Mixer circuit

Discussion in 'General Electronics Chat' started by Aurbo, Jun 14, 2005.

  1. Aurbo

    Thread Starter New Member

    May 6, 2005
    9
    0
    Greetings,


    I need to take 4 audio inputs from 4 separate (low power) MP3 players and combine then so they will all play off a single set of desktop computer speakers.

    ganging all the inputs right now lowers the output and the distortion increases for each input added.


    I have been told a "Summing Amp" will work, but I cant find one that is low votage (under 12Vdc)

    Will I need to isolate each input ( diode? ) prevent and back-feeding into the other units?


    Anyone have a diagram that might work?

    Cheers
    Steve
     
  2. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    No.
    This one should.
     
  3. Aurbo

    Thread Starter New Member

    May 6, 2005
    9
    0
    Thanks David.

    I'll give it a go in the morning.

    Cheers
    Steve
     
  4. Aurbo

    Thread Starter New Member

    May 6, 2005
    9
    0

    So +power goes to pin 3 instead of pin 7?

    Steve
     
  5. David Bridgen

    Senior Member

    Feb 10, 2005
    278
    0
    No Steve.
    The potential divider provides a point which is mid-way between the supply rails. With a 12V supply, for instance, it is at 6V.
    With pin 3 at mid-rail the output will sit at 6V without a signal (it will have a d.c. offset) but swing symetrically around 6V with a signal.

    Without the mid rail connection the output would sit at or near 0V without a signal and couldn't respond correctly to the input.

    If the 6V, or whatever, offset is a problem, e.g. the device driven by the output is direct coupled (unlikely) stick a capacitor in series with the output.
     
  6. pinball8

    Member

    Jun 12, 2005
    16
    0
    buy a small audio mixing board.
     
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