alternator whine (what am i missing?)

[omgosh]

I've got some terrible interference in my stereo....here's the story.

I was going 70 or so down an off ramp blasting some tunes, and my amp came unbolted. I believe it shorted itself out on my other amp..So anyway it made some pretty loud static and I immediately turned off the radio. I got home, reconnected it (ground was loose), and now I have this awful alternator whine coming from the REAR ONLY among other things. Here is a list..


-alternator whine
-still noisy with motor off
-speakers hit when any light turns on (dome, headlights, fogs, whatever
-I can hear my fuel pump and e-fans through the speakers
-sub hits when motor is powered down (I've heard this is normal but it never did this before.)

setup:
-kenwood hu powering front speakers
-4(2maybe?)ga power /grounds w/inline fuse
225 watt bazooka amp powering 8" tube
180 watt 2-channel powering 2 Pioneer 6x9 3ways

what I've tried already:
-moving ground
-adding grounds
-redoing engine/chassis grounds
-new RCA cables
-new amplifier
-grounding RCA outer shield to chassis, also to amplifier ground in trunk
-ground headunit to chassis, also to amplifier ground in trunk
-disconnected and reconnected everything like 3 times.

The ONLY way I can get rid of the noise is if I run the RCA's off of the front speaker pre-amp instead of the subwoofer/rear pre-amp. I don't want to do this, nor do I know why the fuck this works. Did I blow out the pre-amp somehow? Is this possible? The headunit works fine otherwise...

I'm stumped, unless my headunit is in fact broken. I have no spare to test it with If anyone has any insight it would be greatly appreciated.

[lolsrc]

try a ground loop

[omgosh]

Originally Posted by lolsrc

try a ground loop

I had everything grounded to the same point. Wouldn't that eliminate a ground loop problem? I might try one anyway..

Also, I was talking to a friend, and reading some, it seems that alternator noise is a low frequency? Around 50 or 60hz is what I was reading. The noise in my car is MUCH higher pitched than that.

[custom240sx]

No you will hear engine whine through a high's amp which is the charging system at work hence it getting louder as you rev the motor. My money is on the headunit. I have seen this many times with pioneer headunits and the preouts going bad. Kenwood doesn't seem to go bad near as often but it still can. Borrow a headunit from a friend and see if that solves the issue.

[omgosh]

^yeah I was calling around to see if I could find a headunit last night. None of my friends can even put a patch in a tire themselves, much less have extra car parts lying around.

It looks like I may have damaged the preamp. Has anyone else done that before? I currently have my front speakers wired to the rear channel and my rear speakers are using the front channel preamp, with no audible noise. My fader is backwards, but oh well, at least I don't have to buy a new headunit.

[the727kid]

Go to Best Buy, buy a headunit... and test it... if it's not the HU, just return it and continue on searching, but my money is on the HU.

[TJElite]

Most likely, the ground for the RCA input, either at the deck, or at the amp, is bad, causing a loop. Try grounding one end, then the other. Just take a piece of wire, ground one end, strip the other, and wrap it around the collar of the rca (the metal part that surrounds the pin)

Toby

[Notladstyle]

Because you say the front preamp doesn't give the hum, I doubt it is the ground because the front preamp uses a common ground with the rear preamp.

Id say purchase a new deck or get an EQ and split the front preamp through the eq to the rear, front, and the sub.



Although, you might have melted the ground inside the amplifier but it would still have damaged the preamp is you did.

[TJElite]

I've seen decks where one set of outs would whine, and another wouldn't. Grounding the RCA's at the deck fixed it...don't know why...maybe the grounds are seperate at some point, before they become common. Doesn't hurt to try grounding the rca.

Toby

[kapone]

Originally Posted by omgosh

.

Also, I was talking to a friend, and reading some, it seems that alternator noise is a low frequency? Around 50 or 60hz is what I was reading. The noise in my car is MUCH higher pitched than that.

your friend was wrong ... alternator whine is only present in the high frequencies thats why you will never hear it through your bass amp and subs ....unless there set to full range.

[Notladstyle]

Originally Posted by omgosh

Also, I was talking to a friend, and reading some, it seems that alternator noise is a low frequency? Around 50 or 60hz is what I was reading. The noise in my car is MUCH higher pitched than that.

alternator hum is cause by very small interruptions in between the current supplied by the generator as the magnets travel from coil to coil.

The frequency of the hum is based on the rotational speed of the pulley x the number of coils in the alternator. So if you were at 400rpm with a 2:1 pully and an 8 coil alternator you would have a 6khz hum.

Chokes work by slightly lowering the voltage and using a capacitor to maintain current flow through the dip 'muffling' the dip to something below an audible(and amplifiable) level.

[MCOR]

Sounds like head unit. We have also grounded many RCA's as a last resort to eliminate the noise you are referring to. BTW: if you install an FM Modulated device inline with the radios antennae, grounding the outside of the antennae connector or wrapping it with tape so it makes no connection when plugged in will also eliminate that engine noise-oddly enough...

[omgosh]

It was the headunit. Thanks guys.