On Mon, 2009-03-23 at 16:51 +0300, Paul Fertser wrote: > "arne anka" <openm...@ginguppin.de> writes: > >> And don't forget that the proposed rework doesn't fix wired headset > >> mic, it will still produce a lot of buzz. > > > > how's that? > > i lived under the impression that the buzz is basically one buzz and the > > hw fix is intended to end all buzz. > > > > any sources proving your statement available? > > Schematics. Or ask Joerg. > > Basically the idea is that the buzz gets to the MICBIAS line via the > 4th pin of the headphone receptable (that is mic input). The longer > antenna you attach to it, the more RF you get. > > Then it's detected somewhere inside the Wolfson and comes back via the > same MICBIAS line this time as a very strong audio frequency signal. > > With internal mic you can use a large cap to filter it on one side of > the mic and get the signal from the other side because it's connected > in a differential way. With the headset mic it's not possible because > it has only one line. > > The rework for that would take lifting the can, desoldering one small > R, soldering two of them in parallel to the same place (already tricky > enough!) and adding a big cap to gnd (and free space inside the can is > very limited). So, not practically possible. > > Read the schematics. > > OTOH you can use headphones and _internal_ mic for GSM after > buzz-fixing it. > > NB: Factory-produced A8 will have ferrite beads in place (so RF will > not get anywhere it can be detected in the first place), and that > should probably solve all known buzz problems. >
Just a wild guess, but is it possible to replace the headphone receptable with a shielded one? Would perhaps be more of a DIY job then replacing SMD resistors and add SMD caps. Kind regards, Ed _______________________________________________ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
