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Bridging to MONO - QSC PLX 2402

Discussion in 'Amps and Cabs [BG]' started by frederic b. hodshon, Mar 5, 2002.


  1. frederic b. hodshon

    frederic b. hodshon Supporting Member

    May 10, 2000
    Lake Forest, CA
    None.
    hey all you's QSC peeps,

    please share your experiences with bridging to mono with this amp.

    i've only played one channel into a 212 cab, 4 ohms at 700 watts. the cab is rated at 700 watts.

    not that i'm complainin'....hardly!!

    just curious about any issues i should be aware of before i try it.

    2400 watts bridged at 4 ohms sounds really tempting.

    thanks
    fred
     
  2. ganttbos

    ganttbos The Professor Supporting Member

    Dec 18, 2001
    New Orleans area
    Hi Fred,
    Most of this you know from our past communications. I bridge my 2402 into two 8 ohm cabs. Playing good and loud (but not ridiculously loud) the amp stays cool - tight clean lows - and doesn't seem strained at all. I had talked (email) to Bob Lee about it and he expressed no hesitation to bridging into 4 ohms. I do use speakons all the way. Let me know if I can help with other info.
    Gantt
     
  3. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    I was wondering about bridging a PLX into two 8-ohm cabs, as I have two 8-ohm 410XLT's. Lord Valve has stated that it's better to run these amps in stereo - something about controlling cone movement better. However, to get the same power levels in stereo, you'd need a higher power PLX, which is much more $$$.

    Mr. Lee, can you publicly educate us on this matter?
     
  4. 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
    Go for it. The amp can handle it perfectly well.

    To keep the damping factor high, use good, short, heavy gauge wire for your speaker cables. Run a separate cable from each cabinet to the amp output.

    Watch your levels--don't clip the amp (a little quick flash of the clip LED every now and then is okay).

    You're ready to shake some walls. ;)
     
  5. frederic b. hodshon

    frederic b. hodshon Supporting Member

    May 10, 2000
    Lake Forest, CA
    None.
    Mr. Lee,

    just for clarification with my setup:

    the PLX 2402, with an Aguilar DB659 pre and a 700 watt 4 ohm Bergantino HT212...

    running bridged mono should be fine right?

    Gantt, i know we've spoken about this offline...i just want to be EXTRA careful...hence, the request for extra sources of info.

    anyone know where i can get short heavy guage speakon cables?

    fred
     
  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
    Yes.

    Try Sam Ash, Micworks (Costa Mesa), Orange County Speaker (Garden Grove), et al.

    Or make your own!
     
  7. ganttbos

    ganttbos The Professor Supporting Member

    Dec 18, 2001
    New Orleans area
    Fred, It's really easy to make your own. I can coach you through it - then you'll have exactly the lengths and wire gauges you want. Send me an email if you want to give it a shot.
    Gantt
     
  8. boogiebass

    boogiebass

    Aug 16, 2000
    Yep. And in a pinch, you can buy a 5 footer, 12 ga with quarters from Guitar Center and replace the connectors with Speakons. Neutrik connectors are about 5 bucks a piece. I know 'cause that's exactly what I just did. Ended up costing me $30 but I've got just what I need. Obviously, getting the cable un-terminated is more desirable, but in this case, I needed the quarters for another repair project anyway.
     
  9. Bob,
    How would one use multiple cables while bridgeing? I thought you could only use one cable out to the cab/cabs? And, if you use a speak-on it has to be wired differently at the amp out connection. +1 / +2 I think, and then regular at the cab end -1 /+1.
     
  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're not limited to one cable; the amp doesn't know or care how many you use, as long as the net load impedance with all the speakers hooked up is at least 4 ohms.

    To use the upper Speakon, the connector on the cable must be wired to pins 1+ and 2+, that is correct. What the other end requires depends on the speaker.
     
  11. Carl Brusky

    Carl Brusky

    Sep 21, 2000
    Bob,
    I think the question is if you only have one speakon connector on the amp that can be used when bridged, how do you run two cables from the amp to the speaker cabinets?

    Maybe I am missing something.

    This is what I do on the PLX 1202.

    Bridged, one cable to the 1st cabinet and one cable form the 1st cabinet to the 2nd cabinet.
     
  12. Here's what I do. I use 2 banna to speakon cables and piggy back both bannas into the binding post setup. My amp is an older USA 850 and has no speakons. I think what Bob is saying with the speakons when you bridge the amp that +1 and +2 of both the left and right speakon output of the amp become the - and +. Is that right Bob...Bob....Bob are you there???
     
  13. Carl Brusky

    Carl Brusky

    Sep 21, 2000
    The banana thing would work with mine also. Will have to do that.
     
  14. 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
    Your method works, Carl. I suggested running separate cables to the amp to someone who was concerned about damping factor. With banana plugs, it's very easy to do. If you want to use the Speakon output, obviously you'd have to make or buy a Y cable.
     
  15. Bob, last question (well today anyway) When the amp is bridged, +1 and +2 of channel 1 become - and + (am I right so far) What goes on with the channel 2 speakon when the amp is bridged?
     
  16. ganttbos

    ganttbos The Professor Supporting Member

    Dec 18, 2001
    New Orleans area
    OK wait, now I'm not sure of something.
    The way you're describing the wiring of a (bridged) speakon connector, the PLXamp (channel 1) end is wired +1 +2 (so far so good) but the cab end is -1 +1. You're saying that the +1 connector at the amp end goes to the -1 at the cab end instead of the +1. Wouldn't this make the speaker cone's initial movement be "in" instead of "out" and result in a stage rig possibly being out of phase with the mains?
     
  17. 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 lower Speakon just sits there. Unlike the upper one, it has the output of only one channel, so it's not used in bridged mono.

    On the upper Speakon, in bridged mono:
    1+ = +
    2+ = -
     
  18. So, if I Bridge my 2402 and run one cable to the 4ohm cab and one cable to the 8ohm, would that be the "net load?" If I'm not mistaken that would be more than 4ohms. Also that is assuming I make a special speakon for ch-1 and use a regular speakon for ch-2 outs to cabs..
     
  19. 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
    No. The minimum load impedance in bridged mono is 4 ohms! An 8-ohm and a 4-ohm load in parallel amounts to a 2.7-ohm load. (There are threads on this a couple times a week!) If you need to run both an 8 and a 4, run the amp in stereo or parallel mono.

    And the lower Speakon is not used in bridged mono because it doesn't have both channel outputs—it only has one, which is Channel 2. In bridged mono, use only the upper Speakon.