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stereo / mono wiring

Discussion in 'Beginner Electronics' started by Nottnick, Nov 13, 2005.

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  1. Nottnick

    Nottnick Guest

    I need to make my stereo output from a CD player into a mono signal for a PA
    amp.

    Is it just a matter of joining the 2 grounds together and the 2 signals or
    does it need something else?

    Help appreciated.

    Thanks

    Nick
     
  2. default

    default Guest

    Something else is required.

    Tying two stereo outputs together is almost never a good idea - one
    can be driving positive while the other is going negative and pull
    more current than they were designed for.

    You can add a resistor in series to each output and tie both of those
    together and use that junction as the input to the PA amp. 1K or so
    might be good.

    You want to use the "line" output of a portable (if it has one) a
    component CD player will be line out as a matter of course. If the CD
    player is designed to drive speakers directly the output may need to
    be attenuated before it drives a PA amp - or it will overdrive the
    input stages and cause distortion.

    Grounds are another matter - most portable, and component CD players
    use the same ground for both signals - so choose one and route it to
    the PA (PA and CD plugged into the same outlet to avoid ground loops).
    If you get a lot of hum/buzz there's a grounding problem -

    Car CD players frequently use something called amplifier bridging. Two
    amplifiers are used to drive the signal and signal return (not really
    a ground) out of phase into the speaker - lets them get more watts out
    with the power supply restricted to 12 volts. If you connect the
    "grounds" together in that case you will burn up one or more
    amplifiers.
     
  3. Nottnick

    Nottnick Guest

    in message
    +++++++++++++Is there any chance you could explain this in a bit more detail
    please.

    +++++++++++++What do you mean by tie together - sorry, I'm good at soldering
    etc.

    +++++++++++++ I can follow instructions / diagrams but just don't know the
    theory.


    +++++++++++++++ That's fine - it is a line output on a Denom component
    player.


    Thanks a lot for this advice.

    Nick
     
  4. default

    default Guest

    Take the output of the CD player right channel signal and connect a
    small 1,000 ohm resistor to it. Do the same to the right channel.
    Connect (tie) the free ends of both resistors together and to the PA
    amp mono input. (a total of three connections soldered together - one
    is a wire that goes to the PA input).

    Run one ground wire to the PA from one of the CD outputs. You may
    also run two ground wires from each CD output, but it shouldn't be
    necessary.

    This should be done with shielded (coaxial) cable, but may work fine
    with ordinary hook up wire if the wires aren't too long. The
    potential for noise and hum pickup is dependent on a few variables so
    try it one way and see what happens.

    Then the signal level should be fine for the PA input unless it is a
    microphone input - If you have a choice on the PA use the line input
    (line out (CD) to line in (PA))

    Line levels are usually around one volt to drive the PA to full output
    (it will be in the PA specifications under the term "input
    sensitivity" or some such description)

    Microphone input on a PA amp can be much less - in the millivolt
    range. PA amps usually have both types and a front panel switch to
    select the source(s).

    Your grounding shouldn't be a problem unless you need to run them on
    different power receptacles then you may get hum. If that's the case,
    post again.
    Regards
    bob
     
  5. default

    default Guest

    Change that to "Do the same to the left channel."
     
  6. Nottnick

    Nottnick Guest

    You are a real star, thanks so much for your help

    Nick

    in message
     
  7. DBLEXPOSURE

    DBLEXPOSURE Guest

     
  8. default

    default Guest

    You can, providing that the impedance of the line out is high enough
    to tolerate the loading, or the circuit is short protected. Low
    impedance outputs will merrily self-destruct when shorted. The other
    disadvantage is that the output of one channel may affect the feedback
    in the other channel if it uses op amps.

    Better safe than sorry, and the sound will be cleaner.

    The minimal extra effort required seems well justified IMO.
     
  9. DBLEXPOSURE

    DBLEXPOSURE Guest

    in message


    You mean the impedance of the input you are feeding is high enough not to
    load down the cd player's line output? If you are plugging into an RCA type
    connector chances are it is high impedance.

    I agree, do not do this at 600 Ohms. Use a combining network.
     
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