[maemo-users] Audio connection noise - NOT SOLVED! [was: Audio connection problem]

From: Chuck Robey chuckr at chuckr.org
Date: Sat Mar 15 19:25:11 EET 2008
Hash: SHA1

Mark wrote:
> It's *obviously not* charging, if it's not connected to any power
> source whatsoever other than its own battery. It's just as obvious
> that the source of the noise cannot be fixed with any
> power-source-related device for the same reason. How do you connect a
> GLI or anything else to thin air? Everybody seems to be focused on the
> car audio/power input aspects, when I've repeatedly said that this
> problem exists regardless of what line-in I try to connect to; car,
> home audio receiver, boom box, or wireless headphone transmitter, and
> that the presence or absence of external power input makes absolutely
> no difference. The only two situations where I don't get the noise are
> from the built-in speakers or any set of headphones.
> ... And *I'm* the one who said that *factory* car stereos don't have
> audio noise problems but aftermarket car audio components frequently
> do, and that there's clearly something other than ground loop at work
> because using the same wiring hookups should give the same result.

That's utterly false.  You could use the same the same hookup to an ancient
3 transistor AM radio as to a modern AM stereo unit, would you expect the
same performance?  It's not even true when you have exactly the same units
in every part of your wiring, both because there are switch selections
tahat can affeect thigns, and because one unit can simply have a noisy
componenet in it.  I think really that you meant to say something else,
because this is so obvioiusly incorrect.  Why don't you try again on that?

> ground loop is really such a common problem and so easily/cheaply
> fixed, then why isn't an isolator built into every aftermarket unit?
> (Obvious answer: that's not really the problem...)

Coming from someone who has several times been in on professional noise
hunts, noise problems really are most commonly the cause of the same
thjings, over and over and over again.  Clean your connections, and if you
do that, you fix 50% of all noise problems, either big or small, either in
small user environments or in multimillion dollar installations, it's
always true.  Grounding problems are another huge source of problems, why
do you think that pros are always harping on this?  It's because, time and
time again, it turns out to be the case.  Want to make a BUNCH of money?
I'm not joking here.  Sell yourself as a noise expert, and when you get to
a new installation, bring a heavy wire brush, a set of good wrenches 9for
tightening connections) and, believe it or not, a big pot of grease,
because greasing the connections keeps the oxides off them.  Do this in any
big installation, and I guarantee, beyond question, you will bring the
noise down, and you will be paid huge bucks for your time.

People just never seem to learn.  Yes, there are other reasons for noise,
but what I described about accounts for such a high percentage of noise, it
will form the basis for a nice career.  If you have a bit of a patter for
the other 3% of the cases (yeah, only 3%) you can retire wealthy.  It's
rather disappointing, even hard to believe, that this is really true, but
go ask pros, say folks who work on big communications networks like I did.
 The only thing wrong with your common sense approach is you're relying too
much on the fact that people learn, and see the obvious when it's in front
of their faces.  That's a somewhat innocent approach, isn't it?

>>  There are two reasons that you say (below) that the ground loop isolator
>>  might help noise, and they're both equally likely.  One would indeed be
>>  ground loop problems.  The other would be impedance mismatch problems.  You
>>  might not care which fixes your problem, but if you jump at the easiest
>>  guess, it's going to cost others who hit this problem (and rely upon your
>>  assumtions) some woe, if their problem isn't fixed by such a solution, by
>>  (for example) a ground-loop-isolation system that didn't incidentally fix
>>  the impedance mismatch, something easily possible.
> ...and the "easiest guess" would be ground loop problems, because
> that's every car audio engineer/seller/installer's pet solution. It's
> both easy and cheap to remedy, never mind the fact that it's
> frequently *not* the problem and always has limited success...
> So how does one go about fixing an audio impedance mismatch with a
> GLI? Does than mean I'm going to have to rig up a special audio cable
> that is permanently wired into the vehicle via a GLI? What would the
> schematic look like? How does it translate to my home audio gear? Am I
> going to have to crack those open and hack their wiring?
> (Rigging it into the Nokia's power supply wouldn't work, because
> frequently the Nokia isn't plugged into it.)
>>  I can't tell you which it was, without further testing, but I CAN tell you,
>>  from bitter experience, jumping to conclusions that aren't truly justified
>>  can really burn the hell out of you.  Just don't want to spread FUD.  When
>>  dealing with noise, it;'s ALWAYS a complicated subject, because there are
>>  multiple sources that usually all contribute together.  Sometimes, fixing
>>  the worst one is enough, but if you're a real stereo enthusiast, well, you
>>  get my implication?
> Who's jumping to conclusions? You're the one trying to apply a pet
> solution to a situation to which it doesn't apply!
>>  I'm pleased that your problem is fixed, though, and maybe that's sufficient
>>  for you.
> My problem is *not* fixed - no one has come up with anything that
> applies, much less works!
> From the sound of it, though, I'm the only one having this problem,
> which leads me to believe that the problem is more serious, and that
> it's a defect in my particular unit. Maybe the circuitry that turns
> off the the loudspeakers and switches the output to the headphone jack
> when a plug is inserted isn't fully switching over, and the hanging
> output is what's causing the problem. The load & impedance
> characteristics of the speakers/headphones as opposed to line-inputs,
> combined with the fact that there is no additional downstream
> amplification, might explain the symptoms.
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