Audio Headphone Output

[martinayotte]

Hi,

Is there anyone who already tried the Audio Headphone Output on Debian ?
What need to be done to activate it ? any modprobe ? what is the /dev/<device> that should appear ?

Thanks in advance,

[martinayotte]

My goof : a chinese headphones with broken cable ...

But ... I discover that when no audio player is running, there is a lot of noise at the output ...

Any idea how to fix this noise ?

[rspock]

Same for me. Very bad audio!


Any idea?

[Scutum]

Hi,

I hear strange sound distortion on headphone output when music is played in android player but only when sound volume is low. On hdmi output seems to be ok.
Do you have the same issue?

[Scutum]

I've made some more investigation about audio distortions. Check my pictures from osciloscope...

http://imageshack.us/photo/my-images/211/ini8.jpg/
1khz, max volume

http://imageshack.us/photo/my-images/577/9u16.jpg/
1khz, min volume

http://imageshack.us/photo/my-images/838/3pci.jpg/
40hz, max volume

http://imageshack.us/photo/my-images/703/5ij2.jpg/
40hz, min volume

http://imageshack.us/photo/my-images/5/edms.jpg/
100hz, max volume

http://imageshack.us/photo/my-images/94/kkyn.jpg/
100hz min volume

I think that audio output from A10s is very bad quality or there is some bug in android. Someone can help in this case?

[LubOlimex]

Hey Scutum,

Thanks for the notification. We are investigating the issue.

Best regards,
Lub/OLIMEX

[martinayotte]

Just to let you know : I've start using gstreamer to stream a webcam attached to my A10s, and I discovered that Audio Headphone Output noise is becoming intolerable, I can almost ear every image frames ...
Looking at the schematic, it seems that the amplifier is built-in in the A10s chip itself, so is the problem faced on every AllWinner A10s chips, not only Olimex board ?

[XFer]

Don't know if it helps, but with A20, integrated (analog) audio quality is very good IF the board is not under heavy I/O activity.

If, for example, one starts reading/writing on SD, then a lot of background noise can be heard, to the point that (analog) audio quality becomes very bad.

Did not try digital audio.

Fernando

[olimex]

We've been investigating the problem for two days.

What we found so far is that if RM6 value is changed from 51 ohm as per Allwinner's recommended design to 22 ohm there is improvement in the sound quality and decrease in the low volume noise.

Also changing the inductors L13, L15, L16 that have value of 22 uH (in 0805 package) to ferrite bead 600 Ohms (in 0805 package) improves a bit more the sound quality.

We are going to upgrade the schematic with these changes and will take care  for the boards in stock to change these components.

Our tests were done with higher volume and this didn't allow us to detect these noises, to hear them the sound volume should be low.

Thanks again for the feedback and helping us to improve A10S-OLinuXino!

[benstmax]

I know this is an old topic, however I am still using the A10s OLinuXino Micro boards I bought a few years ago and I want to share my findings on improving the sound quality on these boards.
At the beginning of this week I decided to use the spare A10s I had in my stash as an Internet Radio.
I prepared the Linux image and the rest of the apps, however the sound quality wasn't good.
I decided to experiment a bit and change the parts on the output stage. My board is a Rev C and it had a 51 ohm resistor array. I put 22 ohms instead but the quality didn't improved much.
Then, I tried other arrangements and in the end I found one which works a treat.
The quality of the sound was hugely improved and I am now very happy with the results.
If anyone is still interested in this, let me know and I will prepare a schematic and a few pictures to share.

[LubOlimex]

We are all interested! Let us know what you did, we might try it and include it future hardware revisions of the board.

[benstmax]

I attached a quick schematic I put up in KiCAD. Later on today, I will take a picture of the actual board with the modifications and post it here.
I found out there is some noise when the microSD card is being used, however in my case, using the board as an Internet radio receiver, such a problem is not the case

[benstmax]

This is the list of parts removed/added:
- removed the RM6 resistor network (51 ohms each)
- removed L13, L15 and L16

- added R10 and R20 (22 ohms and 0402 size)
- added R11, R21 (100 ohms and 0603 size) - this is mainly because besides headphones I am also connecting a pair of PC speakers which have their own amplifier and I wanted AC coupling for the signal going towards the speakers.
- added C10, C20 (47uF) - I used this value because this is what I had available. I also used 100uF electrolytic caps (when I was tinkering with soldering various arrangements for the audio filter) and they worked very well too. I haven't kept these caps in the final version of the modification because the electrolytic caps were taking too much space

[benstmax]

And now the actual photos.

You'll notice in the middle of the 47uF caps a 0 ohm resistor. This was placed in order to disconnect if needed the HPCOM from the GND and experiment a bit.
And from another angle

[benstmax]

We are all interested! Let us know what you did, we might try it and include it future hardware revisions of the board.

Are these mods working on your side too? Thanks