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The Magic Cafe Forum Index » » F/X » » Hum in the line (0 Likes) Printer Friendly Version

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Bill Hegbli
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Eternal Order
Fort Wayne, Indiana
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Where do you put the CD/DVD player in relation to the PA. Most PA are not shielded. Is your player shielded. Move the player several feet from the PA. Turn down the Volume on the CD player if it has a sound control, and use the PA sound control.

If the wires are old, replace them with shielded cables.
g0thike
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SethB,

Before others share their ideas, so far it sounds like you don't need a direct box. What Anchor model are you working with?

Is it a all in one solution, a powered/speaker/mixer with builtin microphone receiver?

G0THIKE
sethb
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Inner circle
The Jersey Shore
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To answer your questions, it's an AN-130, which is an AC powered speaker, and there is a built-in wireless receiver. There are also rear mic and line inputs.

The DVD player doesn't have a grounded plug, but it is polarized (so I can't try the old "flip-the-plug-over" trick).

The PA is about 40 feet from the player, connected by a 16-gauge mono speaker line with RCA plugs on either end. I don't believe the speaker line is shielded. The speaker line is not near any AC lines that I know of. SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
g0thike
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SethB,

You got a 20 watt PA system. The fact that you get a hum when turning on the system 1/3 volume and nothing connected, means that most likely it is either the wireless receiver or the unit is at fault.

The best advice I can give you is to contact Anchor Audio.

Though my last guess is to change the frequency (channel) of the wireless receiver. If that is not possible, try testing the unit somewhere else. The receiver might be picking up something, interference.

G0THIKE
Dan McLean Jr aka, Magic Roadie
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Toronto, Canada
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Quote:
On 2009-11-21 18:45, sethb wrote:
The PA is about 40 feet from the player, connected by a 16-gauge mono speaker line with RCA plugs on either end. I don't believe the speaker line is shielded.

If the player-to-PA lines are, in fact, unshielded, that could very well be your problem, or a least a very significant contributing factor. Every cable that is before the amplifier portion of the circuit must be shielded.

Even if the player-to-PA cables ARE shielded, they are "high-impedence & unbalanced" (don't worry about what that means), and 40' is far to long for such a signal.

Both factors (unshielded & 40') could very well cause such symptoms.

Try putting the player near the PA, and using short cables (less that 6'). Don't get the player TOO close to the PA because it will cause a different kind of interference for the wireless receiver. If you still hear a noise, pick up the player and move it around to see if the noise goes away. "Unbalanced, high-impedence" signals are capable of short cable runs.

If the shortened-cable test works, then here is your solution. Run short cables from the player to two direct boxes. Then, run long mic cables from the direct boxes to the PA. The reason for this, is that a direct box's purpose is to convert an "unbalanced, high-impedence" signal into a "balanced, low-impedence" signal. The latter is capable of long cable runs, as long as the PA has "balanced, low-impedence" input connections. In your case, these PA inputs would probably be XLR mic inputs.

If your PA doesn't have XLR mic inputs, then I don't see a solution, other than putting direct boxes at BOTH ends of a long mic cables, therefore going through the second set backwards.

Good luck!
Dan McLean Jr
sethb
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The Jersey Shore
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Thanks for all the input. I realize that we did this sort of backwards -- we should have amped the signal before the 40' speaker cable run.

However, being a public library, funds are limited and we had to cobble a sound system together from what was on hand.

Even with a short player-to-PA cable, I still had hum. So I think what we will do is just try to boost the signal to the PA and use as little of the PA volume as possible. Then I'll put an amp and a speaker into next year's budget and hope for the best. There is a 3-watt amp in the digital projector, but I imagine that is basically worthless for this purpose. SETH
"Watch the Professor!!" -- Al Flosso (1895-1976)
"The better you are, the closer they watch" -- Darwin Ortiz, STRONG MAGIC
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