I have a 1991 Camaro, with Alpine 6x9's in the sail panels, 4x6 in dash (aftermarket, don't know brand). Added an amp and two 10" jl subs and a pioneer deh-6800 head unit. Got it all in and sounding great. Didn't start the car though. When I started the car, got wierd feedback through the amp/subwoofer combination. The subs will sort of 'tick' (only lower pitched) at about 1/2 second intervals. If the car is idling, sometimes will stop. But when the engine is anywhere above 1200 rpm, it's pretty bad. It's a mtx 240 amp. Only 100w per channel. Head unit is 50wx4. Has two rca outs and a seperate sub out. It's definately connected to the sub out, sub is on in the head unit. Ran the amp power wire from the battery, through the firewall, etc. Not too much of a ghetto setup. Since it changes with the rpm, it would seem to be alternator output affecting it. Never had this before. Any clues?
thanks,
Bryan

 

It is probably some sort of ground loop. First check the length and size of your ground cable going to the amp. It should be of the same gauge as the power wire and should be no more than a couple feet long. Also, does it have good contact with the body of the car? If both of these are fine, it is probably a poorly designed amplifier (I had a similar problem with one of my amps; it turned out that my amp had a crappy power source in it) if it is due to the power supply design in the amp then the best way would to buy a ground loop isolator (about $15).

A simple way to test if the amp is designed poorly: disconnect the RCA cables from the amp, take a simple voltmeter, set it to test the resistance (ohms). Put one connector of test meter on the outside of the RCA jack (be sure that it does not touch the body of the amp) and then put the other connector on the meter to the ground terminal on the amp (be sure you put it on the ground and not on the 12v+) there should be infinite resistance (no reading), if it gives you a number, then it is a bad design and you probably need an isolator.

 

Thanks, I will try that tomorrow.

 

You have a Pioneer HU. First take a DMM and measure the resistance from the outside ring of the RCA jack on the HU to the chassis of the HU. It should be vary low. It's possible you damaged the pre-amp out ground IN the HU. If there is a high resistance there we'll get into how it happened. If there is a low resistance there you can move on. But with a Pioneer HU that is where to start.

 

Thanks for the replies. Turned out to be adjusting the gain on the amp. Was previously using the high input off the stock deck. First time I've really put together a system with an amp. Still learning.

 

Another thing to remember is to run the power and RCA cables down opposite sides of the car.