Subwoofer hums under power not hooked to system & hooked up?

Try the following steps to stop subwoofer hum.

1. If the subwoofer is plugged into its own outlet, plug the subwoofer's power cord into an outlet shared by the other components. Use an extension cord if necessary.
2. If the hum persists, and your system includes a cable TV, disconnect the cable line. If the hum stops, install an isolation transformer on the cable.
3. If the hum persists, disconnect the remaining component cables one at a time until the hum stops. Install a coaxial isolation transformer on that cable.
4. If the hum persists, install a line-level ground loop isolator on the subwoofer's line-level feed cable. This usually solves most hum problems.
5. If nothing helps, disconnect all the audio cables from the subwoofer. Leave the subwoofer plugged in and switched on. If the subwoofer hums, it points to a defective unit. Contact the company's customer service to technical support.

I would check the caps on the power supply. They are rather large electrolytic capacitors that will look like they burst and/or leaking. When these die, the caps ground and the sub will make a loud buzzing sound. If you are handy with a soldering iron you can replace them yourself. Replace them with the same voltage or a little bigger and same with the size.

If the cap. says 16v 4700pF on it, for example, a 20v 5300pF or a 16v 6200mF cap. will work for this application.

I suspect the amplifier is damaged. This is not an easy repair to do unless you are well versed in audio electronics. I would recommend a repair shop to look at the subwoofer amplifier.

Hi, The Ground Rules Of all the annoyances that can afflict any audio/video home theater or even a simple stereo installation, the notorious "ground loop" may well be the most difficult and persistent one to track down and eliminate. A "ground loop" is caused by the difference in electrical potential at different grounding points in an audio/video system. (All the grounds in an A/V system should ideally be at "0" potential.) A ground loop typically adds a loud low-frequency hum or buzz as soon as you plug in any of various audio or video components, including subwoofers, cable-TV outboard boxes, satellite-TV feeds, TV displays, amplifiers, A/V receivers or turntables. The buzz/hum is a byproduct of the multiple power supply cables and a ground voltage differential within your system and its network of interconnecting cables.

Here are some methods to help you get rid of ground loops. Try these first and don't waste money on a power "conditioner" which, in most cases, won't help. (There is no need to "condition" the AC power for your system. Your receiver or amplifier already has a power supply with its own filters and transformers. No further filtering is normally required.)

If you get your system up and running and hear an audible buzz or hum, the first culprit to look at is either the powered subwoofer or your cable-TV or satellite-box feed at the entry point to your system.

First, the subwoofer: unplug the coaxial cable that connects to your powered subwoofer to see if the ground-loop hum disappears. If it does, it's likely coming in through your cable/satellite TV feed.

Reconnect your subwoofer's coaxial cable from the subwoofer input to your receiver's subwoofer output and disconnect the cable-TV feed (or satellite feed) from your outboard set-top cable box or satellite tuner. Be sure and disconnect the cable before any splitters. Now see if the hum/buzz from your subwoofer stops.

If that eliminates the hum, you can install one of these inexpensive in-line ground isolators from Parts Express or Bass Home. Note that these transformer-based ground isolators will work fine with analog cable-TV feeds, but depending on their design they may interfere with or block reception of HDTV signals via a digital cable or satellite dish feed.

Install the ground isolator between the cable-TV feed and the input of your outboard cable-TV box or satellite tuner (or the TV display's antenna or cable input if you have a set with a built-in TV tuner or a cable-card ready set). In many cases, the ground isolator will "break" the loop and remove the annoying hum or buzz by isolating the TV-cable ground.

If a hum remains with the TV cable completely disconnected from your system, or you don't want to risk degrading reception of HD signals from a cable or satellite system, then you may have to add a ground isolator like this Radio Shack Model 270-054 between the line-level coaxial subwoofer cable from your A/V receiver and the line-level input jack on your powered subwoofer.

In all cases, if your subwoofer has a ground-lift screw like some of Axiom's subwoofers, try first removing the screw (or replacing it) to see if it increases or eliminates the hum. It may or may not make a difference.

If you do not have easy access to the aforementioned ground isolators, here are a few more tips:

Try plugging the subwoofer into a different AC outlet in the room, one that isn't supplying power to your components (A/V receiver, TV, cable box, etc.). That might fix it.

Try reversing the AC plug for your A/V receiver or the powered subwoofer. If it's a 3-wire plug or a polarized plug, which has one prong wider than the other, you won't be able to reverse the plug. For safety, do not use a "cheater plug" to bypass the 3-wire plug.

With the power OFF, reverse the AC plugs one by one of any other components that have a standard 2-prong AC plug that isn't polarized. Each time you reverse a plug, turn on the system with the attached component and your subwoofer and see if the hum disappears. In some cases, reversing one or more plugs will eliminate the hum.

If you have a turntable, try connecting a separate ground wire to a chassis screw on your preamp or receiver and see if the hum disappears. If you already have a turntable ground wire, try removing it from the preamp. One or the other may eliminate the hum.

Finally, here is another solution that worked well for a member of our message boards who decided to discard his ground-loop isolator on his subwoofer: "I took off the ground-loop isolator I'd been using and connected a plain 14-gauge wire to chassis screws on the sub and the receiver then powered everything on. Although hum was still there, it was far lower than before. Next I unscrewed the ground-loop screw on the back of the sub and that took care of the hum completely."

Almost certainly sounds like an earth loop to me, but can be caused by a poorly made transformer or phase shifts on the mains supply. Visit some power conditioner web-sites like Isotek or Isol-8 (or google "earth loop") where there's plenty of advice on how to reduce/eliminate earth loops and other causes of mains-induced hum (transformer problems etc).

Hum on the speakers usually indicates that there is a DC voltage on the speaker line. DC voltage on the output lines would be caused by a shorted output transistor.


Have a nice day...

HI, I have the same problem with a MINX subwoofer, can any one help.

This is most likely a "ground loop" and is caused by using two different electrical outlets for the two parts of the system -- main receiver and subwoofer amp.

Try using the same electrical circuit (wall outlet) for all of the equipment in the home theater, using a power strip or strips as needed.

check the heatsink, touch it with your finger feel it ,if you can hold it with in 15 sec, then your power amp. component might be working if not then probably you Power Amplifier IC or transistor is shorted.

make sure you have the speaker connection right if you do then it is a ground problem try plugging it in a different outlet

If you have cables hooked up and have not installed them to the components when turned on the speaker will hum.
If your electrical outlet is not grounded properly you speaker will hum.
Personally I'd take it back and get a new one. if you just purchased it.
If this happens again try a grounded curcit first then go from there.

This can be caused due to an increase in local interference. The hum is decreased when you plug in the satellites because the interference is spread over a longer area. You may notice that speakers tend to hum around things like cell phones and power outlets. To see if this is the case, move the speakers to another part of the room if you can, slide the desk around, plug the computer in at another room, something like this. If the hum gets louder or quieter, it is interference at your new place. This can be solved by finding a new area to set up your computer stuff at. Since it's mostly the subwoofer, try elevating it off the ground, there may be a power main running under the floor.