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Old 20th April 2012, 02:46 AM   #4521
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The tool I'd use is ohm's law. By which I mean given an ohmic load, no need to measure power directly as that's a major work up.
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Last edited by abraxalito; 20th April 2012 at 02:49 AM.
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Old 20th April 2012, 02:51 AM   #4522
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Originally Posted by bcarso View Post
I doubt that it is class AB transitional distortion. Even Self (who defines his class B in a somewhat funny way) allows for some quiescent current at 0 volts out. And you don't need much. The objection (as you all know) to "rich" class AB is that the transconductance of the (typically) emitter followers transition to what is typically a lower value as the one device turns off completely at a certain signal voltage. No, I'm pretty sure John Halcro Candy had this under control, whether you like how his amps sound or not.
Well, all the above graphs are from reputable manufacturers that know to adjust their AB quiescent current. And still THD grows exponential below 1W.
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Originally Posted by abraxalito View Post
The tool I'd use is ohm's law. By which I mean given an ohmic load, no need to measure power directly as that's a major work up.
And using ohm's law you measure power? Strange... I always thought that ohm's law does something else:
Click the image to open in full size.

Last edited by SoNic_real_one; 20th April 2012 at 02:55 AM.
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Old 20th April 2012, 02:54 AM   #4523
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My usual test is to whisper in front of microphone and slowly back up whispering. Crossover distortions that are not measurable are audible anyway like loss of naturallness of sounds.

5532 chips in console strip failed such a way against 4558'th biased by 6K8 resistors to + rail.

Human ears and brains are better measurement tools than any selective electronics. Especially when signals intermodulae with noises.
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Old 20th April 2012, 02:56 AM   #4524
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Originally Posted by SoNic_real_one View Post
And still THD grows exponential below 1W.
Sure the THD rises at lower levels, but the important question is - do the harmonics go up in absolute magnitude? I'm saying that I've never seen them go up in magnitude as the signal level falls. But if you have I'm certainly curious to see your data.
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Old 20th April 2012, 02:59 AM   #4525
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Originally Posted by SoNic_real_one View Post
And using ohm's law you measure power?
No, where have I said I measure power with ohm's law?
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Old 20th April 2012, 03:00 AM   #4526
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Originally Posted by SoNic_real_one View Post
Well, all the above graphs are from reputable manufacturers that know to adjust their AB quiescent current. And still THD grows exponential below 1W.
Looks a lot worse than exponential. And also very dubious. Need more resolution. And I doubt that it's going to show much other than the effects of a noise floor.
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Old 20th April 2012, 03:02 AM   #4527
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I have posted the pics on the other page (Arcam HK, Pioneer). If that is not "go up" when you go towards low power, then I don't know what they are.
I am building amplifiers since 1982. Tried all of the variants and I know that a beefy quiescent current just reduces the cross-over distortion, doesn't eliminate it. Only class A takes care of that but... comes with other issues.
BTW, this is how a $53k monobloc class AB looks like:

Click the image to open in full size.

Last edited by SoNic_real_one; 20th April 2012 at 03:12 AM.
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Old 20th April 2012, 03:14 AM   #4528
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The MBL 9011 is ruler flat slope as the Halcro, so ?
Zero distortion, just Noise !

And exactly the point Mr Candy made in his tech paper.
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Old 20th April 2012, 03:30 AM   #4529
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If that monster only gets -88dB THD at 200mW, then there is no surprise that the more economical receivers/amps get worse results than that.
The fact that the words in that paper are not technically accurate doesn't change the reality.
HK990, one of my personal favorites in sound quality, looks like this on 8 ohms:

Click the image to open in full size.

Last edited by SoNic_real_one; 20th April 2012 at 03:34 AM.
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Old 20th April 2012, 03:38 AM   #4530
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Without further information (e.g., spectra), you can't determine what that graph really means nor compare graphs. Noise? A fixed kink at zero crossing?
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