thud sound when shutting off

I just installed a system in my friends car. Including a Alpine headunit, 4 ch. amp, and a mono amp for subs. Currently it is wired so just the sub amp is in use. Plan to wire the 4ch. this evening. The problem is when you shut the car off the sub makes a "thud" noise. If you turn the headunit down or press the power button before shutting off the car it doesn't do it. Any suggestions? Thanks, ian cooper

Check the acc and constant wires on the radio and make sure they are wired correctly. Sounds like when you turn of the car you are taking the constant power from the deck and the radio is turning off before the amp does. Most decks have a remote delay so when they are power they turn on before They turn on the amps and the same when they turn off. They turn the amp off before turnig off themself.

Check to see if the amp has a quiet on and off feature, I know that my amp doesnt, and thats what happens, doesnt hurt anyhting it just takes the "subwoofer surprise" out of the stereo.

Check for "quiet on and off" in the amps owners manual, I know my Rockford doesnt have it but my alpine did.

Just check your connection I bet you have the wires backwards. I should know I have done it half a million times.

Thanks for the suggestions. I thought of the quite shut off thing. So I will look into that. When I was wiring the harness I was under the impression that the amp remote turn on was solid blue, the H.U. said it was blue/white, perhaps i'll change it to the solid blue see what happens. ian

Solid Blue is usually the power antenna wire. I'd stick with the blue/white. Something else you can try is installing an on/off switch for the amps. I use a simple rocker switch, installed on the remote line between the HU and the amp. They are easy to install, and you can get ones that light up as well, its all personal preference. Installing an on/off rocker or toggle switch will give you the control over the amp when the HU is turned on.Squirrel

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Install a 4.7K resistor inline of the remote turn-on lead to bring down the resistance of the wire to 5 volts from 12 volts.Jeff

Velocity Custom Home Theater

Mobile Audio/Video Specialist

Morden, Manitoba CANADA

HUmmm ya i know about the rocker switch I have one in my car. I like the resister idea, I shall have to try that. Do you think it could be a poor ground? ian cooper