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Old 27th May 2014, 04:40 AM   #1121
RNMarsh is offline RNMarsh  United States
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It is important also. However, in solid state deisgns with very wide bandwidth the phase changes at audio freqs are small and relegated to secondary status. More important would be group delay measurements which i have been interested in for decades. But again, with near DC response with digital and SS that isnt an issue.... but with speakers, filters, cross-overs and many tube circuits it is still useful to measure and find ways to reduce or compensate.

We are primarily focused here on the test equipment itself rather than a lot of its' applications.

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Old 27th May 2014, 05:09 AM   #1122
davada is offline davada  Canada
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It is important but I haven't found any FFT software that displays phase. Equipment for measuring phase is very expensive.
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Old 27th May 2014, 05:57 AM   #1123
JensH is offline JensH  Denmark
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I think that the audioTester program can do it, but I haven't actually tried it.
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Old 27th May 2014, 07:48 AM   #1124
1audio is offline 1audio  United States
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You can't really derive phase without a differential measurement. Several of the speaker programs can do it. The best is Praxis for that since Praxis is modeled on a Vector Network Analyzer.



Real network analyzers are expensive.



I'm told that the next gen QA audio box may be able to display phase, but you need to remove the delay for that to mean anything. It all gets pretty involved.





Sent from my XPS 12-9Q33 using Tapatalk
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Old 27th May 2014, 02:44 PM   #1125
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
You can't really derive phase without a differential measurement. Several of the speaker programs can do it. The best is Praxis for that since Praxis is modeled on a Vector Network Analyzer.



Real network analyzers are expensive.



I'm told that the next gen QA audio box may be able to display phase, but you need to remove the delay for that to mean anything. It all gets pretty involved.





Sent from my XPS 12-9Q33 using Tapatalk
Have you looked at AD's network analyzer IC? I don't have time to get the part number now, I'll get it later. The cost is very reasonable. Uses sampling and outputs the real and imaginary parts.
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Old 28th May 2014, 03:53 AM   #1126
RNMarsh is offline RNMarsh  United States
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can't the 2 channels of the qa400 be used to measure I/O phase?

-RM
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Old 28th May 2014, 05:29 PM   #1127
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Quote:
Originally Posted by RNMarsh View Post
can't the 2 channels of the qa400 be used to measure I/O phase?

-RM
There we go.

If I would be the QA400 developer manager, I would have implemented that function. IMO the easiest way is to measure the delay between the generated sine (sweeped in frequency) and the sine wave which is coming back from the DUT. May be by measuring the time difference between the zero crossing time point would be enough.
Click the image to open in full size.Click the image to open in full size.
This investigation is official placed in my TODO pipeline. I have an Aglient MSOX3054A and it has a function generator integrated, with just a simple script I should be able to get a phase measure vs. freq. graph.
I could be I am dreaming an impossible mission, but I will give a shot. Maybe the time delay is very small to be detected with Mhz clock?
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Old 29th May 2014, 10:28 AM   #1128
RNMarsh is offline RNMarsh  United States
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There we go.

May be by measuring the time difference between the zero crossing time point would be enough. ... an Aglient MSOX3054A and it has a function generator integrated, with just a simple script I should be able to get a phase measure vs. freq. graph.

I could be I am dreaming an impossible mission, but I will give a shot. Maybe the time delay is very small to be detected with Mhz clock?


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Old 27th June 2014, 11:46 PM   #1129
1audio is offline 1audio  United States
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Default QA400 interface

Attached are the expressPCB files for my new version. I have not fully checked these files so if someone else is up to the task it would be great. Expresspcb is not really easy for this denser surface mount stuff. Everything is connected and I don't think there are any shorts. If anyone else is up for loading the files into expressPCB and checking for mistakes I would really appreciate it. I will get a set of PCB's ordered in a week and see how successful I was.

This is way more complex and involved than the first gen. Don't feel bad if you find the schematic or the layout hard to follow. I also find this one challenging. I'm trying to use the latest ideas on ground planes, bypassing etc, even though they probably are not significant at the audio frequencies involved.
Attached Images
File Type: png QA400 interface rev 2-1.PNG (42.7 KB, 130 views)
File Type: png QA400 interface rev 2-2.PNG (39.0 KB, 126 views)
File Type: png QA400 interface rev 2-3.PNG (26.1 KB, 116 views)
File Type: png QA400 interface rev 2-Top.PNG (97.3 KB, 126 views)
File Type: png QA400 interface rev 2-Bottom.PNG (88.7 KB, 104 views)
Attached Files
File Type: zip QA400 interface gen 3.zip (96.2 KB, 24 views)
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Old 28th June 2014, 12:26 AM   #1130
CZ101 is offline CZ101  United States
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Quote:
Originally Posted by 1audio View Post
This is way more complex and involved than the first gen. Don't feel bad if you find the schematic or the layout hard to follow. I also find this one challenging. I'm trying to use the latest ideas on ground planes, bypassing etc, even though they probably are not significant at the audio frequencies involved.
Just curious why you chose to use the charge pumps for the split rails? Are ripple and noise not a concern here?
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