3 audio inputs, one audio output

Discussion in 'General Electronics Chat' started by stillgrowingup, Mar 27, 2016.

  1. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Hello all,

    I have had great help here with the AAC community. Thank you all for your support and ideas helping my projects become a reality. :)

    I am looking to create a audio mixer of sorts. The idea is ... there will be 3 audio inputs, out to one audio output. The inputs will be a car stereo of 20 watts RMS and (2) soundboards with 7 watts RMS. These inputs will merge to ONE audio output. This Audio output is for a LED Spectrum graph that responds to the audio being sent to it.

    These 3 inputs will be tapped (Parallel) from a speaker that will also be playing the audio. It would be nice to have a trimmer pot for volume inputs. There will NOT be a selector switch to choose which input will go to the output. ALL 3 inputs will delivery to the same audio output, whenever an audio is played from ANY 1 of the 3 inputs.

    Is this possible to do without Audio interference and popping noise spiking through the LED Spectrum graph when a audio becomes present to the output?

    I have done something like this before. I placed (2) separate 7 watt peak audio outputs to one 20 watt RMS amplifier input. I had to use Electro caps to make it work without a popping sound during playback. It worked fine.

    But what I propose now, seems to be a little more complex. And I am at a lost on where to start.

    TONY
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    Its possible that the car amplifier is a Bridged output, and so you wont be able to use a common ground, you may have to use a differential amplifier on each channel...
     
  3. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    Hi dodgyDave

    For this 3 in, 1 out. It will be a car radio, not a dedicated amplifier. The car stereo is NOT bridge able. Same with the soundboards. Does that make a difference?

    Tony
     
    Last edited: Mar 27, 2016
  4. crutschow

    Expert

    Mar 14, 2008
    13,050
    3,244
    So you know for a fact that all outputs share a common ground(?).
     
  5. stillgrowingup

    Thread Starter Member

    Jul 15, 2015
    146
    2
    @crutschow ... Thanks for chiming in here. I value your input.

    The car stereo use an IC chip for its amplified system. The negative output comes from IC, not directly from ground. .... I actually haven't seen a common ground car speaker system since the 1980's.

    I have contacted the manufacture of the soundboard to confirm if the audio negative output is a ground. I did use my Fluke meter on resistance and measured nothing between ground and the speaker output, while the soundboard was off.

    TONY
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,999
    745
    As per post#2, its a Bridged output, so you'll need a differential amplifier.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Or, use only 1 of the two bridge outputs through a coupling capacitor. As long as it is not class-D relying on the speaker for filtering (like the TI "filterless" class D parts), the two bridge outputs are analog signals 180 degrees out of phase.

    ak
     
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