help for audio amplifier (newbie)

Discussion in 'The Projects Forum' started by vini_vini, Apr 8, 2008.

  1. vini_vini

    Thread Starter New Member

    Apr 8, 2008
    1
    0
    Hello everyone,

    I am newbie & need some help from you all. I have MP3 player which I connect it to my car mp3 player via AUX input. I connect headphone out to AUX in. But problem is even I mp3 player is running on full volume, I barely hear song getting played. So I thought I need a basic amplifier which will amplify mp3 audio out to some exceptable levels.

    can anybody help me with it. I'll provide all necessary informatio on request.

    Thanks in advance.
     
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    I have had the same problem. many of the cheaper mp3 players are indeed poor performers when it comes to output and distortion at reasonable output levels.

    some kind of non inverting x4 to x10 gain amp may be able to sort you out.

    one for each channel.

    try looking up non inverting op amp amplifier.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It's most likely an impedance mismatch problem.
    Your MP3 player's output is designed to drive headphones with an impedance somewhere between 8 and 32 Ohms (depending on make & model), whereas your AUX input impedance is upwards of 10k Ohms (ballpark number).

    Sometimes, just an audio impedance matching transformer (1 per channel) is enough.

    At any rate, whether you use a Z match transformer or a solid-state amp circuit (such as a dual op amp) you'll need to match impedances on both the inputs and outputs, or you'll have rather nasty distortion, even at moderate level settings.
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Hi Sgt. Wookie,
    The impedance in RF transmitters is matched. The impedance in audio circuits is never matched.

    An amplifier input impedance (10k ohms to 100k ohms) is much higher than the 0.1 ohms or less output impedance of an opamp or a headphones driver.
    An audio power amplifier has an output impedance of about only 0.04 ohms so that it can damp the resonances of an 8 ohm speaker and so that the mis-match does not waste power.

    Sometimes a 200 ohm dynamic microphone has the input impedance of its preamp matched at 200 ohms so that its resonances are damped. But then its voltage is reduced to half.

    A "matching" transformer steps up the voltage. An opamp with gain has an extremely low output impedance but its minimum allowed load is about 2k ohms.
     
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