[gta02-core] Audio ECNs, a bit of progress

[Werner Almesberger]

Rene Harder wrote:
>>   I wonder if we shouldn't get rid of R4405/7 completely instead of
>>   making them 0R. We'll have to add some EMI and ESD protection, so
>>   there will be room for interrupting the circuit, if necessary.
>>   
> 
> Thanks, I planed on removing them that's why I wrote this into the ECN.
> Actually, I wanted to discuss this first but I probably forgot about it.
> Any comments? Otherwise I'll remove them.

I'd say kill 'em. With all the little audio changes, having fewer
components to squeeze in can only help.

>> - rear ECN: merge 18 pF + 47 pF into 56 pF
>>   
> 
> Do we have already 56pF in the BOM or does that mean we need a new
> component?

That's a new component. Luckily, we remove the uniques C4119 and
C4122, so the number of different components stays the same. Oh,
and I should have written 18 pF + 39 pF -> 56 pF.

> This needs to be checked more in detail because we'd use polarized
> tantalum caps for output coupling which can get damaged when operated
> inverse.

WM8753L manual page 46 says that the output can be connected to VMID
via 40 kOhm (or is it 90 kOhm ? the table says 40, the text 90.)
However, if the user forgets to switch to line in mode before
connecting external equipment, the scenario may be less happy. Hmm,
how is this usually solved ?

- Werner