Tda2822m gain control

Discussion in 'The Projects Forum' started by Col16, May 2, 2013.

  1. Col16

    Thread Starter New Member

    May 2, 2013
    3
    0
    Hi everyone

    Please can someone let me know if the TDA2822M audio amplifier chip is capable of being used with an attenuated gain. I don't need all the gain specified in the data sheet and would like to keep my signal to noise ratio as high as possible.

    Thanks in advance!
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    Use a volume control as in figure 17.
     
  3. Col16

    Thread Starter New Member

    May 2, 2013
    3
    0
    Thanks #12, although that will attenuate the input signal it won't alter the gain. I would like to lower the gain as apposed to decreasing the input signal to maintain a high signal to noise ratio. Hope someone out there can help!

    I know the data sheet specifies a closed loop gain but not too sure if this means I can not alter the gain.
     
  4. patricktoday

    Member

    Feb 12, 2013
    157
    42
    There was some discussion of this chip in an earlier thread:
    http://forum.allaboutcircuits.com/showthread.php?t=13124

    It looks like it's a fixed-gain amplifier. If the (-) input were that of an op amp, you could just feed back some of the signal from the output to reduce the gain, but the internal circuit is already feeding back a fixed amount to control the gain; you're not provided direct access to the inverting pin of the internal differential amplifier.

    Now, I think you could decrease input noise by using a lower-resistance pot at the input to (+) but I don't know if it would be substantial. Johnson noise decreases with decreased resistance in the signal path. Here is some light, entertaining reading on the topic:
    http://www.physics.ucdavis.edu/xdzhu/Physics122_2008/Johnson Noise Manual_2008.pdf

    http://www.edn.com/electronics-blog...istor-Noise-reviewing-basics--plus-a-Fun-Quiz
     
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