QuestionHi Brian,
I have a problem with noise in my car audio system, I have had a lot of research about it and I know there are several issues causing the noise. I just installed a Fusion 600 watts amp, and Alpine CDE 102E head unit into my car. The amp is placed under the front seat and all the cables are under the carpet (my power cable and RCA cable runs same side). I know it is not a good idea to do that but my mate's system is working fine with the RCA and power cable run together.Anyway, I have very annoying noise from the speaker every time I turn on the car, the noise rises up every time I turn on the head lights and when I accelerate. But it's gone when I turn off the engine. So I bought the group loop isolator but the problem still not solved. I also did a test with my amp and it works fine with different head unit. Can you help me to solve it please, that's much appreciate. Thanks in advance Brian.
AnswerHi Alex,
First, let me apologize for the delay in answering your question.
As you're finding, it can be very difficult to track down a noise problem in a car audio installation. I agree with you about the practice of routing the signal cables near the power wiring; I haven't personally seen negative effects from this, and I wouldn't expect to. I'm pretty certain it's not the cause of your problem.
I'm not completely clear on the details of your noise problem: is the amplifier a 4-channel model, running the front and rear speakers, or is it driving a subwoofer? Are you hearing the noise from all the speakers? And when you say you tested the amplifier with a different head unit: was this in the same vehicle, or was the amp removed and tested in a different vehicle?
From the context, it sounds like your amplifier is running the speakers that are producing the noise. RCA connections between a head unit and an amplifier are called "single-ended" connections. The audio signal is carried as an AC signal on one conductor, terminated in the center pins on the RCA plugs; the "shield" on the plug is the reference ground. For example, if the AC audio signal has peaks of +1 volt and -1 volt, there has to be a stable "0 volts" point. In a car audio system, the 0 volt reference is usually tied to the chassis ground of the head unit. If there's a problem with that chassis ground point, so that it doesn't rest at 0 volts but instead has a voltage on it, that voltage will become part of the audio signal.
So with that in mind, here's what I'd check: make sure that your head unit has a good, solid ground connection. If necessary, connect the head unit ground wire directly to the vehicle chassis metal instead of (or in addition to) the ground wire in the radio harness; and it wouldn't hurt to connect a wire from the head unit chassis to the ground point as well. Also, make sure the RCA plugs fit tightly into the RCA jacks on the back of the head unit; if they're loose, you might try pinching the shields on the RCA plugs slightly with a pair of pliers, so they make a tighter fit. You can also try wrapping some bare wire around the RCA shields, and connecting the other end of the wire directly to the head unit chassis as well--just in case there's a problem with the head unit's internal signal ground connection.
I'd also take a close look at the battery and alternator wire connections. Loose battery terminal connections can result in audio system noise, and it's a strong possibility in yours: you said the noise increases when you turn on the headlights, and this might be the result of increased current through a loose connection. There should be a wire running from the negative battery terminal to the vehicle chassis metal--I'd inspect both ends of this wire for corrosion or loose connections. Also, at some point there's a wire or ground strap running from the engine block to the vehicle's chassis. It might be hard to find this wire, but it's an important part of the chassis ground system; because when the engine is running, the alternator's case becomes the ultimate ground point for the electrical system.
Another potential cause of audio system whine is a defect in the alternator or the battery. A problem with the alternator can result in excessive AC "ripple" in the vehicle's electrical system; one of the battery's functions is to filter out the ripple, but a battery that needs replacement might not do this as effectively. You can test for excessive AC ripple with a multimeter, testing for AC volts at the battery terminals; the reading should be under 300mV with the engine running.
If all else fails, you might try using a high quality, 4-channel line output converter for the amplifier connections instead of the head unit's RCA pre-outs. Many installers turn up their noses at line-output converters, but when I've used them they've always sounded just as good as the regular pre-amp outputs; and sometimes they can get rid of a noise problem that can't be fixed in any other way.
Hope this helps, and I apologize again for the late answer.
Brian
