[ANN]: GTA04 (Beagleboard inspired Openmoko Upgrade) - Early Adpoter Program

Hi Sam,

Please note that it does *not* include the LCD module, case and
battery, because it is a motherboard-replacement to existing
Openmoko units (Freerunner and Neo1973).

how much work is it to do this motherboard replacement? do we just unscrew our old openmoko, and put it in? does it need soldering? would it be reversible?

Yes - it is reversible.

It is essentially the following steps:

* remove battery, SIM, SD
* open the Openmoko (screws)
* remove the motherboard
* unplug the GPS antenna
* remove the Display (this is quite tricky without breaking the module or ripping off the cables)
* glue to the GTA04 motherboard
* scratch a little to widen the USB connector hole (the GTA02 has a Mini-B socket, the GTA04 a full OTG which is slightly wider)
* install the GTA04 board
* plug in the GPS antenna
* close the Openmoko
* install (different) SD card, SIM card, battery

We plan to make a video of this process.

If you don't want to tackle with the display I recommend to add a new display module for
the new board.

Also what has been done to improve sound quality?

Sound is handled by completely different components.

The main audio codec is within the TPS65950. The interface
to the UMTS module is PCM (digital). So the only deterioration
of sound quality is between the microphone and the TPS.

We have ordered a sample of a digital microphone chip. So we may
replace the analog path at all and make it more robust.

On the speaker power amplifier the TPS design has much bigger
coupling capacitors than the GTA02 had. So the "bass-fix" is
already designed in.


TPS65950 output amplifier is very very low, so the sound volume is low either.

2010/12/22 Dr. H. Nikolaus Schaller <hns@computer.org>

TPS65950 output amplifier is very very low, so the sound volume is low either.

What is “low”? What is “very low”?

That is relative and largely depends on the speakers and your expectations. You can’t expect
a subwoofer in a smartphone…

Output power of the TPS is specified with 400-700 mW (depending on battery voltage).

The Freerunner uses a Wolfson WM8753 and uses a LM4853 driver (with just 1uF
coupling capacitor which is a known design flaw). The LM4853 is specified as
“Mono 1.5 W / Stereo 300mW Power Amplifier” and is running in stereo mode.

From that I would deduce that sound quality and volume is not worse than a GTA02.

Doing real comparisons needs a little more work we have not yet done.
This is an area where the Early Adopters are invited to jump in.

I mean TPS amplifier has low power on output. I don’t have Freerunner speakers but Sennheiser headphones and others with the resistance 16-32 Ohm play with low volume.

2010/12/22 Dr. H. Nikolaus Schaller <hns@goldelico.com>