Static when playing music and Droid is charging - is this normal?

[LilDavy]

I just got me Droid two days ago and I noticed that when playing Pandora in the car when the Droid is connected to the car charger there is quite a bit of static. If I remove the charger, the static disappears. Is this normal? Wondering if I need to exchange.

 

[compywiz]

How is the phone connected to the stereo? Do you have a non-oem stereo or a rigged charger? The reason I ask is automobile electrical systems can be very finicky, and I can see an aftermarket head unit being installed in a way that can create interference with a device plugged into the cigarette lighter (which is probably on the same circuit as the radio.

Got another car to try it in?

 

[LilDavy]

I have an '07 Camry with the OEM JBL sound system. I am using an OEM charger as well (the one that came with the car dock. Its connected to the AUX jack of the head unit via 2.5mm plug. I plan on trying it in my wifes car when I get home later - but hers is a Toyota Highlander with the same sound system. Thx for the reply.

 

[Amadeus]

Ground loop?

I had this problem. It turned out to be a ground loop between the cig lighter and the stereo via the line input plug. I had to isolate one of the grounds. At the time, my choices were using an isolation transformer on the 2.5m jack (yuck), or using an isolated dc-dc converter for the charger.

I chose the dc-dc converter route. Works great.

I did not try to lift the ground off the 2.5mm plug. That may work also.

Fundamentally, I think that the problem is most portable devices use a small resistance on the ground side of the power input to sense current draw from the charger. When you plug your 2.5mm plug into the same grounded system, it attempts to short out this resistance (diverting some current from the charger through the audio jack), and causes the noise - along with other problems.

I would think that by now there would be a simple commercial solution to this problem, but I have not looked it up, so don't know.

Logically, I would think that you cold also introduce a resistance in the audio ground to solve the problem. Say 1K, or so. That should prevent current draw through the jack. Never tried it. Could work. Typical impedance the audio would normally see from the stereo should be 10K+.

HTH

 

[LilDavy]

I had this problem. It turned out to be a ground loop between the cig lighter and the stereo via the line input plug. I had to isolate one of the grounds. At the time, my choices were using an isolation transformer on the 2.5m jack (yuck), or using an isolated dc-dc converter for the charger.

I chose the dc-dc converter route. Works great.

I did not try to lift the ground off the 2.5mm plug. That may work also.

Fundamentally, I think that the problem is most portable devices use a small resistance on the ground side of the power input to sense current draw from the charger. When you plug your 2.5mm plug into the same grounded system, it attempts to short out this resistance (diverting some current from the charger through the audio jack), and causes the noise - along with other problems.

I would think that by now there would be a simple commercial solution to this problem, but I have not looked it up, so don't know.

Logically, I would think that you cold also introduce a resistance in the audio ground to solve the problem. Say 1K, or so. That should prevent current draw through the jack. Never tried it. Could work. Typical impedance the audio would normally see from the stereo should be 10K+.

HTH

Cool thanks - where did you get your converter from?

 

[JP 5.56]

This is pretty normal for most audio devices (zune, ipod, phones with mp3, etc) in most cars. Both of my ipods as well as my BB and now my droid, have this noise when using the car charger, in all cars I've tried.

I am interested in Amadues' post on how to fix, unfortunately I don't really understand electrical systems all that well. Can you give me some links to the DC/DC converter you used and any specific information I might need to know?

Thanks

 

[Amadeus]

Looks like Radio Shack has a line level solution:
Xitel Ground Loop Isolator - RadioShack.com

This will isolate the ground on the audio side of things. Easier and less expensive than the dc/dc solution.

I built an isolated dc/dc power supply (4~5 years back?) similar to this one listed at DavidNavone.com.

David Navone - Adaptor Products - Car Audio Engineering
N-IP12A2 $165! (ouch).

Basically, I tapped into the cigarette lighter power, ran it into the dc/dc converter and ran the output into a new cigarette lighter socket. Both sockets remained working, one was used only for low current loads (<2 Amps) that needed isolation. I used something similar to Murata part number UWR-12/1250-D12A-C. I forget the part number of the exact one I used. It had a remote power sense line that I tied into the radio. Cost me about $40 in parts. Still working after all these years. It was built to power my Nomad Jukebox when they first cam out.
Digi-Key - 811-1901-5-ND (Manufacturer - UWR-12/1250-D12A-C)

Lifting the ground will only work if the charger is connected, so that is a poor choice.

Adding a resistance to the audio ground will limit the current flow in this path, but may not remove actual noise, so this may be a poor choice also.

Easiest thing, especially if you don't know how to solder is to use the Radio Shack isolator, or similar. I just googeled ground loop isolator. Some stuff poped up.

You would think in 2010, someone would have a cigarette lighter dc/dc converter option for less than $40 on the market. It's not rocket science, and a better solution than isolating the audio ground IMO. Oh well.

 

[LilDavy]

Well its definitely a problem with my vehicle. I tried it in my wife's vehicle (which is almost the same) and I don't hear any static at all when the Droid is charging. I even switched chargers. I'll have to figure something out

 

[tr0nllam]

I had the same problem in my car and a $6 ground loop isolator from ebay fixed the issue.

 

[LilDavy]

I had the same problem in my car and a $6 ground loop isolator from ebay fixed the issue.

Is the jack on the Droid 2.5mm or 3.5mm? I checked Ebay and I found a few isolators. Thanks

 

[tr0nllam]

The jack is 3.5mm

 

[ezekiel2000]

So something like this is all that's needed?

Ground Loop Isolator Noise Filter PDA Cell Phone IPOD - eBay (item 110452783587 end time Mar-31-10 15:38:58 PDT)

 

[LilDavy]

I think so - I just ordered one so I'll find out soon enough. For $7 its worth a try.

 

[tr0nllam]

yep, that's the same one I bought.

 

[Amadeus]

Say, that is a nice solution. I may try one out myself (different vehicle).