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Test & Measurement interface for Soundcard
Test & Measurement interface for Soundcard
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Old 12th March 2019, 06:02 PM   #881
Rory Christ is offline Rory Christ
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Originally Posted by Rax View Post
I was going to effusively report lower noise figures after Cu shielding and grounding the shaft last night, but at the end of it I thought it'd be "interesting" to use the wrong supply (identical jack) - 12V from my headphone amp - to supply it.
I would start by checking the input and output voltages on the DC-DC converter. The data sheet says the absolute maximum input voltage is 10V, so it may have been damaged from having 12V applied to it.
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Old 15th March 2019, 06:41 PM   #882
Rax is offline Rax  United States
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Well, that's interesting. It seems the part I would have bet some good money would withstand this if any part would, failed - the ESD protection diode. It would short the power supply through the fuse, and keep the interface offline.

Anyway, I seem to have lowered THD+N by about 0.01%. I used copper foil for shielding, and grounded also the shaft. Is this what others have observed?

I will go next to the caps suggested.
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File Type: png 1kHz Spectrum After shielding and shaft grounding.png (582.8 KB, 283 views)

Last edited by Rax; 15th March 2019 at 06:44 PM.
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Old 16th April 2019, 09:41 PM   #883
mnichols30030 is offline mnichols30030
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Default Another data point / Sound Card

I just completed Peter Millett's sound card interface. Still on the learning curve with ARTA and calibration. The only addition was to use copper tape to line the upper half of the box.

I am using an ASUS Essence STX II sound card. The following is the spectrum looped back through the sound card interface.

Still have to calibrate the AC RMS voltmeter and continue exploring this setup.


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File Type: jpg LoopBackwSoundCardInterface.JPG (69.6 KB, 217 views)
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Old 1st June 2019, 10:36 PM   #884
Rax is offline Rax  United States
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Originally Posted by LinuksGuru View Post
2) Added the following ceramic capacitors in order to suppress noise:
1uF - 5V supply (soldered straight on USB socket PCB terminals);
0.1uF - parallel to C22, C7, C8 (near Murata switch mode DC-DC converter);
1uF - parallel to C13, C18, C11.

0.1uF - high quality ceramic NP0 type
1uF - ceramic Z5U type

Choke would be the last option if anything above doesn't work, DC 500mA 10-12mH is quite big, it doesn't fit nicely.
4 terminal chokes (from many switch mode PS) are common mode types, they are not suitable for this application.

Now in loopback mode I've got the following (1.9V from ESI Juli, balanced connections, 192000 mode, 191072 FFT):
1 KHz: THD - 0.0075%, THD+N - 0.082%
20 Hz: THD - 0.041%, THD+N - 0.19%
20 KHz: THD - 0.048%, THD+N - 0.094%
SMPTE IMD 250Hz/8KHz - 0.035%, MD2 - 0.034%, MD3 - 0.0038%
50 Hz noise: -104dB
100 Hz noise: -120dB
150 Hz noise: -120dB
LinuksGuru - thank you, this sinks the floor down quite a bit. Need to look at this more, but I'm tempted to say this, plus running the interface on batteries lowered the noise floor of the interface enough to no longer be the bottleneck between it and my E-MU 0404. I see something very close to 140dB now, both of them in the loop.
Why do this if running on batteries? I suspect my garage is a very noisy environment - dealing with all sorts of gremlins elsewhere - and so anything environmental is likely shunted to ground by doing this. Ah, and there's the DC/DC converter.
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File Type: png PMI EMU after additional decouplers.png (555.3 KB, 116 views)
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Old 1st June 2019, 11:27 PM   #885
Rax is offline Rax  United States
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Updated spectrum, input shorted this time.
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File Type: png PMI EMU after additional decouplers - no tone.png (585.7 KB, 105 views)
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