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Amplifier Modulation Lights Install - HELP

Discussion in 'Home Brew' started by 941Texas, Jul 25, 2010.

  1. 941Texas

    941Texas Member

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    i have seen where xfore and wizard built add LED vu kits to amps. i have found the kits on ebay. now i just need to know how they hook them up.


     

  2. Shockwave

    Shockwave Sr. Member

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    Simple, you take a small sample of the RF output through a resistor or cap. Rectify it with a germanium diode. Then filter the RF out with a ceramic capacitor. If you're on AM the output of this circuit will just be audio to drive the VU board. Very similar to the cheap modulation monitor they put on some (Dosy) watt meters. Where you can plug headphones in and listen to your transmitted AM audio.
     
  3. 941Texas

    941Texas Member

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    thanks much, i was thinking something like that but its better to ask. i found the kits for 6 bucks plus shipping. not bad i guess.
     
  4. bushwacker

    bushwacker Active Member

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    You don't need the kits.
    All you need is a LM3914 or lm3915 led driver IC.
    Rectify the incoming rf...set the level...build up the standard IC circuit and connect up to 10 leds to the correct pins.

    I've built a few of these in some amps....the LM3915 is the better one for this application but either will work.

    I can shoot you a schematic for making one if this attachement doesn't work.
    Its a real simple circuit....the lm3915 IC does all the work.
    If you have any old small cb's laying around that have led S meters on them you can use the LED driver IC's out of them ( most are only 5 led though)
     

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  5. bushwacker

    bushwacker Active Member

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    P.S. The trimmer cap can be connected to the center pin of the output connector on the amp.
    if you have any small old radios around that have led s meters.....pull them out and use the same circuit as above to the input of the IC. They work OK if you only need 5 leds and are easy to find out old junk radios.

    take care
     
  6. 941Texas

    941Texas Member

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    i will give this one a try. i have allready ordered three of the kits but that ok they where only 5 bucks each. thanks guys

    941
     
  7. 941Texas

    941Texas Member

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    here is the finished lights

    Modulation Lights
     

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