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Audio issues - maybe ground related?

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  • Audio issues - maybe ground related?

    Hi all,

    Finally got around to the first proper road test of the car pc yesteday, but came across a problem.

    I had given it a bit of a test by wiring up the car pc +12v and 0v to the same feed as the amp a few weeks back, but had terrible noises.

    So, I've now done the proper thing and run a 12v feed from the battery, and the ground is tapped onto a nice nut in the engine bay - it's a good ground.

    I took the car out, and when i powered up the pc with the audio cable disconnected everything is fine, and the picture on the tft is great.
    When I connect the audio cable, there is a bit of fizzing and popping when the pc boots (I think because the audio levels are at 100%) then when windows loads the outputs go back down to about 10% each and it sounds fine - except i can hear the whine of the engine when i rev it if there is no music playing.
    However, there is now intereference on the tft, best described as a kind of 'bar ripple'. It doesn't ruin the picture but is very visible.

    Is this a ground loop problem?

    The tft is running off the cigar lighter, the pc is run of it's own power and ground, and the amp is too.

    The only thing I was thinking is that, with the way I've built my case, the pc m/b is mounted on plastic lugs so has no metal contact with the case. The pc's ground only comes from the psu. Should I spur a wire from one of the screw holes onto the case and then ground the case from the psu too?

    Thanks in advance,

    Components: Lilliput 8" Touch, M10000 Nehemiah, 40GB Hitachi 2.5" Hdd, WPPS80 DC-DC power supply, custom enclosure, GPS Mouse, MediaRemote, Zippy Illuminated Mini Keyboard
    To Do: Sort out my startup issues - Build tank circuit.
    % Complete: 95