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Subwoofer issues

Discussion in 'Speakers' started by gojays_1, May 5, 2007.

  1. gojays_1

    gojays_1 Well-Known Member

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    Hello all,

    I have a Velodyne subwoofer attached to my receiver. I have noticed lately that it is making a humming sound (or just a low bass sound) even when the receiver is off. I did not notice it before.

    I have turned it off for now as I found it a bit annoying. It's the kind of subwoofer that is plugged directly into an outlet. It has an on switch and an auto switch. In either mode it was still emitting the humming sound. I had to turn it right off to stop the humming. I have not figured out how to make the auto switch work. I was assuming that auto meant it would only go on if the receiver is on, but that was not the case. Unless I'm supposed to hook it up a certain way.

    Any advice appreciated.
     
  2. SHS

    SHS Well-Known Member

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    I'd begin by using a power conditioner, you could be getting some line noise from AC power.

    Secondarily it could be an issue with your amplifier.

    Have you disconnected all lines except the power cord to see if it still makes the noise?
     
  3. SethH

    SethH Well-Known Member

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    Very possibly a ground loop hum.
     
  4. MaxL

    MaxL Well-Known Member

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    yeah, could be grounding issue. auto generally comes on when signal is present, not necessarily all the time receiver is on. it should turn off after some number of minutes without signal, but might not if it's getting too much ground hum. does it have a volume control on the sub? you could try turning down receiver sub settings and boosting subs onboard volume, but this still may not solve problem even if it is an option. any electrical storms lately?
     
  5. Brent_S

    Brent_S Well-Known Member

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    As Scott suggests, I'd start by disconnecting the cable from the receiver to the sub. If the sub still hums, I'd vote for the tranformer being loose. It'll vibrate at AC's 60hz cycle if not held down tightly enough. I've never heard of a ground loop hum interfering with auto on/off or making noise when the rest of the system is off (not to say that it couldn't happen) which is another reason for looking at the transfomer.

    -Brent
     
  6. SHS

    SHS Well-Known Member

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    Ground loop info

    http://www.epanorama.net/documents/g...oop/index.html

    http://www.audioholics.com/tweaks/co...-hum-and-buzz/

    from a quick google search!!!

    In the event that a power conditioner or better yet and isolation transformer is not available then try other outlets as well. Other devices on the circuit can cause ground loop effects and/or humm from making the AC power "dirty". Fans with adjustable speeds, dimmers etc are famous for causing dirty power.

    The loose transformer is a good idea. Also check your connectors, internally and externally, maybe look into you amp/wiring area to see if you have loose or shorted connections. I would think that would cause more drastic results but strange things happen with current if you get shorts that are intermittent or of high resistance.
     
  7. gojays_1

    gojays_1 Well-Known Member

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    Thanks for all the replies.

    I already have the sub connected to a power bar/surge protector made for Home Theater by Belkin. Is that what you guys mean by power conditioner?

    I unplugged the jack going from the receiver to the sub (which is a 'Y' cable-connected to one plug which splits into two to conect to the sub); when I did that the hum went away.

    I recently used a new rca jack which is a single jack. It does not have a totally enclosed brass 'head'. Don't know if that's a cause. I might try a different jack to see if it makes a difference.

    When I adjust the volume on the sub it adjusts the hum.

    Not sure where transformer is located?

    I put it on auto; the sub stayed on. I will check it in an hour or so to see if it stayed on as the receiver is off. I don't think this issue is related. I just wanted to mention it.
     
  8. JohnRice

    JohnRice Well-Known Member

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    Wayne, based on your latest post, it is not a transformer problem. It is a ground loop problem. You need to isolate the ground on the receiver, most likely, to eliminate it.
     
  9. gojays_1

    gojays_1 Well-Known Member

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    So I checked my sub after about an hour after I turned it to auto.

    The red light went on (I assume that means off) instead of the green when it's on after I checked on it about an hour later.

    However the hum remained even when the red light was on. Weird. I again disconnected the cord to the sub. The hum went off, red light on. When I plugged it back in (still in auto mode) to the sub, the green light came on and the hum returned.

    And before that I tried to see if I could get the green light to come on by turning on the receiver in the auto mode. No dice. I'm not sure if I have to plug the sub directly into the receiver (I think it has an outlet) for the auto to work.

    Not sure if any of that is related to the humm.

    John, how do I isolate the ground on the receiver? Do you mean plug it into its own outlet? I have the outlet available if I need it, but I like having it plugged into the surge protector to reduce risk of electrical surge.
    Could it be I need a proper sub rca cord? Or is that just hype by the cable manufacturers?
     
  10. Brent_S

    Brent_S Well-Known Member

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    Scott linked you to a couple of good articles on what ground loop hum is, how to identify, and eliminate.

    Basically, you've got to figure out which component has a different ground path/voltage than the others. If you've recently changed a cable, that's the likely culprit if you didn't have the noise before. CATV lines are a common path since the cable company isn't exactly picky about how well they ground your drop and it may induce a different voltage than the electrical ground of your house.

    -Brent
     
  11. gojays_1

    gojays_1 Well-Known Member

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    I read one of the links that Scott posted on ground loop hum. It's a bit technical and I'm not expert! But I think I understand it somewhat.

    A few minutes ago I tried plugging the sub into a different outlet. No effect.

    Tomorrow I might try a different rca jack. See if that helps.
     
  12. SHS

    SHS Well-Known Member

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    Yes, if you are not familiar with electrical theory this can be a bit confusing but it does not need to be.

    On the power cord to your subwoofer you likely have three prongs. One is the "hot" prong, it would be the smallest of the two prongs and flat, the other would be a "neutral" and likely larger at the tip but not always. The rounded prong is the ground. Some power cords do not have this prong. Let me know if your cord has all three of these?

    1) The belkin surge protector is not a power conditioner
    2) Just moving to another outlet might not get you to clean power, that outlet could be in the same circuit and/or the ground loop could be inherent in the whole house(unlikely).
    2) When you disconnect the RCA cable from the receiver it goes away, likely to be caused by that device or cabling including power to that device, mainly the receiver. You just changed that RCA cable and it started happening? I would suspect that cable first.
    3) A ground loop can develop in many different ways, suffice to say it is basically a difference of conductivity in the neutral and ground combinations within one circuit or between multiple circuits. A voltage difference can occur when, for instance; the ground conducts differently than the neutral and/or interference seeps into one of these lines. This is very simplified though.

    In troubleshooting something like this it is important to use the KISS method. Start with the basics and move on through the equipment, receiver, cables, power etc. methodically. A local hardware store will likely have a device to plug into the outlet to check the power for as little as $5 or so, although at this point I would start with cabling.

    Anytime you have something "start" like this did, I would first suspect the last item you changed or adjusted.
     
  13. JohnRice

    JohnRice Well-Known Member

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    Just an aside on how bizarre it can be to eliminate a ground loop. About 12 years ago I bought a house. The HT is in a dedicated room and powered from multiple outlets on at least 2 different circuits. I had chronic ground loop problems which I couldn't seem to completely eliminate. The house was about 40 years old and all the outlets were original. I decided one day to replace all the outlets in the house because they didn't tend to hang on to the plugs very well. I got normal Leviton outlets, just not the cheapest ones that run about $5/10 pack. I got the better ones, which are still pretty cheap at about $15/10 pack. Anyway, all the ground loop problems disappeared. Go figure. Was it actually the new outlets? Was it refreshing the connections? I don't know, but it unintentionally fixed it.
     
  14. Dave Duncan

    Dave Duncan Member

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    I had a similar problem. It turned out to be a cracked circuit board in my Denon receiver, behind where the sub plugs in. This was a VERY loud humming sound that would shake the house. The sub would come on at full blast at 3 a.m. and wake everyone up. It was as though it was possessed. Denon fixed the receiver under warranty and I have not had a problem since then.
     
  15. Grant*S

    Grant*S Member

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    cheap fix that worked for me on the very same issue is use a three to two prong adapter...2 for 1.49 and no more hum. i believe it makes it a floating ground, but no more hum!!! yay.
     
  16. gojays_1

    gojays_1 Well-Known Member

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    All good advice. I will try changing the rca cable first and go from there.

    The outlets are brand new. Just fininshed the basement so I don't think that's the problem.

    Just a pain the the behind to get to the recevier. We just moved it all back into place last Saturday! [​IMG]
     
  17. SHS

    SHS Well-Known Member

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    If I may be contrary. After new construction it is quite possible to have issues due to poor connections or mis-wiring. Since this is a newly built room for HT or so it sounds, please describe your setup. Maybe something in the details will point to an issue.

    For instance, did you run cabling in the walls? Are all the HT devices powered by the same circuit? Did this noise show up after finishing the basement?
     
  18. JohnRice

    JohnRice Well-Known Member

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    Scott makes a good point. For under $10 you can get a little analyzing unit to check your outlets. It is usually just a little yellow plastic item with three lights on one end and an electrical plug on the other. You simply plug it into an outlet and the lights show if it is wired wrong. Incredibly simple item, and not a bad thing for any homeowner to have. They are also available with an option to short out the outlet with by pushing a red button. this is for testing GFCI outlets. It is a useful feature, but you need to take great care NEVER to push that button on a non GFCI outlet or circuit. Just FYI, a GFCI outlet is the type which automatically disconnects when there is a short, like you should have anywhere near water or outside. They have test and reset buttons on them.

    Beyond that, the "cheater" plugs mentioned are usually the easiest fix. Of course, they carry a risk because they lift the dedicated ground. I know Audio Advisor has a "safe" ground lifter, but it costs $100. If the receiver has a three prong plug, that is usualy the first place to go. Then the sub.
     
  19. gojays_1

    gojays_1 Well-Known Member

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    I'm pretty sure the outlets are not the problem. We had the basement professionally finished with a licensed electrician doing the electrical work. Then the city inspector came and did the inspection and everything checked out ok.

    The only wiring I have in the walls is the rear speaker wire.

    All the equipment (Kenwood Receiver, Toshiba Plasma T.V., Motorola Digital box, Oppo DVD player, PS2, and powered sub) are connected to the Belkin Power Surge Bar). I tried plugging the sub into a separate outlet. Made no difference.

    The only change is I replaced the cable going to the sub from receiver. I don't know if the hum was there before and I did not notice it or it is the cause. I will have to investigate.

    What I also want to know is can the ground loop hum cause damage to my equipment?
     
  20. SHS

    SHS Well-Known Member

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    Again Wayne, I'm not trying to insult a licensed electrician or the inspection process but they do not usually test each outlet under load and an issue with ground loop(if that is what we are dealing with here) is that you can get a voltage difference in the ground and common circuits that should end up in the same place in the panel eventually. It is very possible that there is a loose common or ground or even interference seeping into the system somewhere. In new construction this is not unheard of.

    Why don't you just carry the sub to another room in a different section of the house and plug it in and see if the issue is still happening?
    Better yet to a neighbors house. That would cost nothing and you would eliminate many possiblities if the sound is gone or still there.
     

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