Lighter adapter noise

[RdJay]

I've added a Zune player into my car audio system and am powering/charging it with a 12V adapter the plugs into the cigarette lighter.

With the car not running I get a buzzing noise out my speakers. It goes away when I unplug the power adapter.

I'm looking for a simple, inexpensive solution to remove the noise.

Thanks in advance.

RdJay

[I Am An Idiot]

How are you getting audio signal into your system? Factory deck with an AUX in jack? FM transmitter/FM modulator? Aftermarket deck with AUX input?

[RdJay]

Originally posted by I Am An Idiot
How are you getting audio signal into your system? Factory deck with an AUX in jack? FM transmitter/FM modulator? Aftermarket deck with AUX input?

I purchased a device from Precision Interface Electronics (PIE) that plugs into the back (into the CD changer socket) of my OEM deck. I don't believe the problem is in the PIE device because if I unplug the Zune from the lighter adapter the noise goes away.

Last night I tried wiring the lighter adapter directly to where the power goes into the radio (I read something about "ground loop") and that had no effect.

I also plugged the lighter adapter into a separate power source from the car (one of those "jump start" batteries with a lighter socket) and the noise went away. This leads me to think it's not the lighter adapter but something between the four (adapter, zune, PIE, OEM deck) that is causing the issue.

To try one last thing I changed the cable from the zune to the PIE and it also had no effect.

I'm pretty sure the noise is coming from the zune because when you push buttons or the screen goes dark the noise changes.

Thanks, RdJay

[djQUAN]

you could use a ground loop isolator between the zune and PIE. one thing though, cheap ground loop isolators degrade sound quality.

[RdJay]

Originally posted by djQUAN
you could use a ground loop isolator between the zune and PIE. one thing though, cheap ground loop isolators degrade sound quality.

I'd like to avoid the ground loop isolator because I've heard they degrade the sound quality. Any other way to either eliminate or filter out the noise?

[I Am An Idiot]

A ground loop isolator is a directional device. The only way it will degrade sound quality is if it is connected backwards.

[ppia600]

Use a switching power supply instead of one with a simple ic. I have one that has selectable voltages and a switching power supply like an audio amp has. It creates no ground loops which is what your problem is. You can use the ground loop isolator like others have said and you probably won't be able to hear any signal degradation.. or do a long search for a power converter with a switching supply. That is why there was no noise when you used a "floating" power source, because the grounds were not conflicting.

If you can't find one, a few of the guys here could tell you how to build the switcher. Basically a small transformer, a couple of small transistors, some diodes a few caps and a switching circuit. I have one I got at a flea market several years back and didn't realize how cool it was until I opened it up. Its not the typical type that just uses a dc regulator circuit.

[tsmith1315]

Any other way to either eliminate or filter out the noise?

The only way to eliminate it is to remove the ground loop.

For grins, try wiring to the OEM HU power again, but run the ground wire to the case of the HU. Stranger things have worked.

Otherwise, a quality ground loop isolator will be the easiest fix (unless ppia600's switching supply is cheaper) and I also doubt you'd hear any degradation.

BTW, what does a decent GLI cost these days?

[ppia600]

/\ anywhere from $7 to $15. They just use a couple of isolation transformers, one for each channel. You could just buy the transformers at radioshack and build it yourself but time = $.

Also, I think the mcm part number 29-3340 might be a switching type. Its only $10 too. I just noticed it while reading the sales flyer.

[RdJay]

I picked up a SNI-1 from Pac Audio (recommended by I Am An Idiot) http://pac-audio.com/products/produc...oise%20Filters last night for $20.00 and it has done the trick. Because this is a directional isolator I had to buy two male/male and two female/female RCA plugs to make it work.

Noise completely gone and I don't notice any sound degradation, at least not enough to be a bother in a vehicle.

BTW tsmith1315, I tried the ground to the case but no change. The switching power supply is interesting and might be worth trying. Not sure if the mcm one listed by ppia600 would work (doesn't list 5V as an option)?

Thanks for the help.

RdJay