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Alternator whine

1K views 27 replies 8 participants last post by  Smuggler 
#1 ·
Got an annoying constant whistle/whine thats in time with engine revs whenever the headunit is on. Someone else has installed the sub and amp and speakers but they're in a BMW so battery is in boot etc. I've noticed the amp's earth wire is speaker wire and is connected to the metal part of parcel shelf by a screw, not rubbed down to bare metal either. Could either of those two things cause me to get alternator whine? What if i was to use proper earth cable and connect it directly to the battery, would that improve things?
 
#5 ·
Make the earth better to the chassis with quality cable and connectors.

Also replace the earth strap from the battery to the chassis with better cable. Doing the earth wires from the alternator with better cables works well too.


Adam, I think you mean suppressor mate :p
 
#8 ·
Your electrical knowledge is appauling, to be blunt.

If you are using 4-gauge power wire, why would you NOT use 4-gauge earth wiring? Do you somehow think the power wire is more important?

If you have any circuit with say 50A from the +ive to the component, and 10A from the component back to the -ive... you'll never get more than 10A current flow.
 
#9 ·
No, my electrical knowledge is not appalling lol. I always use the same gauge wiring, but I never did this install as I mentioned in my first post lol. I know the size of the earth wire is important etc. but what I mean is can a poor earth connection cause the whine? It's too cold to mess about with tonight so i'll fix it tomorrow.
 
#10 ·
Yes a poor earth connection is the cause of the whine in most cases.

Typically an undersized wire wont give that though, it will just add a bit of resistance and end up with the amp clipping as it cant draw enough current, so its more likely to be the ends of the wire than the size of it that is causing this problem.
 
#12 ·
Lol cheers chip, i've just put a proper earth wire in to the same point, and the whine has gone slightly now, but it's still there. Maybe the actual earth point i'm using is no good as it's just the same one the person before was using.
Is there any problems with me running it to the battery? I know in most cases you don't, but considering the battery is in the boot?
 
#14 ·
Ok, it's not the earth cable, i've just done a proper cable and the whine is still there. What happens is I seem to get a high pitch whine from the sub, and from the speakers up front. So any other ideas on what this could be? Bearing in mind I didn't install the system, but am having to fix it.
 
#15 ·
Could be a failed or failing diode pack in your alternator - when these go you get a lot more ripple on the electrical line which can present itself on your audio system.
 
#16 ·
Is there any way for me to test this/find out before I go try replacing it yet to make sure? I can't test the speakers normally as they have all been wired up from the amp, but I know the noise goes when I turn the amp off. Otherwise the dvd player/tft screen etc. work fine.
 
#17 ·
If you've got a friend with a scope you could try putting this on a live and ground near the battery then again near the amp. You'll be able to see any ripples on the line then.

Things to try are running the amp with the headlights on and off - if it gets much worse with headlights on then that can indicate a failing coil/diode pack.

It could also be that the power supply in your sub has a crap smoothing capacitor somewhere. Car electrics are notoriously noisy - if you hook up a pair of headphones with a 0.01uf capacitor in series you'll hear a whistle on virtually any car even if the electrics are spot on - my missus brand new Passat will generate interferecence on my mp3 player/fm modulator if you plug it in the wrong cigarette lighter socket lmao

Does the frequency (not volume) of the whine get higher and lower with the engine speed ?
 
#18 ·
Yes, the frequency does get higher and lower with engine speed, and it's not just the sub that whines, all the speakers do too. Headlights on or off doesn't affect it, but if I open a rear door for example, frequency of the whine goes higher for a few seconds then goes off.
 
#19 ·
UPDATE:
Ok, done some more testing and the whine goes away when I disconnect the RCA cables. I have 2 sets of RCA cables, if I pull one set, the sub whine goes away, and if i pull the other, the speaker whine goes away. Am I correct in saying because of this my amp and speaker wiring are all ok? So does this basically mean I have a bad ground/ground loop coming from the headunit, i'm guessing it's using the factory harness as earth.
 
#20 ·
That does suggest an earth loop - ideally you want to earth all your audio to one single decent earth point.
 
#22 ·
try this;

when the systems playing, touch the rca's outer plug sleeve,(earth), with one hand, and the amps chassis with the other hand, does the whine stop?

now try the same thing at the rear of the headunit, only substitute the headunits chassis in place of the amp. does the whine stop?

if the whine does stop then you have a minor earth track fault in the headunit,(common in pioneers), the simple fix is to earth the rca's plug outer sleeve's to the headunits chassis, and the headunits chassis to the cars chassis, this should solve your problem.

HTH
 
#23 ·
Hmm, to be honest I haven't tried the RCA plug thing yet by touching them with my hand, because I can't power up the radio without it being in the cage. I had a look at the radio by taking it out and i've noticed the ground wire is wrapped around the radio chassis, so basically only works when the radio is in the cage and the wire is touching. This can't be adequate surely? I'll try connecting the radio chassis the outer case of the RCA plug in a little while though, see if that makes a difference, cheers.
 
#24 ·
what, you mean the ground wire has been cut and connected to the h/u enclosure? Or do you mean the ground wire is connected to the h/u enclosure in addition to being connected to the battery via the normal ISO connector? If the former is true, it'd almost certainly explain your problem.
 
#28 ·
Nevermind, i'm gonna completely rewire this mess anyway. The extra earth wire I mentioned is not an earth wire at all, it's an earth wire for an RCA noise filter I just found at the back. Will all be coming out at some point and redone.
Thanks for the help.
 
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