Breaking the rules on bridging...

Discussion in 'Amps and Cabs [BG]' started by Gabu, Dec 4, 2002.

  1. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    Hi guys,

    I have an Ampeg SVT400T. It bridges 400w @ 8 ohms. I am thinking that my new cabs will be hungry for power, and my current amp is a bit shy of that. So do you think that if I bridged a 4 ohm load my amp can survive that to some degree? I am not planning on running it turned up to ten, but just trying to squeeze a bit more juice out of it.

    I also can afford to replace it, if I destroy it... But am wondering if the destruction is guaranteed... or it might work? Opinions?
  2. FretNoMore

    FretNoMore * Cooking with GAS *

    Jan 25, 2002
    The frozen north
    I think something must give eventually, because of the higher current something will burn. Perhaps you can run it for some time, but don't count on it. And if your reason for trying is to get more power than you have now, you will of course turn it up until it goes poof. :)
  3. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    It *might* work, but I sure wouldn't recommend trying it. And think of it this way. You say that your reason for considering this is to try to get a little more juice out of the amp. But if you have to be conservative with the amp, and not run it at its limits, then it's quite possible that you wouldn't be able to use whatever power you might gain (assuming your amp is even stable at that low load to begin with). So you could endanger your amp without even gaining much of anything. This isn't a 100% sure thing, but I wouldn't do it if I were you.

    If you can afford to replace it, you can probably afford to buy a second amp, no? So that you can use one amp per cab? This is probably a better solution to your power concern than the dodgy bridging to begin with.

    Or a bigger amp that *can* be bridged into 4 ohms?
  4. I'd strongly advise against doing that. First, you wouldn't notice much difference, especially if you ran at conservative levels. Second, there's a good chance of the amp failing if it is being operated in a way that it wasn't designed to. It might work for quite a long time, but I wouldn't risk it. The least it will do would be occasionally overheat and shut down occasionally, but a catastrophic failure is just as likely. If it shorts an output transistor, there's a good chance it will take out your speakers too, depending on how good the DC fault protection is. Scary proposition!
  5. BruceWane


    Oct 31, 2002
    Houston, TX
    It may survive bridging at 4 ohms if you are very careful with the volume and keep an eye on the heat, but the potential payoff is definitely not worth the risk. Remember a few simple rules of audio - the lowest increment of volume that is easily noticeable by us humans is 3db, and a 3db increase of volume requires a doubling of wattage. In other words, if you want a noticeable increase in volume from what you're getting out of 400 watts, you need to increase wattage by another 400 watts, and there's no way you're gonna get 800 watts out of that head, at least not for more than 20 seconds, and keep a fire extinguisher handy........
  6. Gabu


    Jan 2, 2001
    Woodland Hills, CA
    :D hehe - Okay, I guess I will not do this. It is sounding like lots of risk over a tiny gain. Incidentally, my goal was not to achieve more volume, but rather to give the speakers more wattage. I figured that might make for a more "snappy" response.
  7. If the amp would bridge into 4 ohms believe me the manuf. would brag about it. All you are gonna do is cause the thing to over heat.
  8. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    Usually, when you bridge your damping factor goes to hell, so you're definitely not getting "snappier" response, usually that will worsen just a tad when bridging. You will get more headroom, though.
  9. Running an amp into loads it wasn't designed for makes them heat up most of the time.It doesn't happen right away,it takes time for the amp to heat up enough for the thermal overloads to shut it down.Just about when you get the house rocking is when it shuts down.The audience loses interest,your band mates get on your case and the club owner isn't happy either.It's happened to me years ago and it left a lasting impression.Best case is if your amp turns back on when cooled down,worst is if it's fried for good.It's not too bad if you are just jamming with your buddies but it really sucks when your at a gig.Follow the manufacture's impedence limits and life at the gig will be much easier.
  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
    The damping factor cuts in half. But your overall damping is far more influenced by the resistance of the speaker cable you use than by the amp's spec, so the difference is pretty close to irrelevant, whereas the increase in headroom can be a significant benefit.
  11. Tsal


    Jan 28, 2000
    Finland, EU
    Gabu, just buy some nice 2000w power amp and get it over with.

    Um. I assume the Ampeg has pre out? :confused: