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How to blow an amp?

Discussion in 'Amps and Cabs [BG]' started by Usul, Mar 3, 2001.

  1. OK,no offcolor remarks here! :D

    Just wondering how you can blow up your amp or blow out your speaker.....and how to avoid doing that.I never (ok,rarely)turn up my Crate BFX50 past "3" since I play indoors.I have been told to make sure everything is plugged in before powering up i.e. cable to bass,etc.Also not to suddenly jump up the volume to the higher(est) setting.Any info will be helpful,thanks guys/gals!

  2. Nino Valenti

    Nino Valenti Supporting Member Commercial User

    Feb 2, 2001
    Staten Island NYC
    Builder: Valenti Basses
    There are a couple of ways that I know to blow an amp up, tube amp in particular.

    1-Turn the amp on w/out having a speaker cabinet hooked up.

    2-Not having the correct Ohmage.

    Can't think of anything else off hand.
  3. Oysterman


    Mar 30, 2000
    Connecting an American 120V amp to 240V sockets ain't too good either.
  4. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Just keep it at 3 or below, and you'll be OK.
  5. Brad Johnson

    Brad Johnson

    Mar 8, 2000
    Gaithersburg, Md
    DR Strings
    Most amps don't like to be run hard...if you're maxing at 3 you probably won't make it break a sweat.

  6. damn :D
  7. running ohm load too high or too low
    running your amp into a shorted or blown speaker
    introducing liquids to the electronics
    using the wrong value fuse
    using an instrument cable instead of a speaker cable

    Survey Answer Number 1 is.....

    Loaning an amp to your "friend", I hate to say how many times I have heard this one.
  8. Ehm, hate to bug here... but I'm gonna do it anyway :D

    running an amp with a speaker cab at the rated impedance or higher (including no speaker!!!!!) will NOT damage an amplifier. Under normal circumstances, i.e. at or below max power.

    Severely overdriving a too low power speaker COULD damage the amp when the coil of the speaker is slamming into the magnet pole or the coil simply melts... short circuit!

    Running a cab through an instrument cable will probably smoke the cable and not damage the amp, but only of the molten cable will not short circuit.

    Running a too low power amp with a cab w/ horn will definitely damage the (if unprotected) horn.

    So how to blow an amp? Gunpowder......
  9. Will a real world example work here. There is a club in town that has this huge 1x18" cabinet that is 32ohms (it was originally part of a larger PA sub woofer system and really shouldn't be on a stage) on 2 different occasions that I know of it has blown a GK and a SWR when they were used to drive the cabinet.
  10. And there you have it. With a 32 ohms speaker you tend to turn up the amp too much, because with a 32 ohms load won't give you much power. 32 ohms is the impedance of most headphones; go figure. This speaker was intended to be used with 3 or 7 more in parallel, to get an 8 or 4 ohms load total, and thereby big ass sub bass power.

    When you just turn up the amp, in order to get more power (which you won't get, a few dozens watts at best) you will drive the amp in question WAY past clipping (which you won't hear on an 18"), the speaker will react to that by sending current back into the amp (especially 18"ers will do this: large coil), and this will simply fry ANY amp, no matter what. Hook up a 2.4 kW QSC amp and it will be fried in the end.

    If I remember correctly, I said "under normal circumstances" or something, the above certainly doesn't qualify as normal.

    Don't mean to bug....... I just have to be the one that's right, lol :D :D. No hard feelings, right?
  11. pkr2


    Apr 28, 2000
    coastal N.C.

    "running an amp with a speaker cab at the rated impedance or higher (including no speaker!!!!!) will NOT damage an amplifier. Under normal circumstances, i.e. at or below max power."

    If you adjust the volume control on a tube type amp to 75% max power into a speaker of the proper impedence you wont blow the amp but disconnect the speaker with the same control settings and you WILL fry the output transformer. If the secondary of the transformer doesn't reflect the load back to the primary windings, the transformer will arc across the windings, destroying the transformer.

    A solid state amp w/o an output transformer will not be harmed by an impedence that's too high but too low an impedence (speaker output shorted to ground) will instantly either blow the speaker fuse or short out the output transistors. Probably both.

    I don't mean to sound like I'm disputing your word, Joris. This is meant as fodder for friendly discussion. :)
  12. I stand corrected, pkr2. My comments are only valid for solid state amps. I know close to nothing about tube amps (oh well), so I tend to leave them out of my posts.

    So you say that a tube amp HAS to be loaded? Makes sense. The output impedance of the output tubes (that feed into the transformer primary) is IMO very high, so not loading the output stage through the transformer will sweep up the output voltage. Sparks, maybe even cause fire.

    One learns everyday.....
  13. well i run a 4ohm 15inch and an 8 ohm 15inch parallel in a 4 ohm amp. so i was running a 4ohm amp @ 2.75 ohm's and it went fine.
  14. pkr2


    Apr 28, 2000
    coastal N.C.
    If your amp is capable of driving 2 ohms you probably wont hurt anything. If you have either 4 or 8 ohm output on your amp you are skating on thin ice.

    To start with, one of your 15's is operating at double the power that the other one is operating at. One half the impedence equals double the load on the amp.

    I'm not disputing that you are doing it. I do question why one would run this configuration.

    Most amps will take a certain amount of abuse but to expect the setup you are using to hold up under a high volume situation is unrealistic.

    A good paralell is the sad demise of Dale Earnhardt. He drove into the wall a number of times with no problem. The kicker is that he eventually drove into the wall the same way he always had but that one time when things didn't go right, he paid the piper.

    You may run the setup you are using forever with no problem but that doesn't mean aren't sitting on a powder keg every time you do so.

    I can only advise the newbies and non-techies to match the load to the amp .Period. Always.

    This is not something I'm just making up, guys. The rules of electronics apply to amps and if you violate the rules enough, you WILL pay the piper. Just because you violate the rules and your amp survives doesn't mean that the rules can be disregarded. Keep it up and you'll find out why they are called "rules" instead of suggestions.


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