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

Joerg Reisenweber joerg at openmoko.org
Sat Nov 15 16:56:10 CET 2008

Am Sa  15. November 2008 schrieb GNUtoo at no-log.org:
> Hello, I've the same issue as described here:
> That is to say the "Poor low-frequency audio response with low-impedance
> headphones" problem...
> On IRC I was told that was the fault of a capacitor that lies between the
> audio chip and the headphones jack that is too low and act like a
> high-pass filter and so removes the bass...
> This issue is very problematic for me:
> I've a pma430 that I use like an audio player(linux device with
> proprietary kernel modules and an old proprietary version of qtopia)...but
> it's an old device...and one day the battery will die...
> Moreover it has a lot of bugs that I can't get rid of:
> *mplayer for the pma430 is buggy and I don't have its sources(it's a
> special port because the sound drivers are buggy or specials...)
> *the default player is buggy and I often have to restart the device
> *the suspend button is often pressed when the device is in my pocket...and
> because of the proprietary nature of the device I don't think this could
> be changed...otherwise the openpma devellopers would have changed that...
> So buying an openmoko I thought that I would get a device that would
> replace it as:
> *a real GNU/Linux pda(done(the compiler of the pma430 couldn't be changed
> because of a kernel bug and the kernel couldn't be changed because of the
> proprietary modules,but with openmoko we have openembedded and a lot of
> software))
> *an audio player(here's the problem)
> The problem is that the software fix suggested by the wiki isn't
> sufficient for proper audio quality...
> So what are my options?
> solder myself the capacitor isn't an option...I'm not skilled enough nor
> have the right soldering iron(Long time ago I've broken a graphic card
> trying to do a mod that would make the nvidia drivers recognize the card
> as a quadro card...(the card was sometimes recognized by the 3d driver and
> sometimes not))
> So what sould I do?
> find a shop or someone that would do it for me(I live in Milan in Italy)?
> use the guarantee(I bought it at bearstech)?
> Or would a better software fix be possible(such as re-encoding the ogg
> with special filters?,but that would be problematic as it would use a lot
> of space for keeping the files on my computer...but if it's the only
> option I'll use it)
> adding an external sound card isn't an option either because if I use it
> in my home on a hifi-set I would not be able to feed the openmoko in
> power(as the usb port would be taken by the audio card) or if I use it
> outside...a sound card isn't very compact...
> By the way for determining the version of my hardware, I think I've got
> the hardware fix for the GPS and I bought a released version of the GTA02
> Thanks a lot in advance for your help.

Sorry the audio is definitively broken due to the capacitor issue you're 
mentioning. There is no sw-fix either.
You may get (semi)decent audio by:
o- using a home-stereo line in, which has >1k input impedance
o- using high impedance headphone (>600 Ohm)
o- do a rework on the capacitors (there are different ways to do that, all 
need excellent soldering skills)
o- use a bt-headset

very sorry I didn't achieve to fix this for MP yet
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