GSM-noise "buzz" issue
joerg at openmoko.org
Thu Oct 30 11:11:47 CET 2008
Am Mi 29. Oktober 2008 schrieb Ole Kliemann:
> Hi Joerg and others,
> I haven't followed the whole thread as I only understand 1%. So just one
> quick and dirty question:
> I have the two years EU warranty and am going to send my FR to my
> distributor anyway because GPS is not working with the internal antenna.
> (Independant of SD card.)
> So if I send it in, is there any fix that could be applied for the
> buzz? Or is it worth to wait, say another week, because there will be
> something then?
Seems you always could "upgrade" to the 'botch' fix found in A7 (It *should*
work, as our TPE engineers found it worth to implement in A7 ;-):
replace R4403: 0R -> 2k2
add C4306: NC -> 100uF (probably you won't find a 100uF to fit in anywhere, so
a 47uF might kinda suffice. C4306 pads aren't existent in A5/A6, but you can
use pads of NC R4304 which isn't mentioned in public schematics)
A _yet_unapproved_(!) variant is to use a LM336-2.5 in place of the huge
capacitor, and to
change R4305: 2k2-> 860R (to make LM336 operate on >400uA, when setting
MICBIAS to VDD*0.9)
You also have to
replace R4403: 0R -> 2k2
In theory this rework should yield even better stabilization of MICBIAS
voltage, the path where ripple caused by GSM RF is introduced to audio path.
See all but first 6 pics at http://people.openmoko.org/joerg/buzzfix-lm336/
(first 6 pics are a nasty approach to cut pin4 using some dremel-like mill.
Those are not related to LM336 fix)
> And - if you allow me to be off-topic - is there any improvement fix for
> the headphone jack? I mean this hipass-filtering issue making music
> sound quite tinny.
a) place some decent 100uF (or as high cap as feasible) parallel to C4110 and
C4111. Make sure you don't create another contamination path for RF creeping
inside big can - maybe use a ferrite ring to block RF next hole where you
route some wires from those big caps inside can to C4110/11.
b) *short* C4110 / C4111, and insert the 100uF somewhere else in audiopath,
b1)e.g. near R4405 / R4407 (you can even replace these R by 100uF
You should remove R4117 and R4117 then, and instead place these 1k from
JK4401:pin2 and pin3 (! for JACK_INSERT function) to GND
b2) or even place the 100uF outside FR in the housing of your hs-plug or
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