speaker buzz

Discussion in 'General Electronics Chat' started by ogglecoggle, Sep 22, 2012.

  1. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    My new alarm system control panel is in my loft. Unfortunately that means that my wife cannot hear the beeps from the panel to know if it is set or unset. I thought I had a simple solution when I ordered a Spy Bug kit from Maplins:http://www.maplin.co.uk/media/pdfs/N50FL.pdf . I hadn't realised it was a kit, but made it up in my office and it worked fine. Longer leads had to be used from the loft to the speaker than the test ones. I also incorporated a little switch on the box I put the speaker in order to switch it on or off. The setup works, except that whenever it is switched on, there is a continuous buzz from the speaker. Can someone please give me an idea of how I can get rid of this?
     
    Last edited: Sep 22, 2012
  2. Audioguru

    New Member

    Dec 20, 2007
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    The microphone must be connected with shielded audio cable because ordinary wires pickup mains hum from the electrical wiring in your home.

    EDIT: It might be easier to connect the mic to the circuit using very short wires then use ordinary wires to connect to the speaker.
     
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  3. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Thanks so much audioguru, they're certainly things I can try. Kind regards.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    As audioguru says, the connection from the mic to the circuit should be as short as possible with shielded audio cable.

    How is your circuit being powered? If you are using a wall adapter you may want to try batteries first and see if the problem goes away.

    AC Line frequency from a mains powered adapter will cause 50Hz/60Hz hum.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    If you take the cover off the alarm panel,there will be a set of External sounder terminals, to bring out a second speaker, possibly 16 ohms.
     
  6. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Thanks MrChips. This is a small unit powered by 3 AA batteries. Any idea where I could get just a small length of shielded audio cable? Thanks again.
     
  7. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Well DodgyDave, now there's a thing. The alarm system is a wireless one and the external alarm is triggered by radio signal. However, there is an internal siren wired to the unit. I think I might just have a look at that. There is an 8 ohm speaker with the spy unit I've installed. Do you think that might do, or is there something I could do that would make it OK. Thanks again.
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    just extend the wires from the internal sounder to where you want to hear it.
     
  9. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Thanks Dodgydave. I've realised that I'm barking up the wrong tree here. It's not the sounder I need to hear downstairs, but the little beeps (counting down) from the panel for exit/entry timing. Do you think there is something in the panel that I could take out to hear those downstairs?
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Yes there will be a small buzzer or speaker that you can extend the wires and bring it from the attic into the house.

    Do you have a remote keypad, as they usually have the beeper on also?

    What is the Alarm make/model number?
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    You probably want to continue hearing the alarm panel beeping at the panel and also to hear it downstairs.
    Your first idea of using a microphone, amplifier and speaker was a good one but to prevent the unshielded microphone wires from picking up mains buzz then mount the amplifier and microphone near the panel and use a short piece of shielded audio cable to connect the microhone. Then use ordinary wires going downstairs and connect the speaker there.
     
  12. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Thanks Dodgydave. All I know of the make is that it is a Defender.
    Could I run another speaker in parallel to the one in the panel, or would I hve to disconnect that one and extend the wires.
    There is a remote key pad, but that only beeps as the keys are touched, not on the countdown. Isn't that a pity? Thanks again.
     
  13. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Thanks Audioguru
    I've messed this PCB about so much that it now doesn't work. I'll need to go over the soldering again. Also, I'm still looking for a small amount of shielded mic cable. The amounts on the Net are 20m. That's more than the unit itself cost. I'll keep looking though as the idea makes sense.
    Thanks again.
     
  14. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Hi Audioguru
    I thought I'd mention that in my garage I have loads of lengths of cable accumulated over the years. Can you give me an idea of what shielded mic cable would look like?
    Thanks.
     
  15. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Hi again Audioguru
    Scrub that last message. I've managed to find what you suggest on eBay. I nearly gave up when there was a shortish length advertised from the USA for just over £5. Then I noticed that the postage was £55. However, I did find it sold by the metre at Maplins Electronics (the same place I bought the unit). It is stereo and the mic connection only has two solder points. I guess as the mic and the PCB both have two, then it shouldn't matter which two I use so long as I connect +ve to +ve?
    Thanks again.
     
  16. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Disconnect the one in the panel and extend it.
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    Shielded audio cables are used to connect the signals from an audio source (pc, MP3 player, DVD player, cassette deck, record turntable and many other signal sources) to an amplifier. Even my cable TV digital converter came with some shielded audio cables.

    In North America almost all audio sources come with shielded connecting cables with RCA plugs on each end. They are FREE!
     
  18. ogglecoggle

    Thread Starter New Member

    Sep 22, 2012
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    Hi Audioguru
    My shielded mic lead finally arrived and I've connected up as suggested. I think I have to give in on that one. I must realise that I'm probably expecting too much from a unit costing £8.99. Thanks for all your help.
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    If you connect the wrong wires in the stereo shielded cable then the signal wire is not shielded.
     
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