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power help

Discussion in 'Amps and Cabs [BG]' started by softscrubmonkey, Dec 24, 2004.


  1. softscrubmonkey

    softscrubmonkey

    Nov 19, 2004
    St. Louis
    alright i searched the ohms FAQ thread and could not find an answer to my question. so my guess is this is a stupid question, but...i still need an answer. so here goes. if ive got a 4ohm and a 8ohm cab that both handle 500 watts RMS, how exactly do i figure out what is too much? would a power amp with 750 watts @ 2 ohms be ok?
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    i'm assuming that you plan on wiring both cabinets to one side of that poweramp. or is it a head? Let's pretend that you are wiring both cabs to one side of a poweramp or to a mono head that puts out 750 watts at 2 ohms safely. You'll have a 2.67 ohm load so it won't put out quite 750 watts. Let's pretend that it does. In that case the 4 ohm cab gets 500 watts and the 8 ohm cab gets 250. So you're safe. Even if your amp puts out more power than the cabs can handle, you're still ok as long as you dont turn the amp up all the way, AND if you listen to the cabinets carefully to make sure they're not being overdriven. Lots of us use more power than our cabinets can handle for headroom.
    Now, onto the amp in question. Is it a mono head that can put out 750 watts into a 2 ohm load safely? or is it a stereo poweramp than can put out 750 watts into 2 ohms per side safely? Only a few commercial and very very expensive poweramps can power a 2 ohm load in bridged mode. If you're using a stereo poweramp, you'll have more flexibility and control by connecting the cabinets to the 2 sides in stereo mode.
     
  3. Your total impedance running both the 4 and 8 ohm cab would be 2.67 ohms. The 4 ohm cab would consume 2/3 of the wattage while the 8 ohm would consume 1/3
    750 would be the absolute max.
     
  4. softscrubmonkey

    softscrubmonkey

    Nov 19, 2004
    St. Louis
    yeah its a seperate power amp with stereo 750 watts @ 2ohms
     
  5. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    in that case i would run the 4 ohm cab off of one side and the 8 ohm cab off of another. Find out what the power amp puts out per side at 8 ohms and 4 ohms to figure out how much juice each cab is getting. You can use the input gain knobs for the 2 channels of the poweramp to balance the volume of the two cabinets. BTW, don't worry about having unequal loads on the two different sides of the poweramp, there's nothign wrong with that and a lot of us do it .

    what you cant do is run that amp in bridge mono mode into both cabinets at once. Amps that are good for 2 ohms per side stereo will only safely bridge into a 4 ohm load. I wouldn't worry about not being able to do that. You should have plenty of volume running the cabs as stated above.