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