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whoops!! Need advice on recently fried amp

Discussion in 'Amps and Cabs [BG]' started by pablomigraine, Nov 20, 2005.


  1. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    So, Like a complete dufus I was trying to carry on two conversations at once while hooking my rig up and I wired it up like this: Power amp Bridge / mono out to speaker cabinet in #1 AND power amp input into the cabinets parrallel input #2, AND TURNED THE BASTARD ON!!!! Basically I looped 1200 watts thru my amp. Speakers flapped, sparks flew, the room was filled with stench. Thank God the Speaker Cabinet is fine, probably cuz the amp's peak power is well below the rating for the cab.

    Now, only side A of the Power amp ( Crest LT1000 ) works, and I'm afraid to use even that. Side B reads Clipped when you turn it on and is totally non-functional......

    BEST PART YET: I have Three shows in the next five days, only one of which I can run a DI.

    Advice......?
     
  2. I would have to try the good side and see if I could limp through the gigs. Maybe you could borrow someones cab in case your amp is ready to fry speakers! ;)
     
  3. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    hahah, I would never use someone else's gear with potentially dangerous equip. But I wou8ldnt use my beloved schroeser either.....

    Is this a fix or replace? Is there an expert out on talkbass land who can give me an idea whether using side A is safe right now?
     
  4. Since both speaker leads are HOT when running bridged, part of what you did was short out one output amp channel to ground (from input of power amp connected to speaker jack). Could be the cause of the sparkage.

    Also set up a heck of a feedback loop to the input to probably get full power out into that short circuit in a hurry.

    I'm thinking you might get lucky and one channel of the amp will work. Try it at home. You might be able to get by on the one channel, it'll be a lot less power. But here the 1/2 the power = only 3dB less headroom works in your favor for a change.

    Take my amp for example... 1500w bridged at 4 ohms and 1000W at 8 ohms bridged. If I go with 1 channel instead of 2, I'd go from 1500W @ 4 ohms to 500w@ 4 ohms single channel. That's only 4.7 dB less power. You can get by on that probably, and send the amp in when the shows are over.

    Take your 8 ohm bridged power and divide by 2, that's your 4ohm power from each channel. The 4 ohm power bridged is twice the 2 ohm power per channel.

    Incidentally, that's a heck of a good reason to go with speakon instead of 1/4" jacks... but that was another flameridden thread....

    Randy
     
  5. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    yeah, one side works, and sounds fine, but I'm nervous. I really dont want to risk damaging the Cabinet, or further damaging the amp.

    It's not under any kind of warranty. This sort of repair takes weeks around here from any shop.

    Any other advice anyone?
     
  6. The 2 sides of a stereo amp are 2 independent amps, if one side works, you should be fine. They only share the power supply. Take it out of bridge mode, obviously, and make sure the unused channel is turned down all the way to minimize any chance of signal getting applied to the damaged output sections. If it doesn't blow the amp circuit breaker from a dead short in the output driver transistors, you're "probably" ok.

    Check for fuses on the output, or a circuit breaker of some kind, it could just be protection tripped instead of fried on that channel. Worth a try. Might be internal fuses protecting the output circuit on that side that is blown.

    Randy
     
  7. pablomigraine

    pablomigraine Supporting Member Commercial User

    Feb 9, 2005
    New York
    VP & Managing Director - Willcox Basses
    See your point. I definetly saw a spark of some kind from inside the amp. I cracked her open and couldnt find anything visibly blown or busted.

    Thanks for the advice....
     
  8. Output fuse?