On Thu, Jun 18, 2009 at 10:59:16AM +0000, Jacob Meuser wrote:
> I played with this a bit and was unable to get rid of the pop.  I
> left outputs muted, and still got the noise.  as far as I can tell,
> the pop happens when the codec is powered up.
 
I think the codec has a "virtual ground" tied halfway between 5V and 0V
or whatever its power supply is. The output is then connected to the
real output with a capacitor to avoid a 2.5V DC offset at the output
(this is commonly done when you only have a single supply but need a
split one).

When the codec is powered up, all of it is at 0V. The virtual ground
will rise to 2.5V, causing a very loud spike as the output capacitor
charges. It's not possible to mute this except with a mute transistor
after the output capacitor (haven't seen any sound card with one of
those) or a very slow-rising power supply, making the narrow, tall spike
into a wide, low pulse that you can't easily hear. Surely not somehing
you can fix without physically poking the hardware, though probably not
very difficult if the noise is really annoying.

-- 
Jussi Peltola

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