Line out for Sansa E200?

[PolloLoco]

I have a Sansa E280 that I promptly rockboxed using the current build.  I use it in a Griffin Power Dock which features a line out - to a mini amp and headphones.  If I boot the current Sansa firmware, modifying the volume has no effect on the line out - which is what I would expect.  My mini amp makes the player sound great.

However, if I use my rockbox setup - the volume varies as I move the wheel.  The sound quality seems to suffer as well - though that might be my imagination.

Does rockbox disable true line output from the Sansa E200?  Or do I have to enable it somehow?

Thanks.

[saratoga]

I skimmed the code and the datasheet for the DAC a while back, but couldn't see any obvious reason why this should be happening.  If I get a chance I'll check again later. 

[PolloLoco]

Thanks for the reply - and good luck with the research. 

Since posting, I found a very long thread on the Anything But Ipod forums, and saw that someone was able to fix the issue by recompiling Rockbox with a modified dac.  He reported little change in audio quality, but less noise than through the headphone jack.

That's significant to me, since I believe my portable amp is magnifying the noise.  I'm hoping there's a build out that's already included the fix - because I don't yet have the experience to recompile Rockbox on my own.

Here's the reference thread from ABI:

http://www.anythingbutipod.com/forum/showthread.php?t=3387&highlight=line

The post highlighting this issue in Rockbox is number 73.

[saratoga]

That's significant to me, since I believe my portable amp is magnifying the noise.  I'm hoping there's a build out that's already included the fix - because I don't yet have the experience to recompile Rockbox on my own.

Here's the reference thread from ABI:

http://www.anythingbutipod.com/forum/showthread.php?t=3387&highlight=line

The post highlighting this issue in Rockbox is number 73.

He says the line out is disabled in rockbox, which is obviously false if you're able to use it, so I don't know what hes talking about.

[PolloLoco]

He says the line out is disabled in rockbox, which is obviously false if you're able to use it, so I don't know what hes talking about.

You are, of course correct.  I wonder if he misworded  it when he described the line out as disabled.  I can confirm that the output is not line level as compared to the official firmware.

[Llorean]

At least via the headphone jack the OF has shown signs of digitally altering the gain (the option to choose whether the volume is normal or loud, if I recall correctly) so the OF may not be the best signatory of what "line level" is for the hardware. Not saying it isn't, but it bears consideration.

[eevan]

I've just looked to the AS3514 block diagram and the relevant audio path goes like this: I2S -> 18 bit Stereo DAC -> Stereo Gain -> Mixer -> AGC -> Line_Out. The last block has the level control 0..–46.5 dB, 2*32steps + mute. So, the line out level from this codec can be programmed. „Stereo Gain“ block has to be set to 0 dB.

This document also states:

Line Outputs
– volume control via serial interface
– 32 steps @1.5dB and MUTE
– 1Vp @10kΩ

[PolloLoco]

Does that mean that line out would still allow volume modification per the Sansa specs?

I was just concerned that in Rockbox, line out merely meant a duplication of the headphone port.  I know that a firmware update to the official firmware locked down the volume of the Sansa's line out.  Originally, it was affected by the volume wheel.

[eevan]

That's right. The AS3514 codec allows that. So it depends on a firmware how the codec will be used.

I'd set the Mixer and Line_Out gain to 0 dB and shut off the AGC (if it can be done, I have no datasheet):

[PolloLoco]

Thanks for the help.  I'm not sure where the Mixer and AGC modifications are made, but I did set the volume gain to 0db on the Sansa - and ramped up the volume on my portable amp.  As a result I've gained the clarity I was expecting and had noticed from the official firmware.

By playing around I noticed that if I modified the gain too much - then I'd introduce a good amount of noise.  I have to say, that outside of the noise factor - I don't notice any improvement in sound over the headphone port.  But that noise reduction IS DEFINITELY significant.

[bertrik]

The reason that the line-out level changes when changing the volume is that in the current situation, the total 80 dB volume range is achieved by changing both the mixer gain and the headphone gain. The mixer gain influences the line-out level. Going from silent to loud, the mixer gain is first turned up until some maximum value after which the headphone gain is increased.

To keep the line-out level constant, the mixer gain could be set to a fixed value but that would reduce the total volume range to just the 48 dB that can be set in the headphone stage.
Maybe a nice compromise would be to make the line-out gain stage exactly compensate for any changes in the mixer stage.

I won't mind coding up some proof-of-principle code for you to try.

[PolloLoco]

Thanks Bertrik, but I think I'm satisfied with the current solution offered by just setting the overall volume to zero.  Since I see no option to set the mixer volume independently - I assume I'm setting it via the overall system volume?

Probably the main reason I'm not anxious to try new code, is that I'm a major newbie, and my simple attempts to try different versions of Rockbox have resulted in failure.

[bertrik]

OK. I think this would be a nice chance to improve rockbox. I guess this part of rockbox is not normally tested very well since there are not that many people with a dock.

[PolloLoco]

If you'd like to test it as an opportunity to improve Rockbox - I'd be happy to try.  If you could recompile Rockbox to include your code - I'd install it and test vs. the offilial firmware.  Let me know.

I ended up buying an E280 to experiment with, within hours of hearing that it offered a true line out.  I saw that the docks are pretty inexpensive as well. 

My Cowon X5L started to die, and I needed something to tide me over temporarily.  Though the Sansa definitely doesn't have the sound quality of the X5L, it's also filled the niche of a sport mp3 player at a very cheap price.  So I'm quite happy with my purchase.

Let me explain my previous retisence - I was unwilling to try code when I thought it would only help me, because I'm fairly happy with the current setup.  But if it helps the community - I'd be happy to test it out to try appropriate line level output.

[gorman]

Any news on this?

Do I understand things correctly if I think that by setting volume to 0 I'd be getting "true" line-out results?