how to isolate input ground?

[Zero Cool]

I need to build a simple opamp based preamp/buffer for an automotive project.

The Buffer is going to be used to interface an MP3 player to a car stereo. the problem is, a ground loop is created when the charger is plugged into the MP3 player as well.

Now the ugly cheap and easy solution is a radio shack ground loop isolator. yuck.

I need to come up with a better solution to do this.

The audio coming out of the MP3 player is unbalanced with a common ground. I have balanced inputs available going into the car stereo, or it can be used unbalanced. The radio shares ground with power, data and audio internally.

I dont have much room inside the case to hang iron and getting small, high quality iron is difficult and costly. so i am looking for some other solution.

Can i simply tie the opamp input neg side to ground through a 100 ohm resistor? Would that be enough to break the ground loop? I thought i had seen that done elsewhere. But wouldnt noise on the ground line then inject noise into the neg side of the opamp?

Help would be greatly appreciated.


Zc