Audio ECNs, a bit of progress

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Audio ECNs, a bit of progress

Werner Almesberger
Some news from the ECN front:

- I finished ECN0031, which describes how to use the codec interrupt
  for HOLD and JACK_INSERT instead of involving the CPU directly.
  This is from Joerg's "Mega-ECN".

- I updated ECN0015 (removal of the Calypso's rear entrance through
  the audio jack) with the changes that have actually been done.

  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.

  Once the final fate of R4405/7 is decided, we can move ECN0015
  to "Done".

- we have one regression: the ESD protectors D3001 and D3002 (at
  the front speaker) were lost in translation.

I still have more items to process from the "mega-ECN". Here's my
"to do" list:

- new ECN: add ESD to jack

- buzz prevention: remove 22 pF caps around jack, place EMI filters
  (C4403, C4404, C4405), remove common-mode choke B4102

- bass fix: add component, remove R4405/7 (0R for us)

- bass fix: big caps (~100 uF), tantalum, no cer

- new suppression:
  we might consider making each of C3012/13 a 4u7 + 47p couple
  as that should rather completely short any RF induced to the "hot" side of
  those C (chip side) to GND

- buzz fix: provide place for bigC

- rear ECN: merge 18 pF + 47 pF into 56 pF

- new ECN: swap rear choke / caps

- new ECN: remove C3020

- new ECN: increase input caps from 100 nF to 1 uF (ceramic)
  (1uF) according to wolfson appnotes
  - mic out caps
  - RXN/RXP (modem to codec)
  - MONO1/MONO2 (codec to modem)

- new ECN: route LOUT1/ROUT2 back to LINE1/LINE2

- make sure C3012/13 are well separated from micbias and any other source of RF
  iirc there's even a special note about those 2 C in 8753 app notes

Lots of small critters ...

- Werner

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Re: Audio ECNs, a bit of progress

Rene Harder
Werner Almesberger wrote:
> Some news from the ECN front:
>
> - I finished ECN0031, which describes how to use the codec interrupt
>   for HOLD and JACK_INSERT instead of involving the CPU directly.
>   This is from Joerg's "Mega-ECN".
>  

So far, looks good to me, I'll do a full review later today.

> - I updated ECN0015 (removal of the Calypso's rear entrance through
>   the audio jack) with the changes that have actually been done.
>
>   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.

>   Once the final fate of R4405/7 is decided, we can move ECN0015
>   to "Done".
>
> - we have one regression: the ESD protectors D3001 and D3002 (at
>   the front speaker) were lost in translation.
>  

Right, they got lost. I'll add them.

> I still have more items to process from the "mega-ECN". Here's my
> "to do" list:
>
> - new ECN: add ESD to jack
>  
Yes, it's probably a really good idea to add ESD protection to all pins
of the Jack as it is in Joerg's  proposal.

> - buzz prevention: remove 22 pF caps around jack, place EMI filters
>   (C4403, C4404, C4405), remove common-mode choke B4102
>  

I'd definitely go for the Pi filter in all of the headphone lines and
remove B4102.

> - bass fix: add component, remove R4405/7 (0R for us)
>
> - bass fix: big caps (~100 uF), tantalum, no cer
>
> - new suppression:
>   we might consider making each of C3012/13 a 4u7 + 47p couple
>   as that should rather completely short any RF induced to the "hot" side of
>   those C (chip side) to GND
>
> - buzz fix: provide place for bigC
>
> - 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?

> - new ECN: swap rear choke / caps
>
> - new ECN: remove C3020
>  
Sure, it's NC right now, so there shouldn't be a problem with removing
C3020.

> - new ECN: increase input caps from 100 nF to 1 uF (ceramic)
>   (1uF) according to wolfson appnotes
>   - mic out caps
>   - RXN/RXP (modem to codec)
>   - MONO1/MONO2 (codec to modem)
>
> - new ECN: route LOUT1/ROUT2 back to LINE1/LINE2
>  

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.


Rene

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Re: 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

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