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Thread: Hard disk interference noise. (long)

  1. #1
    Maximum Bitrate MikeHunt79's Avatar
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    Hard disk interference noise. (long)

    Ok, this is the strangest problem i've had yet, and I can`t figure it out at all...

    Here is a rough diagram of my setup
    (red = 12v wire, blue = ground wire, green = audio signal wire) :



    Quick overview of setup:
    p75 powered by sproggy, running mpxplay. Has numeric keypad & text lcd display. I've been running this setup for around 6 months, using just my rear amp (in the boot/trunk) with no problems, until now.

    I spent yesterday putting in an amp for my front speakers, as my headunit got nicked. I mounted it in the glovebox, and used the same power wire that the computer was using, as the computer is (still) in the passenger footwell.

    Once I got everything wired up, I tested it with my minidisc player, and everything sounded great, all 8 speakers going. I used a Y lead to split the signal between the two amps.

    BUT.... When I tried the new front amp computer, it didn`t go well... As soon as I turned the computer on, I got whine from all of the front speakers powered by the front amp. It got worse when it started to boot, as everytime the computer accessed the hard disk, I would get a kind of rumbleing noise from the front speakers. Changing tracks Sounded horrible.

    SO.... I tried listening to the computer with just the rear amp (and rear speakers) and everything sounded ok again, perfect sound.

    I even tried pluging headphones in the jack of the computers soundcard, again great sound.

    I tried grounding the audio ground to the power ground on the computer, again, no luck. Still lots of rumbling.

    It's really strange that this is only happening with one amp, I would hae thought it would have been all or nothing. Looks like I`m stuck with no front speakers for the moment.

    The only thing I can think of is that it`s some sort of power issue, since the front amp and computer share the same wire (and fuse) from the battery, but I run seperate power wires to the rear amp.

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    Maximum Bitrate osirisdon's Avatar
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    Re: Hard disk interference noise. (long)

    Nice paint skills!!, But on a serious note.
    Originally posted by MikeHunt79
    The only thing I can think of is that it`s some sort of power issue, since the front amp and computer share the same wire (and fuse) from the battery, but I run seperate power wires to the rear amp.
    I agree with you.

  3. #3
    Maximum Bitrate MikeHunt79's Avatar
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    osirisdon: i was in a rush... paint had to do!

    Sometime this week i'm gonna try wiring the computers power seperately to the front amp to see if that makes any difference. If there is anything useful I can do to help solve this, please post. I'm well and truely stuck.

  4. #4
    Maximum Bitrate osirisdon's Avatar
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    I would venture out and say your amp is pulling more power than your computer, and since you have connected to the computer, it is making all that noise. But im not at that stage yet with my install. So I would not be 100% sure on this. Give it a try, once resolved let us know how it went.

    The Paint comment was a joke

  5. #5
    Maximum Bitrate MikeHunt79's Avatar
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    heh, I thought so..

    I think you are right about the amp tho, I`ll have to give it another shot with different wiring when i get time. I might try a beefier fuse also.

  6. #6
    Low Bitrate Ritalin Kid's Avatar
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    I had the very same problem and it turned out that (1) My Audio Cables were running down the same side of the car that the power cables were. (2) That grounding your carputer with some other piece of equipment is not a good idea because it can also cause ground loops and (3) Your car puter might be under powered as mine was which causes teh hard drive interference.. I replaced the PSU with a stronger one and got much better results.

  7. #7
    Maximum Bitrate MikeHunt79's Avatar
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    Originally posted by Ritalin Kid
    I had the very same problem and it turned out that (1) My Audio Cables were running down the same side of the car that the power cables were.
    I thought it was that aswell, but my audio cable is totally seperate, plus the cables only about 1 metre along. But, I have been getting some occasional crackling from one of the channels when using my minidisc on the front amp, so I`m gonna check the plugs on the amp (it was from e-bay afterall).

    Originally posted by Ritalin Kid
    (2) That grounding your carputer with some other piece of equipment is not a good idea because it can also cause ground loops.
    Agreed. I`m gonna try wiring the front amp and computer seperately, as I have no problem with the computer connected to the rear amp, which has seperate power wires to the battery.

    Originally posted by Ritalin Kid
    (3) Your car puter might be under powered as mine was which causes teh hard drive interference.. I replaced the PSU with a stronger one and got much better results.
    This things only a p75, 8meg ram, 10gig HD. It uses very little power (less than 30 watts i think), and doesn`t need a fan at all. My sproggy is easily capable of powering this, otherwise i`d consider adding another rail to the PSU or something.

    Thanx for the replies everyone.... gave me a few more ideas to help me figure this one out. (i`ll keep u posted when i get to sort it, but any more replied are appreciated).

  8. #8
    Variable Bitrate euro320i's Avatar
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    Wink Answer to you dilema..

    Hi Mikehunt79,

    I had the same problems as you and have spent many many hours pondering and very desparately tried almost every thing possible. Of course the first thing many of us as well as myself is to throw money at the problem. I tried a Ground loop Isolator - it works fantastic, but cuts off highs and lows. I tried a 1-F Cap, it helped with the VGA screen stability but now with the whine, I tried another AMP, and still had that nasty whine, I tired a more expensive Ground-loop isolator, same results, then I tried a chassis-loop isolator - then the PC wouldn't boot. I ripped the whole thing out and thought that the cabling was broken. (I can turn on the PC from the Drivers seat -PC in trunk) Then I visited a CARHIFI shop (high-end) in Frankfurt and they could not get rid of the whine either. But they gave me excellent advise, they say when they install high-end equipment, they never use the battery ground. As I saw on your diagram you have the amp connected to the battery posts. This will give you a ground potential difference, what you hear is the swinging of Power to and away from the battery. Try connecting all your ground to the chassis and you will feel better for it. It worked wonders for me. I have a Epia M800 with 80G IMB HD 384MRAM, GPS, with DVD drive, running into a Clarion DXZ 928R with Dolby ProLogicII Decoding with Coax AUX inputs. Hey! I watch all my vids in Dolby Surround!! Music comes out in multi channel as well!
    Don't give up, just change the grounding and it will sound sweet.
    Good luck ..

    o/______\o
    (oo_OO_oo)
    []o-----------o[]
    '94 320i


  9. #9
    Low Bitrate Ritalin Kid's Avatar
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    This things only a p75, 8meg ram, 10gig HD. It uses very little power (less than 30 watts i think), and doesn`t need a fan at all. My sproggy is easily capable of powering this, otherwise i`d consider adding another rail to the PSU or something.
    I would make sure normally you're talking 75 watts max as mine was 85 Watts and it seemed that the hard drive was pulling power from the sound card which cause the problem. Also remember older motherboards and parts are not as energy efficient as newer parts and processors especially older processors.

    Also I noticed you ran your ground from your battery to your amp.. this can also cause a very bad ground loop.. remember this is Direct Current. it's best to make the ground as short as possible to the frame or chasis of the car.

  10. #10
    Maximum Bitrate MikeHunt79's Avatar
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    Again, thanx for the replies. When I get some spare time (probably in a couple of weeks, due to copious amonts of coarsework), but when I do, I`ll first try grounding everything to the cars chassis, and then go from there. Plus the fact that i've already run two power wires to the dash means that I can use each one as for each component (front amp and computer), which I wanted to do anyway. I also know not to bother with a ground loop isolator now aswell. Thanx euro320i

    Also, this is a kinda temporary computer setup, but it's nice to get the problems smoothed out before i get my final system in there. (Celery 500 which should be able to do multi-channel surround like euro320i mentioned).

    Edit: One last thing... I`ll have to measure how much power this system is pulling, but I think it should be within the specifications of the sproggy design. Even tho it's using older, less power effeicient components, the PSU has coped fine for a good while now. It wouldn`t hurt to check anyway. I think it`s the way the power is getting to the sproggy thats the problem.

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