3 Volt audio mixer. Requesting advice

Discussion in 'The Projects Forum' started by copper dog, May 1, 2013.

  1. copper dog

    Thread Starter New Member

    Apr 15, 2013
    7
    0
    Hi;

    I recently designed a system to interface two transceiver radios to a single shoulder mounted microphone. The user carries both radios back mounted and controls volume and transmitter selection from a small front worn control module. The system works well but now I want to expand it by outputting the mixed audio to a video camera microphone in jack and capture this radio traffic on the video sound track. The caveat is I can't lose the ambient sounds the camera would normally pick up with its own mic since the cameras mic will be cut out when an external source is jacked in.

    I'm planning to to do this by capturing the ambient sound with a separate condenser mic mounted on the camera (replacing the cameras microphone) then mix that with the radio traffic and jack the entire mix into the camera. This mixer must be very small and light weight since it will be on a head mounted camera.

    I need advice on a good mic amplifier and op amp to use as a mixer that will operate on a CR2032 cell. I also don't have a clue what kind of mic is in a video camera like the Contour Roam or Go Pro. They pick up sound very well. Right now I'm using a basic condenser mic to prototype the circuit.

    Any suggestions?
     
    Last edited: May 1, 2013
  2. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    The Analog Devices SSM2166 is a microphone preamplifier with compression and noise gating - exactly what you need. It needs a 5V supply though. Have a look at similar devices from Analog Devices (www.analog.com). I think they make a cut-down device that will operate from 3.3V. Alternatively you could use two 3V cells.
     
  3. copper dog

    Thread Starter New Member

    Apr 15, 2013
    7
    0
    I've already drawn up the circuit using the SSM2116 so I guess I'm on the right track. I'll be mixing the radio audio (an already mixed output) with the mic audio prior to injecting the total mix into a camera. Is there any particular op amp you used for a second stage to the 2116 that you had success with? I'm thinking I'll use a dual Op-Amp, one circuit to mix the mic/radio signals and the other to increase the output a bit prior to the camera. I've been looking at the LME49722MA with a 22V/us slew rate but it seems like over kill.
     
    Last edited: May 10, 2013
  4. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    I don't have any specific recommendations. Obviously you should use one that has low current consumption and is able to swing its output near the supply rails, since the supply voltage is so low. You don't need a separate gain stage; just increase the feedback resistor value on the mixer stage to increase its gain. Good luck!
     
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