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  1. wotan's Avatar
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       #1  
    I've got the sprint charger and get horrible noise through my FM modulator. I've tried two different 12v splitters and 3 different FM modulators as well as 2 different vehicles. EVERY time I've got both the phone plugged into the charger and the FM modulator, I get noise. I can run the phone on the charger with headphones and it works.... I can also run the phone off the charger into the FM modulator and it works great.

    What should I do? I need both FM modulator and charger to work at the same time.... do I try another charger or ???????

    I'm stumped and frustrated!
  2. Samatva's Avatar
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    #2  
    My FM modulator has a USB port (and SD slot) - will read MP3s right out of the phone, so no audio cord is needed.

    I'm not near that car, and don't remember the brand/model - it's a cheap one ($21 about 2 yrs ago).

    In my regular vehicle, I bought a JVC 80 watt power amp that has line-level inputs, and run the earphone output into it. It was $89 from WalMart and works great - no discernible charger noise - but I don't know that WalMart carries it anymore.
    I have no radio (except my Nokia N800). I used to find something great to listen to via thestreamcenter.com/pda/ on my 700p, but can't yet get reliable streaming on my Pre...
    Palm VIIx -> Kyocera 6135 -> Kyocera 7135 -> Palm 700p -> Palm Pre
  3. #3  
    I've had the same problem. Not sure there's anything you can do about it. This happened with my old charger and with my new charger for my Pre. I drive a 12 passenger van now that has two built in charging ports and having them plugged into the two different ports has greatly reduced the noise (it's still there, but barely and definitely tolerable). If I use my splitter I still get the noise in the van, so the problem is definitely being plugged into the same splitter. I guess my one option I haven't tried is using my inverter to plug my wall charger into the splitter with my FM modulator...seems like that'd be a bit bulky but could possibly fix the issue...I'll try it later today and let you know.
  4. #4  
    Okay, I tried it out. With the FM Modulator plugged into the splitter with the car charger, lots of noise, would get really annoying on a long drive. With the FM Modulator plugged into the splitter with my phone plugged into the USB of my inverter (sorry, forgot to look at the model, but it's a simple inverter that plugs into one of the car charger ports, not one that hard wires to your battery) the noise was reduced, but probably not enough to spend the money on it. In addition, I'd forgotten the inverter has a fan in it which was another unnecessary noise added to the mix...but I blast my music so that wouldn't be an issue. Also tried the actual plug for the inverter instead of the USB, no noticeable difference with the USB, tho possibly a little more noise. Good luck finding a solution. I'm curious about Samatva's FM Modulator that has a USB port on it...I have the Scosche FM Modulator.
  5. dbett's Avatar
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    #5  
    It's a ground loop.

    Look for a Ground Loop Isolator. Amazon sells them, as does Radio Shack.
  6. JKTex's Avatar
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    #6  
    Quote Originally Posted by dbett View Post
    It's a ground loop.

    Look for a Ground Loop Isolator. Amazon sells them, as does Radio Shack.
    Bingo.
  7. #7  
    The alternator is most likely putting interference in the electrical system. I have seen this with HAM radio stuff. Some sort of filter possibly? Not sure if it is only noisy on the electrical side, or just in general over the air noise.

    Ok someone else already covered it...ignore me ;P
    Last edited by kc0eks; 08/03/2009 at 06:31 PM. Reason: cuz!
  8. wotan's Avatar
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       #8  
    This makes sense to me.... but why does my ipod not do it?
  9. JKTex's Avatar
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    #9  
    Quote Originally Posted by wotan View Post
    This makes sense to me.... but why does my ipod not do it?
    Is it connected to the same things, the same way? My guess is no therefore it's not the same ground loop issue.
  10. wotan's Avatar
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       #10  
    Quote Originally Posted by JKTex View Post
    Is it connected to the same things, the same way? My guess is no therefore it's not the same ground loop issue.
    It's connected to a different charger (an ipod charger) but the same FM mod... no ground loop.
  11. dbett's Avatar
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    #11  
    Quote Originally Posted by wotan View Post
    It's connected to a different charger (an ipod charger) but the same FM mod... no ground loop.
    I'm not an electrical engineer, so I don't know the specifics. But certain chargers can (by design or luck) prevent the ground loop.

    If you have a local Radio Shack, pick up an isolator (may also need RCA to headphone jack adapter cables) and try it out. If it doesn't fix it, return the items. Nothing to lose.
  12. #12  
    I am an electrical engineer, but ground loops are one of those things that exist in the practical world (as opposed to the "physics" wires we use in school with zero resistance). However, from what I understand, the issue is that when you connect your Pre to your FM modulator with a cable, you've created a bigger system. If you charge your Pre with another cable, it has a ground (0v) as defined by the car charger, which is connected to the cigarette lighter. Your FM modulator also has a ground as defined by its charger connected to a different cigarette lighter. If there is any resistance whatsoever between the ground in the first cigarette lighter and the ground in the second cigarette lighter, then they will be at different voltages. But since the Pre and FM modulator are connected via the audio cable, which also has a ground level, the grounds of the two cigarette lighters will "talk" to each other through the audio cable, causing noise. This is what is meant by ground loop (the loop is from power A to Pre, Pre to Modulator, Modulator to power B, power B to power A through the chassis).

    An isolator fixes the problem by breaking the circuit, generally by inserting transformers into the connection. You can have an isolator anywhere in the circuit so long as it breaks the loop. The easiest thing to do is have an isolator in the audio connection, since you can get to that connection readily. You do have to ensure that the GLI has a good frequency response so it doesn't impact your audio, but I think there are lots of these around.

    I think that if you charge the Pre via the Touchstone it shouldn't cause a ground loop. The Touchstone would do the same thing an isolator would do (it's a transformer). But after some searching, I haven't found too many people talking about this. Other chargers may also break the ground loop by using a transformer somewhere. An inverter, for example, probably uses a transformer, so it makes sense that you wouldn't get a ground loop when using it to charge your Pre.
    Palm III-->Handspring Visor-->Sony Clie PEG-NR70-->no PDA -->Palm Treo 755p-->Palm Pre-->HP Veer
  13. #13  
    It would be awesome if the Pre had a built in modulator. Of course, that would make it more bulky.

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