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Thread: would a VGA "amplifier" solve LCD hum??

  1. #41
    Variable Bitrate
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    it just occured to me, that since the noise from the alternator (That exists just with the car running, even if the m4 is closed) can be heard with a speaker, it must be around the sound spectrum (20hz to 20khz).

    when building a low pass filter, the ω cutoff is = 1/RC . ω= 2πf . so Fcutoff (above that , it starts to block) = 1/2πRC. but with the R being very small, (since it's just the cables ) , i would need a really BIG capacitor, to swallow that low frequencies , if i was to filter the line before before it feeds the PSU . (becouse the noise with the car turned off, is more liveable).

    so i would need a "competition" capacitor around 1 farad?? what do you guys think?

    P.S (apart the fact that i have tried the mickz's method once before, and did not seem to work, it focuses on HIGH frequency noise, wich i don't seem to have a problem with)

  2. #42
    Raw Wave
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    No, you'd use a choke.

    Not that filtering like that is the solution.

  3. #43
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    but why would i use a choke? choke's are for high frequencis. mine dosent seem to be high

  4. #44
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    http://home.comcast.net/~jbperkins/a..._whine_filter/ this guy seems to have the same problem as me. the cure was a large cap and inductor. i will have to try this...

  5. #45
    Raw Wave
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    Quote Originally Posted by settra View Post
    but why would i use a choke? choke's are for high frequencis.
    WTF? Chokes only pass low frequencies.

    Cokes are the complement of caps. (Remember?)

  6. #46
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    yes. by "choke's are for high frequencies. " i meant they BLOCK high frequencies. they let low F pass, so why would i use one??
    (The only real reason i can find, is it will *** well act as a resistor, )

  7. #47
    Raw Wave
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    Exactly.
    Chokes are often used for filtering power lines as well as signal.
    Generally caps are only used for signal filtering.

  8. #48
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    So. today i finanly got my friend to come, and we wired the PC , in HIS battery. the result was , that the noise was ALMOST gone. this means, that appart from the noise comming from the Altarnator, i must have a ground loop , that produces noise , even with the car turned off (noise gets better when i turn off the engine).
    and it also means, that dispite my bad opinion about M4, it is not the main culprit in my case...

    so as soon as the month starts, and i have money to buy food once again, i will build a filter for the line, and investigate the ground loop, and post the results!!

    thanks allot everybody !!

  9. #49
    Constant Bitrate
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    Quote Originally Posted by heavymetals View Post
    Sounds like alternator noise to me.
    Thought so.

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