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Platinum BFuk Member
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Discussion Starter #1 (Edited)
2004 E46 318ci - Alternator whine/ground loop problem (FIXED)

Hello everyone,

last week i pulled my alpine out and put the business HU back in,

Im useing two high level to RCA adapters to run two amps (one for front comps the other for sub)

One adapter is off the front speaker wireing and the other is off of the rear speaker wireing,

So the problem, i have an annoying ground loop problem. It is only present when the engine is running and it increase in pitch with engine speed. So its deffinatly a ground loop issue

I have tried a few things already,

I have disconnected:
the RCA's from the amp and the noise goes away, so this makes me belive the noise is related to either:
RCA's
or the RCA adapters

On the rca adapter there is a negitive wire,
I have connected the wire directly to the chasis - Still noise
I have connected the wire to the -ive on the amp - still noise
I have connected the wire directly to the -ive of the battery - still noise
I have disconnected the wire and it maginally improves

So at the moment, i have both of the -ive's on the rca adapters disconnected and i have a ground loop isolator installed which has almost removed the annoying noise, but i can still hear it,

Does any one have any ideas?

Thanks
 

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Touch the -Ve outer of the RCA to the chassis at varying points of the car to see if the noise comes in and out. Run the front speakers from the rear LOCs (assuming they are in the boot area) to see if the whine is in both F&R units or is relative to the position in the car.
 

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Platinum BFuk Member
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Discussion Starter #4
Touch the -Ve outer of the RCA to the chassis at varying points of the car to see if the noise comes in and out. Run the front speakers from the rear LOCs (assuming they are in the boot area) to see if the whine is in both F&R units or is relative to the position in the car.
If i swap RCA's on my amps,

So what is from the front now goes to the sub
and what is from the rear goes to my front speakers

I still have the same issue

I will try the other bit tomorrow in the light

Thanks
 

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Platinum BFuk Member
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Discussion Starter #6
LOC??? is that line output converter?

being the rca converts?

no they are not, the rear is below the rear seat, connected in to the left and right rear speaker wireing on the passenger side

and the front is wired into the fronts behind the glove box,

So they are at diffrent locations, and i am getting the same noise, front or back
 

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Have you tried ferrite rings on the live or negative??

Maplin do them and I found they work really well for my VHF radio I put in my car when I had the whine....
 

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Platinum BFuk Member
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Discussion Starter #8
Have you tried ferrite rings on the live or negative??

Maplin do them and I found they work really well for my VHF radio I put in my car when I had the whine....
Maybe worth a try, although i feel that the whine is caused by rca adapters
 

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I think mine cost about £2.50ish about 2weeks ago

If they don't work and you remove them, remember to put insulating tape/heat shrink where you put the as it pierces the cable!!
 

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Have you tried grounding the amp at the LOC (Line Out Converter) inthe back and using that audio out?

But yes you have a ground issue. Consider capacitively coupling the -Ve to remove the DC.
 

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Platinum BFuk Member
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Discussion Starter #11
Have you tried grounding the amp at the LOC (Line Out Converter) inthe back and using that audio out?
Sorry i dont understand,

I have tryed grounding the LOC directly to the amp, but this has no effect
 

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Sorry i dont understand,

I have tryed grounding the LOC directly to the amp, but this has no effect
Well that's the same test so no dice.

You want the biggest capacitor you can find in series with the audio RCAs. One for each -Ve and -Ve cable.

So many people have problems with this I start to suspect there is DC offset on the HU outputs. Any pots you can tweak in the LOC to adjust the balance on the speaker level inputs to cure DC?
 

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I have this issue. I have a four chanel amp, if I run the sub and the 6x9's from it, it sounds like I have a supercharger...
It's only one or the other though, I can run the 6x9's or the sub on the same chanel on the amp and it'll be fine, if I do both though it sounds shit. :confused
 

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Platinum BFuk Member
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Discussion Starter #14
Well that's the same test so no dice.

You want the biggest capacitor you can find in series with the audio RCAs. One for each -Ve and -Ve cable.

So many people have problems with this I start to suspect there is DC offset on the HU outputs. Any pots you can tweak in the LOC to adjust the balance on the speaker level inputs to cure DC?
This is what i have installed, no adjustments
just two rca's, speaker -ve/+ive right a left and a negitive


I also tried wireing the negitive of the loc in to the negative of the HU, hopeing that this may help, again no change

To me i cant really understand how wireing in the negative to the chasis makes it worse,

i will look into capactiv coupling, Thanks
 

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This is what i have installed, no adjustments
just two rca's, speaker -ve/+ive right a left and a negitive


I also tried wireing the negitive of the loc in to the negative of the HU, hopeing that this may help, again no change

To me i cant really understand how wireing in the negative to the chasis makes it worse,

i will look into capactiv coupling, Thanks
Any specs on those? Impedance transformation? voltage level transformation?
 

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Discussion Starter #16
no specs, all i know

AUTOLEADS PC1-601

how ever just looking at the instuctions it says:

Common earth radios: connect the white and grey leads(left -ive and right channel input) to the black ground wire. then connect all three to the chasis earth

does that make any sense to you?
 

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Discussion Starter #17
how ever just looking at the instuctions it says:

Common earth radios: connect the white and grey leads(left -ive and right channel input) to the black ground wire. then connect all three to the chasis earth
I understand that now,

for when the -ive of the speaker wire dosent exist, it use the ground
 

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Discussion Starter #20
Ive jus had a thought,

If i cut the negative in the loom to the back of the HU, then run a new negative to the HU from a bar,

then if i run the gnd's from my loc's to the bar now all the negatives are connected at the same place, i could run a return from the bar all the way to the battery

This would put the HU and both of the LOCs at the same potential

Do you think that would eliminate the noise?
 
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