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QuantAsylum QA400 and QA401
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Old 9th September 2013, 08:34 PM   #331
JensH is offline JensH  Denmark
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QuantAsylum QA400 and QA401
Regarding MiniDSP I am looking at the possibility of using an external clock for the MiniDSP USBStreamer. I think I have found a method to do so. I am close to finishing the layout of an isolated interface board. If it works as intended, I will be able to get 8 channels in and 8 channels out (10 each with an add-on board), with a clean master clock.
I have also prepared the design for the use of an externally applied master clock, so that the clock can be chosen freely (as long as they are 24.576/22.5792MHz) and placed close to the converters. The internal clocks from the USBStreamer have too much jitter in my opinion.

When this is done I plan to design an ADC/DAC board to connect to this interface board.
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Old 10th September 2013, 04:27 AM   #332
davada is offline davada  Canada
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Hi Bear,

I dug out my QA400 and took some screen shots.

This is an overlay. Green is the left ch and red is the right.
192k. I'll post another at 48k
This is using the left out gen.

The 4th pic is with the gen running but not connected to either input.
You can see the crosstalk into the right channel but the left channel doesn't seem to be effected.
Attached Images
File Type: jpg QA400.JPG (126.1 KB, 789 views)
File Type: jpg QA4002.JPG (124.5 KB, 754 views)
File Type: jpg QA4003.JPG (128.6 KB, 743 views)
File Type: jpg QA4004.JPG (129.3 KB, 685 views)
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Last edited by davada; 10th September 2013 at 04:41 AM.
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Old 10th September 2013, 06:18 AM   #333
1audio is offline 1audio  United States
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QuantAsylum QA400 and QA401
Quote:
Originally Posted by davada View Post
Just little off topic or maybe not so off topic, has anyone checked out the products at MiniDSP.com? A lot of very interesting stuff there at reasonable prices. All by DIYers.
I spent some time with the Minidsp guy at AES last year. They are very together. Not DIY really but pro operation trying to eke out a living in Hong Kong. The boxes are good and they are among the best for XMOS design.
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Old 10th September 2013, 06:22 AM   #334
1audio is offline 1audio  United States
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Quote:
Originally Posted by RNMarsh View Post
Your input got lowered --- near zero in first 2.... -3.5dB on last test. Run it again with higher - zero - level and then compare.

THX-RNMarsh
I tried that with the loopback, the distortion was still much higher. I need to rework the prototype to get unity gain through it.
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Old 10th September 2013, 12:26 PM   #335
bear is offline bear
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davada, ur results appear to suggest that the source of the "extra" harmonics is in the generator side? Also I think I see your THD number is ~0.003%? That seems higher than spec??

I hope to be able to check a few more things over the weekend, including taking the osc from the VP-7725 and seeing how that looks, also doing the shorted input test...

Time permitting I could try running the output of the two gen channels to the VP-7725 and see how they stack up as well...

Anyone besides Demian, Davada and me actually have the box??

_-_-
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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 10th September 2013, 03:10 PM   #336
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
I spent some time with the Minidsp guy at AES last year. They are very together. Not DIY really but pro operation trying to eke out a living in Hong Kong. The boxes are good and they are among the best for XMOS design.
I thought their product line was a bit too developed for DIY. No DIYer has that kind of time unless retired. The USB stick is just what I need to get going.
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Old 10th September 2013, 04:28 PM   #337
31697B is offline 31697B  Thailand
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Quote:
Originally Posted by bear View Post
davada, ur results appear to suggest that the source of the "extra" harmonics is in the generator side? Also I think I see your THD number is ~0.003%? That seems higher than spec??

I hope to be able to check a few more things over the weekend, including taking the osc from the VP-7725 and seeing how that looks, also doing the shorted input test...

Time permitting I could try running the output of the two gen channels to the VP-7725 and see how they stack up as well...

Anyone besides Demian, Davada and me actually have the box??

_-_-
I probabaly do. Or similar-something like it.

-RM
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Old 10th September 2013, 06:04 PM   #338
bear is offline bear
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Sorry? probably do? lost you on the curve...

----------

Fwiw, I looked again at the QA site at their own images for each channel and noticed that they too are showing similar harmonic spurs. Now with 20-20 hindsight I realize the significance of what is being shown...
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http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 10th September 2013, 11:30 PM   #339
31697B is offline 31697B  Thailand
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Bear ---

Make that a - yes I do.
Just following along at the moment.
sup?

-RNM

Last edited by 31697B; 10th September 2013 at 11:38 PM.
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Old 10th September 2013, 11:40 PM   #340
31697B is offline 31697B  Thailand
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Join Date: May 2012
Quote:
Originally Posted by JensH View Post
Regarding MiniDSP I am looking at the possibility of using an external clock for the MiniDSP USBStreamer. I think I have found a method to do so. I am close to finishing the layout of an isolated interface board. If it works as intended, I will be able to get 8 channels in and 8 channels out (10 each with an add-on board), with a clean master clock.
I have also prepared the design for the use of an externally applied master clock, so that the clock can be chosen freely (as long as they are 24.576/22.5792MHz) and placed close to the converters. The internal clocks from the USBStreamer have too much jitter in my opinion.

When this is done I plan to design an ADC/DAC board to connect to this interface board.
Sounds very interesting. what is your current progress... what has been done to date? And, what still needs to be done..... ETA?

-RM
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