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Old 20th May 2012, 05:43 AM   #1
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Default Do DAC's emit much RFI?

Greetings,

I'm currently building a preamplifier with two DAC modules in it, the Twisted Pear USB DAC/receiver and a S/PDIF converter, currently in a group buy. S/PDIF power supply will be a 9V battery to isolate it from power to various analog circuits (gain stage and active X-over) just in case. I have single ended "line level" wires (tightly twisted with ground, of course) running all over the inside of this chassis. The question is: will the DAC modules emit enough RFI that they need to be shielded?

Any advice would be helpful.
Thanks, Byron
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Old 20th May 2012, 09:47 AM   #2
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Yes they do, and TP products do this more. The best practice of EMC is to fix the issue at it's root. So you'll need ferrite beads, ferrite cores on all the wires, to tightly shield all I2S lines

Check out marce's post here:
I2S and digital signal path - in-line resistors?

Lots of really good links.

And my post here for TP products:
I2S and digital signal path - in-line resistors?

If you don't have a good RFI measurement setup (noone has it's pricey, involving RF amps, wide bandwidth spectrum analyzers, special treated rooms etc). You'll need a radio, preferably battery powered, and as much bands as you can get, with external antenna. Tune it to materclock frequency multiplies, and hear the noise with the dac ON/OFF, SPDIF connected/disconnected.
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Old 20th May 2012, 01:59 PM   #3
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That is so not what I wanted to hear.
Fortunately, I'm not using TP's I2S module, but I'll try to digest some of that plethora of links you pointed me to and put together a plan.

Thank's for your help,
-Byron
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Old 22nd May 2012, 01:01 PM   #4
PET-240 is offline PET-240  Australia
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Just so you know, brass mesh is the best way to shield RF I have found or been informed about, I know the Army uses it for their radios and test facilities.
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Old 22nd May 2012, 01:19 PM   #5
wwenze is offline wwenze  Singapore
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Interesting... I would've thought otherwise, since the metal enclosure isn't always grounded, and some DACs don't even have a metal enclosure.

Now how do I sneak a laptop and a DAC into the test chamber...
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