[sound]: capacitor that act like a high-pass filter and so removes the bass on the headphones jack

Joerg Reisenweber joerg at openmoko.org
Fri Nov 28 19:22:44 CET 2008

Am Sa  29. November 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> |> I think I understand. I built one 10 F capacitor into the adapter (at the
> |> mass), so the problem with the headphones should be fixed. I also
> measured a
> |> 1,59V current at the capacitor when plugged in and silent. Sound is
> good as
> |> before.
> |
> | It's beginning to sound very appealing.  I was very disappointed to
> | discover that my FR is unusable as an MP3 player (and I'm not demanding:
> | I usually find 64Kb/s Vorbis files good enough for such a use).
> |
> |> Unfortunately, the internal speaker sounds really bad now (distorted).
> |> So I think i'll remove the silver again and find somebody who can help
> |> me with the soldering...
> |
> | Hmm... why does it distort the interal speaker?
> With the caps the transducer experiences -~1.5V .. +~1.5V worth of
> deflection "down" and "up"; without the caps it experiences 0 .. ~3V
> worth all "up".  So it's physically unable to deflect enough linearly I
> would think.

Please note the internal speaker isn't connected via the 1uF capacitors. 
See "SPK LOCATION:41XX" page6 schematics GTA02.
So shorting them will not directly cause a different DC-offset situation on 
internal speaker, and shouldn't make any trouble for it.
A short to GND when applying the silver-varnish on the other hand might cause 
the distortion you have heard.

I won't recommend shorting the DC-blocking capacitors. A decent rework/fix 
comprises finding a place for 2 100uF, and then connecting these in parallel 
to the 1uF, preferably by by shielded two-wires-cable. If these big 
capacitors are located outside can, I strongly suggest to place a ferrite 
bead directly on the hole where the cable enters he can, to block RF from 
entering the can (homebrew buzzissue).

BTW: be aware you easily may destroy headsets or speakers by applying DC for 
prolonged periods of time. Strongly deprecated.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 194 bytes
Desc: This is a digitally signed message part.
Url : http://lists.openmoko.org/pipermail/hardware/attachments/20081129/1236ad3a/attachment.pgp 

More information about the hardware mailing list