Has anyone here built a noise filter?

[spooney]

Ever since I have installed my Pioneer head unit into my Ford Taurus I have had this annoying low level noise through the speakers both connected to the head unit and ones powered through a seperate amp. This leads me to believe it is the decks problem and not the amp. I have tried various ground points to no avail . I have checked the shield ground on my head unit and it is intact. The noise does not change volume or tone with the rev of the engine. It is just kinda of a random higher pitched but very low volume squeal that dies away completely at times. It is inaudible under most driving and listening conditions. I have considered buying one of those little noise filters they sell through parts express thats good for approximately 10 amps of current but then started thinking I might like to make my own if possible. Does anyone know of or maybe have a schematic for this type of thing that they may be willing to share.

[Perry Babin]

The noise may not be related to the 12v power source. I've seen it happen when the head unit, the speaker wires or the RCA cables were too close to electronics (OEM components) in the vehicle.

I'd suggest pulling the head unit out of the dash and disconnecting all speaker wires, the RCA cables, the antenna and any other cables (changer, etc...) that are not absolutely required. Connect a test speaker with short wires to one of the outputs on the head unit (with the head unit pulled out of the dash). Does the noise persist? If so, the noise may be due to the 12v power source. If not, slide the head unit back into the dash to see if the noise returns. If it does, the noise is being induced by something around the head unit. If it doesn't, re-connect one speaker wire at a time to see if the noise returns. Continue connecting the rest of the cables until you find the source.

[ppia600]

+1. Sometimes a dimmer/dash lighting circuit or fuel pump wire can be close enough to induct noise into the speaker wiring or if you're using passive crossovers the inductors in the crossovers could be close to a fuel pump or dimmer ciruit wire and pick up noise.