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#482412 04/13/11 02:46 PM
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We are having a weird problem at work...our auditorium system consists of a Mackie DX8 and 3 Crown Com-Tech 1600 amplifiers, all 70 Volt.
If someone bumps the podium mic, or goes to plug a 1/8 inch cable into their laptop through a direct box, it will often cause a loud pop, then the system surges and shuts off. I can't figure out why or how to fix this, besides turning the channels all the way down when someone is plugging in. The devices in the rack are connected to power strips on 2 different circuits. Sometimes the breaker on the power strip will trip, but usually the breaker in the panel trips instead.

Any ideas?


Jeff Moss

Moss Communications
Computer Repair-Networking-Cabling
MBSWWYPBX, JGAE
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#482413 04/13/11 11:09 PM
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First off you should always have the volume off on empty inputs. What is shutting off? Is you direct box a passive device or does it have isolation? Have you checked the current load to make sure you are not overloading your circuits? Put and amp meter on the feed and monitor the current and see if it spikes when this happens.


Merritt

Business Telephones & Equipment + Commercial Audio/Video Products
Commercial Communications . . . Turner, Maine
If it was built after 1980 don't expect it to work right.
#482414 04/14/11 01:36 AM
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Quote
Originally posted by metelcom:
First off you should always have the volume off on empty inputs. What is shutting off? Is you direct box a passive device or does it have isolation? Have you checked the current load to make sure you are not overloading your circuits? Put and amp meter on the feed and monitor the current and see if it spikes when this happens.
aok

Exactly!

Sam


"Where are we going and why are we in this hand basket?"
#482415 04/14/11 02:23 AM
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I just took a peek at the manual for the Crown Com-Tech amps. Check out the current draw for a 1600 at 50% duty cycle [on page 43 on manual K-80636]. That "pop" when somebody plugs into a live input is easily equal to 50% duty... probably more!

If these are the 120V units, it is close to 20 amps. If they run on 240V, it is only about 9 amps.

But blowing the breaker is only a symptom. As others have said, you need to figure out how to stop people from plugging into inputs that are live. They have actually been lucky so far...

Jim
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Speaking from a secure undisclosed location.

#482416 04/14/11 03:38 AM
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Merritt,
The breaker will trip thus shutting the mixer and amplifiers off. The direct boxes are passive, these are the ones we use: https://www.artproaudio.com/products.asp?type=90&cat=13&id=104


Jeff Moss

Moss Communications
Computer Repair-Networking-Cabling
MBSWWYPBX, JGAE
#482417 04/14/11 11:01 AM
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Those channels should be near off or completely off when plugging in or unplugging anything. Also check the level controls on those amps, you could try turning them down so the power to the system is not so high on those loud sounds.

#482418 04/15/11 11:39 AM
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Sounds like you need a limiter to me...

-Hal


CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.
#482419 04/15/11 02:07 PM
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Very good advice Hal that may even save the speakers. [Linked Image from fc00.deviantart.net]


Merritt

Business Telephones & Equipment + Commercial Audio/Video Products
Commercial Communications . . . Turner, Maine
If it was built after 1980 don't expect it to work right.
#482420 04/15/11 04:27 PM
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The mixer does have all kinds of built in stuff through the software so I can try a limiter.
I talked to Crown and they said at peak those amps can draw up to 13 amps. The way we have spaced out the power is with the wireless mics, one mixer, and 2 amps on one circuit, and another mixer, cd player and 2 more amps on the second circuit (the rack has equipment for 2 rooms in it)
Unfortunately we only have 2 circuits for the rack, without putting in anything new. I should have the electricians come check with a clamp on meter when we are running it...


Jeff Moss

Moss Communications
Computer Repair-Networking-Cabling
MBSWWYPBX, JGAE
#482421 04/16/11 01:39 AM
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If each amp can draw 13 amps at peak I think they should each be on a dedicated circuit. Have 2 new circuits run in for the mixers and other stuff.


Merritt

Business Telephones & Equipment + Commercial Audio/Video Products
Commercial Communications . . . Turner, Maine
If it was built after 1980 don't expect it to work right.
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