I would like to know the best way to filter DC current in car. What I currently have is a power supply based on switching step-down converter to convert on-board voltage to 5V. This power supply was used for charging my PDA in car, but as it has a very big power reserve (max 2A@5V), I connected some additional devices to it as well.
One of these devices is a Bluetooth stereo receiver which is connected to AUX input of head unit (HU) and is used to stream music from PDA to this HU. But the problem as we know is that in-car DC voltage usually has much AC noise. I can hear engine revs through speakers, fuel pump or something similar (constant noise while engine is on).
Whay I want to know is a best way to filter all this junk. It definitely comes from power source, because I also tried a mains AC-DC power supply and there was no noise at all while receiver was placed in the same place in car.
What do you suggest? Ferrite beads? Chokes? Power supply shielding?
I suspect best way would be to use choke designed for audio frequencies, but where to put it? Before power supply or after? Or maybe in both places to have a better efficiency.