Engine interferance!!

[riske]

Fitted headunit and front and rear speakers etc but when i turn my engine on i get severe interferance/noise form engine. I know about running wires on opposite side of car from live wire but still doing it! Battery is in the boot. Any ideas????:?

 

[PobodY]

Put a suppressor on the electrical components?
Put a capacitor across your battery?
(Yes, I appreciate that a suppressor is a capacitor already - but they're sold as suppressors when they're small and capacitors when they're large)

Do you know what it is that's causing the interference?
Does it change with engine revs? - That's often the alternator.

 

[riske]

Yeah it does change with engine revs mate. Its high pitched and mimicks the engine. So does the capacitors reduce the loudness or just removes the electrical interferance? Also when you say electrical components do you mean amp, head unit, speakers?? or just amp because that then distributes the sounds to the speakers? Thanks for the help so far mate.

 

[PobodY]

The suppressor is essentially just a small capacitor, it works by ironing-out the waveform from things like the alternator (because the 14V is a pulsing signal as the commutator goes round). - If you think of a classic sine wave, you've probably got more of a saw-tooth pattern. A capacitor smooths off the edge of that to give you a smooth wave again. (Any electricians are free to correct me - it's years since I sat in electrical engineering 112)

It may not be the alternator, but that's a logical place to start because it generates electricity and will spin faster with the engine.
By electrical components, I mean the engine electrics; alternator, distributor, even the spark plugs or starter motor (but that shouldn't be spinning when you're driving).

Quite a few audiophiles will have a capacitor (as high as 1 farad) across their battery just to keep the power-draw nice and smooth... it's the strangest thing because the stereo will be quiet until the cap has built charge, and then it suddenly kicks in.
I would have thought that you could just put one across the amp if it's just those speakers that are picking it up... I would have thought it would be all of them.

Anyone know if a ferrite lug would help? That's not uncommon on data cables, but I don't think I've ever seen it on speakers.
A ferrite lug on the amp power lead might just take enough of the noise out (electrical noise I mean).

 

[riske]

Well ATM all the speakers are running from the same amp. I used to have individual amps per set of speakers but my new amp can handle front and rears ok. I will buy a cap and put it on the battery and maybe one on the amp depending if it works. Safe mate for the help.

 

[jambo_gtir]

Power caps are used mainly due to the fact that the battery can't supply enough power to the amp in the time that it needs it. Caps store power so when the amp can;t get enough power from the battery, the cap discharges giving it the extra power it needs.
I suspect the noise you are hearing is due to the fact your sharing the earth connection with something else. I wired my stero earth to the earth from my boost gauge temporarily and when i revved my car there was interferance also. Try taking your earths directly to the chassis, or even battery and see if that helps.
Also, there is no AC (sine wave) coming off the alternator, it has an integral rectifier so the output is DC; in order to charge the battery.
Hope that helps.

 

[jambo_gtir]

Ferrite beads are generally used on power cables to remove spikes and high frequency components; usually when dealing with sensitive equipment. I haven't seen them used on data cables myself, but i suppose you could. But with audio i can't see them having a noticable effect. Better to used screened cable

 

[riske]

cool I'll re-earth my headunit to the body. And hopefully that will work!

 

[Fusion Ed]

I would, it may be an earth loop problem caused by the battery being moved to the boot.

 

[riske]

so how do i get out of this loop?

 

[PobodY]

Also, there is no AC (sine wave) coming off the alternator, it has an integral rectifier so the output is DC; in order to charge the battery.
Hope that helps.

Yeah, but the rectifier is converting an AC source back into DC by inverting half of the sine wave. If it's on the way out it'll do a bad job and you'll get a chop chop chop from it.

I'm not an electrician, and you seem to know what you're talking about. I will concede that I might be wrong.

I wasn't sure if a ferrite lug would help a stereo - Maybe on the AC lead for one to keep line noise down... maybe not on a 12V source eh? I just figured that if it was a high-frequency noise that might be a cheap way to iron it out.

I hadn't considered feedback through the earth, but that does seem more plausible than anything I suggested. Especially if the battery is now earthed elsewhere on the chassis.

 

[riske]

I have re-earthed my head unit to the body and it still has the intererance! If i disconnect the RC cables to the head unit meaning there is no sound being sent to the amp it makes no sound. Does that suggest its my amp or headunit? May just connect speakers straight to headunit see if that works but music will be quiet. Anyone got any ideas? Thanks

 

[jambo_gtir]

Yeah, but the rectifier is converting an AC source back into DC by inverting half of the sine wave. If it's on the way out it'll do a bad job and you'll get a chop chop chop from it.

Yes you are correct mate, i thought you meant there was AC coming off alternator and to the battery in your other post.
There should be a cap in there as part of the inverter to smooth out the chop, but like you said when they are on there way out i suppose it could start to get worse.

Have you run the earth from your amp to a new location mate aswell as the head unit?
If you have and your getting the noise when u plug RC leads in, perhaps the leads themselves are crap?
trouble is dealing with interference is a nightmare, but it's always a good start to check the obvious; cables in good condition, good earths and i suppose cable location (ie. not sat next to dirty cables).

 

[riske]

The amp and cables came stright out of my previous car which didnt have interferance. The cables are relatively high quality and run along the other side of the body to the power cable. My battery is in the boot with power cable is running down passenger side. The rc and speaker wire run on the drivers side. My headunit has the standard connectors to sock connectors with it now earthed to body. My battery is earthed twice to 2 seperate body areas. My amp is earthed from battery and powered from the battery(obviously). I really don't know what else to do. Is ther anything that will cut out the high frequency range?

If the engine isnt on it works fantastic with no interferance whatsoever.

Thanks for all the help so far btw.

 

[riske]

Disconnected amp and just connected standard wire from headunit and i have no interferance. Dunno if anyone has any ideas about reducing the interferance from the amp? cos i definatly know its the amp side of things now. much love

 

[jambo_gtir]

hmmm, the amp is obviously picking up some crap then from somewhere. May sound silly but where is amp located? i know in the boot but is it sat next to your battery or anything else power related?
It mite be a long shot but where i work with sensitive rf components etc, interference is a big problem and youd be amazed what silly things can cause it. EMI is a nightmare.

 

[riske]

Its on the back of my back seats. Its bout 1 foot from the battery. I'll see if puttin it on the other side works.

 

[jambo_gtir]

How is it going mate?
I have spoken to one of the engineers where i work who knows alot about this. He suggested the problem is the amp is too succeptable to the typical noise you have on your power lines. This noise would be worse than normal as the battery is mounted in the boot, so nice long cables to pick up noise. Maybe use some sort of filter/Cap on the 12V input to ground on the amp could help.

 

[riske]

Cool so where will i be able to get this filter thingy from?