Car Stereos: high level to low level converter, rca cables, level converters

Question
I am working on a 2005 Jaguar VandenPlas.  I have installed a high level to low level converter so I can install a woofer in the car.  I get a strong humming noise when i power up the amp.  What are somethings I should be looking at to eliminate the noise?

Answer
Hi Mooky,

Your issue will either be ground loop, or signal interference.

First, for ground looping:

Ensure that your amplifier is grounded out on bare metal with no paint on it.  Make sure it makes a very clean connection, is bolted tightly to the car chassis with no welded parts preferably.  And make the ground wire as short as you possibly can.

Second, for signal interference: make sure that your RCA cables themselves are as far away as possible from power wires, and if they have to cross, they do it perpendicular to one another.

One of the downsides to high -> low level converters is the possibility of ground looping and engine noise since high level signal outputs are more susceptible to interference.

If it continues to be an issue, your only real fix might be to get a deck with low level outputs, or rewire the factory speakers with better shielded high level speaker wire.

Good luck,
Justin