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Old 8th May 2013, 08:11 AM   #2611
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by davada View Post
How's this for almost 20kHz.

The lamp multiplier didn't work out. Too microphonic when the lamps are hot.

I moved on to another multiplier idea of mine which is rather unusual.
Very good !
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Old 8th May 2013, 08:12 AM   #2612
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Samuel Groner View Post
Notch depth is not of cruical importance for a THD measurement (it is for THD+N, though).

Samuel
I agree.
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Old 8th May 2013, 08:31 AM   #2613
RNMarsh is offline RNMarsh  United States
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Default Audio precision 2722 specs

Here are the "typical" performance THD+N numbers et al for the Audio Precision 2722.
This is to compare against our oscillator results.

Thx-RNMarsh

AP2722.jpg

Last edited by RNMarsh; 8th May 2013 at 08:35 AM.
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Old 9th May 2013, 03:12 AM   #2614
RNMarsh is offline RNMarsh  United States
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Default Analyzer compared

Here is the THD+N from the same signal generator and looking at two different THD analyzers' residual output/monitor ports.

First is from Panasonic VP-7722A, second is from ShibaSoku AD725D analyzer;


7722.JPG

725.JPG



Thx-RNMarsh

Last edited by RNMarsh; 9th May 2013 at 03:26 AM.
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Old 9th May 2013, 04:08 AM   #2615
RNMarsh is offline RNMarsh  United States
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The modified 339A also seems to attenuate the upper harmonics. And/Or it doesnt resolve as well as 725 does. Similar to 7722.

339.JPG


Thx-RNMarsh

Last edited by RNMarsh; 9th May 2013 at 04:11 AM.
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Old 9th May 2013, 04:14 AM   #2616
1audio is offline 1audio  United States
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What would help a lot would be to add a marker at a known level, say -120 dBC. You will need some matching/mixing network that matches impedances and levels. The attenuator on the KH or the AG16 should be good enough once the basics are established. Victor suggested this idea. I tried it and it works well. It won't show on the analysis output of the 725D. I even tried to match the frequency of a harmonic. You could easily see the beats.
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Old 9th May 2013, 06:31 AM   #2617
RNMarsh is offline RNMarsh  United States
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Demian.... it isnt relavent to these pictures. You only need to see the 3H is lower in some analyzers -compared to the 2H. It could be 10% THD... or .001% THD it doesnt matter.

[I also did as you suggested already and pointed out some interactions with that signal a few lines back.]

Here, I dont care what the absolute levels are. I am showing differences in the recovered Harmonic levels for the same input voltage/source/freq.

If the 2H and 3H do not have the same relationship in level to each other then what are some of the possible explanations for it ?

With the 725, the 2H and 3H are at similar levels to each other. With the other analyzers, the 2H is much higher than the 3H.



Thx-RNMarsh

Last edited by RNMarsh; 9th May 2013 at 06:39 AM.
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Old 9th May 2013, 06:55 AM   #2618
RNMarsh is offline RNMarsh  United States
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I just read my voice mail--- from ShibaSoku Rep.... he called factory -- they cant/won't sell me a service manual.

-RNM
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Old 9th May 2013, 07:03 AM   #2619
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Quote:
Originally Posted by RNMarsh View Post
If the 2H and 3H do not have the same relationship in level to each other then what are some of the possible explanations for it?

With the 725, the 2H and 3H are at similar levels to each other. With the other analyzers, the 2H is much higher than the 3H.
Well, I'm quite desperate as I've tried to explain this issue probably half a dozen times now... Apparently I can not phrase this good enough. Surely this text (page 44ff) does better:

http://cds.linear.com/docs/en/applic...note/an43f.pdf

In particular make sure you follow the section on "Distortion Measurement Accuracy".

Samuel
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Old 9th May 2013, 07:38 AM   #2620
davada is offline davada  Canada
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Basically when it come to distortion measurements we're screwed.

Good article.
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