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Old 15th March 2013, 07:05 AM   #21
richiem is offline richiem  United States
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I would call this autocorrelation....
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Old 20th March 2013, 05:42 AM   #22
1audio is online now 1audio  United States
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Default QA400 interface update

I got the prototype board running. Attached are some measurements made through it.

The layout as is works with the THAT parts. The TI differential receiver needs a few small changes to work. The holes for the minijack connectors are the wrong size, I'll post an updated version to support both input amps cleanly.

The output gain is too high. I can only get about 8V out single ended before clipping. The output driver has a gain of 2 so I need to figure out the optimum gain for the boost stage. 10X is too much.

The performance seems to be good enough to not be a limitation. I'll try to measure its real performance limits in the next few days.

The USB passthrough works on the USB3 ports on my laptop. The USB2 ports may not have enough available power and you would need two ports to power the interface and run the QA400.
Attached Images
File Type: png QA400 + QA interface + KH4400a 7V div 10.png (34.6 KB, 671 views)
File Type: png QA400 + QA interface loopback at 8.3V.png (36.3 KB, 664 views)
File Type: jpg QA400 Interface test 1.jpg (637.5 KB, 546 views)
File Type: jpg QA400 Interface test 2.jpg (513.4 KB, 527 views)
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Old 20th March 2013, 06:04 AM   #23
RNMarsh is offline RNMarsh  United States
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Very nice, Demian :-)

Can you sqeeze the THD+N below .001% ? So very close already.

Which usb drivers are you using?


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Old 20th March 2013, 06:13 AM   #24
1audio is online now 1audio  United States
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The noise is related to the measurement bandwidth and the internal noise of the ADC. And the noise from the surroundings. The loopback test has 20 dB of gain in the input booster plus the 6 dB I didn't expect from the differential driver as well as the differential receiver from THAT. The composite performance is quite good.
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Old 20th March 2013, 08:04 PM   #25
RNMarsh is offline RNMarsh  United States
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which usb drivers are you using?

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Old 20th March 2013, 08:26 PM   #26
1audio is online now 1audio  United States
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The ones in the latest release. DL and install it. There is a step where it runs a driver installer. It takes a few minutes for the installer to complete. Its running OK on both the USB2 and USB3 ports.

Attached is a plot from the Shibasoku generator. All the harmonics are from the interface + the QA400. I'll measure the interface tonight if time permits.

I think the noise calculation may need tweaking, especially to be consistent with other instruments. My wish list includes noise measurements per the various standards (A, C, CCIR, CCIR/ARM) and measuring in rt/Hz for noise analysis.
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File Type: png QA400 + QA interface + 590AR -5dBV.png (50.4 KB, 508 views)
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Old 20th March 2013, 10:00 PM   #27
RNMarsh is offline RNMarsh  United States
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Looooking good. i mention that THD+N as a benchmark number; it is what the A-P SYS-One spec's to be Less than .001% etc. Those gen/analyzers are coming down in price on eBay and other places.

I am ready to get back with what you are doing.... FFT so i can put away the big bulky HP swept analyzer and have PC control and save files etc.

I would suggest the 80KHz filter (not 30KHz) and A-weighting. The rt/hz would be really nice.

Thx-RNMarsh

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Old 21st March 2013, 05:40 AM   #28
RNMarsh is offline RNMarsh  United States
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The BenchMark ADC1 USB has some nice features and specs to look at for ideas and compare. -RNM
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Old 22nd March 2013, 03:14 PM   #29
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Quote:
Originally Posted by 1audio View Post
The ones in the latest release. DL and install it. There is a step where it runs a driver installer. It takes a few minutes for the installer to complete. Its running OK on both the USB2 and USB3 ports.

Attached is a plot from the Shibasoku generator. All the harmonics are from the interface + the QA400. I'll measure the interface tonight if time permits.

I think the noise calculation may need tweaking, especially to be consistent with other instruments. My wish list includes noise measurements per the various standards (A, C, CCIR, CCIR/ARM) and measuring in rt/Hz for noise analysis.
Hi Demian,

Bummer to have missed this thread until now while I was struggling with various soundcards and software! This looks like a very good unit. I already have Pete Millets interface so that would put me into business.

I am looking at various s/w packages and one that appeals to me is Virtins (although it sets you back $ 200 for the professional version). What I like in Virtins is that you can apply FFT filtering, meaning you can just take the fundamental out of the signal and output the residual, which can be pretty handy.

Anyway, I guess my question is whether you have tried the QA with any other measurement software except it's native package? If so, any issues?

jan
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Old 22nd March 2013, 03:40 PM   #30
1audio is online now 1audio  United States
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The QA400 only works with its own software. They chose to not use the normal sound interface on Windows since its problematic. They do have programmable access to their software and its pretty capable already.

I will look at the Virtins package. I have played with ARTA and HPW. I still return to Praxis for real work that the QA400 can't do. Its more expensive but comes with calibration and control hardware and very capable software.

Having tried most of the commercially available soundcards I find the ESI Juli@ the most usable and consistent in a desktop environment. The RME is close but more complex and no additional features that are useful. I have not tried a Lynx but its too expensive for me. I am finally getting OK results from EMU stuff but they are a hassle to setup. The 0404 on XP is OK and the Tracker pre on Win 7. But numerous driver issues to deal with.
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