buzz fix (was: Pulster offer - Freerunner now 249 eur)

Helge Hafting helge.hafting at
Thu Jan 29 13:51:04 CET 2009

Al Johnson wrote:
> On Tuesday 27 January 2009, Helge Hafting wrote:
>  > Al Johnson wrote:
>  > > On Tuesday 13 January 2009, Yorick Moko wrote:
>  > >> buzz and gsm fixes are even documented on the wiki (no need to search
>  > >> in the e-mails)
>  > >> only the audio-fix (big capacitator to provide more bass isn't; hoping
>  > >> to see that one documented as well
>  > >
>  > > There's some fairly detailed discussion of audio mods on the hardware
>  > > list which could be copied into the wiki, but there is no 
> 'official' mod.
>  > > I suspect there won't be one either, mostly because big caps won't 
> fit in
>  > > the space available, and relocating them to outside the screening can
>  > > could easily reintroduce buzz.
>  >
>  > Another option:
>  > Short the too small capacitors, so there are no capacitors at all. Then
>  > add the big caps outside the screeming, but this time with no need to
>  > connect to anything inside the screening.  Just break the connection
>  > anywhere, and insert a nice big cap. The easiest place of all then, is
>  > obviously to add the caps to the headset. Of course then you only have
>  > one useable headset.
> Yes, that's one of the options discussed, along with some resistors you 
> might
> like to remove. You could put the caps in a 2.5mm to 3.5mm ( or even 1/4in)
> adaptor cable to make it usable with generic headphones. I don't personally
> like this solution for 2 reasons; one day I will forget and stick dc on a
> headset, and it will probably prevent use of the serial debug interface to
> the gsm. The second objection won't be a consideration for the vast majority
> of people though.
>  > Or break the connection between the plug and circuit board, and put the
>  > caps somewhere inside. There is lots of room above the SIM card.
> This is harder than it sounds IIRC, but feel free to try. I had my eye 
> on that
> space for caps too as the existing caps are very close to it. You could make
> a small hole in the screening can to pass the wires through, but would need
> to be careful to avoid creating an rf pathway.

Seems I wasn't clear enough.

My second suggestion was to put the caps above the SIM, but *without* a 
hole in the screening. No new way for buzz to get in then! Electrically, 
this is the same as the "caps in headset" variant, but with the 
advantage that any headset will work because the caps is now between the 
plug and the shielded unit. (The small caps inside the shield must still 
be shorted.)

There will be some wires, but they will go between the caps and the 
plug. These wires might pick up something, but it will be the same stuff 
that the headset wires pick up already. Presumably, the circuit board 
way into the shielded area is protected, or a plain headset would cause 
buzz too?

My hope is that the plug is so big, that re-soldering it won't require 
special skills. And the small caps can apperently be shorted without 
soldering, as suggested on the hw list.

Helge Hafting

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