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Thread: Audio hum in car using AC-DC Power adapter.

  1. #1
    Join Date
    Feb 2005

    Audio hum in car using AC-DC Power adapter.

    Has anyone a fix for this? I'm using a 2 AC plug output AC-DC adapter in my car to power my xbox and LCD Panel. I noticed when I unplug the lcd panel (says 12v. but multimeter reads 16v, which is why I didn't try to hard wire it instead, 7inch 16x9) it gets just a LITTLE quieter but still definitely hear it. Now, when i turn the XBOX and LCD off, i still here the humm. It's not alt. wine, as it's always the same sound, no matter if I gas it or not. As soon as i flip the switch off, it goes away. I believe it's a Linksys model AC-DC convertor rated well beyond the power i'm needing.
    Anyone else found a cure for this? I haven't try running the power and RCA's separately yet, HOWEVER, even with the power adapters unplugged, I still get the hum, noticeably. I'm so down right now, as i've spend my time over the past 2 weeks fiberglassing a nice looking mold and all to fix everything all beautifully, and spent my time pulling everything apart to keep a professional looking install. So i'd really like to get this working without any audio hum. It's patched through my Sony Head unit input. Thank a bunch for any feedback you can give me for help here. :-)

  2. #2
    Variable Bitrate Osiris's Avatar
    Join Date
    Apr 2004
    Atlanta (kennesaw) GA
    I know this sounds really simple but try adjusting or wiggling the audio wire connections at the point they connect at. That what worked for me.
    Osiris Networx

    --Tuning is all about price vs performance. You've got to find your own medium.--

  3. #3
    Join Date
    Feb 2005
    Nope. Didn't work. Of all things (1 week old only) the invertor had a little smoke come out of it, so i gotta buy another. Damn it! Either event, using a power adapter to power an XBox and 7inch lcd panel (as long as it works at all even, meaning it's not pulling that much current verses the DC-AC can actually throw out.) there shouldn't normally be any reason for getting any buzz or hum through audio jacks right? If all these people here are using a computer and such hooked up to there head units, and no apparent sound hum, then convertors in general should be just fine to use for my xbox purpose? Unless it was a fluke that mine was in the process of going bad, and that's the cause of the noise, since it went out on me after 1 week, Heck, didn't even use it but once (for 2 minutes) But since the cig. plug was cut off to hardwire, i doubt CompUSA will swap it out for me. Sucks.

    But in general as mentioned, power convertors shouldn't cause any kind of audio buzz, or noise right?

  4. #4
    MySQL Error MatrixPC's Avatar
    Join Date
    Sep 2003
    Beach City, Socal
    Which one making a "hummmm"? The inverter? Xbox's PSU? LCD?
    Buy one of those true sinewave inverter and your problem will be gone, but those aren't cheap.
    Another option is 'hacking' the PSU. There are some old thread regarding hacking the PSU to remove couple filter/rectifier inside the PSU. I havn't done yet so I don't know.
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  5. #5
    Join Date
    Jan 2005
    Hi, the problem with cheap inverters is that they do not create nice clean sine waves. They create square waves that contain many different sine waves put together called harmonics. Some of these "other" sine waves can be at a frequency that you speakers and your wiring system in your car will pick up, this creates the hum. Usually products that produce lots of high power harmonics such as inverters are well shielded, that is they are encased in a metal box and the metal box is attached to a ground (negative).

    My sugestion is this. Open up your unit, and check if the metal casing is properly grounded (meaning there is a wire hooked up to the case that attaches to a ground). If not, and if no other electronic comonents touch the case, then wire a ground (negative) wire to it yourself and hook it up to a ground (negative) point.

    If you find that the case is already hooked up to ground, then your next step would be to either build your own metal case, put the inverter into it, and ground your new case. Or you could possibly try wrapping your inverter in metal window screen material and hook the screen to ground with a wire.

    With either solution you must ensure that your new metal casing does not contact any other open wires in your car since your case is now a ground point and you don't want to short out and fry other stuff in your car.

    Hope that helped. Good luck.

  6. #6
    Join Date
    Aug 2004
    Personally I wouldnt go modifying my inverter if I didnt have much knowledge in electronices.

    I had a buzz that used to occur only when I had the car running. I fixed it by earthing one of the screwes in the back of my computer power supply to a good ground on my car body.

    But I not sure if the problem your describing is that same one I had

  7. #7
    Join Date
    Feb 2005
    I appreciate the help here guys. I'll try the grounding the case. One thing i did try tonight is i grounded the RCA cables directly to car ground. Some went away, but when i used an inline RCA filter, and grounded it (RCA ground) again, a lot of feedback hum went away. Still get SOME, but not quite as bad at least. I'll have to try grounding the case of the invertor and see if that helps more. If any idea's, please lemme know.

  8. #8
    Join Date
    Feb 2005
    Hey, cool. I went out and bought yet another AC-DC power invertor yesterday from Walmart up the street. It's $44.95 and it outputs 375 watts continuous (750max). And it has a modified sine wave output,build in speed controlled fan, 2 separate transformers for stability. Now, my Xbox and TV display never glitches at all, It's super stable, and i today took out the ground loop isolator adapter i was using with the ground on RCA grounded to chassis of vehicle, and found it wasn't need due to the modified sine wave output. NOT that it's COMPLETELY silent, BUT when music/movies are playing in it, you can't hear much of any difference. Similar to using an RF modulator with a 10 disc changer (for other MECP installers out there.) Good enough. Too bad my gear doesn't have an optical input. Hehe. Everythings working great though.
    I might try to put a small computer in it after all. In addition. So i can use a Garmen USB GPS device. Ultimately that's what i'm wanting in the longrun. Everything i need my XBox already does (games, media system, dvd player, music player, arcade games, internet browser, e-mail client, & linux box.) I know some have got some USB GPS devices working fine on xbox in linux, but i really just don't like linux. Compiling, debugging, building drivers, just not me. I guess i'm just too into windows. To each it's own i guess.

  9. #9
    Constant Bitrate csnowman00's Avatar
    Join Date
    Feb 2005
    Wilkes-Barre, PA
    i had a similar problem with my first car pc, the problem was ground a search and your learn all about it. i picked up a ground loop isolator between my carpc and my head unit and it stopped the problem.
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