Record sound from RCA audio out to electret microphone input.

Discussion in 'General Electronics Chat' started by thirsty2001, Apr 21, 2015.

  1. thirsty2001

    Thread Starter New Member

    Apr 21, 2015
    2
    0
    Hello.
    I have a camera in my rally car, an AEE SD 21, and it accepts audio in from an electret microphone/mono plug. I use a Peltor 3M™ FMT120 Intercom that has a RCA audio output socket. I am asking for help with a convertor/amplifier to record the conversation between driver and co-driver from said intercom.
    Thanks Ross
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    To go from what probably is consumer line level to microphone level is attenuation, not amplification. There are adapter cables you can buy on eBay to do this. No electronics, no battery or other power source, just two resistors built in.

    ak
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,059
    3,822
    @AnalogKid,
    Do you think a simple RCA to mono-plug adapter has in-line resistors already installed? That would make it very easy for the OP.

    Alternatively, a good recorder will have some type of compression as well - loud sounds may be slightly distorted.
    [​IMG][​IMG]
     
  4. cornishlad

    Member

    Jul 31, 2013
    196
    25
    Line level can be up to 1000 times greater than mic level, so as AnologKid has already said you need an attenuating lead. If you order one online make sure you get one that has the 3.5mm jack at the mic end. Some will have a 3 pin XLR plug. Straight phono/jack adapters don't have the pad built in afaik. If you like making stuff you could try a 1K resistor across the mic jack terminals and a 330K resistor between mic live and phono centre pin (All in the lead and screened). Change the 330k higher or lower if necessary to get the level right.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    also need a blocking capacitor, dc is fed to the electret amp through the audio cable. aprox 1 mfd should do.
     
  6. thirsty2001

    Thread Starter New Member

    Apr 21, 2015
    2
    0
    Hello.
    I have a camera in my rally car, an AEE SD 21, and, I have been informed by the manufacturer, it accepts audio in from an electret microphone source current/voltage. I use a Peltor 3M™ FMT120 Intercom that has a RCA audio output socket.
    As noted an attenuated cable with a RCA male plug to a 3.5mm mono male plug seems to be the go.
    I am a low level novice at electrical, but I can understand a circuit, and make something to suit with a circuit diagram.

    Can anyone advise a source for such a cable or do a diagram for me?
    Thanks Ross
     
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