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Reduce volume of AC buzzer

Discussion in 'Electronic Basics' started by Steve Greenland, Feb 6, 2008.

  1. I've got an old Gralab darkroom timer with a buzzer that is, to my
    taste, way too loud. Some Gralabs had a volume adjustment knob, this one
    doesn't. I'd like to add one.

    The buzzer is labeled:

    U.S. Controls Corp
    120V, 50-60Hz. 4W
    Pat. Pend. Int. Duty
    25%W/Max. Ontime
    30 [email protected] Max
    10037-63

    Googling part numbers turned up nothing useful, but I'm guessing that
    it's a simple vibrating electomagnet type thingy that strikes the metal
    plate attached to the bottom of the black box.

    Now, it seems that wiring a pot in series with buzzer should reduce
    the voltage it sees, reducing the amplitude of the vibrations and thus
    its volume. Or do I need something fancier?

    If a pot is sufficient, how to size? Is it as simple as Ohms Law would
    imply? That is: 120V 4W -> 0.033 A and 3600 ohms, and thus a 5K or 10K
    pot would provide plenty of adjustment? Or is such a buzzer likely to be
    more sensitive to voltage, making a 5K pot too sensitive?

    Thanks,
    Steve
     
  2. It might take a resistor rated for several watts to get what
    you want, and pots with that rating are rare and expensive.
    So it might be better to try a few values of fixed
    resistors and pick one to install, permanently.

    Or you might use a series capacitor that is rated for plenty
    of AC voltage (say, 250 VAC) to drop the extra voltage
    without producing heat. Something between 0.1 uF and 1 uF
    might do it.
     
  3. Cover the buzzer with something. The more you cover it, the weaker
    the sound will be.

    If it was an electric bell, you could weaken the sound by damping
    the actual bell, or putting something between the hammer and the bell.

    I'm not actually that familier with many buzzers to know what might
    be directly applied, assuming one can get at the works, but something
    similar is bound to work.

    Michael
     
  4. John Larkin

    John Larkin Guest

    Duct tape.

    John
     
  5. Ross Herbert

    Ross Herbert Guest

    On 06 Feb 2008 20:45:00 GMT, (Steve Greenland) wrote:

    :I've got an old Gralab darkroom timer with a buzzer that is, to my
    :taste, way too loud. Some Gralabs had a volume adjustment knob, this one
    :doesn't. I'd like to add one.
    :
    :The buzzer is labeled:
    :
    :U.S. Controls Corp
    :120V, 50-60Hz. 4W
    :pat. Pend. Int. Duty
    :25%W/Max. Ontime
    :30 [email protected] Max
    :10037-63
    :
    :Googling part numbers turned up nothing useful, but I'm guessing that
    :it's a simple vibrating electomagnet type thingy that strikes the metal
    :plate attached to the bottom of the black box.
    :
    :Now, it seems that wiring a pot in series with buzzer should reduce
    :the voltage it sees, reducing the amplitude of the vibrations and thus
    :its volume. Or do I need something fancier?
    :
    :If a pot is sufficient, how to size? Is it as simple as Ohms Law would
    :imply? That is: 120V 4W -> 0.033 A and 3600 ohms, and thus a 5K or 10K
    :pot would provide plenty of adjustment? Or is such a buzzer likely to be
    :more sensitive to voltage, making a 5K pot too sensitive?
    :
    :Thanks,
    :Steve

    Maybe you can get advice from the manufacturer.

    http://www.gralab.com/serviceRepair/index.asp
     
  6. Bob Masta

    Bob Masta Guest

    How about a diode?

    Best regards,


    Bob Masta

    DAQARTA v3.50
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, FREE Signal Generator
    Science with your sound card!
     
  7. default

    default Guest

    Is that safe, in an inductive load?

    I've never done it , in spite of using caps for LV supplies. My
    concern is that I might form a series resonant circuit and get some
    reactive voltages much higher than I was planning on.

    Just curious on what you think.
    --
     
  8. I doubt it is a very high Q inductor, but, it is possible
    that there is a resonant capacitor value that would peak the
    voltage measurably above line voltage. That would make it
    louder, so I doubt the O.P. would use that value for long.
    But that possibility is the reason I said the cap should be
    rated at twice line voltage. No point in having the cap pop
    during a momentary test.

    But as long as the capacitor value is considerably less than
    the resonant value (somewhere around 2 uF, I think), the cap
    will drop the voltage applied to the buzzer, even though the
    sum of the cap drop and the buzzer drop may add up to more
    than the line voltage. I.e. he might like the sound where
    the voltage across the buzzer is 3/4 of line voltage, and
    the voltage across the cap is also 3/4 of line voltage.
     
  9. I am reluctant to advise that without knowing how the unit
    works. It my include a permanent magnet. Inductive loads
    and diodes often do not get along.
     

  10. Duck tape is better. It keeps all your ducks in a row!!! ;-)




    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  11. Well, covering it doesn't do much, because, it turns out, quite a bit of
    the noise is from it being bolted against the case. Installing a bit of
    rubber padding between the two helped a lot. Whether or not it's enough,
    we'll see.

    I've also e-mailed Gralab, as suggested, to see if they'll sell me the
    volume control part. If not, I guess I'll need to dig out my EE280 text
    book and figure out how big a capacitor I need.

    BTW, I pulled apart the box, and, as I suspected, it's just a coil with
    a metal bar that strikes the base plate.

    Thanks for the replies.

    Steve
     
  12. Rich Grise

    Rich Grise Guest

    Put a couple of thicknesses of duct tape on the spot where it hits.

    Good Luck!
    Rich
     
  13. Unfortunately, the way the coil is mounted in the metal clip/base
    doesn't allow disassembly by the amount of force I'm willing to apply.

    I could stick a bit of tape on the end of the center cylinder, I
    suppose, but it's not very big, and if it came unstuck it would probably
    jam things nicely.

    The good news is that Gralab is going to send me a copy of the parts
    catalogue they use. Presumably I'll be able to order the volume control
    thingy.

    Steve
     
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