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Thread: Strange issue - probably not ground-loop problem

  1. 08-26-2006, 05:37 AM #1
    Jirka Jirout
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    Strange issue - probably not ground-loop problem

    I have a strange issue with my installation. What I want is on attached image "audio1" - a setup with computer (Mac mini powered by Car Netx P1900) + USB audio adapter, a DVD player, A/V switch and a head unit (old Sony CD-XA900). The idea is that I could freely choose the source of sound to be brought to the headunit's aux input.

    When I connect this, the sound from DVD player is perfect, while the sound from the computer suffers from what looks like a ground-loop problem ("brumming" noise). There is no difference whatsoever between situation when the engine is and is not running. No change either when I disconnect the DVD player from the A/V switch. OK, the A/V switch seems to be the source of problem.

    So I remove the A/V switch and connect the output from the USB directly to the head unit's inputs (Audio3.png attached). Voila, the sound is perfect as well. Therefore it looks like it really is the switch.

    Since I want to be able to play the DVD player sound thru the head unit, I connect the player's output to the input of the usb audio adapter and use software that simply routes the input to the output (Audio2.png attached). Guess what? The problem is back.

    I have verified all the grounding points, experimented with different grounding wires etc. but absolutely no success. What puzzles me that I am not able to isolate the piece of equipment that is causing this.
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  2. 08-26-2006, 02:19 PM #2
    Jahntassa
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    Did you try switching cables around? Try disconnecting wires while everything is on (the audio wires, not power, obviously) and see at what point the noise goes away. You need to isolate if it's the DVD player, the switch, or if there's some odd voltage going between the USB audio outputs and the DVD player.

    Hook it up the way you want it to be, then listen to where the hum is, and start unplugging things, at least see if that gets you anywhere. Also try switching the inputs to the switch you're using. See if swapping the connections between the DVD and USB adapter on the switch makes the hum follow, or if it's a particular input.
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