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Old 15th May 2005, 03:56 PM   #1
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Default PCM2702 on / off noise

I'm building a USB soundcard with a PCM2702. I have built the thing on a breadbord to test it. It sounds pretty good, but when I unplug the USB connector from my laptop or when I turn off my computer I hear a very anoying noise.

This is very anoying because I have my headphones on when I turn off my laptop.

How can I get rid of this noise?

Do you have any other advise for my project?
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Old 15th May 2005, 05:42 PM   #2
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Perhaps putting a inductor on the Vbus line? It could be some voltage fluctation when you pull out your plug.

http://www6.head-fi.org/forums/showthread.php?t=105088
http://www6.head-fi.org/forums/showthread.php?t=109671

Ask them if they hear any noise, because they have a inductor on that Vbus
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Old 16th May 2005, 11:29 AM   #3
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I placed a 100uF capacitor between Vbus and GND. With the USB output resistance, it functions as a low pass filter.

The off noise is fully eliminated, but there is still a small on noise. I think the on noise is now produced by the charging of the 100uF capacitor. I will try a smaller capacitor.

I will also try a coil in the Vbus line. That functions as a low pass filter too, but maybe it works better.
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