Amplifier Problem

Discussion in 'The Projects Forum' started by litoblee, May 10, 2012.

  1. litoblee

    Thread Starter New Member

    May 18, 2010
    5
    0
    Hello,

    I built an audio amplifier with the LM386. It works.

    I have a circuit with a microcontroller that controls an mp3 player with two 8 ohm speakers with functions of Play/Next/Reset. It works.

    I connect the amplifier to the circuit through a jack. My reset function stops working.

    Now my reset function simply sends LOW then HIGH signals to the mp3 player, shutting it off completely and turning it back on.

    I believe the amplifier connected to the circuit is keeping my mp3 player ON through the aux/jack. I'm not sure if thats possible.

    I've even tested it with two seperate power supplies.

    Anybody have any input how to solve this problem?
     
  2. P-MONKE

    Member

    Mar 14, 2012
    83
    5
    Well, I may not be able to solve your problem directly.

    But I can help speed things along by asking you to post a circuit digram, because that's just about the first thing that you're going to be asked by someone that can help! :D
     
  3. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Schematics are definitely a good idea.

    Are the amplifier circuit and microcontroller circuit totally separate circuits powered by their own power supplies?

    Be sure to explain exactly what signals are being sent over the wires through the jack. Verify that these wires are connected correctly on both microcontroller and amplifier circuit.

    Don't forget to post a schematic.
     
  4. litoblee

    Thread Starter New Member

    May 18, 2010
    5
    0
    The circuit is a bit big, so i cropped out the concentrated section and labeled the vital things.

    [​IMG]
     
  5. litoblee

    Thread Starter New Member

    May 18, 2010
    5
    0
    They are both sharing the same supply, a battery supplying 7.4V.

    The wires are connected correctly.

    Using only the 8ohm speakers, the mp3 player's functionality for resetting works.
    Putting the amplifier on, resetting the mp3 players doesn't work.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Do you know what the resistance to ground - load - is provided by the 10K pot on the amplifier input? You could try just connecting a resistor of that value to the MP3 player output, to eliminate the LM386 circuit. Maybe the MP3 player is not behaving properly with that load, and the problem has nothing to do with your LM386 circuit. Just speculating.
     
  7. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    How exactly does your RESET work? What is the difference for this module for RESET and turning off/on?
     
  8. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    The "Minus" pin will always be a few hundred mV above the GND. Is there a difference in voltage on that pin in your two configurations?

    What MP3 module are you using?
     
  9. litoblee

    Thread Starter New Member

    May 18, 2010
    5
    0
    The MP3 module is just a dissected mp3 player from eBay.

    To reset the MP3, I am just shorting the power out and putting it back with the microcontroller, sending a LOW then a HIGH signal.

    These functions work without the amplifier. Once I connect the amplifier in, these functions do not work.

    The MP3 gets 3.5V whereas the amp gets 7.4V
     
  10. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Is transistor T1 used for the RESET? In that case you are really just trying to eliminate the current flow to ground from the mp3 module. Maybe there is enough current to ground through the AUX connection to stop you module from reseting. It may be better to try to disconnect the positive side of the power from the module rather than the ground, similar to the way you have done it with the microcontroller.
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The LM386 amplifier will oscillate at about 300kHz and draw a high power supply current if the amplifier circuit is built with sloppy wiring on a breadboard. The input and output are in phase and will assist oscillation if their wires are near each other.
     
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