[maemo-users] Audio connection problem

From: Larry Battraw lbattraw at gmail.com
Date: Fri Mar 14 00:58:36 EET 2008
On Thu, Mar 13, 2008 at 1:42 PM, Mark <wolfmane at gmail.com> wrote:
> I am very familiar with the ground loop problem, and this is not
>  related to that. Ground loop problems are a result of noise created by
>  other devices, whereas this noise is created by the Nokia itself. It's
>  also a completely different kind of noise - ground loops usually cause
>  a whine (that varies with rpm's in a running vehicle), but this is a
>  swishing white noise that seems to vary with the sound that the Nokia
>  is playing. Also, no other devices, including my standalone mp3
>  player, exhibit this noise when connected identically.
>  The reason the cassette adapter works is not because of isolation but
>  because of completely different power and impedance characteristics -
>  it's a lot closer to headphones than to a line input.
>  Mark

We're obviously talking about different things.  Mine only occurs when
charging and is a pronounce alternating hum and buzz as the n800 draws
current and pauses (Easy to see on a charger w/a LED).  It stops the
second I remove the charger.  To demonstrate my point about the
coupling I've connected the n800 to a switch-mode charger connected to
batteries: it removes the noise completely.  I used the term
ground-loop because from the reference of the receiver your input has
a ground, particularly if it's hooked to a PC as mine is which has a
grounded output.  The charger is not grounded and so floats in
reference to the receiver except for the AC current induced by the
switching of the power supply and current to the n800, coupled via the
mains lines going to both the receiver and charger.  Hence the noise.
It doesn't necessarily fit the classic definition of a ground loop but
was the closest thing I could think of.

I'm puzzled by your description of low output levels.  If anything,
with both the "speaker volume" and the application volume up all the
way I have to turn it down a bit to avoid overdriving what I'm
connected to.  The only thing I can think of is that you're not
resetting the device volume to the maximum after plugging something
into the headphone jack since that drops the volume automatically a
fair bit.
I've hooked it to plain amplified speakers, a guitar effects box, a
cassette adapter, a Sony receiver, and myriad other devices with and
without inline volume controls.  I really don't think impedance has
anything to do with it; my receiver measures at around 100K ohms for
the inputs which is essentially infinite compared to the internal
speakers or headphones and works well outside the charger noise.  I
did have one thought: when you connect it to whatever amplifier you're
using have you tried using a 4-conductor audio plug?  I believe the
tip is powered (with a pull-up resistor) to support the headset
microphone and your plug might be partially contacting that, causing


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