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Topic # 98259 28-Feb-2012 11:17
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Hi,

If I'm charging my phone (galaxy s2 - micro-usb connector) when listening to music via a 3.5mm connector in the car I can hear the engine revving up in the speakers. If I remove the power it goes away.
I tried two different chargers and it does the same so I tend not to blame them necessarily.

Any idea if there is such a filter?

Thanks.

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309 posts

Ultimate Geek
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  Reply # 587758 28-Feb-2012 11:19
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In days gone by, some people would have suggested a suppressor on the coil.

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  Reply # 587771 28-Feb-2012 11:49
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tcpdump:
Any idea if there is such a filter? 



Is it called bluetooth to the stereo? 

 
 
 
 


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  Reply # 587778 28-Feb-2012 11:55
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Where is the USB power coming from?  Perhaps a/some filtering cap across the DC to the USB plug might help, especially if it's an el-cheapo chinese cigarette lighter to USB thing, might not have anything except a regulator and heatsink in there (if you're lucky).
 




---
James Sleeman
I sell lots of stuff for electronic enthusiasts...




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Ultimate Geek
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  Reply # 587780 28-Feb-2012 11:57
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Actually they are not exactly cheap (one of them is a Belkin adapter and the other one came with the TomTom GPS).
That was actually my question: What kind of filtering would I need?

gzt

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  Reply # 587818 28-Feb-2012 13:31
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What kind of car / year are you driving?

Does it happen with other cars?




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  Reply # 587824 28-Feb-2012 13:37
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I have a cheap Chinese Cig->USB adaptor and when I am charging my iPhone and listening through a 3.5mm cable I get the alternator noise also.

I do not know how to fix it but would be interested in a solution also.

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  Reply # 588177 29-Feb-2012 09:30
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It may be an easy fix, or a convoluted fix ..
May be as easy as adding a couple of capacitors across the 12v supply going to the cig lighter ( 0.047uF - 0.47uF), or sliding ferrite beads along the wire ..
http://jaycar.co.nz/productResults.asp?keywords=noise+suppression&keyform=KEYWORD
Or ask advice from a car radio installer - they would see this quite a bit




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  Reply # 588447 29-Feb-2012 17:31
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I don't think this is electomagnetic interference, it's probably AC ripple from your alternator affecting the power supply.

Is the noise a ticking static type of noise or more of a whistle high pitched noise?  

If it's the ticking static noise it is most likely ignition interference, but I suspect that its a whistling noise you have, then doing as SepticSceptic suggests with the capacitors should fix it.




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  Reply # 588474 29-Feb-2012 18:48
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If the pitch of the noise changes when you rev the engine, then it's almost certainly the usual alternator problem. I need to fix the same issue in my car as the replacement headunit puts out more voltage than the previous one did and now if the RCA leads run too close to the 12V lead then I get the loop noise, move them away, noise goes away. It's not loud and only noticable when no music is playing, so one workaround is to just play something.

In the case of a charger, you can't really do much about the grounding issue other than fix it with the caps\filters suggested above.

It's a very common issue, car stereo outfits would probably be able to sell you an easy, but not necessarily cheap, solution.




gzt

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  Reply # 588484 29-Feb-2012 19:07
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Jaycar stock a power filter for car stereos, maybe wire that to your cig plug if you can resist overloading it with your cig lighter..

seen a few 3.5 to 3.5 aux noise filter cables on amazon, not seen any here.

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  Reply # 588517 29-Feb-2012 19:45
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stevenz: If the pitch of the noise changes when you rev the engine, then it's almost certainly the usual alternator problem.


Ignition interference noise will also change with RPM, though I agree it's most likely to be alternator noise.




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  Reply # 588599 29-Feb-2012 22:14
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Its a ground loop between the ciggy lighter and the stereo and the fact that car audio is retarded and uses unbalanced inputs.

I solved it by putting tape around the ground on the ciggy plug so that it only grounded via the 3.5




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  Reply # 588634 1-Mar-2012 00:57
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Try this for a ground loop problem.

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