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Old 30th May 2012, 05:14 AM   #11
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Here are what the output pins from the DAC look like.

1 KHz
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5KHz
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Quote:
Originally Posted by stephensank View Post
You can, and should, also look at your squarewaves directly at the output pins of the dac chip.
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Old 30th May 2012, 09:59 AM   #12
alkasar is offline alkasar  France
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RMAA will do sweep sine to provide frequency domain information.
for example, my measurement in loopback of my own soundcard (akm4396 dac)
RightMark Audio Analyzer test : E-MU0204 24-96
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Old 30th May 2012, 11:44 AM   #13
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Yes, I think you're right. I need to do a sweep sine wave test. But I have absolutely no confidence in the built-in ADC in my computer. So I'm thinking about a way to do this with an oscilloscope. Perhaps a long exposure of the camera while the sweep takes place would reveal something. Or maybe a low-pass filter on the input to the scope might give me a relative reading of the RMS at a particular time. A long sweep and a long exposure of the camera might be able to capture it.

What do you think, short of me buying a really expensive ADC with some sort of USB input to the computer?

Dave

Quote:
Originally Posted by alkasar View Post
RMAA will do sweep sine to provide frequency domain information.
for example, my measurement in loopback of my own soundcard (akm4396 dac)
RightMark Audio Analyzer test : E-MU0204 24-96
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Old 30th May 2012, 12:11 PM   #14
alkasar is offline alkasar  France
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do a sweep sine without the proper-equipment with just a scope is beyond my knowledge

if your computer has line input, you can run RMAA in loopback (output straight into line-input) and measure how good, or how bad, your computer audio is.

IHMO, use your computer soundcard is sufficient to get the frequency response of the dac5 and have a first understanding if there is, or not, a big issue. If you find an issue at some freq, then you can use your scope to investigate more precisely.
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Old 31st May 2012, 05:02 AM   #15
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Here are the results I get from RMAA 6 comparing the DAC5 output against my computer's speaker out, as seen at my computer's line in:

RightMark Audio Analyzer test: comparison

Dave
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Old 31st May 2012, 11:52 AM   #16
alkasar is offline alkasar  France
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humm.. seems indeed the bandpass is limited in the heights. The low pass filter comes in a bit early. Without surprise, the other measurements are not up to expectaions due to the fact the soundcard input is the weak point.

According to schematic, the dac5 output filter follows almost exactly Wolfson recomandation and should filter above 100k with no impact in the audio range.
Here is the output stage of the dac5 in an on-line simulator
https://www.circuitlab.com/circuit/8...c5-output-lpf/

Can you recheck the components values on board ?

BTW: In RMAA you can specify a range 20-20kHz instead of 40-15kHz. More common for the results in the first table.

Can you run a test at 48kHz ? also make sure you adjust volumes in your audio driver to measure in the best conditions. You can see that real time in the home window of RMAA.
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Old 31st May 2012, 03:48 PM   #17
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Thanks very much for looking at these results. I will change the default range and try again. I will also run a test at 48Khz.

I tried various levels into the DAC. I seemed to get the least distortion and lowest noise floor with the computer's output level control at 100%. That required me to set the line-in levels at what I thought were ridiculously low levels, such as 3%. Maybe I need a resistive pad between the DACs output and line-in on my computer.

I noticed when I was measuring some DAC chip outputs that some of the values of capacitors on the board in the LPF were not as specified in the schematic, but they were not far off, either. I'll provide the exact values as my sample was built.

That's an interesting simulator you're using. I tried out the simulation, and the output looked flat to 20 KHz and almost to 40KHz. I'm not sure what to make of the -14 degree value at 20 KHz. I guess group delay is not flat to 20 KHz?

Dave
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Old 1st June 2012, 10:36 AM   #18
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Unfortunately the free copy of RMAA that I downloaded will not let me edit the range for frequency response. I even changed the values in the Windows registry to 20-20kHz, but, the program immediately changed them back to 40-15kHz as soon as I started it, and it wrote 40-15kHz back to the registry. Maybe only the Pro version allows you to look at a wider spectrum.

Anyway, here are my results at 48kHz:

RightMark Audio Analyzer test: comparison
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Old 1st June 2012, 02:45 PM   #19
alkasar is offline alkasar  France
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oops, you're right! Needs PRO version. In the interactive screens you can see the -3dB freq when move the mouse on the curve.

The measurement at 48kHz is strange as even the green curve shows a cut at about 15kHz

You can also try ARTA Steps. it performs sweep sine and provides very accurate measurements.
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Old 2nd June 2012, 02:58 AM   #20
repeet is offline repeet  Australia
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I have a newer version of this board V1.7. I'm not sure of the differences but there are 2 small dip switches on this version.
I also fitted OPA827 and LT1364 Opamps.
The seller was eBay Australia: Buy new & used fashion, electronics & home d?r
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