Ever since I installed a 7-station intercom system (hard-wired), 20 years
ago, I had an annoying buzz when I used the system in the evening, i.e. when
three kitchen fluorescent lights were on. The intercom does not buzz when
the lights are off. I am not referring the slight buzzing noise that comes
from the T-12 ballasts, I am referring to the induced buzzing in my
How can I eliminate this type of 50-cycle interference? Can I put filter
capacitors in line with the ballasts? How about replacing the old T-12
ballasts with new electronic ballasts and T-8 fixtures? Would that help? I
believe modern ballast operate at a very high frequency. Maybe I should
connect the intercom master unit (also in the kitchen) to a different
After 20 years, I am getting mighty tired of all this buzzing in the
evening. Of course, it only buzzes when I actually use the intercom to
answer the door or to suggest to my wife to fix dinner.
Thanks for any suggestions from those who have been there, done it.
My guess is you didn't use twisted pair wiring for the intercom.
Another possibility is switch polarity of the power wires and see
New ballasts MIGHT help, but the electronic transformers on some low
voltage lighting also causes noise on intercoms and AM radios.
First thing to do is to find out how the noise is coming into the
intercom system, Through the air or AC wiring. All kinds of things we
can try uing caps. inductors, chokes, etc. Try battery operated AM radio
in the kitchen, do you here buzz?
You can find in expense clamp chokes at some electronics supplies. I would
first try power to intercom filter, then each line going out of main box,
assuming there is a main box.
From your post, I'm guessing that the buzzing occurs even when not
using the icom ... right? The problem as I see it is that icom
manufacturers seem to refuse to use balanced lines to the stations.
There is usually a 'hot' input to the amplifier run to each station to
the master where the amplifier usually resides. Station speakers are
usually connected to the output of the amplifier, so they can be called.
A lot depends on the particular design of your unit. I recently
purchased a simple, now discontinued, NuTone icom/doorbell. Nice idea.
It provides 2 indoor stations and 2 door stations with an electronic
chime. But, if I put my ear close to the speaker, even when not using
it, I hear a slight buzz. In my case it's not enough to hear, even in a
very quiet house. But, in the instructions, there were all kinds of
warnings to not run the wires close to electrical wires, etc. Yeah
right, that's totally impossible. Even for this simple unit, it was
impossible. When it is in use, you definitely hear some 60Hz buzz in
the speakers. My plan is to someday redesign it but there are other
priorities. Also, as an icom, it's not really that good. Unless you
are close to the speaker, it's hard to understand. I previously
designed an icom for my previous house that worked very well. There was
no hum or buzzing and sound was very clear.
As to your system, do you use it as an intercom or just as a radio, as
many people do? If you don't use the icom features, it might work to
remove the input to the amplifier at the master. Filtering would be
tough because it is harmonics of 60Hz which are in the same band as
voice, that you are hearing. Different ballasts, i.e. electronic
"ballasts" might help also. Electronic ballasts are actually a
switching power supply at a higher frequency. You might try to replace
the ballast on one light that produces the most noise with all the other
lights off. If this works, you might have a chance.
W hen I have installed caps, and preferably on the down side of an
inductors, typically I use .05 mf 600 vdc caps. The most I use is .1 mf.
Sometimes it works better with a resistor in series with the cap to prevent
ringing, and they sell them that way. The caps should be inside an
enclosure, preferably metal. Values for 120 vac lines.
"500 watts wasted?" -- Not if the power factor in the home is lagging.
Then, the 100 mf capacitor would help to improve the power factor on the
circuit and the power company would love you. (naw, I went too far).
Capacitors are cheap. Go to Radio Shack or elsewhere. Buy some ceramic
caps in the range of .01 to .05, at least 500volts. Put them across the
ac line right where the wires enter the ballasts. If you dont want to
screw around doing all of them, just do one and disconnect the other
ones. It could be just one light causing it too. Disconnect them one
at a time.
Maybe the intercom should have had shielded wire going thru the walls???
If nothing else, try an electronic ballast on just one light, shut off
the others and try it.
For car radio buzz from the cars ignition they make filters for the 12v
lead. Of course you cant use them on 120v, but they may sell a 120v
version. That would also be a capacitor, but has a choke too.
Thid might be a question to post to one of the electronics newsgroups
It was said once before by others, but I'll repeat it. There are two ways
radio interference can get into the intercom: (1) through the power wires
from the fluorescent ballast and (2) directly (radiated) from the
fluorescent lamps themselves. The intercom wires or intercom units act like
The gas inside an operating fluorescent lamp is a low pressure plasma and,
like a spark gap a perfect generator of radio frequency interference, so the
lamps are where the interference starts.
With am/fm radios, I've found both kinds of interference to be significant
especially when the signal is weak, but fluorescent ballasts these days have
to pass some FCC tests, so it's likely that replacing your T12 lamps and
ballasts with T8 electronic types will help since the ballasts already have
noise supression built in. Look for an FCC notice on the ballast label to
Getting rid of T12 lamps is a good idea in any case since they will be
regulated out of existence later this year. T12 ballasts are already gone.
Check the grounding of the fluorescent fixtures. That's essential since
fixtures can act like antennas too.
On Mon, 06 Feb 2012 12:12:04 -0600, email@example.com wrote:
Nobody has asked - does this intercom connect directly to the 115v
AC or does it have a transformrt?? Many run off of a transformer like
a doorbell. Possible the filter capacitors in the low voltage power
supply section are bad.
Nobody has answered the question either about whether twisted pair
wiring was used to connect the stations - twisted pair provides common
mode noise rejection which can eliminate induction coupling of the
inputs to power lines, and also reduces the "antenna effect" which
picks up hum from things like flourescents.
Also, are all the flourescents GROUNDED???
Unless Walter comes back, we may never know.
Twisted pairs would help, but if the circuits are not balanced on both
ends, only ferrite clamps will help.
I pretty much gave up on getting rid of household wiring noise. It's so
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