engine noise when using MP3 jack

[jahern]

I have an 07 Mazda3s with the aux. input jack in the armrest console. It works fine, unless I use *either* of the 12V DC plugs to power/charge the mp3 player. Then I get alternator whine and ignition noise (one's a whine, the other a fast ticking that changes with RPM).

This is true whether I use my Archos player with it's 12 V cord (I've actually tried aftermarket adapters, too), or my zut capri Tom Tom 910, with its rather bulky, fancy 12V adaptor. Do others have this problem, or should I take it in (car has about 1200 miles on it!). Yes, I can run w/o charger, but not on long trips. Oh, I've tried ferrite cores on every combo of DC line, audio line, both, both players, etc. Thanks for any help! - Jud

Some additional info:
A friend says he thinks it is a ground loop. He's a lawyer with an EE undergrad and Extra class ham, so he may well be right. But it seems odd, especially if you use the 12V jack that's inches from the aux input. You'd think they'd be grounded to each other or at least to 2 point very close to each other. AS I understand it, ground loop results from potential difference from using 2 grounds with significant resistance (voltage drop) between them,

 

[icspots]

It is infact a ground loop. It's not so much that the audio port and the 12v port need to be grounded together, as it's the difference in grounding potential between the HU and the 12v port.

Crutchfield sells a 3.5mm-3.5mm ground loop isolator for about $17. You can also get one from radio shack, however it's RCA-RCA so you'd end up having to buy adapters to get it all hooked up. That and the crutchfield one is smaller and flatter so it's easier to hide.

 

[DusterAZ]

I ended up getting the Radioshack one a few weeks ago and it fixed the issue on my MP3 player (Creative Zen Vision: M).

 

[terpkristin]

Some additional info:
A friend says he thinks it is a ground loop. He's a lawyer with an EE undergrad and Extra class ham, so he may well be right. But it seems odd, especially if you use the 12V jack that's inches from the aux input. You'd think they'd be grounded to each other or at least to 2 point very close to each other. AS I understand it, ground loop results from potential difference from using 2 grounds with significant resistance (voltage drop) between them,

Yep. I concur with your EE undergrad/Extra class HAM friend (how on EARTH did he end up a lawyer?!). The ground loop isolator has been mentioned in this thread already, though if you need a direct link to the one at Crutchfield that requires no extra setup or cables, this is it:
http://www.crutchfield.com/S-kKub65...81150&I=127SNI135&search=ground+loop+isolator

/tk

 

[jahern]

Thanks

Thanks to all for the info. It figures Mike would be right. I have a GLI on order from Crutchfield. Whis I'd had it the last 36 hours, because I drove 10 hours up to Springfield, Mo, and back the next day! And found out my air conditioning is feeble, but that's for another forum, and for Mazda to fix.

 

[Smoke286]

I ended up getting the Radioshack one a few weeks ago and it fixed the issue on my MP3 player (Creative Zen Vision: M).

I have the same mp3 player and I bought my mp3 adapter at Radio Shack, are you saying I can buy a car charger for it from radio shack?

 

[Rotus8]

I have the same mp3 player and I bought my mp3 adapter at Radio Shack, are you saying I can buy a car charger for it from radio shack?

No, you need a ground isolator that goes in the audio connection.