Car PA System Aux Input

Discussion in 'The Projects Forum' started by Tissue901, Apr 22, 2012.

  1. Tissue901

    Thread Starter New Member

    Apr 22, 2012
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    For my car I have a Siren/PA system and what I'd like to do is make it so I can plug my iPod into it. In some attempts I've been using the Microphone and splicing an Aux cord onto the leads for the microphone so when i press the button on the mic it goes to the AUX cord. This semi works but it sounds awful. I tried to do this last year but all i could find was something about how the signal from the Microphone would be a lot different than the signal from the Aux and that i needed to put something in the circuit to change how the aux signal is sent. I really have no clue, but if anyone could give me some advice for hooking the Aux to the mic input that would be great. I had some pictures of the inside of the PA system but I just had to put a new HD in my comp so I no longer have them. I'll have to rip the PA system out of my car tomorrow when its light out.

    Heres a rough schematic of what I'm trying to do.
    http://zyphox.com/Mic.png
    [​IMG]

    But i remember someone saying i need to convert the aux signal or change the resistance or something. I can wire that up fine, as ive done it already, just didnt sound great. Though i just took the aux leads and placed the inside the Mic casing so it was still running the mic when i pressed the button. Ill have to try actually sniping the wires and just goin with it. Any suggestions on sound quality improvements would be great though. Like the sirens that get the sound file directly from the system sounds great. Want music to sound like that as well instead of just holding a speaker up to the microphone. I also want to just wire this all into my stereo so i can change tracks from my head unit and not have to deal with doing it from my ipod directly.

    **EDIT** I did a little more searching found this:

    But this is mic to aux, i need aux to mic. But at least now ik that the mic is a low signal which is what i was trying to remember from last year.
     
    Last edited: Apr 22, 2012
  2. Audioguru

    New Member

    Dec 20, 2007
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    Use two resistors in series between the ipod signal and ground to make an attenuator that attenuates the 500mV line-level signal from your ipod to the 10mV level where the two resistors are joined that is used by the mic input.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  4. Tissue901

    Thread Starter New Member

    Apr 22, 2012
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    How do i Figure out what size resistors i need. and in the link Kermit2 gave me, it goes by DB of the mic? The last one is an electret microphone, so i assume i could just go with those values?
    C1 +Line level in --||----R1----+-- +Mic level output + | | +----R2----+ | Ground (input)----+--------------- Ground (output) R2 = 1 kohm R1 = 10 kohm C1 = 10 uf
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    A 10k resistor feeding a 1k resistor reduces the signal to only 1/11th which is not enough reduction. Try using a 10k resistor feeding a 200 or 220 ohm resistor.
    Use a series capacitor if you want.
     
  6. Tissue901

    Thread Starter New Member

    Apr 22, 2012
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    K so i finally got around to doing this and it works for the most part, except the low notes dont go through anymore or they crackle. The high notes sounded good so I assume it was attenuated to much? Would I decrease the 10k or the 220k resistor? I assume changing the 220k to a lower one would be better?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    An attenuator reduces the levels of low notes and high notes exactly the same if the values for coupling capacitors are enough.
    Maybe the music source cannot drive a load as low as 10k ohms, then increase the values of both resistors.

    "Crackle" is caused by something wrong with the amplifier or speaker.
     
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