Thanks Demian. It does blow my project, which called for monitoring the residual in real time with some circuit changes going on.
Unless I get another low noise generator.
Jan
Unless I get another low noise generator.
Jan
Jan-
I think one of Viktor's oscillator plus the Boonton (with the QA400 on the monitor out of the Boonton) would get you where you want to be. I have a mod for the Boonton that allows monitoring the input simultaneously with the distortion. Its pretty simple to implement.
Perhaps you can share what you are trying to do?
I think one of Viktor's oscillator plus the Boonton (with the QA400 on the monitor out of the Boonton) would get you where you want to be. I have a mod for the Boonton that allows monitoring the input simultaneously with the distortion. Its pretty simple to implement.
Perhaps you can share what you are trying to do?
Yeah I ordered one of Victor's boards. What I am trying to measure is changes in THD when some circuit parameters are changed on the fly - I'd rather not go into details yet. 😉
I want to catch the changes at the moment of change on the analog residual output, and the FFT picture before-and-after.
I have the Boonton 1130 schematics, I guess you take the input buffered & ranged signal to a BNC output?
Jan
I want to catch the changes at the moment of change on the analog residual output, and the FFT picture before-and-after.
I have the Boonton 1130 schematics, I guess you take the input buffered & ranged signal to a BNC output?
Jan
Not easy. First the FFT depends on measuring over time and during which the change you are looking for will change.
Second is separating the DUT changes from all the external instrumented changes that could be happening simultaneously.
Exactly. Use an isolated BNC and grab the signal from the motherboard. I use an isolation resistor to prevent artifacts from the loading. Its autoranging which is great for a scope monitor.
Something odd is going on here. These measurements are far different than what I posted here:
http://www.diyaudio.com/forums/equipment-tools/231401-quantasylum-qa400-9.html#post3676966
I got between -117 and -111 (approximately).
_-_-
http://www.diyaudio.com/forums/equipment-tools/231401-quantasylum-qa400-9.html#post3676966
I got between -117 and -111 (approximately).
_-_-
It is a mystery for me as well. I'll do more testing and see if I can make sense of the results. At least I get similar to Jan on the same instrument.
AK4414 Distortion
Just for comparison here is an AK4414 (from their demo board) distortion spectrum. The reference (top line) is -90 dB. The level is -6 dBFS. The marker is at 3 KHz a level of -124 dB. The second is about -108 dB. The noise issue with the QA400 is not present here so I'm not sure what is going on. There is no noise issue looking at the residual from the distortion analyzer on a conventional scope.
Next step is to look at its transient behavior. I need toi fix the board first. Something is wrong with the 3.3V supply and the pass transistor heats up a lot.
Just for comparison here is an AK4414 (from their demo board) distortion spectrum. The reference (top line) is -90 dB. The level is -6 dBFS. The marker is at 3 KHz a level of -124 dB. The second is about -108 dB. The noise issue with the QA400 is not present here so I'm not sure what is going on. There is no noise issue looking at the residual from the distortion analyzer on a conventional scope.
Next step is to look at its transient behavior. I need toi fix the board first. Something is wrong with the 3.3V supply and the pass transistor heats up a lot.
Attachments
I'm wondering if the noise issue with the QA400 gen isn't a signal QA puts in there for special purposes when running in loop mode. Some filtering on the signal could reveal this.
I used the Shibasoku. I wanted to get as good resolution as I could. On the Boonton I get 90+ dB THD+N with a 30 KHz band.
I'm still lost as to the noise in the QA400. Also the claims floating around that delta sigma is inherently much nosier than a ladder dac. I just don't see that normally. I was hoping I might see something here. There is noise above 220 KHz but that is easy to get rid of, and also present on ladder dacs.
I'm still lost as to the noise in the QA400. Also the claims floating around that delta sigma is inherently much nosier than a ladder dac. I just don't see that normally. I was hoping I might see something here. There is noise above 220 KHz but that is easy to get rid of, and also present on ladder dacs.
They are inherently more noisy but much is done to lower that noise or at least to move it to out of band so filtering is easier. Latter dacs have glitch to deal with but this can be managed with a sample and hold on the output of the dac. It gets quite costly.
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I have read that as well but don't see it in practice, unless the QA400 is what they are talking about. In the AK4114 the noise is really quite low in-band.
Sample and hold's are quite glitchy as well and need low pass filters. Now that DSD is the new darling of audiophilia the noise issue becomes more real since that by definition needs noise shaping to work.
I need to get back to the interface board, much more relevant that this discussion for now.
Sample and hold's are quite glitchy as well and need low pass filters. Now that DSD is the new darling of audiophilia the noise issue becomes more real since that by definition needs noise shaping to work.
I need to get back to the interface board, much more relevant that this discussion for now.
Comparison -
Here is a comparison between Audio-Precision 2722 and QA400... same oscillator source (from HP-339A); No notch filter in front of QA400 - both are straight into each analyzer with approximately 0.7 v signal level:
The QA400 produces Harmonics beyond the 6th that are not in the source generator, at least not at the levels shown as per reference - AP2722. The 2H-5H seem to show the same relative levels to one-another but at higher levels.....
Thx-RNMarsh
Here is a comparison between Audio-Precision 2722 and QA400... same oscillator source (from HP-339A); No notch filter in front of QA400 - both are straight into each analyzer with approximately 0.7 v signal level:
The QA400 produces Harmonics beyond the 6th that are not in the source generator, at least not at the levels shown as per reference - AP2722. The 2H-5H seem to show the same relative levels to one-another but at higher levels.....
Thx-RNMarsh
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Thanks for sharing. Just curious, do you have a current USB interface and ARTA running for a comparison of all three?
Dave
Dave
Richard:
Can you do the following test?
Generator (Either AP or Shibasoku) into AP (or Shibasoku) with a T. Set the generator for 600 Ohm out. Set level to .7V. Look at the distortion on the loop both without and with the signal connected to the QA400. You should try this on the other instruments you have.
I noticed a significant increase in distortion with some instruments in this test. Level and ranging affect the results. Its possible that the distortion you are seeing on the QA400 is from the input amp on the input side.
Can you do the following test?
Generator (Either AP or Shibasoku) into AP (or Shibasoku) with a T. Set the generator for 600 Ohm out. Set level to .7V. Look at the distortion on the loop both without and with the signal connected to the QA400. You should try this on the other instruments you have.
I noticed a significant increase in distortion with some instruments in this test. Level and ranging affect the results. Its possible that the distortion you are seeing on the QA400 is from the input amp on the input side.
Only a eMU 0404 and I have downloaded ARTA.... but, I haven't used either one and not together, yet.
-RNM
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