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QuantAsylum QA400 and QA401
QuantAsylum QA400 and QA401
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Old 21st April 2014, 09:22 AM   #1061
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by davada View Post
Maybe we need to start importing them for DIY.
5 years ago they stopped selling this tea is in any shop in Germany
But I found it again in Switzerland.
If you intend to establish this tin box as the corporate diyaudio casing - here is a vendor who could serve reasonable quantities.
New Design Lipton Tea Tin Can - Buy Lipton Tea Tin Can,Lipton Tea Tin Can,Lipton Tea Tin Can Product on Alibaba.com

Last edited by ChocoHolic; 21st April 2014 at 09:28 AM. Reason: ...grammar...
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Old 23rd April 2014, 02:19 PM   #1062
bear is offline bear
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choco, perhaps run the same test(s) with the bandwidth up at 192, and avg = 0 and avg = ~10?

It looks very free of LF pick up, and noise in general, surprisingly so.
Also, perhaps run a screen of the unit "native" in loop back, and with the input(s) shorted?

I found the two channels are slightly different, I think everyone else has as well...

Looks interesting.

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Old 23rd April 2014, 05:18 PM   #1063
31697B is offline 31697B  Thailand
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Is there a circuit that will do auto scaling that is simple and easy to make? Some sort of comparitor perhaps. Thinking of driving small signal relays to select taps on a divider at the input.


THx-RNMarsh
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Old 23rd April 2014, 05:18 PM   #1064
ChocoHolic is offline ChocoHolic  Germany
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Hi Bear,

the sweet spot of my unit is at 500mVrms.
So I am always adjusting the buffers to run the QA in the sweet spot.
The shown results with filter and buffer are looking identical between
Output gain =1 (input gain also 1) up to output gain =7 (input gain adjusted to 1/7). When the output buffer has to deliver signals above 5Vp, then the distortion starts to rise.

Attached the loop back results of the QA400 alone - done some weeks ago, right after I received the unit
Also my QA has small difference between left and right.
Overvall the right chanel is slightly better, that's why I am using it.


Will look into 192kHz next....
Attached Images
File Type: jpg Left1kHz.JPG (69.9 KB, 333 views)
File Type: jpg Right1kHz.JPG (65.5 KB, 275 views)
File Type: jpg LeftDualTone.JPG (68.3 KB, 274 views)
File Type: jpg RightDualTone.JPG (64.4 KB, 269 views)
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Old 23rd April 2014, 06:12 PM   #1065
1audio is offline 1audio  United States
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QuantAsylum QA400 and QA401
Quote:
Originally Posted by RNMarsh View Post
Is there a circuit that will do auto scaling that is simple and easy to make? Some sort of comparitor perhaps. Thinking of driving small signal relays to select taps on a divider at the input.


THx-RNMarsh
We can use a stripped down version of the Shibasoku autoranging circuit. Its self contained and reports back to the host what the gain setting is. It has much finer stepps than would work with the QA400 (1 dB vs. 20 dB) so the stripped down version should be simple. It could report back to the host what the current gain is to get corrected display settings but that adds considerable complexity.

My suggestion would be the following as giving the most flexibility-
300 mV, 3V, 30V and 300V full scale. This would make the display easily understood. The interface box would get more complex and expensive with 6 relays and protection circuits etc. The input connectors will be an issue etc. (All why I used the interface cable to deal with the issue).

On the low pass filter at the input. I realized the industry standard is 20 KHz low pass, not 200 KHz. Also the ADC has enough dynamic range that it probably would not be an issue but I'll try it with a switching amp soon to confirm. However if you want to measure a non-oversampling DAC with no reconstruction filter there could be lots of issues.
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Old 23rd April 2014, 07:07 PM   #1066
31697B is offline 31697B  Thailand
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Just want to measure amps/preamps which have higher output voltage potentials than the QA400 can handle directly. So an autoranging circuit in front of it will be auto-protecting.

Maybe 100mV, 1v and 10 and 100v RMS would make scaling and display easy to interprete?

If the SkibaSoku autoranging is simple and easy, then I'll go for it --- can you provide a schematic?


THx-RNMarsh
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Old 23rd April 2014, 11:36 PM   #1067
waltzingbear is offline waltzingbear  United States
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maybe look at the input protection of the hp8903b, not autoranging, but disconnection. if safety and preservation is all you want.

Alan Garren
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Old 24th April 2014, 07:06 AM   #1068
31697B is offline 31697B  Thailand
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I do want auto-scaling. That way a large signal can be measured..... just goes thru a resistive attenuator... selected by the auto-scale/range circuit.



THx-RNMarsh
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Old 24th April 2014, 07:17 AM   #1069
31697B is offline 31697B  Thailand
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Quote:
Originally Posted by ChocoHolic View Post
Hi Bear,

the sweet spot of my unit is at 500mVrms.

Attached the loop back results of the QA400 alone - done some weeks ago, right after I received the unit
....
When I did a parallel test and compared the harmonics measured by a much, much more expensive and accurate units, the harmonics shown by the QA400 could not be used below -100dB. They were very different. I used the AP-2722 and the ShibaSoku 725D for reference. Only when you drop the input level via a notch filter circuit did the data shown below -100dB begin to measure what the ref units data measured.

THx-RNMarsh
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Old 24th April 2014, 07:36 AM   #1070
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by RNMarsh View Post
Is there a circuit that will do auto scaling that is simple and easy to make? Some sort of comparitor perhaps. Thinking of driving small signal relays to select taps on a divider at the input.


THx-RNMarsh
I have a half-formed project using a Boonton autoranging input card in a stand-alone fashion with a small micro and a couple of detectors and comparators. Which actually are on another Boonton card.

Jan
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