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Thread: Audio Distortion/Interference

  1. #1
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    Audio Distortion/Interference

    I finally managed to through all my carputer components in car...it's in beta testing period

    My audio has a humming/buzzing noise in the background.
    I'm running on an dc-ac inverter (350watts) and a clarion fm modulator (powered and grounded to cig lighter) The computer and sound card are powered through inverter and grounded to chasis. The power cable (10 awg) is going along with the rca cables.

    Here's what I've observed:

    1) There is no buzz when I used headsets in the truck directly after my sound card (external usb extigy)
    2) The buzz remains constant (volume -db) while moving the volume level up/down on computer volume control.
    3) The volume varies, increases/decreases respectively when changing volume on Head Unit.

    So far i'm concluding either the rca cables themselves picking up interference from power cable (and head unit just amplifies it) or the fm modulator is not grounded properly.

    I'm not sure if ground loop isolator will work, so far I haven't tried it. Ideally, I would like to fix the problem by fixing the cause and not bandaging it.

    Has anyone else had similar observations and has a remedy? Anyone know if ground loop isolator will help?

    Can someone please share their opinion and help me...?

    Thanks

  2. #2
    Variable Bitrate lawrence's Avatar
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  3. #3
    Variable Bitrate lawrence's Avatar
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    had the same condition -- tried a optical to a dts prossor and noise was gone
    the ran sound card to aux input of a sony head unit and all is good +
    all in all get rid of fm mod = pc makes to much rf to use fm mod..

  4. #4
    Maximum Bitrate Snootch's Avatar
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    I assume that you are using the stock stereo? My recommendations:
    1) check all your grounds, keep them as short as possible, and make sure they have a good bond to clean, solid metal.
    2) Make sure the ground to the FM mod is good. Ground it to the same spot as the factory radio.
    3) Ditch the FM modulator. If you want to keep the factory radio, see if there was a factory option for a CD changer for the radio you have. There might be a way to get an aux input to the factory deck. If not, you will want to install an aftermarket unit.
    The proximity of your RCA's to your power wires mean nothing. What is the current running through that power wire's return path? It's the ground through the entire body of the car. There is no way to get your RCA's away from that. However, your RCA's might be close to a factory wiring harness, and they might be picking up noise from that.
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  5. #5
    Maximum Bitrate falconey's Avatar
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    I've heard the ground loop isolaters work, but all they do is hide the problem(s). I've had an fm modulater running and had no issues. HU got stolen so I bought another one with AUX ins. You have to make sure the modulater has a good ground. Also make sure you don't ground it with any other components to your system. I've found that this is the best way to ground modulaters. In the end though what you have IS a grounding issue so you just have to trouble shoot to come up with the exact problem.

  6. #6
    Maximum Bitrate Snootch's Avatar
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  7. #7
    Variable Bitrate Ashlawn Kemling's Avatar
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    Quote Originally Posted by falconey
    I've heard the ground loop isolaters work, but all they do is hide the problem(s). I've had an fm modulater running and had no issues. HU got stolen so I bought another one with AUX ins. You have to make sure the modulater has a good ground. Also make sure you don't ground it with any other components to your system. I've found that this is the best way to ground modulaters. In the end though what you have IS a grounding issue so you just have to trouble shoot to come up with the exact problem.
    Ground loop isolators DO work! I had the worst time with engine noise interference. I tried grounding directly to the frame instead of straight to the battery. The battery ground worked better, but I still had to put something in there to remove the noise. The Passche $20 filter from Wal-Mart works nicely.

  8. #8
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    EDIT #2: Well, just drove my car today and the noise is back. It's weird. sometimes it's there and sometimes it isn't. I'm gonna keep working on this, but can anyone else think of a solution?

    EDIT: Figured it out. It was a grounding issue. I grounded the computer and all the noise went away.

    I'm having a similar problem, only I know it's not the FM modulator I'm using. The reason I know this is that I can plug my portable CD player into the modulator and everything plays fine with no noise. As soon as I plug in my computer I get the noise again. I think it has something to do with the power to the computer. My inverter is in front under the passenger seat and then I run an extension cord to the trunk where the computer is. I'm thinking it might be the grounding. I'm pretty sure the inverter is grounded correctly. It may not be though because I had CircuitCity install it because I wasn't comfortable drilling through my car firewall. I'll have to check on it. The computer ground would just be going through the inverter then. Should I put another ground on the computer? If so, how should I go about doing it?

    Thanks

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