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HELP NEEDED!! Subwoofer Problem

Discussion in 'General Hardware' started by SabreWulf69, Oct 2, 2010.

  1. SabreWulf69

    SabreWulf69 New Member

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    Even though I'm pretty sure I may know the answer, I had thought it be in my best interest to ask anyway, to the more electrical and electronics savvy on here.

    Ever since I got my new subwoofer for my 2.1 channel set up and I turn my amplifier off or on, the subwoofer produces a sudden thud. It's not a ground loop or anything like that, there is no minute hum or anything once the amplifier is either on or off. It only occurs when I turn my amplifier on or off and sometimes when other devices (lights in the same room, the washing machine) goes on or off. I believe it may just be feedback from less than ideally clean power. I have searched around and apparently other than annoyance, it really does no harm.

    Still, I would like to prevent this from happening, and have not got a definitive answer searching for answers myself. I have a theory that a Power Conditioner from the likes of Equi-Tech, PS Audio or Belkin may eliminate this problem or barring that some form of complete AC Regeneration unit would solve it, though these solutions are far beyond my budget. Any help on what this could be and even more so on how to combat it cheaply would be greatly appreciated. Current audio system specs are here --> Custom Hi-Fi Systems/Car Subwoofers for PC Speake...
  2. AsRock

    AsRock TPU addict

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    Maybe it's just the amp. Don't know really but i know what your on about i have heard it before as well as that humm although i have always put the humm down to a earth dunno about a thump.

    Mine sub hums if i turn the amp of though the UPS as the subs on another inlet. Sounds like feedback front he amp to me. Or maybe because you using a car sub ?. Does it have it's own amp or ?.
  3. digibucc

    digibucc

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    the pop is because the line is live when(before) you turn your amp on. mute your stereo first and that should never happen.

    your amp should always be turned on before your input is turned on or up, to save from destroying speakers (with higher end systems)
  4. robn

    robn New Member

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    Many amps mute output for the first half second when they are turned on to prevent what you are hearing. It's a small design issue really - amp circuits don't necessarily behave nicely as they power up. As for light switches and washing machine, that is sparking in their switch gear causing interference on the audio input either at the signal cables or in the amps themselves. That can be lessened by improving shielding on them, i.e. earthed metal cover on amp, cables with foil in.
  5. SabreWulf69

    SabreWulf69 New Member

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    I do believe as part of the design of my particular amplifier it is already muted before it turns on. There is this feature called volume ramp. First you press the power button, at the same time as the relay/s make that click sound from the actual amp that's when the thud occurs, it starts muted, then turns itself up to the remembered volume within about a second. The problem only occurs with the subwoofer which is self powered and not the connected speakers. The input cables I am using from the computer to the amplifier and from the amplifier preout to the subwoofer line in input are heavily shielded.

    When I unplug my sub from the amplifier, I get humming from the subwoofer, but this disappears when I plug it into the amplifier. This new subwoofer is a replacement too, as the powered amp in the last one suddenly died. The model of amplifier I have is the Cambridge Audio Azur 740A and the model of subwoofer I have is the PSB SubSonic 5i. All other specs for reference as mentioned before can be found here --> Custom Hi-Fi Systems/Car Subwoofers for PC Speake...

    Quote from PSB Facebook page that seems somewhat similar to my problem but still confuses me -
    "I noticed once I shut down my t.v. and I'm lying in bed... i hear a "thud" noise. I assume it's coming from the subsonic 5i but I am not sure. The sound is like a powerful system is being powered on type noise.

    I assume it's coming from the sub but I am not sure... any ideas?

    Also... if I am going away for say a week - should I turn my sub to off or can I leave it on forever? Currently, I've had the sub for about 3 years and I have never turned it off. I figure since the t.v. isn't on then it's not working.

    PSB Speakers - The thud you hear is the signal from your TV going dead and the amp in the Sub still not on stand-by yet. It is more of a issue with your amp then the sub. All amps handle the drop in voltage differently, yours must send a few volts down the line to the sub that results in a little thud. It will not damage the sub and is totally common.

    When the Sub 6i does not have a signal coming in, it will go into standby. But it does draw a small amount of electricity in standby. So if you are not using it for a few days I would say to shut it right off so that you are not paying for something you are not using while on vacation."
    Last edited: Oct 3, 2010
  6. SabreWulf69

    SabreWulf69 New Member

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    They taught me in my Sound Engineering course at least with Pro Audio gear (PA and such) when powering a system on, the inputs get plugged in and powered on first, then the amp is the last thing you turn on. In reverse for powering gear down, the main amp where everything is plugged into gets turned off first then any inputs plugged in get turned off and unplugged.

    Using this logic I'd love to be able to do this with my Sub, first turn the amp on then the sub when powering up, or first turn the sub off then the amp when powering down. The only problem is this isn't too feasible in my situation, as the power switch is like most subs around the back of it and is annoying and very awkward to get to. So instead I rely on the auto shutdown feature of the sub instead (it turns itself on when signal from the line level input is detected and turns itself off when no signal from the line level input is detected after 15 minutes). Quite simply, would it be recommended everytime that I turn my amp on or off, before doing either action to make sure the sub woofer is off? It just annoys me that after so long with electronics in the world that this problem is bothering me.
    Last edited by a moderator: Oct 3, 2010
  7. Batou1986

    Batou1986

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    when i turn stuff on and off like say a lamp that's on the same line as my sub it thumps as well
  8. AsRock

    AsRock TPU addict

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    If your bothered about electric usage while your away you might want to turn it off. I have not tested mine and what power usage it takes while on but idle but i know my amp takes 70w idle or in use so i would of thought it is using power just don't know how much..

    How ever mine turns it self on \ off when sound is or not detected and works flawlessly.
  9. SabreWulf69

    SabreWulf69 New Member

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    As I wish mine did too *sigh*. Price of PS Audio Power Plant Premier $4500 AUS, AC Regenerator droolage. May consider something like this though with some shielded power cables or something --> http://www.thoroughbredaudio.com/SPI240AU6/index.html as it (still no where near what I wanted to spend on something that should be a simple fix) is only $500 AUS.
  10. INSTG8R

    INSTG8R

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    I have the PSB Subseries 1 Sub and I have never heard either a hum or the thump. How is it your connecting it? I have it running thru the RCA low level input and mine switches on after its gets some low frequency output from my amp. So technically it comes on after my amp is switched on.
    Yours should work the same.
  11. SabreWulf69

    SabreWulf69 New Member

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    As once again mentioned my system specs indicate that I am using high quality shielded RCA's to connect it from the Line Level out of the amplifier to the Line Level in (low level in) on the subwoofer. It does the Auto switching but if for whatever reason I want to turn my amp off, then it does the aforementioned problem if I don't wait for the sub to auto turn off first. The same happens if the sub is still on when I turn the connected amp back on.
    Last edited: Oct 3, 2010
  12. robn

    robn New Member

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    The shielded power cables and "isolated outlets" stuff is BS really, so don't waste your money there. If a switchmode power supply was causing noise (like a hum or hiss) it would be the one inside the amp. In all honesty there is always noise on mains power, but it won't get *through* a power supply.

    Good. That means earthing is working well between them then.

    Anyway, if your amp features volume ramping during on and off, then you shouldn't hear that thump. So something isn't working right. Best option if you really must diagnose it would be to get a digital logging oscilloscope plugged into the amp's subwoofer line out to see if there is a power spike coming through.

    Edit: Instead of a real oscilloscope you could feed the amp's signal into a PC line in, and record a few seconds with something like Audacity as you switch the amp on and off.
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  13. SabreWulf69

    SabreWulf69 New Member

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    Cheers, will try this tomorrow and see what happens when I turn off the amp. Seems to be along the lines of what PSB has said in relation to someone else's sub doing the same thing when they switch their TV off, "PSB Speakers - The thud you hear is the signal from your TV going dead and the amp in the Sub still not on stand-by yet. It is more of a issue with your amp then the sub. All amps handle the drop in voltage differently, yours must send a few volts down the line to the sub that results in a little thud. It will not damage the sub and is totally common".
  14. zaqwsx

    zaqwsx

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    Get an isolation transformer you should be good to go.
  15. SabreWulf69

    SabreWulf69 New Member

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    Isolation transformer to go where? For the power of the sub? For the power of the amp? Both? For the Pre Out of the Amplifier? Also my subwoofer has a High Level input, would anyone recommend this as a possible solution by hooking up the Speakers "B" output of my amplifier directly to the high level inputs of the subwoofer, and disconnecting the low level input, there by using the Speakers "A" output of the amplifier to drive my main speakers, whilst the Speakers "B" output is left to drive the subwoofer? Would this cause any theoretical ill effects like possible impedance issues and issues regarding damping factor?

    A note from the manufacturer REL Acoustics:
    "For two-channel audio systems, a high-level connection, using the supplied cable with the Neutrik Speakon connector, is always the first choice. By connecting to the amplifier's speaker outputs the sonic signature of the entire amplification chain is folded into the signal for the sub, thereby keeping timing and timbre cues consistent".

    ^^^ Would anyone think that this has any truth?
    Last edited: Oct 3, 2010
  16. AsRock

    AsRock TPU addict

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    I have tried it with mine although mines just a cheap ONKYO amp and it disables surround sound.

    My sub has connectors to do what your saying although with my sub being at the rear of the room LFE option is best due to amount of wires.

    Not sure if ya said but you looked in to extra earthing from the sub or even the amp ?.
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  17. robn

    robn New Member

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    Yeah you could try the high level inputs instead, there is a big chance that would solve it.
  18. Solaris17

    Solaris17 Creator Solaris Utility DVD

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    that wont help. I use power conditioners and a separate circuit and my sub thumps on power on and off.
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  19. SabreWulf69

    SabreWulf69 New Member

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    Hmm kinda glad I know that option would be a waste of money, although with the sequenced turning on and off of devices I would have thought that would have certainly solved the problem. Looks like the High-Level connection set up may (hopefully) be my best bet.

  20. zaqwsx

    zaqwsx

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    How is everything hooked up for you do u have a receiver with pre outs to an amp or you have a pre amp connected to the amp. What is the make and model of the stuff you have?
  21. SabreWulf69

    SabreWulf69 New Member

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    PC plugs into my Integrated Amplifier (Cambridge Audio Azur 740A) through it's RCA's Line Level inputs, speakers are plugged into the integrated amp through the speaker out's, the subwoofer is plugged into the integrated amp through it's Pre Out RCA's plugs. All specs of my whole audio system are found at this link here --> Custom Hi-Fi Systems/Car Subwoofers for PC Speake...

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