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#1 naturegazer

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Posted 27 March 2005 - 12:58 PM

At our church we have a crown D150A series ll  amp and it puts a loud hum through the speakers, is there a filter that can be installed inline to quiet this noise or do i have a problem in the amp itself. the amp is driving  EV sentry 500 speakers any help would be appreciated.

#2 DGlass

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Posted 28 March 2005 - 09:29 AM

A Loud Hum? Hmmmmm  smile.gif That could be caused by several things. First let us lay some groundwork: audio systems can exhibit "hum" and they can exhibit "buzz," which are two separate situations. To solve the problem, you need to determine whether your system is exhibiting hum or buzz.

Sixty(60)-hertz hum (fifty(50) hertz internationally) is a result of having a ground loop in the audio system. This is where there are two or more ground references in the system, and current is flowing from one ground point to another. Any piece audio equipment requires one ground reference. Ground loops can be formed in a number of ways. For example: An audio power amplifier obtains its ground from the AC power cord. The mixer, which drives the power amplifier, also receives its ground from the AC power cord. When the audio cable connects the mixer to the power amplifier the amplifier now sees a second ground from the mixer. If the mixer and power amplifier are both plugged into the same AC power strip and are connected with a balanced 3-wire audio interconnect cable then the shield wire of the audio interconnect cable can be cut to eliminate this problem.

Also make sure you haven't defeat the ground connector on the AC plug. This is what we refer to as a DDT (Donít Do That) wacko.gif. Not only can using one of those nasty ground lift adapters (or cutting off the ground pin) cause all sorts of problems it is a serious safety issue.

Another cause of system "hum" is electrically induced, such as having a very sensitive component too close to a power transformer. Power amplifiers have large power transformers and can induce a magnetic field into other equipment. If you suspect this may be the cause of your problem then placing more distance between the two components is the only practical solution. Simply move any processing gear that may be sitting right on top of the amplifier.

Excessive "noise" on the AC mains can cause "buzz" in certain components. Lighting dimmer packs are notorious for inducing noise onto the AC mains. If this is your problem try putting the lighting system on a different AC mains feed.

Try unplugging the inputs to the amplifier if the hum goes away it could either be a system related issue, an AC ground issue or both.  If the hum is still there it is more than likely that the amplifier needs to be serviced.

If it turns out to not be an amplifier related service issue than I would suggest you contact a local sound system installer to look over your system. I have seen things like this turn out to be as simple as an oxidized connector or as complicated as needing major rewiring.

By putting in a so-called hum blocker device in the input signal path before the amplifier you are really just putting in an Isolation transformer. It does eliminate the issue in most cases but doesn't address the cause, if it is system related, as the hum will probably pop back up someplace else when another piece of gear is added.

Ground loops, induced hum, and all kinds of nasty noises are sometimes hard to pin point. You may have to try several different approaches before arriving at a solution. For more information on AC connections you can call our Tech. Pubs Department and ask for the Sound & Communications reprint of "The AC Connection." written by Dave Engstrom one of the other gentleman here in Crown Tech Support. You might also want to check out www.audiosystemsgroup.com . They have many good articles on grounding and one on the Pin 1 ground connection of balanced audio connectors.