In my Chevelle I finally managed to get everything for the stereo working beautifully, except for when the engine is on. I get that lovely audible tach sound. The car has a high energy ignition with racing wires, which I think might be the culprit, but I'm not sure. Let me tell you what I have overall so that maybe you can offer some suggestions as to what could be done to correct the problem.

The head unit is a Clarion with the four amplified channels powering four Pioneer tweeters mounted on the dash. There is a preamp signal wire running to the trunk of the car where it is conected to a Precision Power amp that is powering a Rockford Fozgate subwoofer. The crossover from that amp is going into a Sony Xplode amp that is connected to two Pioneer 6x9s mounted by the rear window. The ground is connected to the frame directly in the trunk. The positive side of the power is connected directly to the positive battery terminal and run to a small circuit breaker right in front of the firewall. It then runs through the firewall, along the transmission hump and under the rear seat into the trunk. In the trunk it goes through a small fuse panel and into the Xplode. Also, there is another fuse in line between the fuse box in the trunk and the Xplode. I'm not sure why, but the amp for the sub was never connected to this line, and instead was connected to a very small wire running to I'm not sure where. My next order of business is to move this over to the large cable with the Xplode. That wire is 4 guage I believe. The wiring is a little sloppy in the trunk and needs to be cleaned up because I just did everything temporarily to make sure it all worked, but I don't believe that the ignition noise is coming from there. The noise seems to be most prominent in the 6x9s, but is noticible in all the speakers.

Does anyone have any suggestions as to how I could eliminate the noise?

Thanks,
Chris

 

Ignition noise can be a pita. Make sure you ground all of your amps to the same grounding point (I used a distribution block). Next remove the signal from each amp (RCA's) to see if you can narrow it down to a particular amp. Also, you might have a bad patch cord - have a spare on hand to switch around with. If all else fails, you might have to use one of those PAC noise filters inline on the RCA from the head unit.

 

Go to a very dark place at night and lift your hood with the engine idling. Look for sparks along each spark plug wire. Check all grounds from one end to the other of each shielded cable interconnecting head to amps. All coaxial cables should be double shielded (foil and braid).

 

The plug wires are racing wires and there are foil shields over the ends of each of the wires to protect them from the headers. For some reason a few of them definitely do arc to the headers. The wires appear to be in good condition with no signs or any cracking or any other aging. This may just be because it's a high energy ignition causing it to leak through the cables themselves but I'm not sure. I tried using a different RCA pair back to amp, but it picks up the noise just the same. It's a Rockford Fosgate cable, so I think it's a decent quality wire. I think that a PAC filter may be the best bet to eliminating the noise in the system, as I don't want to pull the carpeting right now to re-run new RCA wires and I don't think much can be done for the ignition system. What are your opinions on this, and if you think a filter is a good idea which do you recommend?

Thanks,
Chris

 

Have you tried using a different head unit power and ground wires? Or maybe one directly from the battery to make sure noise isn't being picked up there?

 

I don't think the noise is in the head unit. The only speakers connected to the amplified signal from the head unit are the tweeters on the dash, but I can't here any noise from them, just the two amps in the trunk.

 

If the obvious things fail, replace the spark plug wires. Often race wires are not shielded and bleed noise. Get a set that says shielded. Also, make sure power and rca are separated as much as possible, and try sanding the ground point.

 

You have a ground and/or power loop between the two amplifiers or possibly your head unit. It makes the RCA's act as an antenna for the ignition/alternator noise.

Try pulling out the RCA connectors just enough to disconnect the outer ground sheild but leave the center conductor connected. Check this between the Sony and PPI, and between the PPI and HU. To fix it, make sure the two amps are grounded and powered from the same point; ideally run the same ground to your deck also. Alternatively you can use a ground isolator.

 

Try disconecting all the RCA's and see if the noise goes away, if the noise is still there after the RCA's are unpluged the your problem is with the ground, if there is no noise after the RCA'a are unpluged try to conect them one by one untill the noise comes back, that is the easiest way to find out. good luck

 

Ok, I'll try that next time I go home from school. The noise was present before I added the Sony amp tp the system, so I imagine it is picking it up in the signal from the HU. I had tried to connect the Sony directly to the HU with a different RCA but still got the same noise in the amp. Both amps are on the same power source and are also both grounded to the same location in the trunk. I have a feeling it is probably a ground problem as you have suggested. I was thinking about it and unless it is done through the wiring harness on the back of the HU I'm not sure that the HU is even grounded through the chassis because it is mounted under the dash in a plastic housing.

If I cannot fix it by the ground alone will a PAC filter in the RCA cable take care of all the engine noise in the system? It's just annoying since the amps are always on when the car is running, so even if the volume is all the way down or the HU is muted the noise is always there.

Thanks again,
Chris

 

You might try a power supply filter to your head unit. They basically have a coil and capacitor internally to filter out the high freguencies generated by the ignition pulses. Most of the ones available are current limited by the size of the coil windings. So, don't attempt to use it on an amp power feed. These filters are moderately effective and will help dampen some, but probably not all, of your high voltage ignition system pulses.

 

It has been my experience that spark plug wire noise is a popping sound and can come from RF as well as through the electical system. If the noise is a whine, it may be defeatable with an inline coil as described previously. I would place such a coil on the HU power input first if that is the case.

 

Try this first, it’s quick, easy and you won’t have to move any wires or components to do it.
Grab a Voltmeter and check the voltage at your battery and all of your ground points. If it shows at least 12 volts then you have good ground points. If not, alter them.

Rule of thumb measures to keep in mind. (If you haven’t done these things yet, do them.)

Keep ground wires as SHORT as possible (under 3 feet is ideal).

NEVER run a ground wire from the back of the car to the battery in the front. That will only increase the possibility of INTRODUCEING noise in your system and is just a waste of wire.

Ground amps at the same spot, making sure there is no paint, grease or dirt to interfere with the ground.

Run power wires and signal wires on separate sides of the car from each other.

Last but not least, as said above, if all else fails check your plug wires or use a ground loop isolator (but only as a last resort, it will effect sound quality)

P.S. With the high performance nature of that car I am assuming you have already upgraded the electrical system under the hood? (i.e. Fat power and ground wires to Alt, block and chassis?) :yesnod: