Signal Noise from Tuner

[Timothy Mark]

Ok guys I'm new and helpless. I've searched for a while and haven't seen a thread addressing my troubles, so here goes:

First, I have a Pioneer head unit in my '91 S-10 that gets poor reception in general and frequently gets signal noise from some other part of the truck. The noise changes pitch when I change engine RPMs.

The alternator is new, and the noise was also there before I replaced it, so I don't think it's the alternator itself causing it.

Should I add another ground wire to the head unit? Anyone else have bad reception in their S10?

The second problem is a fairly substantial engine vibration that's pretty strong at about 1500-2000 RPMs but is less severe above that. IT's a 4.3 V6. Motor mount? maybe a bolt missing from the flywheel or something?

Thanks for any help you can give.

[movin2stereo]

On my cd player I get a slight wine and it changes with the rpms.I can only hear the wine if the cd player is turned completely down to 0 and then it's only fait.There are noise filters you can buy that goes on the power wire of the stereo.

[eti engineer]

I used to install radios/stereos for a living, even back when 8-tracks were popular.. (Hey, I'm 56!!)

Anyhow, there are usually two major causes of noise in car stereo equipment, ignition and charging systems.

With the ignition, the sound is caused by rf generated by the spark jumping the gap at the plug and sounds like a buzz that increases in pitch and frequency with engine rpm's, obviously. The best way to get rid of this noise is noise suppression spark plug wires, resistor type plugs, and there is also a resistor network available for the coil wire.

If, however, you have installed an aftermarket system such as I have, all bets are off. I have a Jacob's Pro-Street system which basically renders the AM portion of my radio useless (which is usually no big deal, except I like to listen to conseervative talk radio once in a while). The FM is fine, but I usually listen to my own CD's anyway. I have never been able to get rid of the ignition noise.

As far as the charging system is concerned, there are two sources of noise -- the regulator and the alternator. Nowadays with the solid sate regulators, it is rare indeed to get noise from these. The alternator noise is like a whine which increases with engine speed. You can install what is known as a choke in line with the power lead going to your stereo system. It is an assembly that looks like a transformer, but only has two leads. Nowadays, the configuration could be even different as some solid state assemblies are available which incorporate a choke, solid state devices, and other filters, etc., to cut down the noise. The main thing with this is, if you have a high power system, make sure the choke/filter assembly is rated for the current you draw. Some of these systems are amazing in the amount of current they use to produce the bass that shakes people's cars apart.

One last thing, if the noise only occurs when you are listening to you radio, make sure the antenna and antenna lead shield are grounded. If the ground is not intact, you will get a lot of noise.

Hope this helps...

Merry Xmas and Happy New Year...

eti engineer

[Timothy Mark]

Thanks guys. The noise is only while I am listening to the radio. No buzz with the CD player.

So if the cause of the noise were coming from the spark plug wires or the alternator I would hear it regardless of whether I were listening to CD or radio? In that case it must be my antenna.

[eti engineer]

Originally Posted by Timothy Mark

Thanks guys. The noise is only while I am listening to the radio. No buzz with the CD player.

So if the cause of the noise were coming from the spark plug wires or the alternator I would hear it regardless of whether I were listening to CD or radio? In that case it must be my antenna.

It could be your antenna if the noise is coming only while you are listening to the radio, but this is not necessarily the case. If it were charging noise, you get this normally through the power lead coming into your system and the choke assembly I spoke of in the earlier e-mail would cure the problem. But you would normally hear this on the the radio and the CD player as the noise would enter the system on your power lead.

Do you get the noise in both AM and FM modes? If it is much worse in AM than FM, chances are it is just ignition noise and needs to be cleaned up by the methods I described earlier. Just go to Radio Shack or your local stereo shop and they will be able to help you out with noise suppression.

But as I mentioned at the end of the earlier e-mail, check your antenna if it is only noisy on the radio. Your CD player and radio operate totally differently from one another in the fact that the CD player does not use the antenna, but the radio does. However, spark plug, or ignition noise is an rf source and is normally only heard on the radio and not the CD player, since the CD player is not subject to rf (radio freq.) noise, and the radio obviously uses rf to operate.

Check the ground on your antenna -- the shielded braided portion of the cable connecting your antenna to your radio. It should have a good solid connection to the car body. You can use a jumper wire to check this if you want.

Not knowing what kind of antenna you have (windshield, fender mounted, or whatever), all I can say is that sometimes water can get into a fender mounted antenna and partially short it out. This weakens the incoming radio signals and make existing motor noise sound louder. If you can, substitute the existing antenna with a new one, ground the base and see if the noise goes away. If not, you have to pursue getting rid of the motor noise via the methods I mentioned earlier.

Hope this helps -- slightly convoluted, but the essential are here.

Let me know if the noise is worse on AM or FM or the same. This can provide a clue...

eti engineer