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Old 25th May 2012, 10:10 AM   #11
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Originally Posted by PMA View Post
I am very skeptical. I have solid state and tube line level preamps with almost same distortion profile, but they sound VERY different. THD is IMO very poor measure for subjective evaluation of sound quality.

Anyway, try to avoid ANY design with distortion rising with frequency. In this case THD is an INDICATOR that something else is just going wrong.
And in the case where you have a design where the THD does not rise with frequency the the much larger overall THD will indicate that there is still something wrong and maybe matters have been made worse.
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Old 25th May 2012, 10:13 AM   #12
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Non linearity at 10 kHz and 20 kHz matters because it will cause intermodulation products with music signals that have multiple frequencies.
Fully agree, even higher frequencies than 20 khz can have an inpact.
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Old 25th May 2012, 10:16 AM   #13
SY is offline SY  United States
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I think that the question is somewhat meaningless. HF distortion is a symptom, not the disease, so you can't categorize the "sound" of it, independent of knowing the cause. THD in particular is a very incomplete number- it lumps together very different pattens of nonlinearity with different causes, different effects, and different cures.
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Old 25th May 2012, 10:28 AM   #14
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The OP mentions amp simulations. As one who is trying to learn about computer simulations and programs, when modeling an amplifier, and obtaining information such as distortions present, what load is being used? Is it a resistive or complex load, i.e., do you use the complex crossover components and loudspeaker parameters, say, of an LS3/5A (or other known quantity) in the simulations?
Thanks, trying to learn.

Terry
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Old 25th May 2012, 10:40 AM   #15
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Default Harmonic distortion above audible freq

I've always wondered how harmonics of say,a 10khz fundamental, manifests itself in audibility. 2nd harmonic is arguably on edge (or out of) hearing range, and higher harmonics are even further. Without further technical understanding on my part, I would think that modulation interactions and effects in the highest frequencies could be a problem. At most it would sound a bit edgy, unless really high distortion. At any rate, I'm not positive I could hear anything above 16-17khz anyways...
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Old 25th May 2012, 11:07 AM   #16
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The same nonlinearity that distorts a single sine wave at HF, producing thd, would produce intermods when more than one HF tone is present ... in particular a second order nonlinearity would produce the difference frequency, which is much lower and audible; third order harmonic disto implies third order intermods which are HF but similar in frequency to the two tones, etc, even if all the harmonics are inaudible.
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Old 25th May 2012, 01:03 PM   #17
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Originally Posted by mirlo View Post
T. in particular a second order nonlinearity would produce the difference frequency, which is much lower and audible; third order harmonic disto implies third order intermods which are HF but similar in frequency to the two tones, etc, even if all the harmonics are inaudible.
In case there is no slew rate issue, CCIF 19+20kHz is pretty same like THD 1kHz (and NOT like THD 20kHz). I have plenty of measurements that prove this.
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Old 25th May 2012, 01:20 PM   #18
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Originally Posted by PMA View Post
Why not consider different possibilities of reduction of distortion, like distortion cancellation. I have not stated that high loop NFB would be my preferred solution
When i read "distorsion cancelation" , i translate with "NFB in disguise"....
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Old 25th May 2012, 01:35 PM   #19
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Originally Posted by wahab View Post
When i read "distorsion cancelation" , i translate with "NFB in disguise"....
Funny you should say that. I was thinking the same recently. I guess we'll have to accept that any truly high-performance amplifier uses nested feedback of one flavor or another.

Anyway, 10 kHz distortion is just a handy way of getting a handle on high-frequency intermod in simulation. As most designs show distortion increasing with frequency, the point is that if it's OK there, it should be anywhere. Always look at the spectrum rather than just the THD number though.

Incidentally, just about any case where someone thought to have proven the audibility of ultrasonic tones eventually turned out to be caused by plain ol' amplifier HFIM...
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Old 25th May 2012, 02:01 PM   #20
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Originally Posted by wahab View Post
When i read "distorsion cancelation" , i translate with "NFB in disguise"....
Then you have too few tools in your toolbox.

When I read “distortion cancellation” I translate it to “making the amp as linear as possiblebefore NFB is applied.

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Stein
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