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Thread: Alternate sound

  1. #1
    Maximum Bitrate GoHybrid's Avatar
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    Alternate sound

    after a raging 10 hour solderfest i finally got my P1900, eclipse AVN5435, tsunami 1.2F cap, and eclipse xa5000 installed. I plug in my mac mini and am greeted by horrible noise. I can get it to sound reasonably clear at high volume but when the music gets soft or quiets down... *crrrrrrk* *crrrrrk* with the mouse and HD. So i do my troubleshooting.

    What is the source of the noise? In my mind, it's the mac. I plugged in my mp3 player to the same cable that was going to the mini's speaker jack and nothing but pure high fidelity. Same goes for CD player, DVDs, AM/FM,... no noise, no hum, no alternator whine... it's all perfect until we get to the mini. I think i can rule out faulty cables or induced noise from the power supply or alternator.

    For those who might ask, I'm running 4ga from the battery to the cap and amp. Resistance to the negative battery terminal from that ground point is 2 ohms. P1900 gets 8ga straight off the battery and grounds to a factory grounding point measuring 0.1 ohms (negligible). Power runs on the driver's side, rca signal runs straight down the middle, and speaker wires run on the passenger's side. Amp and cap are mounted to MDF. I've also added an additional 4ga wire from the chassis to negative battery terminal. Every connection excluding the 4ga wire is soldered and heat-shrinked.

    So the point of all that is to show what i've done to try and prevent induced noise, ground loops etc... and it seems to have worked for everything else. Would I be correct in assuming that the sound hardware inside the mini is generating all this noise? Would an external USB sound card solve the issue?

    It's 3am, i've been working on this for the last 10 straight hours. I'd like to preemptively apologize for anything that manifests itself as rambling. or if i've missed something terribly obvious here. This is pretty much the last hurdle for the carpc project so i'm anxious to get it right.

    thanks in advance for any help.
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  2. #2
    QCar Creator Jirka Jirout's Avatar
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    Quote Originally Posted by GoHybrid
    Would an external USB sound card solve the issue?
    It is rather likely it would. It did solve very similar problems I had (with a PPC-based mac-mini). If you have a new (Intel-based) Mini, you might also be able to use the optical output (if the rest of your audio setup supports it).

  3. #3
    Maximum Bitrate GoHybrid's Avatar
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    okay, redo: did a little homework and came up with this:

    http://www.core-sound.com/transit/1.php

    Looks like i could connect with the same connector on both ends... and come out with the 1/8" headphone jack that plugs right into my cable. Anyone had experiences with this? Am I on the right track?
    Et ipsa scientia potestas est.

    Worklog for my 2007 Civic Si ...f*** it...
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  4. #4
    Constant Bitrate
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    u can also try this,
    http://www.griffintechnology.com/products/imic/

    I am using the older version (now with ppc mini) and it works well

    they also have the firewave but have not tried myself and have heard mixed results....ymmv
    __________
    rgds, raceer


  5. #5
    CarFrontEnd Creator iamgnat's Avatar
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    It could still be a ground loop, though you do seem to know what you are doing. Since your other devices aren't running off the P1900, it's hard to rule it out. You could run an extension cord out to the car and power the Mini off AC, then you would know if it is the Mini or P1900 for sure.

    You mention that it happens when you move the mouse. I know my Al PB has some CPU chatter when I move the mouse and my G5 does it to some degree too. I haven't noticed it in my Mini, my wife's Al PB, or our old dual 800 G4. Maybe you have a bad case of that going on? You should notice it if you take it inside and hook it up to some speakers if that is the case.

    Really it depends on where the issue is as to if an external sound card will help. I don't know how they effect the CPU chatter issue and if it is a ground loop and not powered/grounded to a different point then it shouldn't matter there either.

    -dave
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  6. #6
    Maximum Bitrate GoHybrid's Avatar
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    Thanks. I'll try running the mac off AC. If that clears up the problem... what steps do i need to take to fix it at the P1900? It seems like it is adequately powered/grounded. I have other factory ground points i could use i suppose, but would that fix it?
    Et ipsa scientia potestas est.

    Worklog for my 2007 Civic Si ...f*** it...
    Pictures of the Corolla (retired)here
    Need to make something? Here are a few ideas.

  7. #7
    CarFrontEnd Creator iamgnat's Avatar
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    Quote Originally Posted by GoHybrid
    Thanks. I'll try running the mac off AC. If that clears up the problem... what steps do i need to take to fix it at the P1900? It seems like it is adequately powered/grounded. I have other factory ground points i could use i suppose, but would that fix it?
    If it is fine off the AC, then it is a ground loop. Check the Audio forums FAQs as they have some good info.

    Just because a spot works well for one ground, doesn't mean it is good for other grounds. Try the other ground points (though you don't want to run too far to ground) to see if they help, you may also have to make your own.

    -dave
    My pathetic worklog.
    CarFrontEnd (now it's own sub-forum!!!!)

  8. #8
    Maximum Bitrate GoHybrid's Avatar
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    fair enough. i'll post results as soon as i have some.
    Et ipsa scientia potestas est.

    Worklog for my 2007 Civic Si ...f*** it...
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  9. #9
    Maximum Bitrate GoHybrid's Avatar
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    i worked the problem a little bit. I ran 8ga ground straight off the battery to the P1900, still no improvement in the noise. So i disconnected my ground and found out something interesting... the P1900 continues to run despite having no ground. I have to wonder if by some perversion of electronics the P1900 is grounding itself through the mini 18v connector, through the motherboard and out through the RCA's and back to the chassis ground that way. I'm thinking i need to install an isolator on the audio output, or just use a USB soundcard and go optical from the mac then rca to the head unit. Any more ideas?
    Et ipsa scientia potestas est.

    Worklog for my 2007 Civic Si ...f*** it...
    Pictures of the Corolla (retired)here
    Need to make something? Here are a few ideas.

  10. #10
    Maximum Bitrate GoHybrid's Avatar
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    I believe I've confirmed my theory. With the mac plugged into the AUX input, and the power connectors from the p1900, the P1900 will run without a ground. As soon as I remove the headphone plug, the power supply shuts off. Before I start dropping money, does anybody agree that a ground loop isolator would solve this by eliminating the ground path through the RCA plugs?

    [further testing included running off wall AC which yielded zero noise, inverter AC which was almost as good. the P1900 is the only part that seems to want to ground anywhere but where it should.]
    Et ipsa scientia potestas est.

    Worklog for my 2007 Civic Si ...f*** it...
    Pictures of the Corolla (retired)here
    Need to make something? Here are a few ideas.

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