speaker system help

Discussion in 'General Electronics Chat' started by w a n, Oct 4, 2009.

  1. w a n

    Thread Starter New Member

    Aug 25, 2009
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    0
    Hi. I'm trying to build a small portable speaker system using 4 8ohm, 1watt speakers hooked up in parallel. The speaker system will accept input from a 3.5mm audio jack that can be connected to various mp3 players such as an ipod via a double male audio cable. I know that the maximum output voltage of an ipod is 1.110v RMS (reference), but I need roughly 2.8v at 0.35i to power the speakers at max volume. I've looked online at various op amps to amplify the signal but I'm yet to find one that meets these requirements.

    Me being my newbish self, I'm completely helpless on my own. Does anybody know if there is some op amp IC that will fit these requirements to drive my speakers?
     
  2. Johnnz

    Active Member

    Dec 31, 2008
    55
    0
    Hi,

    I did a similar project a while back. Only using one speaker with a LM386 IC. Might be of interest/help to you:
    http://forum.allaboutcircuits.com/showthread.php?t=21188

    Cheers.

    Still works great (clear, and loud for what it is) and haven't even had to charge the amp battery yet. Just keeps on going!
     
  3. w a n

    Thread Starter New Member

    Aug 25, 2009
    8
    0
    I actually just recently found this op amp (LM675) that looks like it could work. I'm not experienced with these kinds of electronics at all so let me just get some confirmation on this. I would hook up the input from an ipod to the first pin (+IN) and to ground. Then I would hook up the fifth and third pins (VCC and -VEE respectively) to a 9v power supply. Next I would connect the fourth pin (output) to the second pin (-IN) for negative feedback and also to my speakers.

    Would that work? How much would that amplify the voltage by?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Four 8 ohm speakers in parallel makes a load of only 2 ohms for the amplifier that is almost a dead short. There are a few car radio amplifier ICs that can drive a load as low as 2 ohms but they need at least 12V at high current for a power supply and the output power will blow up your tiny speakers.
    2.8V RMS across an 8 ohm speaker is 1W which is not loud. The speakers must be tiny to have a power rating that is only 1W.

    The LM675 is a power opamp not an audio amplifier but it can be an audio amplifier. Its output when it has its minimum supply of 16V is 2.2W into one 8 ohm speaker or 4W into two 8 ohm speakers. Your tiny speakers might blow up.
     
  5. w a n

    Thread Starter New Member

    Aug 25, 2009
    8
    0
    They are pretty tiny speakers, but I figured four of them would be loud enough (after all, I'm not planning on this to be a particularly loud speaker system, just something so that I could listen to music without headphones). Would anyone happen to know of an amplifier that could drive a load of 2 ohms at 2.8v?
     
  6. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    I was going to ask if you are making a stereo system (two channels)?
    Then I thought that since you have 4 speakers then maybe it is surround sound (four channels)?

    An LM380 in the 8-pins case can drive 1W into one 8 ohm speaker with low distortion when its supply is 12V. Use one for each speaker.
     
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