Question about Sunfire True Sub MK II Subwoofer

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60 HZ hum

I own a Sunfire True Subwoofer Mark II. Since day one (about 3 years ago), a 60HZ electrical ground hum is present. I found this to be the problem by arresting the hum with a HUMX sold by Ebtech: http://www.ebtechaudio.com/humxdes.html The sub is located across the room in a home theater configuration and is likely fed by a different electrical ground than what feeds the main surround system components. The HUMX works just fine most of the time with the HUMX. However, during operation under what seems to be duress, the sub cranks-up the hum again and can only be stopped by a power-off reset (unplug and re-plug). I have run another power feed from the main component room to the sub, but it still performs the same way? It hums? The hum can be arrested? but, certain audio frequencies (probably 60 HZ) will trigger the continual hum again that requires a power off/on reset. I have disconnected the cable (satellite receiver) and this does not stop the problem either.. Also disconnected the satellite power cord with no success. I have not used a signal hum arrestor. Could this be the fix?.. or is there a hardware problem with the sub? The HUMX? Or another component? Your help is is greatly appreciated? Ron Reynolds ? (501) 884-4414 ? ronlinda@artelco.com

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  • Ron Reynolds Apr 23, 2011

    You may not believe this, but IT IS miraculously TRUE ! .. I read somewhere in cyberspace that a problem exist within the sub's gain control pot and all that is needed is to tighten it. So, I simply removed the gain control knob and tightened the mounting nut for the gain control. You cannot believe what a relief this turned-out to be.. The sub works perfectly and spectacularly. The HUMX is no longer needed. The sub is as quiet as a mouse. It's fixed!

  • Steve Refsland Apr 25, 2012

    So how do you do this? How do you remove the gain control knob? Is there anywhere with a step by step?

  • Steve Refsland Apr 25, 2012

    So how do you do this? How do I remove the gain control know and which one is the mounting nut? I have owned this sub for 10 years and never been able to figure out the hum. Is this something that requires opening up the unit? If so are there more detailed, step by step instructions somewhere?

  • Ron Reynolds Apr 25, 2012

    Steve.. This is a very simple process. There is a volume knob on the control panel of the Sub. 1) Pull the knob off. 2) using an open end or closed end wrench, tighten the nut that holds the volume control stem to the panel. 3) slide the volume knob back on the stem.. Your done!

  • NitroFreakManHo Apr 25, 2012

    Steve, like Ron said, the solution is really quite simple. First, pull the ' VOLUME' knob off..it should slide right off. You will see the nut behind the knob..just tighten this nut with the appropriate wrench ( or socket ) and the hum should go away ( just be careful not to over tighten it and strip it ) This is such a simple fix for such an annoying problem. My hum went away instantly, and thankfully, hasn't come back. GOOD LUCK!

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Rolinda303 you are my new audio hero! I bought this used Bob Carver True Sub MK II used last season, it's been something I wanted for the last 20 years, but was disappointed with the annoying hum which you described, sand have tried several things to solve it short of shipping it out for repair. Last night I read your solution of tightening the nut on the nut on the gain control and guess what..my hum went away!!! I can't believe how simple this was. THANK-YOU for sharing!

Posted on Jan 28, 2012

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Rita's Vintage Audio Repair is a Bob Carver Company & can repairs & updates Subs at a reasonable cost try calling them.

Posted on May 06, 2009

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Everybody has the same problem the 2 1500mf 200volt capacitors are bad.....

Posted on Apr 21, 2011

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1 Answer

Subwoofer is hummig what is this noise


Hum is a constant low-frequency buzz, usually at about 60 Hz or 120 Hz, which results from voltage differences between true "ground" (what you'd get shoving a copper pipe into the ground) and the electrical "ground" of your receiver's chassis When this voltage differential exists, it's called a "ground loop," and the hum it produces is darned annoying. You'll hear the hum mainly from the subwoofer because it's a low-frequency noise, you will need a ground loop insulator they are about $20 at any electronic store

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I hear a humming noise from my Sunfire subwoofer - occassionally. I bought a kit from Radio Shack that supposed to cut down on noise from the electric outlet - it didn't work. Please help!


How to isolate annoying background hum.

As long as the music or movie is playing, you can forget about it, at least until a quiet passage occurs, then there it is again: HUMMMMMMM! Be gone, bad hum, you think. But, like a bad odor at the back of the fridge, it takes some dogged persistence to track it down and eliminate it.

Hum is a constant low-frequency buzz, usually at about 60 Hz or 120 Hz, which results from voltage differences between true "ground" (what you'd get shoving a copper pipe into the ground) and the electrical "ground" of your receiver's chassis, the incoming cable-TV feed, or any video or audio components interconnected within your system, including powered subwoofers. When this voltage differential exists, it's called a "ground loop," and the hum it produces is darned annoying. You'll hear the hum mainly from the subwoofer because it's a low-frequency noise, but there will also be hum from your floorstanding front speakers or even compact bookshelf models.

First, try disconnecting your subwoofer from the coaxial sub cable from your AV receiver but leave the subwoofer turned on. Does the hum go away? If it does, then the ground loop is entering the system from your AV receiver and/or your cable-TV system set-top box (or satellite dish and decoder).

Disconnect the incoming TV-cable or satellite feed to a set-top box or to your TV and the A/V receiver. If the hum disappears (and you don't use a satellite dish) complain to the cable-TV company. They may know what you need and supply you with a ground-isolating transformer. If they don't know what you are talking about you'll need to order a video ground isolator and install it in-line with the TV cable before it enters your set-top cable-TV box. Axiom has special wide-band isolation transformers that will not interfere with any digital TV or HDTV signal. (N.B. You CANNOT use one of these with a satellite decoder box.)

Before you order one, you can try plugging your subwoofer into a different AC outlet in the room, ideally one that is not on the same circuit as your AV receiver and video equipment (TV, DVD player, sat or cable TV box, etc.) That may solve the problem. If it doesn't, see if the back panel of your sub has a "ground-lift screw". It will be labeled as such. Just remove it. That may remove the hum. If it doesn't and you have a standard cable-TV feed (not a dish), then order the ground-isolation transformer. (Axiom has special wide-band isolation transformers that will not interfere with any digital TV or HDTV signal.)
Axiom Audio Ground Isolator

If that still doesn't eliminate the hum, or if you use a satellite dish video feed, then you could try one of these from Radio Shack, which goes between the subwoofer and the coaxial cable from the receiver's subwoofer output.

With persistence, all ground-loop problems can be solved.

Hope it helped..

Have a nice day...

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1 Answer

Sunfire MK II Subwoofer hum. I have a Sunfire MK II subwoofer that hums when it is plugged in (it even hums when no signal is connected). I've tried multiple outlets on different circuits, but hum...


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Check your cabling to make sure you dont have a ground fault. if you still have humming, buy a "groundless" adapter for your power plug (takes the ground away) and plug it back into the power outlet and I bet your humming will be gone

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