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Force amp to heat up

Discussion in 'Sound, Music, and Intercom' started by Harrison, Feb 16, 2017.

  1. Harrison

    Harrison Member

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    I have a couple or Crown CL series amps that were pulled out of their rack because they went into protect mode 10-15 minutes into running. My theory is that they are overheating (I'm curious as to if the fan is being activated, as I've tested the fan outside the amp and it works), but what's the best way to get the amp heating up in order to trigger the fan to turn on (apparently it has to reach a threshold to activate)? I don't really have a place to blast music or something, is there another way besides putting an actual load with speakers?
     
  2. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    You can pick up a few of these resistors and simulate a speaker load, then play pink noise or a drum kit track to drive the amplifier. A pink noise signal is better for testing continuous loading, but a drum kit track is ideal for testing program material where you have more peaks with a lower continuous level. I would stay away from a 1kHz tone -- while commonly used for testing, it is representative of the worst case condition for loading an amplifier and can misrepresent potential thermal issues, making a perfectly healthy amplifier look like an easy bake oven.

    I've also heard the heating coils for water heaters are a low impedance, higher wattage load. That's a little more complicated to set up though because you need to mount the coils inside a metal trash can and fill it with water to keep the coils from burning up. The end result is something that looks suspiciously like a bomb -- a trash can, heated up, with wires sticking out of it.

    The resistors are probably the easiest way to go for you in terms of simulating a load.

    It may not be worth anything to test them outside of the rack. If they aren't getting enough airflow through your amplifier rack and you test them while they're removed, your test may reveal that the amplifiers are okay, but they may still give you headaches when you drop them back into the rack with the others and your cooling issue presents again.

    I would also look at the manual and see all of the other possible causes for going into protect mode. If the amplifier doesn't support a 2-ohm load but that's what you've got after 3-4 speakers have been daisy-chained together on a channel, that may also present as a Protect Mode failure. I'm sure there are other potential causes listed in the manual as well.

    Other thing to look for is if there's any dust that's clogged the filters or the internals of the amplifier. A thick layer of dust would cause thermal issues, and would be a better explanation for multiple amplifiers presenting issues at the same time than say manufacturer defect or old age.
     
    Last edited: Feb 16, 2017
  3. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    And then there are folks who mount amps with front to back ventilation in the same rack with amps having back to front airflow and end up with warm air travelling in circles within the rack while warm amps cook each other. Lots to watch out for when racking amplifiers. Some are intentionally designed to be racked adjacent to each other without any vents in between.
    Toodleoo!
    Ron Hebbard.
     
  4. FMEng

    FMEng Well-Known Member Fight Leukemia

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    It could be as simple as filters or heatsinks plugged with dust. I'd start with cleaning the insides. I've had fans that appear to be working, but they run slow due to failing bearings, so they don't move enough air. Usually bad bearings make noise, but not always. Fans are a very common failure item.
     
  5. themuzicman

    themuzicman Active Member

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    When I worked in repairs for a large rental shop, our usual way of getting amps to thermal fault was to wrap a few packing blankets around them and let them run for a while. Some of the better built amps needed to be under load so I'd plug them into a dummy load box, feed them an input signal, wrap them in the blanket and see what happened.
     
  6. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    As a quick guess, how many flaming blanket fires did you need to extinguish? Did you happen to try this with any Flame Linears?
    Toodleoo!
    Ron Hebbard.
     
  7. TimMc

    TimMc Member

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    Hi Harrison-

    If you need a dummy load I suggest taking your multi-meter to your local thrift or second-hand store and test the various clothes irons or electric skillets and find one that is 4-8 Ohms. You might get a few odd looks in the store but you'll avoid the terrorist contraption look the water-bath heating element system has. And if you're testing a long time you can freshen your wardrobe or fry up lunch, too. :pizza:
     
  8. themuzicman

    themuzicman Active Member

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    Only one ever got the blanket smoldering, but that was on me when I went to lunch without unplugging it. Usually a fuse will pop before they catch fire when thermally faulting, however the theater it was installed in had thrown fuses that were rated much too high because they were trying to get through a weekend of shows without it turning off.
     
  9. EdSavoie

    EdSavoie Active Member

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    While I understand the mentality of needing to get the show through the weekend, blowing a fuse means that your equipment is faulting, and possibly a safety hazard. Putting a fuse rated higher than spec is just moving the weakest link to somewhere potentially more dangerous...
     
    RonHebbard likes this.
  10. themuzicman

    themuzicman Active Member

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    Not my show, just the gear I was paid to fix. You can tell the Local 1 stagehands that did that your thoughts on the matter though!
     

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