2 amplifiers in an 8 ohm series circuit

Discussion in 'The Projects Forum' started by jagga, Oct 19, 2009.

  1. jagga

    Thread Starter New Member

    Oct 19, 2009
    3
    0
    Hey,

    This may be a dumb question; truth be told I don't know.

    I want to connect two amplifiers to an 8 ohm pa system in series set-up.

    Can this be done and will it have adverse effects on either amplifier?

    Thanks in advance.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Don't do it.

    Get a single amp that will match your PA speaker impedance.
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Do you really understand what series means?
    Do you mean one amp driving the other or both trying to drive the speaker?

    If you mean the second you may have heard that it is possible to connect some amps together to drive a speaker system.

    But this is not a series connection, it as known as bridge mode.
    You can only connect some amps this way and you need a special driver circuit.
     
  4. jagga

    Thread Starter New Member

    Oct 19, 2009
    3
    0
    I mean something like this....

    [​IMG]
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Generally a switch (4PDT) is used to switch one speaker as microphone and the other as speaker, and reverse this connection, for a intercom.

    You can't really do what you're wanting to do directly, though the phone company uses some fancy audio transformers to come close.
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
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    513
    Draw in some power supply and earthing rails and look for short circuits.

    Try explaining further what you want to achieve.
     
  7. jagga

    Thread Starter New Member

    Oct 19, 2009
    3
    0
    ok a simple as possible,

    There's an existing pa system with one amps, I'm want to connect a second so I can broadcast over the system without having to use the other one. What i need to know is could it wreck the other amp...

    I know for a fact that it's an 8 ohm pa system.
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    If you connect both amps at the same time it is almost certain you will damage at least one of them and maybe start a fire into the bargain.

    You need a switch to switch both poles of the input to the distribution system between amps. This is a two pole changeover or (double pole double throw) switch and should be rated for the PA system current and 120 volts AC.

    However this is likely to cause unwanted problems in the form of switching thumps from the speakers. You also have the problem of who controls the switch, especially if the amps are remotely located.

    A better solution might be to switch the input to the one amp, if for instance you want to do voiceover of the PA music or whatever. This would also save you an amp if you haven't already bought it.

    I seem to have done a lot more typing than you have - you owe me a beer.
     
    Last edited: Oct 19, 2009
  9. rogs

    Active Member

    Aug 28, 2009
    279
    37
    Instead of spending your money on a second amplifier -which, as the others have advised, won't do what you are trying to achieve, you'd be better off getting somthing like this : http://www.rolls.com/pdf/M_DU30b.pdf .
    It's designed to do exactly what you need. It's even got a schematic attached, so you could get an idea of how it actually works.
    Might even encourage you to build something yourself,if you feel so inclined!
     
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