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About bridging?

Discussion in 'Amps and Cabs [BG]' started by justBrian, May 30, 2003.


  1. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    I have a QSC MX700. It will put out 700 watts@4ohms bridged. How do I go about bridging it? Do I need to get a couple of jumpers for the terminals on the back of the amp? Help???
    Thanks in advance.
    BD
     
  2. http://www.qscaudio.com/pdfs/mxusr.pdf
    The mx700 has been discontinued however it probably works like to bigger mx line. From what I can see you slide the switch to Bridge, connect an input to channel one only, turn the volume all the way up on channel 2 and use the channel one volume for gain. Connect your speakers across the 2 red (+) posts. The best way to do this is to buy a speaker cable with one end to match your speaker and the other with a banana connector. Plug the banana connector into the (red) binding posts on the back. Good luck.
     
  3. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    Thank you Grey Beard. I'll give it a shot when I get home.
    :)
     
  4. One small note about the speaker polarity when bridging the MX, as per the nice .pdf that Greybeard linked :cool:

    The speaker's '+' lead should go to the amp's '+' speaker out for ch. 1,

    The speaker's '-' lead should go to the amp's '+' speaker out for ch. 2.

    QSC MX700 - mighty fine amp, by the way. Should give you a bazillion years of great service. :)
     
  5. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    Dude, you know what else is cool? I only paid $40 for it. Had one of my EE friend fix channel one ($12 in parts + a case of beer). Now I've got a kick ass amp for less than $100. WooHoo!
     
  6. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The MX 700 didn't have a bridge switch. The way to bridge that model was to use two wire jumpes on the input screw terminals: one from Channel 1 + to Channel 2 -, and the other from Channel 1 - to Channel 2 +.

    Plug your preamp into Channel 1's input. Connect your speaker cable to the two red output terminals. Set the gain controls on both channels to the same position. If you turn one up, you have to turn the other one up too. Likewise, if you turn one down, you have to do the same on the other one. Then you're all set.
     
  7. So running the same signal, but out of phase, to both channels is all that bridging consists of?
     
  8. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    Thanks Bob-- can I make the jumpers myself? Does radio shack have'em?
     
  9. Bingo! It's as simple as that.

    Think about it for a while. It makes sense. One channel pulls on one side of the bridge, the other channel on the other side. Because the 2nd channel is in counter phase, it'll double the voltage across the bridge.
     
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You sure can make your own just by taking two short pieces of wire and stripping the ends. You can use stuff as simple as doorbell wire. It'll take less than 4 or 5 inches or so.

    You can buy the wire at Radio Shack, but if you ask for jumpers for bridging an MX 700, they'll probably gaze back at you with the look of the lost.
     
  11. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    :D They do that every time I ask them something. ;)

    Thanks again, Bob.
     
  12. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    Got it done and man! is it loud. My set up looks like this:

    SWR IOD-->QSC MX700-->Avatar CB112(8ohm). It really sound awesome for a semi-compact rig.

    Now I need to by a rack. Oh well... :D
     
  13. Good choice of equipment.

    Next, connect the IOD to the QSC using a balanced XLR to TRS cable.

    Zero hum.
     
  14. justBrian

    justBrian

    Apr 19, 2002
    Kansas City, MO
    OK--what's a TRS?

    BTW, I lived in Sacto for almost 7 years. Get back to visit every once in while and always hit Zelda's Pizza. :D