Reduce volume of AC buzzer

[Steve Greenland]

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 Sec.@65C. 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

 

[John Popelish]

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 Sec.@65C. 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?

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.

 

[Michael Black]

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.

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

 

[John Larkin]

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 Sec.@65C. 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

Duct tape.

John

 

[Ross Herbert]

On 06 Feb 2008 20:45:00 GMT, [email protected] (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
at. Pend. Int. Duty
:25%W/Max. Ontime
:30 Sec.@65C. 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
late 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
ot 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

 

[Bob Masta]

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.

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!

 

[default]

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.

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.
--

 

[John Popelish]

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.

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.

 

[John Popelish]

(snip)

How about a diode?

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.

 

[Michael A. Terrell]

Duct tape.

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

 

[Steve Greenland]

Cover the buzzer with something. The more you cover it, the weaker
the sound will be.

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

 

[Rich Grise]

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

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

Good Luck!
Rich

 

[Steve Greenland]

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

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