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Help me not blow up my new rig.

Discussion in 'Amps and Cabs [BG]' started by Duncorama, Mar 24, 2009.


  1. Duncorama

    Duncorama

    Nov 7, 2007
    I'm in a two piece (drums and bass guitar) and to get a louder, meatier, harder sound i've decided to start using sansamp rbi preamp with a Crown XLS 602 Power Amp (http://www.crownaudio.com/amp_htm/xls.htm).
    The cabs i'm gonna use are an ampeg svt 410he 500 watts 8 ohm and a Marshall MBC 115 300 watt at 4 ohm.
    Becuase both cabs are different ohm ratings i was going to run the power amp in stereo seeing as the sanamp has two out puts.
    So would i be right in thinking that this would work?
    Also, are there any warning signs i should watch out for? I notice that the ampputs out much more than what the speakers are rated at, will this damage them?!
    Also, if i'm using both out puts on the power amp should i have it set to stereo on the back?
     
  2. Mo'Phat

    Mo'Phat Supporting Member

    Oct 1, 2003
    San Diego, CA, USA
    Technically, you won't blow up anything. Setting your power amp on Stereo is the best bet.

    However, with two different impedence cabinets, you'll get different apparent volumes.

    When you say you're going to run your RBI stereo with the two outputs, you're not really running stereo. You don't have independent level controls so you won't be able to adjust the volume going into each channel of the power amp independently.

    BUT...since your 15" is the lower impedence cabinet, it might be better if it sounds louder than the 4x10 in your particular setup.

    Bottom line is that you won't blow anything up, and you should just try it out. If you feel like you need independent level controls for each cabinet, you could get another preamp.
     
  3. Duncorama

    Duncorama

    Nov 7, 2007
    Cheers for the reply fella.
    I actuallyy have 2 of the marshall cabs so would it be better if i set it up differently and used the 2 115's?
    I just assumed that the svt cab would be better.
     
  4. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Actually, that's not correct. He can't set different input levels fo each side, but the power amp itself has separate gain controls for each channel, so he can still set the relative volumes for each cabinet by using the power amp gain controls.

    Mike
     
  5. Mo'Phat

    Mo'Phat Supporting Member

    Oct 1, 2003
    San Diego, CA, USA
    Generally the only time you might risk blowing something up is if you run your cabs at a lower impedence than your amp is rated for. Like chaining your two 4 ohm cabs to 2 ohm and going into one channel of your amp...most amps will hate that.

    Since you've got a lot of options, try some out and see what works best for you.

    With that amp, I'd recommend using your two Marshall 15's. Running one into each channel of your amp. OR just use the Ampeg 4x10, with your amp bridged into 8 ohms.

    Since your amp can't handle a 2 ohm load, don't chain the cabs that way. 4 ohm stereo or 8 ohm bridged mono will harness the most power and headroom.
     
  6. Mo'Phat

    Mo'Phat Supporting Member

    Oct 1, 2003
    San Diego, CA, USA
    Over the years, I've been browbeaten into submission by myriad power amp gurus that the input gain controls on the power amp have very little relation to volume. Volume comes from the preamp.

    I don't know what's right...all I do is set my channels to about 3 o'clock (not cranked...just back a bit from cranked) and control my volume with my pre.
     
  7. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    The setting of the gain control on the power amp is just one piece of the volume puzzle. In this case, though, the two channels are getting exactly the same input. If you set the gain higher on one channel than the other, it will boost the input signal more. That's not the only factor affecting the volume--the impedence and efficiency of the two cabs will also make a big difference--but you can adjust the *relative* volume between the two cabinets using the amp gain controls.

    Mike
     
  8. Duncorama

    Duncorama

    Nov 7, 2007
    Sorry if i'm being a dumbass but by amp gain controls do you mean the two volume knobs on the front of the power amp?
     
  9. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    Yep.
     
  10. Bassmec

    Bassmec

    May 9, 2008
    Ipswich UK
    Proprietor Springvale Studios
    Yes thats the gain controls he was referring to:ninja:
     
  11. They'll work fine like mikezimmerman said, but technically they're not gain controls, just attenuators.
     
  12. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    I stand corrected. :) The manual just described them as "level controls".

    Mike
     
  13. Jack

    Jack

    Sep 6, 2003
    Northumberland, UK
    You don't need to run two cables from two outputs to two inputs on the power amp, you could just run one into channel A and set the amp to dual mono or parallel or whatever Crown call it. That will make whatever you throw at channel A come out the back on both A and B.

    Saves you a cable. :)
     
  14. mikezimmerman

    mikezimmerman Supporting Member

    Apr 29, 2001
    Omaha, Nebraska
    I was going to suggest that, too, but when I glanced (briefly) at the online manual, I didn't see where Crown had a parallel/dual mono setting. Too bad, since that's a lot simpler.

    Mike
     
  15. Duncorama

    Duncorama

    Nov 7, 2007
    Yeah it doesn't have a parralel option, sorry i didn't mention that.
    The only way i can use it with one cable coming out the pre is by using one output out the back of the power amp and i don't have 2 cabs that are 8 ohms each. The ampeg is 8 ohms but one cab on its own doesn't really move enough air to fill out a two piece.
     
  16. zagnut

    zagnut

    Jan 4, 2009
    Back in Detroit
    If the drivers are run past there rated handling for long periods of time, you could burn the voice coils out. If your playing some kind of weird synth bass, subharmonics could destroy your drivers, this is what a Lo-cut or high-pass filter is for. Depends on what your playing and at what volumes and for how long.
     

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