GSM-noise "buzz" issue

Angus Ainslie angus.ainslie at
Fri Oct 31 20:24:45 CET 2008

On Thu, Oct 30, 2008 at 8:18 PM, Andy Green <andy at> wrote:

> Angus, I talked to Candy here in .tw the last few days about this, she
> actually did the work to perform the tests Joerg is talking about.

Did she use a 100uF cap ?

> One thing you can try that is quite simple and easy is to override
> MICBIAS net by a ~1.5V battery on it to 0V.  She told that this alone
> removes the buzz, it would be good to know if you can reproduce.
That probably would work. I don't think I'm going to try it as I have had
some results with the cap fix.

Initially I tried using the 100uF cap that was suggested. It kind of worked.
there was no buzz but there was also almost no gain from the mic. Voice
wouldn't get transmitted but blowing on the mic would. I removed the 100uF
cap and then used a 1uF cap. Ther buzz was gone, a slight hum still remains
that might have been coupling from one of the other devices in the room. I'm
going to try in a less signal saturated environment later.

I think I'd also like to try it with MICBIAS raised to the 0.9 multiplier.
Is that done in the bootloader or in kernel space ? Could someone generate a
an updated kernel with the higher mic bias ?

Prep the ground plane for the 100uF cap. The to photos are the same the
smaller one is just for bandwidth reduced diets.

Cap in place

Jumper wire attached

With the 1uF cap.


Angus Ainslie
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