Question about JBL ESC-300 Speaker

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Humming from SUB333

I just bought this as a used system, got home, noticed that the power plug has been changed to a 3 prong one with only 2 connections (earth connector has no wires attached). Anyways, turn it on and plug in RCA cables and it hums, tried to plug it into my computer via digital coaxial cable...hums. And now it hums constatnly with no cables attached.

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  • felkai_cs Jun 21, 2009

    Thanks for the help, but I took the plug part appart, and there are only 2 wires coming from the sub, a blue and brown and none of them are touching the "earth" connector.

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  • JBL Master
  • 1,114 Answers

Replace the plug, they most likely had a ground loop where it was plugged in and cut the common to get rid of noise. Replacement ends are easy to find at Home Depot, Lowes, ACE, etc. Try that first, if you still have an issue, post a comment and I can help you further. Hope this helps

Posted on Jun 21, 2009

  • Frank Fulton
    Frank Fulton Jun 21, 2009

    Try reversing the wiring they have on the plug that was replaced. If it still hums, touch the input on the sub with your finger and listen for changes in the noise, you may have a loose conection on the input or a bad input board. Hope this helps

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  2. Find the coaxial cable running from your cable or satellite receiver to your service provider, and while listening to the hum, unscrew the connector and disconnect the cable.
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The second cause of hum is called a ground loop, and it almost always shows up right after you bring home a brand-new, self-powered subwoofer, or perhaps an external amplifier.
Take a look at all the plugs on the power cords on your home theater equipment. In most systems, the receiver (or amplifier) has a three-prong power plug, but most of your other devices have only two-prong plugs. This is not by accident; the device with the three-prong power plug is grounded. This means that device "owns" the ground. As long as no other power device has a three-prong plug, everything works well.
When you bring home a self-powered subwoofer and plug it in, though, you might notice it has a three-prong plug; this is for safety reasons. However, when you connect an RCA cable from your receiver to your subwoofer and turn everything on, you suddenly notice a loud hum.
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The proper, safest way to solve this problem is to buy a special subwoofer cable with little arrows on the wire to show the signal direction (see ).
[img src="http://oreilly.com/images/hacks/htheaterhks/figs/htheaterhks_0601.jpg">
Figure 1. Subwoofer cable with directional arrowUnfortunately, many people have been ridiculed when asking about these sorts of cables at their local electronics store: "But cables don't really have a direction. My expert friend at work laughed at me when I asked about this!" Yes, your friend is right. Cables don't have a direction, but these little arrows indicate that this cable will prevent or solve your ground loop problem.
Remember when I said the hum started when you connected the RCA cable? That RCA cable really contains two wires: the center wire and something called the shield. The center wire carries the audio signal, but the shield tries to define 0.00 volts. The shield is the wire that lets the two different components (the receiver or amplifier, and the subwoofer) see each other's ground, and causes the fight. What if you took your subwoofer cable and disconnected the shielding from just one end? Wouldn't that solve the problem? Yes, it would. This is exactly what a subwoofer cable with little arrows does. The shield is not connected at both ends. The shield has to be connected at one end, for connecting to your receiver or amp, so you should run the cable so that the arrows show the flow from the receiver to the subwoofer.
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