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Old 20th April 2012, 12:30 AM   #4511
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Quote:
Originally Posted by a.wayne View Post
I had a similar conversation with Mr Audio Note some 15 + yrs ago and he was of the same mindset , that first watt got all of his focus ...

You have to take inflation into account.
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Old 20th April 2012, 12:30 AM   #4512
bcarso is offline bcarso  United States
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Quote:
Originally Posted by a.wayne View Post
NO , it's B&K audio .... They made amplifiers , et al .......
OH. As Emily Latella would say, That's very different then.
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Old 20th April 2012, 12:36 AM   #4513
a.wayne is offline a.wayne  United States
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Originally Posted by bcarso View Post
Yep ---what do you find discrepant? The claim is 8.9% distortion (excluding noise as I read him) at a milliwatt, unspecified (but presumably larger) at 1 uW, again excluding noise.
My error you stated 82db below .....
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Old 20th April 2012, 12:41 AM   #4514
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Quote:
Originally Posted by a.wayne View Post
"My name is Steve Keiser, the 'K' of B&K components, and presently design engineer with Luminance Audio. I have developed a measurement system which is able to quantify distortion levels at micropower quantities down to 1/1000th of a watt.
1mW is -50dB wrt full output of a typical 100W amplifier. Not particularly low level - D/A converter chips are normally characterized at -60dB wrt FS.

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These measurement techniques are unprecedented, and have revealed a number of revelations of amplifier distortion characteristics, at micropower levels, which are in direct opposition with traditional and scientific assumptions up unto this point.
Unless he's not telling us something vital, its hardly 'unprecdented' to measure THD at -60dB for DACs, so what makes it so for amps?

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The emphasis of my work is to definitively quantify low level signal linearity measurements of power amplifiers, and attempt to correlate these measurements with subjective listening results, as well as establishing the significance of low level distortion. Conventional test equipment generally does not resolve meaningful distortion measurements below 100mw, since the measurements become predominated by noise.
Conventional test equipment in the world of audio means AP, that has had this capability ever since the dual domain AP1 which is a couple of decades old now. The DAC manufacturers routinely use AP to show the distortion performance of their chips (with -60dBFS stimulus signal) down to -140dB or so.

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To give you an example: the Halcro DM58 amplifier measures .007%THD at 2 watts, whereas at 1/1000th watts, THD measures 8.9%!
That does sound like an astonishingly poor result. The Halcro is nominally 200W so 1mW is -53dB and the THD is around -74dB? Stereophile shows the performance at 157W output, its noise-dominated at 0.0006%. Its jolly hard to believe therefore that the stated 0.007% @ 2W is correct as it would imply that the distortion harmonics rise as the stimulus goes down in level. Even relatively poor digital systems manage to keep them roughly the same under those conditions.

What am I missing?
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Old 20th April 2012, 01:19 AM   #4515
tvrgeek is offline tvrgeek  United States
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Quote:
Originally Posted by a.wayne View Post
B& K is out of Business , he is with Luminance Audio, send him an email there I guess ...

Luminance Audio KST-150 - YouTube

i sent Steve an email, he may respond ....

Strange goings on. I get their main page now, but last time I got an advertising redirect when I clicked on the link on the audiogone profile.

The link for details to Virtual dynamics is dead. Last update on Luminance was 2 years ago.
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Old 20th April 2012, 01:21 AM   #4516
bcarso is offline bcarso  United States
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Originally Posted by abraxalito View Post
What am I missing?
I doubt much of anything
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Old 20th April 2012, 01:29 AM   #4517
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Quote:
Originally Posted by abraxalito View Post
That does sound like an astonishingly poor result. The Halcro is nominally 200W so 1mW is -53dB and the THD is around -74dB?
What am I missing?
He measured the associated VOLTAGE dB with those power levels, not the actual POWER dB. Do you know of any THD measurement device that deals with POWER directly?
That makes for the 1mW/200W ratio -106dB, not -53dB...
Quote:
Originally Posted by abraxalito View Post
Its jolly hard to believe therefore that the stated 0.007% @ 2W is correct as it would imply that the distortion harmonics rise as the stimulus goes down in level. Even relatively poor digital systems manage to keep them roughly the same under those conditions.
Those "digital systems" don't have a class AB output stage that generates cross-over distortions at low levels:
Click the image to open in full size.Click the image to open in full size.
Click the image to open in full size.Click the image to open in full size.

Last edited by SoNic_real_one; 20th April 2012 at 01:43 AM.
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Old 20th April 2012, 01:43 AM   #4518
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Quote:
Originally Posted by SoNic_real_one View Post
He measured the associated VOLTAGE dB with those power levels, not the actual POWER dB. Do you know of any THD measurement device that deals with POWER directly?
Amp tests are done into a resistive load. Thus knowing the voltage we can infer the power.

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That makes for the 1mW/200W ratio -106dB, not -53dB...
Only if you were asleep during EE class. Power ratios are always 10log, voltage ratios 20log.
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Old 20th April 2012, 01:45 AM   #4519
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Like I already said (even you prefer to ignore it) probably he didn't measured power, he measured voltage. What tool would you use to measure directly the THD for POWER?
So when he said 1mW he measured the associated voltage on a specific load. 11.19mV on 8 ohm. Didn't measure the current too.
Sure, not correct in verbiage... but offers an explanation of his results.

Last edited by SoNic_real_one; 20th April 2012 at 01:49 AM.
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Old 20th April 2012, 01:46 AM   #4520
bcarso is offline bcarso  United States
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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.
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