Home DIY Subwoofer troubleshooting tips?

Discussion in 'General Electronics Chat' started by Butterworth, May 6, 2009.

  1. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Hello everyone,

    I have been in a dilema that I cannot firgure out the solution for some time now finally I am seeking outside help! So as my first post ever! (yay?) I am proposing the situation to any of the electrical gurus in this forum to throw their ideas and questions that could help me figure out my issue.

    The issue is:
    I own an old HT subwoofer with a blown amp board. I have since replaced it entirely with a new discrete 200W audio amplifier from the local electronics store. The installation went well, but the subwoofer was missing something, the LPF. I have since purchased a passive subwoofer LPF with a cutoff freq. of 100Hz. I installed the item inline from the input line between the amplifier input. Now the subwoofer will not play sound once hooked up to my stereo receiver/amp, however, it does hum. :confused: The amp I used in the subwoofer is a Velleman K8060.

    If anyone has input to what I can do to troubleshoot this mess, please let me know. I am open to any suggestion.

    Thanks,
    Butterworth

    EDIT: Added some pictures to show you what I am dealing with.
     
    Last edited: May 6, 2009
  2. Audioguru

    New Member

    Dec 20, 2007
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    If the passive LPF has a pretty big coil and a capacitor or two then maybe it is supposed to connect in series with the sub-woofer speaker, not at the input of the amplifier.

    The Velleman K8060 "200 Whats" amplifier produces only 70 Watts RMS at clipping into 8 ohms. Its distortion is low with an output of only 10 Watts.
     
  3. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Interesting, I tried to place the LPF in series with the subwoofer, but still no result. Could there be a specific way to wire in the LPF? I can supply a basic diagram later showing the exact layout I have it in now. Perhaps I will post a picture to help.
     
  4. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Bump, added pics and a crude wiring diagram. :)
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The huge coil and 188uF non-polar electrolytic capacitor are a passive crossover network that cut high frequencies. They connect between the output of the amplifier and the sub-woofer speaker.

    The crossover network has an input, an output and a common which is the ground of the amplifier and the ground of the speaker.
     
  6. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Alright, so how should the crossover be wired into the circuit?
    I had the output of the amp wired into the input of the crossover +/- and the speaker leads on the output +/- to the woofer. I got nothing in terms of sound. What am I doing wrong?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    It sounds like you connected the crossover circuit correctly.
    It should look like this:
     
  8. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Sorry Audioguru, I am not as fluent in electronics, I am more of a mechanical type of person :p I do not understand how that diagram works. The LPF has 2x inputs (+ & -) and 2x outputs (+ & -). How does that diagram work with what I currently have? I don't know if I mentioned before, there is a Volume Potentiometer on the input. It is a 52k Pot intended to adjust volume but when I turn the dial, I get humming on the 0V position but nothing on full Vol. *sighs* Thanks again for your help thus far! :D
     
    Last edited: May 7, 2009
  9. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Bump!

    Still at a loss, I get some sound but nothing like a regular subwoofer would pump. My woofer also has a fixed volume, it does not go up or down with the receiver volume. Any input on this one?
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    The LPF has only 2 parts, a coil and a capacitor. My drawing shows how they simply connect together.

    Since you have hum then you are not using shielded audio cable or are using only a single wire on the input of the amplifier instead of a shielded audio cable.

    Since the volume control doesn't work then you have more wiring problems.
     
    frosr6 likes this.
  11. flat5

    Active Member

    Nov 13, 2008
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    Your pictures don't clearly show how you have wired the three units together. The second pic looks (to me) like you have connected the speaker to the input side of the lpf.

    If you leave out the lpf and connect the speaker to the amp do you get normal sound? Are you sure your new amp is getting a proper signal?
     
  12. Butterworth

    Thread Starter Active Member

    May 6, 2009
    135
    3
    Well as it is now, the input goes to the amp, from the amp the LPF has been hooked up as instructed by Audioguru, the speaker now makes noise! but it only works when the input signal is coming from the left or right channel on the receiver. The LPF also plays voices but the higher freq. are cut out. I do not get any signal from the receiver when I plug the woofer into the "subwoofer" output on the back. The receiver is set up to output the subwoofer signal, but the woofer doesn't like to work with it.

    Yes, the woofer plays sound through the amp when hooked up to the Left or right channel output on the receiver without the LPF.
     
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