[gta02-core] Audio rework

Rask Ingemann Lambertsen ccc94453 at vip.cybercity.dk
Thu Jun 25 19:24:34 CEST 2009

On Mon, Jun 22, 2009 at 04:27:19PM -0500, Rene Harder wrote:

> If we connect JACK_INSERT to the GPIO4 pin, the codec will switch
> automatically between earpiece and headset. However we still can select
> the output with the corresponding register settings of the codec.
> What do you think, is it necessary to do that in hardware?

   I think the GTA02 situation, where the hardware leaves a job half done,
is bad. If we do it in hardware we should get it right. The automatic
switching between speaker and headset in hardware would be useful in case we
support suspend during calls.

> We increase the cap size to at least 100uF (better more). This results
> in a dramatically increased physical size of the capacitor. I think the
> maximum capacity for a common 1206 ceramic cap is 100uF at 6.3V.
> (f_cutoff=50Hz @Z_headphone=32OHM and C=100uF)

   200 uF if possible, perhaps as 2x100 uF to keep the height down. See
The WM8753L datasheet uses 220 uF, see page 47.

> Also in the GTA02 schematics there are 33 OHM resistors in series of the
> headphone stereo path, they will increase the lower cutoff frequency but
> will limit the maximum volume of the headphone.
> Although it will increase our lower cut off frequency, I think we should
> remove those completely. Also wolfson doesn't recommend any resistor in
> the headphone paths.

   Removing the 33 Ohm series resistors would make it possible to attach
unpowered external speakers, wouldn't it? So IMHO go for it.

Rask Ingemann Lambertsen
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