# Wrong wall-wart



## DMXtools (Aug 26, 2004)

The MC for Elgin's "Miss Hispanidad" pageant wanted a wireless lav. I've got wireless handhelds, but no lav of my own, so I rented one, a really nice UHF diversity unit. Tonight was dress rehearsal. I hooked it up and turned it on and got a few seconds of a really nasty hum before the receiver died. The rental outfit had packed a 14 volt AC wall-wart (plug-power supply) with a receiver designed for 12 volts DC. The moral of the story is always (especially with rental gear) make sure the rating on the wall-wart matches the rating on the gadget it's supposed to power. The brand doesn't tell the whole story: this wall-wart was from the same manufacturer as the receiver, but apparently for a different piece of equipment. The show will go on, but the MC will be using one of my handhelds.

John


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## ecglstec (Aug 27, 2004)

Never had an equipment die from overvoltage of only 2 volts. Sure it wasn't the polarity that did it?


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## DMXtools (Aug 27, 2004)

Agreed, in most cases 14 volts won't fry a 12 volt device. The smoke came from trying to run a 12 volt DC device from 14 volts AC. I recognized the smell of a toasty electrolytic capacitor - they're used for filtering the incoming DC, but they're polarized (except for special types) and feeding them with AC, even if it's lower than their rated voltage, usually fries them. With luck that may be all that went.

John


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## ecglstec (Aug 27, 2004)

That will do it.


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## DMXtools (Aug 29, 2004)

Well, I found the correct, or at least a correct, wall-wart, and, with permission from the owner, opened up the receiver and replaced a toasted electrolytic cap and a char-broiled resistor and voile! The trick she is done! The show went on as scheduled... but the MC decided a handheld was better. After all that, the lav was only used for the opening introduction and welcome.

Meanwhile, the contestants had to walk to the end of a runway, out in the middle of the audience and, there, in front of my speakers (which were stacked on either side of the stage), introduce themselves and answer questions from the judges. The best mic. I had for that was a fairly tight hypercardioid - not really very good for the application, but you do what you can with what you've got. With constant gain-riding and frequent tweaks on the EQ, we got by.

John


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## ecglstec (Aug 29, 2004)

Had the same problem with a comedian that liked to walk in the house. Stuck a sabine feedback eleminator in the channel insert with an EQ. Worked like a charm.


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## DMXtools (Aug 31, 2004)

Got a feedback eliminator... in the monitor mixes. Sitting FOH, I can usually hear the little bit of resonance that precedes feedback in the mains and notch the frequency by hand before feedback actually occurs, so the main mix just gets a good 31-band graphic. For most of the gigs I do (rock concerts), monitors are the most likely source for feedback, especially if the singer wants to stand a couple feet from the mic, sing quietly, and still hear himself over the instruments... through his earplugs.

John


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