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Buzz when using 12V aux power and aux audio

Discussion in 'Gen 3 Prius Audio and Electronics' started by joshjta, Nov 17, 2012.

  1. joshjta

    joshjta New Member

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    When my 2012 Prius II has audio in aux mode, for using the 3.5 mm aux audio jack, a super-loud and annoying buzz is created when I plug my laptop's power supply into the car via a 12V DC to 115V AC power converter plugged into either of the car's 12V aux power jacks.

    I'm trying to listen to video lectures on DVD played on my laptop, feeding audio from my laptop to the car (2012 Prius II) using the 3.5 mm aux audio jack. I get clear sound when the laptop is running off battery. However, when I plug a 12V DC to 115V AC power converter into one of the 12V aux power jacks, there is a quiet and slightly annoying buzz. When I then plug my laptop's power supply into the power converter (whether or not my laptop is connected to its power supply), the buzz's loudness and annoyance get magnified 10-fold, even if nothing is plugged into the aux audio jack. If the Prius audio mode gets switched to USB mode (with no input from the laptop), there is no buzz, so this seems particular to aux mode audio. (I cannot drive the car's audio from a video player on my laptop via USB mode, can I?)

    I thought I remember reading a warning about this buzz and someone had a workaround, possibly involving some extra interface, but my searches on this forum aren't turning up anything. I plugged a surge protector into the power converter and got a mid-volume buzz, which went back to a full-volume buzz with the laptop power supply plugged in.

    Any ideas?

    Thanks
     
    #1 joshjta, Nov 17, 2012
  2. dhancock

    dhancock 2 Prius Family

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    Your issue is due to ground loops (the aux input ground in a loop with the 12 v ground used on the laptop power supply). I ran into a similar problem years ago with my 07 Prius and a MP3 player using a charger cord. The answer is to purchase a Ground Loop Isolator, such as this one from Radio Shack and connect it (using some audio adapters going from RCA pin jacks to 3.5 mm) between the laptop audio out and the Aux jack.
     
    #2 dhancock, Nov 18, 2012
    bwilson4web likes this.
  3. joshjta

    joshjta New Member

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    Tried that Ground Loop Isolater and it reduced the buzz from intolerable to merely annoying. Thanks for the tip! I bought a second Ground Loop Isolater for comparison from Best Buy and it didn't seem to help much at all. I tried linking the two up in series and got no improvement. Maybe I'll try the same from Fry's.

    Other people have complained about the ground loop between the Aux Audio and Aux 12V power. In 2008 Toyota issued a fix for this problem for 2007-2008 Prii and other Toyotas: http://www.toyotapart.com/NOISE_FROM_AUXILIARY_PORT_WITH_EXTERNAL_DEVICE_T-SB-0067-08.pdf.

    However, when I went to the dealer, they said because I was running a DC-to-AC converter that the problem was the "after-market accessory" I was using and not the car. Of course they said the T-SB from 2008 did not apply in any case. I told them I would test a Ground Loop Isolater and if it helped, then that would indicate the problem from 2008 had never been fixed in the 2012 Prius. I might try to call the Toyota hotline today.
     
    #3 joshjta, Nov 21, 2012
  4. dhancock

    dhancock 2 Prius Family

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    I didn't catch the DC to AC converter thing before. The problem is that the converter's 60Hz output has all sorts of harmonics (hence the buzz). There are some "Pure Sine Wave" inverters, but I don't know how "Pure" they really are.

    Perhaps the solution is to run the laptop only on batteries and to purchase an extra battery or two.
     
    #4 dhancock, Nov 21, 2012
  5. joshjta

    joshjta New Member

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    The problem is that my laptop's display is extremely dark except when it's plugged in, so that I can't find the pause button, etc. I'll look into the Pure Sine Wave inverters - thanks!
     
    #5 joshjta, Nov 22, 2012
  6. cwerdna

    cwerdna Senior Member

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    There may be a power plan setting for different brightness levels depending on whether you're plugged in. Can't you press the keys needed to turn up the brightness?

    Also, some laptops, like Lenovos have a CMOS setting to prevent/allow you to access higher brightness levels while on battery. I'm guessing they did it so that people don't complain about crap battery life and/or they can do better on battery rundown tests (in reviews) on "full" brightness.
     
    #6 cwerdna, Nov 22, 2012
  7. tach18k

    tach18k Member

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    on Dell computers you can get a dc power supply that plugs into the dc power socket (cig lighter)
     
    #7 tach18k, Nov 23, 2012
  8. bubbatech

    bubbatech Member

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    Your problem is the dc to ac inverter. You will have much better luck with a computer power supply designed for a car. Dc inverters often generate a tremendous amount of electrical noise because they chop the DC up and step it up with a transformer. The output from these can be a near square wave, generating a large amount of harmonics.
     
    #8 bubbatech, Nov 23, 2012
  9. joshjta

    joshjta New Member

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    Thanks for the help, folks. I now have 3 live options: 1) use a ground loop isolater to make the buzz tolerable. 2) Change the power mode to get full screen brightness when using the laptop on battery (had failed to find a way before, but finally figured it out). 3) Don't use the Prius audio system, instead sending laptop audio to a Jabra Cruser2 bluetooth speaker that hung from the sun visor of my old car to use with my phone.

    It would be cooler to use the Prius sound system with bluetooth, but the Prius doesn't think it's the headset that my laptop wants it to be and my computer isn't the mp3 player that the Prius wants it to be. Too bad I can't get my laptop to emulate an mp3 player somehow (though I'm getting the sound from playing DVD's) or get a software driver from Toyota that I could download to my laptop to pair the Prius to my laptop.

    That leaves the future possibilities of a purer inverter or a dc laptop power supply (found one of the latter for $108). The former would be more versatile (though not as certain to work), allowing me to power other stuff and making my laptop more easily replaceable.

    Lots of possibilities now - thanks!
     
    #9 joshjta, Nov 25, 2012
  10. jnadke

    jnadke Junior Member

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    Yeah, your problem is part ground loop (this will only cause noise to show up that's generated from the car), and part the inverter itself.

    Try to find a Pure Sine Wave inverter.

    Most 120V car inverters rapidly pulse 120V to produce what "seems like" 120V. For most things, this is fine. The problem is, this "rapid pulsing" has its own frequency that is ABOVE 60hz (frequency aliasing), and typically isn't removed by your computer power supply (because it's not expected to be there).

    This gets transferred to your audio jack, since it's pulling from that power.

    [​IMG]
     
    #10 jnadke, Nov 27, 2012
  11. tach18k

    tach18k Member

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    also make sure your cable in plugged in all the way
     
    #11 tach18k, Nov 27, 2012
  12. joshjta

    joshjta New Member

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    #12 joshjta, Nov 28, 2012
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