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newbie amp/cab question

Discussion in 'Amps and Cabs [BG]' started by jaggedsphere, Jul 15, 2002.


  1. jaggedsphere

    jaggedsphere

    Jul 15, 2002
    Ottawa
    'lo all, this is my first post on talkbass. i have been lurkingfor the past few months...
    anyways, what i would like to know is what is the circumstance where i might 'blow' my amp or cab...
    I realize that you cant just go plugging this into that. so, what do I have to watch out for? watts, ohms (impedance) has to do with this right?

    thanks alot in advance!
    jaggedsphere
     
  2. jaggedsphere

    jaggedsphere

    Jul 15, 2002
    Ottawa
    hello is this thing on???!?:confused:
     
  3. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    Aside from wiring errors, good ways to blow your amplifier are:
    Too low cabinet impedance (transistor amplifier)
    Too low or too high cabinet impedance (tube amplifier)
    Voltage spikes (bad building wiring)

    Speakers can be blown by:
    Too much power
    Not enough power

    This last one is not obvious, but here’s what happens. If you push your amplifier too hard, it tends to abruptly clip the peaks of the signal going out to your speakers. The speaker has a much harder time with this signal than a larger smooth signal because it is asking the cone to make a very abrupt change. This can instantly destroy your speaker.

    Essentially, you need to make sure your speaker impedance is properly matched to your amplifer, and you have to make sure you have more than enough power for the volume you need to play at, and then be disciplined enough not to turn it up too high. To protect against voltage spikes, get a surge protector for $20 from a computer store (make sure it has a warranty to cover the cost of repairing/replacing your equipment).
     
  4. thelastofus

    thelastofus Guest

    Jul 3, 2002
    Bakersfield, Ca
    match the ohms on your cab with the ohms on your head, do not play a head which exceeds the handling on the cab. ex. do not plug a 500 watt head into a 400 watt cab. you can do the reverse however (and is usually the case) plug a head which has a lower watt rating then the cab (400watt head, 600watt cab) or they can be the same. You most likely aren't going to blow your amp or speakers, just don't crank it up too much. If you're playing and hear a really nasty speaker distortion (happens to me frequently), turn down. Once you reach that point you most likely will not get any more volume but just have your sound be more broken up. So....as long as you don't frequently turn your amp up to 9 or 10 you should be fine, and if your head is a tube head, let the tubes warm up for 30 seconds before you flip on the standbye switch. Also don't use a speaker cable to plug your bass into, be sure it's an instrument cable, that can damage your amp. Um, if it's a tube amp make sure that your tubes are the right kind for your amp (6L6's vs. el34's, something like that). That's about all, it's not too complicated and you're more than likely not going to damage anything.
     
  5. Steven Green

    Steven Green

    Jul 25, 2001
    Pacific NW
    This isn't really necessary...

    just don't give it so much power that the speakers can't handle it. I use 2000 watts with cabs that can handle only 1200 watts. They work great...I just make sure the speaker cones are not taking a beating. Extra clean power is less likely to blow a speaker than not enough power (during clipping). The more power the better!:D
     
  6. LiquidMidnight

    LiquidMidnight

    Dec 25, 2000
    I always thought it was the other way around. You could plug in a head that is rated higher than your cab and if you plug a head rated lower than your cab, you have a chance of overworking the poweramp and burning your head up.

    I'm buffudled now. :confused:
     
  7. Steven Green

    Steven Green

    Jul 25, 2001
    Pacific NW
    You can do either and be fine. If you run less power than your cab can handle, just make sure you are not clipping the power amp to get the volume you need. If you have a lot of power (more than the cab is rated for RMS), just don't give to speakers all of it. The rest you don't use is your headroom, which keeps your tone nice and clean!:)
     
  8. 44me

    44me

    Jun 17, 2002
    Bedford, NH USA
    Like Steve said, the key thing is to avoid clipping. If the amp has a lot of power, this is fairly easy to do. When the amp power is small (not real small, like a practice amp), it’s much easier to run out of headroom. I think more newbies blow speakers this way than with overpowering the speakers.
     
  9. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    There have been a lot of threads on this; a search would probably tell you a lot.

    Steven's right: you can do things either way. The key thing is that in either setting, when your rig is in use, you don't give the speakers more than they can handle on an ongoing basis, whether by overdriving a smaller amp or putting out too much clean power with a bigger one.

    Oh yeah, in practice, clipping *in itself* isn't what harms speakers. If it were, no Marshall or Mesa guitar speakers would ever last for more than 5 minutes. The problem comes when clipping results in too much power being delivered to the speakers. Example: if you clip a 400 W amp, you could get it to put out *much* more than its rated power. (Remember, amp ratings are done under low-distortion conditions.) When this happens, you could indeed harm a 400 W speaker. But you can clip a 10 W amp into an 800 W subwoofer all you want, and you'll never hurt the speaker.
     
  10. Steven Green

    Steven Green

    Jul 25, 2001
    Pacific NW
    Very true Richard. Doesn't clipping cause subharmonics, which can cause overexcursion of the speaker cone too?
     
  11. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Not AFAIK, but then, I don't know nearly as much about this as folks like Bob Lee/QSC do. I would trust someone like Bob's expertise over mine.

    Here's an article on clipping I've found interesting:

    http://www.rane.com/pdf/note128.pdf