stereo whistling
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  1. #1
    1000+ Posts cav91's Avatar
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    Default stereo whistling

    My car's stereo has had a whistle that goes higher and lower pitch with engine revs. It's running a 5 channel amp. So all speakers are amplified.
    Ive tried making bigger earth cables, and better RCA leads. However nothing helps. It has engine noice supressors on the Rca's just before they go into the amp. It also has supressors on the power from battery and power from ignition to the stereo. I have no idea what else to check.

    Anyone got any other ideas?

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  2. #2
    Fellow Frogger! 908HDI's Avatar
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    Sounds like the regulator or possible non resistor type sparlk plugs in use.

  3. #3
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    Quote Originally Posted by cav91 View Post
    My car's stereo has had a whistle that goes higher and lower pitch with engine revs. It's running a 5 channel amp. So all speakers are amplified.
    Ive tried making bigger earth cables, and better RCA leads. However nothing helps. It has engine noice supressors on the Rca's just before they go into the amp. It also has supressors on the power from battery and power from ignition to the stereo. I have no idea what else to check.

    Anyone got any other ideas?
    Sounds(!) like alternator whine.
    Try and figure out if it is coming from the deck or the amp. You could feed your ipod etc directly into the amp and see if the whine is still there.

    If it is, then I would suggest to try powering the amp via wires direct from the battery, both positive and negative. Have the amp body not grounded at it's mounting position, use rubber mounts etc.

    Cheers
    spiz

  4. #4
    1000+ Posts schlitzaugen's Avatar
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    Maybe your filters may not be efficient on the frequency you're trying to chop off. Most of what you listed is designed to cut off radio frequencies, whereas the whine is a low frequency (somewhere around 10kHz-12KHz maybe)?

    I would try to find out where the noise is coming from, say by powering the unit off a different source (whilst still in car). Switch the engine on, Any noise? Start the engine. Any noise now? If no, then it's coming through the power wires. Repeat procedure with the unit powered by the car battery (engine off, then on, see when the whine appears). If noise comes with switching on the engine, try disconnecting the alternator (run engine off battery) see if the noise is still there.

    I think it's all about taking your time and finding clear cut experiments like these to help you understand where the problem comes from.
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  5. #5
    1000+ Posts cav91's Avatar
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    Quote Originally Posted by 908HDI View Post
    Sounds like the regulator or possible non resistor type sparlk plugs in use.
    I do like the idea of the resisted spark plugs. Not sure what its got, but I did change them about 3,000kms ago.
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  6. #6
    1000+ Posts cav91's Avatar
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    The alternator has been changed, it was whining with the old one and the new one. The amp is mounted on a piece of wood. So it not getting earth there. However the earth cable does go to the body in the boot. I'll try the i pod trick.
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  7. #7
    1000+ Posts cav91's Avatar
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    Quote Originally Posted by schlitzaugen View Post
    Maybe your filters may not be efficient on the frequency you're trying to chop off. Most of what you listed is designed to cut off radio frequencies, whereas the whine is a low frequency (somewhere around 10kHz-12KHz maybe)?

    I would try to find out where the noise is coming from, say by powering the unit off a different source (whilst still in car). Switch the engine on, Any noise? Start the engine. Any noise now? If no, then it's coming through the power wires. Repeat procedure with the unit powered by the car battery (engine off, then on, see when the whine appears). If noise comes with switching on the engine, try disconnecting the alternator (run engine off battery) see if the noise is still there.

    I think it's all about taking your time and finding clear cut experiments like these to help you understand where the problem comes from.
    The Whine is a really high pitch so I assume its high frequency not low.

    When powering the radio from different source, do you mean get wires direct from the battery of use a battery that has nothing to do with the car in question?
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  8. #8
    1000+ Posts schlitzaugen's Avatar
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    Separate battery.

    I meant radio frequencies above 12kHz (or say 20kHz given that the audio band doesn't really reach higher than that). Considering radio frequencies go to about 300GHz, 12kHz is not that high.
    Last edited by schlitzaugen; 16th May 2012 at 04:20 PM.
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  9. #9
    1000+ Posts schlitzaugen's Avatar
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    Quote Originally Posted by cav91 View Post
    The alternator has been changed, it was whining with the old one and the new one. The amp is mounted on a piece of wood. So it not getting earth there. However the earth cable does go to the body in the boot. I'll try the i pod trick.
    That experiment doesn't prove anything in regards to the question whether or not the noise is alternator related. You need to remove the belt (i.e. completely remove the alternator variable from the experiment to have some useful outcome) and run the engine out of the battery to eliminate (or on the contrary) the alternator as a source of noise.
    ACHTUNG ALLES LOOKENPEEPERS

    Das computermachine is nicht fur gefingerpoken und mittengrabben. Ist easy schnappen der springenwerk, blowenfusen und poppencorken mit spitssparken. Ist nicht fur gewerken bei das dummkopfen. Das rubbernecken sightseeren keepen hands in das pockets-relaxen und watch das blinkenlights.

  10. #10
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Default Condeser

    Hi.

    When I've had this problem it has been the alternator suppressor condensor (a capacitor) falling off. In 504s etc this is a cylindrical capacitor with an integral mounting tag which can fatique. The condenser drops off, the while is audible in the sound system and, after a little while driving (a few hours) the lead also lets go and the capacitor falls out on the road. The replacement alternator is then fitted without one ("It didn't have one before mate, see?")

    The capacitor goes between the alternator output and ground (usually on the alternator frame) and supresses the noise from the alternator rotor. The rotor is typically 12 pole. The maximum speed is usually 10,000 rpm and the pulleys are sized to get this at maximum engine RPM (1.8 to 2 to one) so at normal speeds you get around 12 kHz whining noise from the ripple in the retifier output.

    The suppressor condenser is a different value, from memory, than the condenser on the points in old cars with coil and contact breaker ignition.

    If it is still whining with a good capacitor, then one of the retifier diodes has failed closed and the alternator will get hot quickly and only prduce about 33% of its rated current output.

    Best of luck,

    Bruce.
    Last edited by Bruce Llewellyn; 17th May 2012 at 11:25 AM. Reason: typo

  11. #11
    1000+ Posts cav91's Avatar
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    So you mean go to autobarn and get an aftermarket capasitor? Should resolve the issue?
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