Mono audio output on GTA02?

joerg joerg.twinklephone at
Sat Feb 9 01:33:18 CET 2008

Am Sa  9. Februar 2008 schrieb Clarke Wixon:
> joerg <joerg.twinklephone at ...> writes:
> > The amp is for the speaker(s) only, and GTA02 has only one of 
> > them (mono). That's fine, for one good speaker will yield a better sound 
> > 2 small ones.
> Unfortunately, I don't think we're getting "one good speaker" in the 
> The second speaker was removed to make room for WiFi, so the remaining 
> is likely to be of comparable (identical?) quality to half of the original 

:-( Anyway, 2 speakers don't make a stereo output yet, when built in such a 
small case. So it's  not so bad to lose one of them.

> But you're right, the headphones should still be fine.

However without circuit diagrams, we can't say for sure what they 've done and 
why. Seems i was wrong with direct connection of HPh to codec chip.

see spec of wolfson mixer codec chip:
On-chip Headphone Driver with cap-less output option
- 40mW output power on 16Ω / 3.3V
- with 16Ω load: SNR 90dB, THD –75dB
- with 10kΩ load: SNR 94dB, THD –90dB
On-chip speaker driver with 0.5W into 8R

I don't know why they use a dedicated amp LM4853, which is good for nothing it 
near same power, mono *OR* stereo output, no capacitor-free bridge out for 
stereo. Additional parts needed for headphone detection to system.


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