Pulster fixe(s) and rework

Helge Hafting helge.hafting at hist.no
Fri Mar 6 10:22:32 CET 2009

Andy Green wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> |> I have suggested a refinement on the second approach: short the small
> |> capacitors. Add big caps outside the shielded unit - there are places
> |> with room. But don't put wires from the caps into the shielded
> |> unit. Connect them to the headset plug instead, and break the plug's
> |> normal connection to the circuit board. This approach won't pick up any
> |> more buzz than the headset based solution, or the current bassless
> |> setup. And you can use any headset you want.
> |
> |> The big question is - is it safe to short those small capacitors? Or
> |> will that have other side effects, such as draining the battery or
> |> disturbing sound on the built-in speaker?
> There are a couple of 1K resistors to 0V that will then connect directly
> ~ to the amp outputs all the time before the new DC blocking caps you
> will add back in.  But thanks to some recent patches by Mark Brown on
> andy-tracking, we should  keep the amp turned off more often.
Can these be safely removed? Are they there just to make sure the 
capacitors slowly drain, so you don't get a pop when plugging something in?

Or do they have other purposes as well?

> |> Another question - is a single big capacitor enough, if it is put into
> |> the ground line  instead of having one cap for each of the stereo
> |> channels? Or will that wreck stereo sound? One could then use a even
> |> bigger cap.
> You'd need to do both channels; the one with the unchanged cap will
> sound the same as always otherwise.

You misunderstand. I did not propose to do only one channel.
I planned on shorting both the small caps. Then, instead of one big cap 
on each of the stereo lines: LEave the stereo lines connected as-is. 
Break the ground line (which is common to both channels) and insert a 
single big cap there instead. Slightly less work, and perhaps a bigger 
capacitor will fit. (It'd probably have to be bigger too, as the two 
channels often enough have the same signal.)

> |> There is lots of easily accessible room next to the battery, above the
> |> SIM card.
> |
> | I'd love to see a good answer to those questions.  Currently, it's
> | unusable as an MP3 player and that's an important use for me (if
> | I could use it as an MP3 player, I'd carry it with me that much more
> | often, which would in turn increase my use of it).
> Lifting the can and meddling with the caps is nontrivial.  Somebody did
> give this plan a go on the list about 6 months ago and reported some
> success though.  But I don't recommend considering it unless you are in
> an experimental frame of mind and can deal with the fiddling and risk
> involved.

I understand that it won't be trivial. Maybe not for me. But if openmoko 
creates a standard procedure for this improvement too, then I can have 
an electronic repair shop do everything in one go - both buzz and bass 
fixes. That will cost me less than having the fixes done separately, 
even if both fixes together may cost a bit more than buzz only. I hope 
to ship the phone only once, the repair guy will need to open it only 

A mass fix will be especially cheap - a good technician doing identical 
fixes on a big stack of phones won't need much time on each. It seems 
like pulster might set up something like that - but they surely need a 
procedure, before they can train someone for the job!

I hope some thought goes into this for the gta03. Sound output from a 
phone obviously has low power, but it should be as hi-fi as the sound 
chip allows. Ideally, a balanced output that don't use (or need) caps. 
One can play uncompressed wav files, and use a high-quality headset or 
connect to a regular stereo system.  Openmoko could have sound 
enthusiast customers, as well as linux enthusiasts.

Helge Hafting

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