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Inline fuse protectors for horns?

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  • Inline fuse protectors for horns?

    Hey guys, since my old Peavey 22a drivers are hard to come by and would need to depend on aftermarket diaphragms for replacement, I would like protect them best as I can. I have no knowledge of this except for the info which I have been finding on the net so I would appreciate if you guys here can help please?

    First, the drivers are around 40 watts continuous [80 Peak], there isn't a documentation available anymore for the 22A but peavey tech said I can go by the 22T:

    I want to use an Amp which is around 300W at 8 Ohms per channel so how does one know which fuse to get and also which is better a one-time or self-resetting please? Thx.

  • #2
    FWIW, I use fairly low power series resistors to my horns. My application is hi-fi though, so that may not be appropriate for PA use.


    • #3
      Fuses either blow too soon or not soon enough. One method of protecting HF compression drivers is with 24v aircraft light bulbs. When they heat their resistance goes up, so more voltage is dropped by the bulb, less by the driver, and worst case they blow.
      The only sure way to protect drivers, be they woofers or HF, is with a limiter that inserts between the mixer and power amp.


      • #4
        Bill has a good point. Does your loudspeaker management box have a limiter you can set?


        • #5
          Oh I see, I had thought the fuse would be the simplest thing which works. Yes we can set the limiter.


          • #6
            Fuses react to current. The current into a driver varies with frequency, so what would protect the driver at one frequency would not at another.


            • #7
              Fuses are a little iffy even protecting electronics, except from gross overload.


              • #8
                A couple of appropriately sized zener diodes back to back across the compression driver will do the job


                • #9
                  Originally posted by frustrated View Post
                  First, the drivers are around 40 watts continuous [80 Peak]
                  Note that the manual says 40W, 17.9V band limited to 500 Hz to 15 kHz.

                  That's not actually 40W.

                  But you could go by the 17.9V rating. Bill's suggestion of an inline limiting "bulb" is a good one and I'd consider putting one in place even if you do use a line-level limiter, to avoid any accidents or misconfigured settings damaging the drivers.. 24V might be a bit high though. Maybe a 12V lamp might be sufficient. I'd even consider going a step further and putting a PTC in line with both, to prevent both from seeing excessive voltage (and therefore burning out the lamp).

                  Brian Steele


                  • #10
                    24v bulbs are used because experience has shown 12v bulbs aren't up to the job.



                    • #11
                      There is a lot of confusion about fuses. The trick is for it to fail before the load. Fuses come in many different alloys, different standards for peak vs average current ratings and how quickly they react.

                      A self resetting "fuse" is not a fuse, but a thermal circuit breaker. Circuit breakers can also be magnetic, or like in a house, both. It may be a good choice for a PA system if you can select the correct one.

                      A light bulb IS a fuse. A bit different from typical wire fuses in that it's resistance goes up with current so somewhat self-regulates the load. Too much current and it will then open like any other fuse. If you have just the right one, maybe a very good option though even the "cold" resistance wil be higher than a fuse by quite a bit. High enough to be a problem? Don't know.

                      So the answer to your question is "it depends" Selecting the most appropriate fuse is a detailed engineering problem. If it blows too soon, it was incorrectly selected. If it blows too late, it was incorrectly selected. That is not the fault of the technology, but of the incorrect application. For home use, one can use a sledge hammer approach, go low and creep up, but for pro PA use, failure on site is a bad thing. So, did the PV tech actually give you a recommendation, or just pass the buck with a printed spec sheet? I might try to get to a more knowledgeable person at Peavey.

                      If you take their spec, 40W, and confirm with 8 Ohm impedance their 19.9V RPM bandwidth limited, that comes out to 4.36Amps as their long term thermal limit. Normal 3AB/3AG type fuses are for average currents, not peaks. I might suggest starting with a 2A slow-blow. Though the thermal mass of the VC is a lot more than the fuse, so the correct answer may be more like a 5A. It depends. It is a REAL engineering problem. Not a forum guesstimate. I only toss out numbers to show I don't know for sure and neither does any one else who did not design the driver.

                      If PeaVey can't help, might I suggest contacting fuse and CB manufactures. They may have some charts that can help you make a more educated guess.


                      • #12
                        The limiter is your safest bet, that's why it's there. I would think you need to limit power at lower frequencies more than at higher to prevent crashing the diaphragm.


                        • #13
                          Limiters are the better solution here. Lightbulbs do work in that they provide some protection for the driver by absorbing some power, but in doing that they change the sound and in my experience that change is not a good one. With a bit of planning the risks of bi-amping can be mitigated.. I have a bi-amped mobile rig with the CDs connected directly to the amplifier that sees regular use and abuse without any issue. The key parts to accomplishing this are to eliminate the possibility of miswiring the speakers.. I use 4 conductor speakon cables for this, the amp used must have built-in speaker protection eliminating turn on/off thumps.. usually accomplished in the amp with a relay, and then the crossover/processor has to be setup correctly. With a personal listening system the chances of somebody coming along and changing something is virtually non existent so if this can be done safely in a mobile environment it won't be hard to do at home. FWIW I have a 350w amp normally driving my CDs but I have used a 500w amp too.

                          Paul O