[maemo-users] Audio connection problem

From: Chuck Robey chuckr at chuckr.org
Date: Thu Mar 13 19:56:34 EET 2008
Hash: SHA1

Mark 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.

Yoiu original complaint didn;t seemo to list that you were charging at the
same time, I think that was guesses at by other respondents, which while it
doesn't rule it out (you could possibly have skipped that part) it makes it
a bit less likely.  However, the possibility raised of impednace mismatch,
that's a very large likelihood, and yes, it could possibly be corrected by
the proper repeat coil (transformer) being put in the way, or even a well
designed amp, though I would personally like the repeat coil idea bettter,
it would be less likely to inject even more noise.  I would hazard a guess
that from the very superior way that those teeny little speakers sound in
their native environment, they  probably went to quite some bother to get a
very good match there ... you'll need to be as exacting yourself if you
want to maintain the quality.  Nokia might respond well to a suggestion of
supplying some aftermarket device to serve as an amp/volume
control/impedance matcher, it wouldn't cost all that much probably, and
would probably be worth it to buy.   Be right up their alley,
designing/building/marketing such an article.

> Mark
> On 3/13/08, Larry Battraw <lbattraw at gmail.com> wrote:
>> On Thu, Mar 13, 2008 at 7:21 AM, David Hagood <david.hagood at gmail.com> wrote:
>>  > I have found that running the N800 through a ground loop isolator helps immensely - especially if you are charging the device as you use it.
>>  >
>>  >  The Radio Shack ground loop isolator (RS #270-054) works well for this.
>> Yes, this is key.  The n800 will transmit noise via the headphone jack
>>  if you are charging at the same time, particularly when charging from
>>  something from something that can leak tiny amounts of AC current back
>>  to the amplifier.  This is pretty much the case every time when
>>  charging and connected to a AC-powered amplifier or even a DC amp
>>  where you're using 120V inverter or 12V charger connected to the same
>>  battery.  That's why it's minimized when using a tape adapter; there
>>  is very little AC coupling between the tape read head and the tape
>>  adapter.  Like the ground loop islolator, an audio transformer will do
>>  the trick too (You'll need a 1:1 ratio on the windings).
>>  Just my 2 cents-
>> Larry
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