12 volt car adapter to usb causes buzzing in car stereo

[mkenyon2]

When I have my cell phone (Samsung Focus) plugged in via 1/8" stereo cable to my Aux input for my car stereo (2008 Kia Spectra stock stereo) I can hear my music fine with no buzzing. If I also plug the USB cable into a 12 volt cigarette lighter socket adapter I get buzzing. I have 3 adapters, some are worse than others.

Do I need a choke or filter for the power line? What do I need and where do I put it? I'm guessing the 12 volt isn't very clean since the buzzing does harmonize with the engine RPMs.

Note... if I don't have the cell phone plugged into the adapter, but the adapter is still in the socket and the LED is lit on the adapter, I do not get the buzzing. It is only when the adapter is feeding the cell phone. (Bigger load, more draw maybe?)

Thanks.

 

[Ian Rogers]

These 5v USB power plugs are extremely noisy.. I have two as well. I'm making a switched mode one as we speak as I have the same problem,, It also happens with my IPod..

Ian

 

[Reloadron]

Agree with Ian. Same symptoms I had. When I replaced it, the noise went away so I never bothered to pursue the root cause or look for a solution. My phone was a blackberry storm but dubt it matters.

Ron

 

[mkenyon2]

Ron, you replaced the adapter? Which brand did you get? I'm guessing the $5 jobs I've been using were the reason for the dirty power.

I'm surprised that the voltage noise is coming through to the output. The audio chip should be getting pretty clean voltage. But I'm guessing whatever amp circuits are using more of the raw voltage straight from the power input, rather than the cleaner stuff that goes to the processing chips.

 

[Reloadron]

Ron, you replaced the adapter? Which brand did you get? I'm guessing the $5 jobs I've been using were the reason for the dirty power.

I am not sure but when I leave work today I'll give it a look. It lays in the truck all the time. The original was a unit that came with my Blackberry. It only screwed with the radio when it was charging the phone. Maybe it was just more pronounced. Finally the phone connector failed so I tossed it aside (always save junk) and I think I stopped at a Radio Shack (I wanted a replacement NOW!) and bought another one. The new one I think was something like $19.95 or $24.95 as I don't remember. However, I noticed, charging or not charging no noise. That unit has sat in the truck, connected always, a few years now. I'll check for a name when I head home and post later this evening.

Ron

LMAO, about all it says is Made in China just like the one before it.