Mp4 player pre-amp problem

Discussion in 'General Electronics Chat' started by Lanz, Aug 15, 2009.

  1. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    Hi,i got a problem.
    My car cd player has damaged.
    So i use my portable mp4 player,i connect it to the pre-amplifier which connected to the power amplifier.
    The earphone(line-out) i connect to the line-in of the pre-amplifier.
    It works perfect,but only for a few of minutes.
    The mp4 battery runs out quickly(fully charged),but it can last for couple of hours if i use it with earphone.
    And the worst is,its hot when i touch it.
    I dont know whats the problem.
    I hate travel for a long journey without music.
    I hope somebody can tell me why its happen like that n is there any solution?
     
  2. flat5

    Active Member

    Nov 13, 2008
    403
    17
    The problem is in the specifics of how you connect the mp4 player to the pre-amp.
    We don't yet have that information.
     
  3. Lanz

    Thread Starter Active Member

    Oct 30, 2008
    153
    0
    [​IMG]

    Here is a rough sketch.
     
  4. flat5

    Active Member

    Nov 13, 2008
    403
    17
    That says nothing about output impedance of the mp4 unit and the input
    resistance of the preamp.

    1) Can you measure the resistance (power off) at the connection of the player
    & preamp with a multimeter?

    This will test for short or too low a resistance at this point.
    Record it and tell us what you measure.
    Hopefully it is 32 ohms or greater.

    2) Measure the dc voltage to ground (power on) at the connection of the player
    & preamp with a multimeter.

    Record it and tell us what you measure.
    Hopefully it is zero.

    3) Measure this point for ac voltage with no audio applied.

    Perhaps there is an oscillation.
    Hopefully there is no voltage.

    If you get other readings than the expected ones above:

    You might try to put a 470uf capacitor in series from mp4 player to preamp.
    This provides dc isolation.

    You may need to put a resistor across the mp4 output. Maybe 100 ohms. I say this
    because there may be an oscillation too high for you to hear but consuming much
    power. Probably not, but in a worst case...it could happen.

    If you had an oscilloscope you could check to see if there is dc or an
    oscillation on this line.
     
    Last edited: Aug 17, 2009
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