for a fact that Thorsten has characterised HDA drivers as "sounding like hammered ****". On many other aspects of sound reproduction and componentry however, we appear to agree entirely. Please explain?

Additionally, critical listening (for me at least) was a learned thing. While a 16 year old, I had the oppourtunity when on student exchange in Germany to visit a number of hifi stores in Erlangen when the son in my host family was purchasing a mid - high level turntable as a Christmas present for his father. During the auditions of a number of decks I was totally unable to discern tonal differences, lowered noise floor, more background info, let alone more amorphous things such as PRaT. (This was not as a result of having hammered my hearing, my exposure to rock music was very limited growing up) Nowdays i can easily hear all these things, pick differences in cables etc and so on.

The number of different approaches taken by people in the audio industry is massive. Some favour short paths (Passlabs Zen, AudioNote DAC 5 without digital filter, S&B L/C phono equaliser), some favour only Class A, or only SE, or only triodes, or only DH triodes. Some go multiway in speakers, some hornload, some only go with single drivers, some say only circular fronthorns work. dipoles, boxes, spheres, ribbons, electrostatics, paper cones, HDA cones, carbon fibre cones, aluminium cones. And this is just at the replay end.

If our current level of understanding can't tell us what sort of resistors and caps sound best, what type of active devices sound best, what topology is best, what cables, type of speaker drivers and form of enclosures are best just on the replay end (leaving aside the vinyl, cd, DVD, SACD debate or, deity forbid!, MP3) then how can we even contemplate saying that we have even a partial grasp on the answers?

My current omlette is nice and I'm working on having it a little less overcooked but i doubt I'll ever be able to change it back into raw eggs.

Drew
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Old 14th June 2003, 02:40 PM   #55
SY is offline SY  United States
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FWIW, I'm with you on the HDA drivers. But I'm not coming at the problem from a religious standpoint.
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