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How to remove hum from car cassette adapter

Discussion in 'General Electronics Discussion' started by dietermoreno, Apr 30, 2013.

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  1. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    How to remove hum from car cassette adapter.

    I have a car cassette adapter to allow me to connect a digital music player to my car's stereo system.

    Unfortunately, my listening experience is killed by every time I step on the gas pedal I hear a whine that increases in frequency the harder I press on the gas pedal (presumably the fuel pump), in addition to there is a constant hum (presumably the spark plugs).

    These cassette adapters unfortunately use unbalanced unshielded lines. That seems perplexing to do that in such a noisy environment as a car, but perhaps cost saving was the motivation, as this only cost $3.99 at Walmart.

    Is there any way to cancel out hum on the line, perhaps buying speaker wire and winding two speaker wires in opposite directions around the line so that any hum will be canceled out before it reaches the line conductors?
     
  2. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    The whine is possibly due to the alternator which varies in frequency with the engine speed. If the hum is due to the ignition, that should also vary with the engine speed.

    Shielded wires would help. Winding the connecting cable on a ferrite core may help but it is all trial and mostly error.
     
  3. GreenGiant

    GreenGiant

    842
    6
    Feb 9, 2012
    Unfortunately I have never found any fix for these, even buying the expensive, shielded, and supposed "high quality" ones dont make a difference. The way these work means that they are EXTREMELY succeptable to noise. The noise is coming from the tape reader in the car, where the information is transferred from the adapter to the player.

    Unless you want to replace the tape player with a better shielded one, and have better buffering/smoothing of the power coming into the radio its nigh impossible to help the noise (at that point you can buy a new radio with an MP3 jack for cheaper)
     
  4. shrtrnd

    shrtrnd

    3,802
    507
    Jan 15, 2010
    Yeah, the alternator does that. Electronics stores like Radio Shack used to sell a
    capacitor-based assembly to eliminate the whine, but I haven't seen one in a long time
    because most radio manufacturers started building their rigs to filter the alternator
    noise out. You might ask some radio installers at some of the installation places if
    they've got something now that can be installed to filter the noise.
    If you try to do it yourself, it's probably going to be a lot of trial and error finding a
    solution.
     
  5. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    When you say installed, do you basically mean installing a new receiver for the car?

    I can't afford to buy a new receiver for my car at this time.

    So its trial and error time.



    There is a constant hum that slightly increases in frequency with the engine speed; the hum is still there when my car is idling. There is also a hum that only happens when I step on the gas pedal and the hum frequency increases the harder I press on the gas pedal.

    How exactly would I wind the connecting cable on a ferrite core? It is unbalanced, there are two speaker wire gauge wires inside a plastic coating which are left and right. So winding the left and the right in opposite directions wouldn't do anything.

    So would I wind two speaker wires in opposite directions over the existing cable and the new wires aren't connected and don't do anything except cancel hum?

    Or would I remove the cable and soder in a balanced stereo line connected to a balun to connect to the unbalanced stereo output of the music player?

    Do balanced stereo lines even exist? When ever I have heard of balanced lines, it has always been mono.
     
    Last edited: Apr 30, 2013
  6. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    To reduce common mode currents, simply take the cable which should be shielded, and pass it through the ferrite ring several times.

    You may be better to drive to warp number one only or even turn off the noise and concentrate on driving.:):)
     
  7. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    So to make a common mode choke with a ferrite ring, when I look at this design, would I have to split apart the two speaker wires and left goes on top and right goes on bottom, or is this design only for mono and the top is hot and the bottom is return?

    [​IMG]

    Or will it still work if the unmodified stereo speaker wires cable is simply wound around the ring?

    If you must know, here is an image of the cable: [​IMG]





    While were at it, just a curiosity: are common mode chokes often used in radio receivers to remove hum if the choke is placed after the detector?

    Or would it be better to put the common mode choke on the antenna wire to remove hum (placed before the detector)?
     
    Last edited: Apr 30, 2013
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