[Bug 1198] New: Audio (via headphone jack) doesn't couple well to some line-inputs

[bugzilla-daemon at bugzilla.openmoko.org]

http://bugzilla.openmoko.org/cgi-bin/bugzilla/show_bug.cgi?id=1198

           Summary: Audio (via headphone jack) doesn't couple well to some
                    line-inputs
           Product: Neo1973 Hardware
           Version: GTA01Bv4
          Platform: Neo1973
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Audio
        AssignedTo: sean_chiang at openmoko.org
        ReportedBy: cwixon at usa.net
                CC: buglog at lists.openmoko.org


Most equipment with headphone jacks can be attached to a stereo system with a
suitable adapter.  I have found that using a 2.5mm 4-conductor plug to 3.5mm
3-conductor stereo jack adapter to connect the Neo does not work in some
circumstances:

- it works fine when connected to regular stereo headphones

- it works fine when connected to some stereo line-in ports

- it makes loud, percussive, rhythmic noises (several times louder than the
content from the media player, for example) when connected to my car's line-in.

My car's built-in line-in jack is functional with all other equipment I have
tried, including a satellite radio receiver, and various MP3 players and PDAs I
have used in the past.  The Neo is the only device that makes these loud noises,
and it happens regardless of whether the engine is running, whether the Neo is
plugged into a power adapter, or whether there is any (intended) sound coming
from the Neo.

As described above, the adapter I have is apparently wired correctly, because it
works with headphones and some other stereo connections.  I originally thought
this was noise (of the sort encountered with intermittent/bad amplifier
connections), but continued listening at low volumes, without moving anything,
and the repetitive/rhythmic nature of the noises, indicate that this is
electronic noise of some kind, probably coming from the Neo.

I will try to find a cheap audio isolator (coupling transformer) in the next few
days to see if that makes any difference.  And if not, I will make a recording
of the noise and upload it here for further diagnosis.



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