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QuantAsylum QA400 and QA401
QuantAsylum QA400 and QA401
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Old 18th June 2016, 02:47 PM   #2051
Davey is offline Davey  United States
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Not a big deal, but one thing I did note when FR testing is the pulse on the "+" outputs is negative going.

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Old 23rd June 2016, 10:25 AM   #2052
miklos is offline miklos  Hungary
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I managed to screw up my QA400 by discharging a 15000uF -40V capacitor through a ground loop, something like this: amplifier - input w a 25k pot turned to zero - QA400 input ground - QA400 USB con. - Computer GND - my grounded soldering iron touching the -40V . Lucky me only two IC-s burnt in it, a low dropout adj. reg. U13 and a boost converter U10 producing the +10V for the analog stages. The whole exercise cost me some nerve wrecking moments, because I don't have $550 for a QA401 and $60 for the parts from Digikey.
Attached Images
File Type: jpg Adjustable low voltage drop regs U13-14-15.jpg (513.1 KB, 717 views)
File Type: jpg Boost converter U10.jpg (521.6 KB, 716 views)
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Old 23rd June 2016, 10:16 PM   #2053
davada is offline davada  Canada
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Quote:
Originally Posted by miklos View Post
I managed to screw up my QA400 by discharging a 15000uF -40V capacitor through a ground loop, something like this: amplifier - input w a 25k pot turned to zero - QA400 input ground - QA400 USB con. - Computer GND - my grounded soldering iron touching the -40V . Lucky me only two IC-s burnt in it, a low dropout adj. reg. U13 and a boost converter U10 producing the +10V for the analog stages. The whole exercise cost me some nerve wrecking moments, because I don't have $550 for a QA401 and $60 for the parts from Digikey.
I surprised this didn't shut down the USB power before any damage. A ground fault should have just burned some thin trace on the ground.
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Old 24th June 2016, 06:20 PM   #2054
miklos is offline miklos  Hungary
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The damage doesn't come from the USB power, it come from the -40V. Once the U13 get shorted, the +5V USB shut down. The U13 low dropout reg. is directly connected to the USB power, the U10 boost converter has the L1 coil in series to the +5V.
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Old 30th June 2016, 07:34 AM   #2055
31697B is offline 31697B  Thailand
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From the HP-339 mod forum.... we used an external notch filter to atten the signal to the ADC for greater linearity in measurement apps. I found a passive notch filter (nill distortion) from B&K 1607. Then I got some help/suggestion on converting it to active for sharper notch width. I have it switchable -- active-passive mode.

Here is the before and after mod affect:

B&K 1607 modified.JPG

passive vs active mod.JPG



THx-RNMarsh
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Old 5th July 2016, 12:17 PM   #2056
miklos is offline miklos  Hungary
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Is anywhere this mod described in details, link?
Thanks.
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Old 31st July 2016, 10:04 PM   #2057
miklos is offline miklos  Hungary
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Silence on the thread, everybody is on vacation.
Here's a little story how I used my QA400 in the last three years and also learned a lot by reading here how to use the QA correctly.
Many forum members disregarding THD measurements as not being relevant to sound quality.
I for one believing in meters, I'm not testing the mains with my tongue, why should I completely trust my ears?
The nice added distortions can foul one easily. So I compared CD players from the cheapest one to the pretty expensive one, from the first generation like the Hitachi DA1000 with a ceramic PCM53 from 1982 to the latest generations mega bucks Esoteric's and everything in between. For me it's easier to see the differences between them than hear it. The Redbook CD is pretty robust system, working well, like the FM radio. In my search I found what I was looking for, the best deal you can have on a player, to buy a 10-15 year old DVD player, those are shed by the owners in favor of the Blue ray ones.
Try the Pioneer DV-45, DV-47Ai or the Sony DVP-S9000es, fantastic players, with hard to beat specs.
An other subject comes up to time to time, that THD is done on a static signal, what music is not. I tried multi tones with
the QA400, like 6 or 12 tones, no numerical result, just visible one. I can see ca. 10dB rise of the noise floor going from 6
to 12 tones. Probably caused by IMD and the increased jitter. Up to this point for more realistic testing ,more music like
random signal is a noise with gap quite reviling, where anything in the bottom of the gap is distortion. Here's a picture of a
test on a ca. 20-23 years old Philips CD921 (TDA-1549 DAC) with the white noise with gap signal.
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File Type: jpg Philips CD921 Noise w Gap.jpg (336.8 KB, 361 views)
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Old 31st July 2016, 10:50 PM   #2058
1audio is offline 1audio  United States
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QuantAsylum QA400 and QA401
How did you generate that file with such a sharp transition to the silent band? I could use that trick.
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Old 1st August 2016, 01:29 PM   #2059
miklos is offline miklos  Hungary
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Did it a couple of years ago in the Cool Edit.
I think it goes like this:
Generate - 44.1kHz 16 Bit - Noise - White - sec.
Effects - Filters - FFT - size 8192 - Blackman-Harris
I also could send you the wav file.
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File Type: jpg FFT notch3b.jpg (261.6 KB, 328 views)
File Type: jpg FFT notch4.jpg (300.3 KB, 318 views)
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Old 1st August 2016, 03:44 PM   #2060
benb is offline benb  United States
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It seems all that noise would be very effective at linearizing the A/D converter as well as dithering. You're likely to see something different than with just those tones themselves around 1kHz.
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