Question about Pinnacle PS Sub 150 Subwoofer

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Loud Hum in Pinnacle 150 subwoofer

I have had this pinnacle 150 subwoofers since 1998. I came home and heard a load humming in my media room coming our of one of the subwoofers (not both). I disconnected the input cable but it did not stop. I had to unplug the power to stop the noise. I left the input disconnected and plugged the speaker back into power and the humming immediately was back. Any suggestions on what may be the issue would be appreciated.

Thx. Don

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Re: Loud Hum in Pinnacle 150 subwoofer

The hum is likely due to either a failed capacitor in the subwoofer power supply or as it was for me, a cold solder joint on the capacitor. The fix is simple, but does require soldering. Unplug the subwoofer and set it on a good working surface. Remove the screws holding the back panel to the cabinet. These screws are the ones near the edge of the panel. Take off the panel by pulling back on it, reach into the subwoofer and carefully unplug the red and black speaker leads noting which one goes to each connector. Orient the panel with the electronics side up and the power cord at the lower right of the panel. Just to the left of where the power cord is soldered to the board is a large cylindrical capacitor. It is by far the largest cylidrical component on the board. This capacitor filters the hum made by the step down transformer in the power supply. If the capacitor is not working the subwoofer hums. The capacitor is soldered to the back of the electronics board. We had to reach in with a modified soldering iron to remove the capacitor. Before removing the capacitor check the orientation, there is a plus and minus, make sure it goes back in the same way. After removing the capacitor inspect the capacitor leads to see if they were both soldered correctly. If one of the leads is not silver the most likely cause is a cold solder and the fix is to simply clean up the capacitor leads by scraping off anything that is not silver, tinning the capacitor leads and re-soldering it to the board. If the leads look like they had a good solder, test the capacitor by using an ohm meter (used to test resistance) between the capacitor leads. The meter should show low resitance and as the capacitor charges the resitance should go up to infinite. If the meter does not behave this way while testing the capacitor, replace the capacitor. Bring the old capacitor with you to the electronics part store to make sure you get one that has the same electrical properties as the one you are replacing. The form of the capacitor might be different but as long as it is has the right electrical properties it will work. - and don't foget to make sure the polarity is correct when you solder it in!

Posted on Sep 14, 2008

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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.

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