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To Bridge or not to bridge????

Discussion in 'Amps and Cabs [BG]' started by Kevinlane, Jul 18, 2002.


  1. Kevinlane

    Kevinlane Supporting Member

    Dec 30, 2000
    Missouri, near Branson
    In the past I have always bridged a full range rig.
    What do you guys do?
    I have a 350watt to 8 ohm stereo amp, and two 350 8 ohm cabs.
    Amp is rated to push the 4 ohm load while bridged.
    I usually bridge, but wanted to hear others comments.
     
  2. zombywoof5050

    zombywoof5050

    Dec 20, 2001
    When you say "stereo" amp, are you talking just the power amp or the both the power amp and preamp?
    I've got a stereo preamp (F2-B) and I like to run true stereo with a stereo chorus.
     
  3. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    A power amp feeding a 4 ohm load in the bridge mode sees 2 ohms per channel.

    Bob Lee of QSC had a nice post in the 2 ohms thread about the tradeoffs when driving your power amp so hard. The thermal load shortens the life span of your amp (I believe he's stated a reduction of up to 50% in another post on the subject). That was enough for me to decide to never run my PLX2402 in the bridge mode at 4 ohms again. I still recall it's warm breath blowing on the back of my neck on stage too.
     
  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
    If someone said that, it wasn't me! ;) It's not possible to quantify a life span reduction due to load impedance in that way. High temperatures will tend to shorten the life of electronic components, but the relationship between temperature and failure rate is not a linear one; the failure rate is very low until you get beyond the specified operating parameters, after which you get a knee and the failure rate increases drastically as temperature increases. So keep in mind that PLX amps are designed to operate safely into 2-ohm loads, or 4 ohms in bridged mono. Statistically, you might find that amps operated that way have a higher failure rate than those operated at 4 ohms/channel or higher, but the difference would be very small, and not anything like a 50% relationship. After all, we say they'll drive 2 ohms per channel, and we fix them under warranty for the first three years (or six if you've got the extended US warranty).

    I run a PLX 1602 bridged mono into an 8-ohm cabinet. I wouldn't have any qualms about running it into a 5.3 or 4-ohm cabinet.
     
  5. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Sorry Bob.

    I thought that I had read something that you had written on the subject, but perhaps my 43 year old mind is failing me. I apologize for any misunderstanding.

    I also want to thank you for participating in this forum...it helps keep us honest.

    My PLX2402 does run hotter bridged at 4 ohms than it does running one channel at 4 ohms with the same speakers at the same volume. I'll stick to non-bridged applications.
     
  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
    That's okay. Maybe I wrote something that was easily misunderstood. My 43-year-old mind doesn't always explain things in the clearest way possible, though I really try. ;)