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Old 22nd February 2013, 12:07 AM   #111
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Hmmm. Just as I got the QA400 running and getting some data -- I am about 5dB different in one vs another test for harmonics... Then the QA400 FFt went nuts on me. stopped working and only works sporatically now. Waiting to see what can be done about it -- fix/replace or what?

But before it bit the dust, it appeared that the ShibaSoku 725D analyser had a fundemental notched null that was at -150dB (!!).

Thx-RNMarsh
What OS are you using?

I solved a problem by with the QA400 changing USB ports and reinstalling the drivers. I couldn't get 192ksps until I did this.
There is a timing issue with XP. What exactly is QA400 doing?
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Last edited by davada; 22nd February 2013 at 12:10 AM.
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Old 22nd February 2013, 12:26 AM   #112
RNMarsh is offline RNMarsh  United States
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Well it fails the self test. BUT it was working perfectly for a couple weeks... so there were no issues until it just decided to stop cooperating. -Richard

BTW - did the reloads et al. [WIN 7]
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Old 22nd February 2013, 12:35 AM   #113
davada is offline davada  Canada
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Well it fails the self test. BUT it was working perfectly for a couple weeks... so there were no issues until it just decided to stop cooperating. -Richard

BTW - did the reloads et al. [WIN 7]
Sound like a warranty issue. Contact Matt.
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Old 24th February 2013, 03:22 PM   #114
RNMarsh is offline RNMarsh  United States
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BTW -- whats the basic difference between a twin-t and Cordell's Distortion Magnifier?

-RNM
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Old 24th February 2013, 03:59 PM   #115
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
BTW -- whats the basic difference between a twin-t and Cordell's Distortion Magnifier?

-RNM
Bob's DM is a null process. The source signal and it's distortions are subtracted from the output of the DUT leaving just the distortion products of the DUT. In the case of the DM it just removes enough of the fundamental to change the percent of distortion from the output of the DUT. The DM output is amplified to a level which an analyzer like the 339A can process. It's done this in a controlled amount. A bit of math has to be done with the reading on the analyzer to get your final result. It's the same math you would do taking a measurement from the monitor output of the 339A. Just scaling.

The difference is the DM changes the relative fundamental to distortion, It increases the THD with out adding too much to it by a controlled amount.

The TT filters the fundamental out without changing the relative FS.

The DM will not work for evaluating oscillators because it would remove the information we are trying to measure.
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Old 12th March 2013, 05:01 AM   #116
RNMarsh is offline RNMarsh  United States
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I still have not returned to the usb issue... too many side-tracks. But I will get it running again.... somehow. probably with seller/company help. Because I dont want to spedn a long time on it fumbling around on my own.

-Thx RNMarsh
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Old 29th July 2013, 04:35 PM   #117
RNMarsh is offline RNMarsh  United States
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A new forum here at DIYAUDIO has just started which shows the B&K 1607 passive Notch Filter modified to active notch filter (switchable... active-passive notch).

-RNM
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Old 29th July 2013, 06:02 PM   #118
RNMarsh is offline RNMarsh  United States
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A nice addition to the tool-box is a fast ADC... such as -->
CleverScope.com
Model CS328A-XS

Thx-RM
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Old 29th July 2013, 06:34 PM   #119
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
A new forum here at DIYAUDIO has just started which shows the B&K 1607 passive Notch Filter modified to active notch filter (switchable... active-passive notch).

-RNM
Can you link to this as well?
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Old 1st August 2013, 06:19 AM   #120
RNMarsh is offline RNMarsh  United States
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One issue I want to look into further is the accuracy of harmonic levels measured by the various methods and test equipment. I have already noticed harmonics of 2H and 3H of the ADC at low distortion levels (below -100dB) are not accurately displayed. Today, I added to my arsenal, an Audio-Precision 2722. This will help as a cross check with the fabulous ShibaSoku AD725D... it is speced to maintain a specified accuracy/tolerance to -130dB. However, if the tolerance was loosened just a little, it is pretty much a straight line to the noise floor at -150dB.

These two instruments represent the SOTA and as such I can test the various ways being discussed here for oscillator distortion and ADC based FFT test data and check and report on their accuracy limits, tolerances and conditions especially at levels below -100dBr.

Thx-RNMarsh

Last edited by RNMarsh; 1st August 2013 at 06:22 AM.
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