Audio Wisdom: Debunking common myths

[jlsem]

Found this interesting post while researching the issue at hand:

http://www.diyaudio.com/forums/showthread.php?postid=676488#post676488

 

[Steve Eddy]

Found this interesting post while researching the issue at hand:

Don't know what you find particularly interesting about it. When I said "sounds best," I didn't mean it to be synonymous with improved objective performance.

se

 

[lndm]

Do you feel that distortion quantity should be subjectively or objectively measured? I mean, it's scientific to put a number to it but my ears are not a distortion analyser.

 

[Steve Eddy]

Here is a snippet from Jones Valve Amlifiers 3ed which supports the point i was trying to make.

Alternatively, by passing the valve's quiescent current through the transformer, we sidestep the problem of low initial permeability and the transfer characteristic is more linear, which perhaps explains the claims for excellent midrange detail in this (SE) breed of amplifiers

Mmmm. But if you look at these curves, which show permeability down to 10 Gauss (which is quite small and is typically the point at which initial permeability is measured) for varying levels of DC magnetization, permeability decreases. So I'm not seeing how DC sidesteps the problem of low initial permeability.

se

 

[Steve Eddy]

Do you feel that distortion quantity should be subjectively or objectively measured? I mean, it's scientific to put a number to it but my ears are not a distortion analyser.

Right. So when you're talking about distortion in an objective sense, you would measure it objectiely. When you're simply talking about what sounds good to you (or bad as the case may be), then you're in the subjective realm and unless you've some desire to try and determine whether it sounds good (or bad) to you due to some objective performance parameter, that should be left in the subjective realm.

se

 

[lndm]

Jean Hiraga
[snip] A unique faculty of the ear is to establish timbre personality and fundamental notes by successive analysis of harmonics starting with the highest order ones, as stated in various works of S.S. Stevens, Von Bekesy, and E Zwicker. This is why our brain has the ability to reconstitute a fundamental note from listening to its partials (this was tested by Carl E Seashore). If the amplifier induces partial or total suppression of some harmonics among those forming THD, this is taken in account by the ear which will detect a corresponding timbre.

This does not exclude the masking effects, more particularly, those for which harmonics relations and relative levels conduct to hear a unique pure tone, referring to extensive works conducted by H. Sakai ("Harmony and Distortion", N.H.K. Journal, 1980), or by a Japanese group titled the Fukuoka Distortion Society.

It is however, important to say this works only for THD values under about 3%, confirming the experiments conducted by H.F. Olson with 2A3 single-stage triodes.
AX, 10/04

 

[jlsem]

Don't know what you find particularly interesting about it.

This part I found interesting:

...that pure 3rd can be amoeliorated with just a wee bit of DC current in the primary or secondary.

 

[jlsem]

This text on magnetic amplifiers shows how the ac input wave becomes distorted as the DC control voltage moves the operating point up and down the magnetization curve. A simple explanation with illustrations begins on page 28. What it doesn't show is an operating point with no DC which would be at the intersection of the B and H axes.

http://www.pmillett.com/Books/mag_amp.pdf

John

 

[auplater]

hysteresis distortion

from what i see, the error in interpreting all these hysteresis graphs to support low level improvements when dc bias is in the primary (as in se amps) is the initial magnetic polarization curve (the one at the B-H origin) is being used to justify operation after the ouside hysteresis loop is established due to an ac mmf being passed.

apples don't equal oranges... as I see it, once the core is magnetized/demagnetized by any ac signal. it will exhibit hysteresis and follow some version of that loop and will not respond in a positive way to lower operating distortion by applying a dc bias; the latest graph shows in fact that dc bias moves the core closer to nonlinear saturation on the half cycle that corresponds to the polarity applied.

But what do I know...I guess this is all out of my "domain" of knowledge

John L.

 

[Steve Eddy]

Re: hysteresis distortion

from what i see, the error in interpreting all these hysteresis graphs to support low level improvements when dc bias is in the primary (as in se amps) is the initial magnetic polarization curve (the one at the B-H origin) is being used to justify operation after the ouside hysteresis loop is established due to an ac mmf being passed.

apples don't equal oranges... as I see it, once the core is magnetized/demagnetized by any ac signal. it will exhibit hysteresis and follow some version of that loop and will not respond in a positive way to lower operating distortion by applying a dc bias; the latest graph shows in fact that dc bias moves the core closer to nonlinear saturation on the half cycle that corresponds to the polarity applied.

That's rather the way I'm seeing it as well. So for now, I'll just wait until someone can actually show an actual transformer behaving more linearly at low levels with a DC bias on it than without.

se

 

[Steve Eddy]

This part I found interesting:

...that pure 3rd can be amoeliorated with just a wee bit of DC current in the primary or secondary.

What exactly do you find interesting about it?

se

 

[jlsem]

http://www.diyaudio.com/forums/showthread.php?postid=1137000#post1137000

You asked for a reference so I thought your word was as good as any.

John

 

[jlsem]

apples don't equal oranges... as I see it, once the core is magnetized/demagnetized by any ac signal. it will exhibit hysteresis and follow some version of that loop and will not respond in a positive way to lower operating distortion by applying a dc bias; the latest graph shows in fact that dc bias moves the core closer to nonlinear saturation on the half cycle that corresponds to the polarity applied.

Please read my lips: The magnetic field never collapses in an SET OPT. There is no "outside B-H loop". The only reason there are charts that show a DC hysteresis loop is because the guy testing the sample switched the DC off. A saturable reactor with a DC control voltage is as close a textbook example as you will find to an SET OPT.

Can't you see that at the origin of the B-H axes the magnetization curve is nonlinear and the application of DC bias shifts the input to the middle (linear) section of the curve?

John

 

[auplater]

Please read my lips: The magnetic field never collapses in an SET OPT. There is no "outside B-H loop". The only reason there are charts that show a DC hysteresis loop is because the guy testing the sample switched the DC off. A saturable reactor with a DC control voltage is as close a textbook example as you will find to an SET OPT.

Can't you see that at the origin of the B-H axes the magnetization curve is nonlinear and the application of DC bias shifts the input to the middle (linear) section of the curve?

John

So what mechanism, exactly, are you proposing accounts for the modulation of the non-collapsing dc field from the applied electrical ac signal?? Perhaps the domains are wiggling around/expanding/condensing, moving away from the easy direction as they must in order to diminish the mmf as the desired ac signal forces the non-collapsing field in the negative direction (and back again)???

Maybe, in doing so, they exhibit the same reluctance (and hence hysteresis) wiggling/expanding/condensing in response to the ac modulation of the DC field you so strongly believe extinguishes this effect?

I don't need to "read your lips"... I'll just keep on listening to non-distorted ss music, and focus on speaker improvements, which are orders of magnitude more rewarding than this discussion

John L.

 

[pinkmouse]

Jlsem, I have removed your offensive post. Any more like that and you'll be spending time in the bin.

 

[jlsem]

That's O.K. It looks as though everyone has taken their marbles and gone home anyway.