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Simple mixer circuit?

Discussion in 'Electronic Design' started by DaveC, Jan 16, 2004.

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  1. DaveC

    DaveC Guest

    I want to pipe music throughout a building using a 70-volt,
    "constant-voltage" PA system. The amplifier has mono inputs and outputs.

    I want to use a standard stereo CD-player as the source.

    What is the simplest way to mix the two channels into one so as to avoid
    the weird-sounding "half-stereo" sound when you use only one channel with
    such a distribution amplifier?

    I seem to remember a simple resistor network...

  2. Bob Masta

    Bob Masta Guest

    Put a resistor in series with each channel and
    tie them to the PA amp input. Put another
    resistor from there to the common ground of
    both channels and the PA input ground.
    Use any convenient value in the 1-10K range
    for all 3 resistors. If you want to also reduce the
    level, make the input-to-ground value smaller.

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  3. DaveC

    DaveC Guest

    Can the third resistor be a trim pot? This way it could be a level control.

  4. Yes.

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    Michael A. Terrell
    Central Florida
  5. Yes, it can. For consumer audio interfaces, the output source impedance
    can be as much as 2 kohms, so it would be best to avoid series resistors
    below 5 kohms or so, to prevent distortion.

    Since you are just summing the two stereo channels, you don't need to
    consider what happens if one source is disconnected. But in the general
    case, if you disconnect one source, the level from the other source goes
    up. The lower you make the resistor to ground (the end-to-end resistance
    if it's a pot), the less increase you get, but the lower the normal
    output level.
  6. N. Thornton

    N. Thornton Guest

    Or if you dont need the level control, 2 resistors is fine, no need for the 3rd.

    Regards, NT
  7. You can use a simple "Y" cable from Rat Snack. Or I would put a
    couple 10k resistors on the back of a triple RCA jack. One resistor
    from each channel to the center pin of the middle jack, which goes to
    your PA.

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  8. N. Thornton

    N. Thornton Guest

    It works perfectly with out it, it isnt needed. Its upto the in and
    output devices if theyre cap coupled or not, but either way it'll
    still work fine.

    Regards, NT
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