Hello,

Some of you may remember me posting here a few times in October looking
for a head unit to replace my dying Kenwood X659. I'm happy to report
that, though I had to compromise a bit on separate high-pass filters
for the front and rear speakers, I found what I was looking for in a
Pioneer DEH-P4800MP.

For the past couple years I've been using my Rio Karma (portable mp3
player) as my only music source in the car. I used to run the RCA out
from the Karma to the aux in on the Kenwood, then plug the charger for
the Karma into the cigarette lighter. This worked fine with the
Kenwood, but plugging in the mp3 player's charger with the Pioneer
causes annoying noise in the signal. I'm almost sure it's a grounding
problem. I have the Pioneer hooked up exactly like the Kenwood, so the
Pioneer must use a less robust grounding system. I wired everything to
the factory-to-aftermarket wiring adapter that's been installed in the
car as long as I've had it. It's a '96 Toyota Avalon, if that makes a
difference.

The way I see it, I have three options:

1. Track down the source of the grounding problem and correct it.
Easier said than done. This probably means I will likely have to hook
up the charger to something other than the cigarette lighter, meaning
that I'll have to take the guts out and do a bit of rewiring. I may
need to ground the unit to the chassis, mean more running of wires in
tight spaces. To me this is a big hassle, as I truly loathe dragging
all my tools down to the driveway and working in the fading light after
I get home from work.

2. Interrupt the ground at the RCA out from the mp3 player using a pair
of 1:1 signal transformers. This is probably the least amount of work,
and is essentially free. It would take about two hours to build and
install. I'm worried about my signal integrity, though, since I don't
know anything about the source and load impedances. Also, there is a
possibility of induced noise from the transformers.

3. Build a new isolated DC-DC converter for the Karma. This is the most
expensive proposition, but is also the easiest. I'd have to order parts
on the internet, but I could build the new supply in the housing for
the old one, then just plug it in and go.

Anyway, I realize that most of you probably don't know what the heck
I'm talking about with 2 & 3. I know grounding problems are common in
stuff like this, though, so I'm hoping someone may have some insight or
any easier path to pursue. If I thought I had a really clear idea of
what to change in my installation to fix the problem, I'd be inclined
to go with the first option. I just don't want to spend hours poking
around and trying to rewire stuff in the dark. Any advice at all is
much appreciated.

thanks,
Jason