On Friday 21 January 2011, Hrabosh wrote:
Hi guys,
yesterday I opened my freerunner to check whether mine FR is affected by
R3004 issue [1].
It was, I put a piece of wire there instead of those two caps and volume
got better!
I have also connected sine wave from generator to the WD8753 mic input
and cheched it on the WD8753's output with the oscilloscope. It seemes
that the audio codec chip gets into trouble (distortion, oscillations)
if the overall audio path has higher gain than 1. I'm going to write
more about this soon, with the scope pictures included (taken by my
camera, I don't have DSO at home :-/ )
That would be interesting to see, but your summary seems wrong or perhaps
oversimplified. Distortion is inevitable if you overload an amp, and
oscillation isn't unusual immediately after overload. It isn't a function of
the overall path gain though. The wolfson has a chain of amps and volume
controls, and it only needs overload at one of them to introduce distortion.
Stick the gain too high on the first stage (mic input) and the distortion
won't go away no matter how far you turn down the gain on later stages. This
has been a long standing problem with the default volume settings.
Yes, it is oversimplified. It is obvious that you can't fix distortion
by lowering the gain of next-in-chain amplifier. You are just
controlling the volume of already distorted signal.
I put that picture from my scope with a short description to my web
page, here:
http://hnet.endofinternet.net/elektro/Freerunner/ALSA/sound_setting.html
I was very surprised how LOW I had to set the audio controls to get rid
of distortion:
Mic2: 0
Sidetone: 1
Strange ...
Great work, thank you very much!
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