ajf@maximo.enet.dec.com (Adam J Felson) (04/03/91)
I have a pair of floor lamps hooked up to a single dimmer. They use 6" spherical incandecant light bulbs. The problem is that they make an annoying buzz when dimed. Is there a better circuit for dimming the bulbs that will prevent that !@#$%^&*&^%$# buzz? __a__d__a__m__
random@cbnewse.att.com (David L. Pope) (04/04/91)
> an annoying buzz when dimed. Is there a better circuit for dimming > the bulbs that will prevent that !@#$%^&*&^%$# buzz? Yes, but since the buzz is being caused by the fillament vibrating at line-current frequency, it would involve a d.c. supply which would require a little engineering (to determine d.c. power max and min for the bulbs you are using). The actual cause of the buzz is the length of the fillament in the bulbs, so maybe you could find large diameter bulbs designed for dimming (that is, with short fillaments). Good Luck, Random
ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) (04/04/91)
In article <1991Apr3.223655.18202@cbnewse.att.com> random@cbnewse.att.com (David L. Pope) writes: >> an annoying buzz when dimed. Is there a better circuit for dimming >> the bulbs that will prevent that !@#$%^&*&^%$# buzz? >and min for the bulbs you are using). The actual cause of the buzz >is the length of the fillament in the bulbs, so maybe you could >find large diameter bulbs designed for dimming (that is, with short >fillaments). O.K...but exactly why do the bulbs buzz when dimmed, but not when at full power? My guess on this always was there was some kind of clamping of the waveform going on, making it look more and more like a square-wave with associated audible harmonics? In that case perhaps a variable-transformer would make life better. -Tom
tonyb@titania.juliet.ll.mit.edu ( Tony Berke) (04/04/91)
In article <7893@jhunix.HCF.JHU.EDU> ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) writes: In article <1991Apr3.223655.18202@cbnewse.att.com> random@cbnewse.att.com (David L. Pope) writes: >> an annoying buzz when dimed. Is there a better circuit for dimming >> the bulbs that will prevent that !@#$%^&*&^%$# buzz? >and min for the bulbs you are using). The actual cause of the buzz >is the length of the fillament in the bulbs, so maybe you could >find large diameter bulbs designed for dimming (that is, with short >fillaments). O.K...but exactly why do the bulbs buzz when dimmed, but not when at full power? My guess on this always was there was some kind of clamping of the waveform going on, making it look more and more like a square-wave with associated audible harmonics? In that case perhaps a variable-transformer would make life better. When you use a normal SCR dimmer, 50% power is produced by shutting the juice off for 50% of each waveform -- right at the peak voltage!!. This makes a really sharp edge, which indeed has lots of high frequency harmonics (it's not a square wave, though). I've always assumed that filaments buzz because they are coiled and have some of the qualities of an electromagnet -- even if the filament isn't coiled, when you vary the current through a conductor you get a magnetic field. As the current changes, so does the field -- and when you use an SCR dimmer, you vary the current quite abruptly, causing the field around the filament to go bannanas. This results in the filament wagging all over the place under the influence of the field. Please note: this explanation might be total bullshit, I'm only guessing. The following is not a guess, however: A company (recently defunct) by the name of LightSync made some dimmers that were essentially switch-mode power amplifiers -- they used giant MOSFETs as output devices and put out DC. Their product was called HUMPHREY (a play on "hum-free"). Switching amplifiers are not simple to design, however, and I recall that they had quite a time keeping the RFI down (40kHz 200V square waves are NASTY!). I bet that zero-crossing dimming would be quieter than the normal scheme, but I think you would wind up with visible flicker if you try to use this scheme for dimming much more than 50%. Have fun! Tony Berke
jgd@Dixie.Com (John G. DeArmond) (04/05/91)
>> an annoying buzz when dimed. Is there a better circuit for dimming >> the bulbs that will prevent that !@#$%^&*&^%$# buzz? Yep. Called a Variac variable autotransformer. You can get 'em small enough to fit into a double switchbox. Since it is a transformer, it delivers nice undistorted power AND regulates all the way down to zero volts. John -- John De Armond, WD4OQC | "Purveyors of speed to the Trade" (tm) Rapid Deployment System, Inc. | Home of the Nidgets (tm) Marietta, Ga | {emory,uunet}!rsiatl!jgd |"Politically InCorrect.. And damn proud of it
fval_ltd@uhura.cc.rochester.edu (Trey Valenta) (04/05/91)
I've been dealing with the same problem recently.... the person who lived in my dorm room before me had installed a touch sensitive dimmer which buzzes like crazy from the waveform. One thing I've thought of would be to place a cap across the bulb. Any thoughts on it's effectiveness? The only problem is finding one of the right size. I eventually came across a 4 micro-F 150V cap, non-polarized electrolitic, but I think that the voltage is too small. I also found a 1MF @200V, a nicer voltage, seeing as the peak should be around 155V. The only problem is, what do I need the cap to do. Seems I could cancel the bulb's reactance, but is there any? Is it essentially a resistor? Would the cap smooth the waveform enough to reduce (but not remove) the buzzing? thanks trey -- Trey Valenta | It's 3am; do you know where your Mac is? fval_ltd@uhura.cc.rochester.edu | CPU Box 272253 (716-274-4233) | Corollary: Rochester, NY 14627 | It's 3am; do you know where you are?
lrk@k5qwb.UUCP (Lyn R. Kennedy) (04/05/91)
ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) writes: > In article <1991Apr3.223655.18202@cbnewse.att.com> random@cbnewse.att.com (Da > >> an annoying buzz when dimed. Is there a better circuit for dimming > >> the bulbs that will prevent that !@#$%^&*&^%$# buzz? > > >and min for the bulbs you are using). The actual cause of the buzz > >is the length of the fillament in the bulbs, so maybe you could > >find large diameter bulbs designed for dimming (that is, with short > >fillaments). > > O.K...but exactly why do the bulbs buzz when dimmed, but not when at > full power? My guess on this always was there was some kind of > clamping of the waveform going on, making it look more and more like > a square-wave with associated audible harmonics? In that case perhaps > a variable-transformer would make life better. > > -Tom Most electronic dimmers turn off at the zero crossing and then switch on for the last part of each half-cycle. This might well cause more buzz than a variable tranformer. Surely you will try it and let us know. ------------------------------------------------------------------------- lrk@k5qwb.UUCP lrk%k5qwb@kf5iw.UUCP 73, utacfd.utarl.edu!letni!rwsys!kf5iw!k5qwb!lrk Lyn Kennedy K5QWB @ N5LDD.#NTX.TX.US.NA P.O. Box 5133, Ovilla, TX, USA 75154 -------- "We have met the enemy and they are us." Pogo -----------------
vermilye@Oswego.EDU (Jon R. Vermilye) (04/05/91)
In article <7893@jhunix.HCF.JHU.EDU> ins_atge@jhunix.HCF.JHU.EDU (Thomas G Edwards) writes: >In article <1991Apr3.223655.18202@cbnewse.att.com> random@cbnewse.att.com (David L. Pope) writes: >>> an annoying buzz when dimed. Is there a better circuit for dimming >>> the bulbs that will prevent that !@#$%^&*&^%$# buzz? > >>and min for the bulbs you are using). The actual cause of the buzz >>is the length of the fillament in the bulbs, so maybe you could >>find large diameter bulbs designed for dimming (that is, with short >>fillaments). The buzz is caused by the waveform the dimmer produces. When the lamp is at full, the waveform is still close to a sine wave, and little noise is produced. When the lamp is dimmed, the SCR or TRIAC in the dimmer is fired sometime during the AC cycle. The rise time of the switching of the SCR is limited only by the impedance of the circuit. Some manufacturers add a choke (coil) in series with the load. This will limit the rise time and noise. In most cases, noise cannot be completely eliminated. By the way, many theatrical dimmer manufacturers are changing from SCR based dimmers to FET's, and chopping the sine wave on the back. This, along with better control of rise (or do we call it fall?) time allows for dimmers without chokes. Since the weight of the choke makes up about 75% of the weight of a 2.4K dimmer, this saves both weight & space. Jon R. Vermilye 315 341 2138 Department of Theatre, Tyler Hall vermilye@oswego.oswego.edu SUNY Oswego ..rutgers!sunybcs!oswego!vermilye Oswego, NY 13126 vermilye@snyoswva.bitnet
rando@skipper.dfrf.nasa.gov (Randy Brumbaugh) (04/05/91)
In article <1991Apr2.162037@maximo.enet.dec.com>, ajf@maximo.enet.dec.com (Adam J Felson) writes: > [ . . .] annoying buzz when dimed. Is there a better circuit for dimming > the bulbs that will prevent that !@#$%^&*&^%$# buzz? > The buzz is caused by the SCR/TRIAC type dimmers which are found in many low cost dimming circuits today. These work by switching the AC waveform on at some point in the cycle. This creates a nasty high frequency spike which is both audible and can cause interference for nearby audio equipment. This is especially bad for theatre light dimming, which have many dimmers and lights over the audience. Most dimmers incorporate a torroidial coil at the output, which slows the rise time and helps some. The coil must match the load for best results. Several manufacturers are selling non-SCR dimmers which gradually ramp the voltage up and down, completely eliminating the buzz. There are several circuits for doing this. I've seen these demo'ed and they are impresive. Some (Kliegl) are also short circuit protected - you can short the output with a crowbar and not blow the supply circuit breaker. The current islimited by the dimmer (of course the voltage drops a lot!). For a quick overview of these dimmers see the latest Theatre Crafts magazine. There is a good article. These new dimmers are still more expensive, but it seems a safe bet that the new technology will replace the SCR before too long. Randy Brumbaugh rando@skipper.dfrf.nasa.gov
f@Alliant.COM (Bill Freeman) (04/06/91)
In article <13181@ur-cc.UUCP>, fval_ltd@uhura.cc.rochester.edu (Trey Valenta) writes: > I've been dealing with the same problem recently.... the person who lived in > my dorm room before me had installed a touch sensitive dimmer which buzzes > like crazy from the waveform. One thing I've thought of would be to place a > cap across the bulb. Any thoughts on it's effectiveness? The only problem is > finding one of the right size. I eventually came across a 4 micro-F 150V > cap, non-polarized electrolitic, but I think that the voltage is too small. > I also found a 1MF @200V, a nicer voltage, seeing as the peak should be > around 155V. This might, indeed solve your problem. Before the capacitor explodes (yes it will) it might manage to take out the dimmer. Then you could replace the dimmer with a switch, and problem solved. IN ALL SERIOUSNESS DO NOT DO THIS. Other netters are correct that the useful ways to get rid of the buzz are special bulbs, a variable DC supply, or a variable autotransformer (Variac). If the light is too bright and the dimmer noise bothers you, try a lower wattage bulb. ;-) -Bill -- -- ...!{decvax!linus,mit-eddie}!alliant!f Bill Freeman KE1G alliant!f@eddie.mit.edu PP-ASMEL-IA(SE) Turbo Arrow N4365Z
rich@pencil.cs.missouri.edu (Rich Winkel) (04/06/91)
random@cbnewse.att.com (David L. Pope) writes:
]> an annoying buzz when dimed. Is there a better circuit for dimming
]> the bulbs that will prevent that !@#$%^&*&^%$# buzz?
]Yes, but since the buzz is being caused by the fillament vibrating
]at line-current frequency, it would involve a d.c. supply which
]would require a little engineering (to determine d.c. power max
]and min for the bulbs you are using). The actual cause of the buzz
]is the length of the fillament in the bulbs, so maybe you could
]find large diameter bulbs designed for dimming (that is, with short
]fillaments).
I always thought it was due to the harmonics generated by the abrupt
cutoff in the wave. Dimmer circuits work by chopping off the voltage
at various phases of the 60 Hz wave, right? This should add a lot
of high frequency harmonics to the wave. Surely the buzzing I hear
in a dimmed lightbulb isn't at 60Hz. So a lowpass filter might do
the trick (?? coming from an electronics novice).durham@w2xo.pgh.pa.us (Jim Durham) (04/06/91)
In article <1991Apr2.162037@maximo.enet.dec.com> ajf@maximo.enet.dec.com (Adam J Felson) writes: >I have a pair of floor lamps hooked up to a single dimmer. They use >6" spherical incandecant light bulbs. The problem is that they make >an annoying buzz when dimed. Is there a better circuit for dimming >the bulbs that will prevent that !@#$%^&*&^%$# buzz? > >__a__d__a__m__ I work at a television station where we have the same problems with dimming studio lights. The problem is the rise time of the scr dimmer circuits. To get non-buzzing light filaments, you need a rise time on the scr waveform of 800+ nanoseconds. We have some 180ns dimmers and they buzz like crazy when dimmed. A quiet way to dim lights is with a small variac or autotransformer. These are quite often available at flea markets or hamfests and could be put in a little metal box. Good Luck! -Jim (durham@w2xo.pgh.pa.us)
burgess@hpfcso.FC.HP.COM (Ken Burgess) (04/09/91)
My daughter disliked the noise made by a dimmed reading light she uses and decided to try different bulbs to solve the problem. Eventually she did a science fair project (largely un-noticed) to determine what types of bulbs made noise and what types did not. She tried bulbs from 8 different manufacturers, all 60 watt types, and found a great deal of variation in the ammount of accoustic noise they generated on a dimmer. I don't remember all of her results but I do know that she found one manufacturers bulb that made no sound whatsoever. Coincidently they were also the cheepest bulbs in the test. She obtained them at a local hardware store; they are made by "EXTRALFE" (model number 60 AFR 2000) in Poland for the Supreme Corp. Mullins, SC 29574. They are advertized as a "generic" bulb but have a nominal voltage of 130 volts instead of the 120 V. usually specified. They claim long life. As a part of her experiment Melissa broke the envelopes to examine the structure to see if she could correlate the fillament construction with the ammount of buzz they generated. What she found was that the tightly coiled fillaments buzzed the worst. The best (including the EXTRALIFE) were multiply supported straight wires. A few of the bulbs used this techniqe for filiment support, but the EXTRALIFE used five supports whereas the others used only three. I thought she did a good job and I was very proud of her, unfortunately the judges liked airfoil experiments better and she didn't even get beyond her school competion. At least I found it useful, our lights don't buzz anymore!
tom@syssoft.com (Rodentia) (04/10/91)
So you can get lightbulbs to buzz at >60Hz by chopping the waveform. This seems to be a case of what might be called base frequency pulse width modulation (if there's a better term for it, let me know). Now it seems that you could do a higher frequency pulse width modulation, and the buzz/whine would be inaudible. This would seem to be cheaper than a variable transformer (then again, maybe not). Comments? -- Thomas Roden | tom@syssoft.com Systems and Software, Inc. | Voice: (714) 833-1700 x454 "If the Beagle had sailed here, Darwin would have | FAX: (714) 833-1900 come up with a different theory altogether." - me |
charless@cory.Berkeley.EDU (Charles R. Sullivan) (04/13/91)
>>> an annoying buzz when dimed. Is there a better circuit for dimming >>> the bulbs that will prevent that !@#$%^&*&^%$# buzz? In addition to all the great suggestions other folks have given, you can try either a different manufacturers bulb, or a slightly different wattage. There are lots of different geometries used, and there is an amazing difference in amount of buzz. Unfortunately there's no simple pattern of what buzzes and what doesn't. Supposedly even the same manufacturer and wattage may be different according to which plant it was made in. If you've got a closet full of spare bulbs, try them all to find the best one. Or play 'musical ightbulbs,' switching them out of all your lamps. Charlie Sullivan charless@cory.berkeley.edu
ghot@ms.uky.edu (Allan Adler) (04/13/91)
I don't know if this is related or not, but here goes. I once took the speaker wires from a stereo phonograph and connected them to the filament of a vacuum tube. I was just learning electronics and knew nothing at the time (now I know a little, not much) and I was hoping that this would make the filament glow and maybe power the tube for other uses. To my surprise, I heard the music I was playing coming out of the tube. Allan Adler ghot@ms.uky.edu
rando@skipper.dfrf.nasa.gov (Randy Brumbaugh) (04/16/91)
In article <1991Apr2.162037@maximo.enet.dec.com>, ajf@maximo.enet.dec.com (Adam J Felson) writes: > [ . . .] annoying buzz when dimed. Is there a better circuit for dimming > the bulbs that will prevent that !@#$%^&*&^%$# buzz? > The buzz is caused by the SCR/TRIAC type dimmers which are found in many low cost dimming circuits today. These work by switching the AC waveform on at some point in the cycle. This creates a nasty high frequency spike which is both audible and can cause interference for nearby audio equipment. This is especially bad for theatre light dimming, which have many dimmers and lights over the audience. Most dimmers incorporate a torroidial coil at the output, which slows the rise time and helps some. The coil must match the load for best results. Several manufacturers are selling non-SCR dimmers which gradually ramp the voltage up and down, completely eliminating the buzz. There are several circuits for doing this. I've seen these demo'ed and they are impresive. Some (Kliegl) are also short circuit protected - you can short the output with a crowbar and not blow the supply circuit breaker. The current islimited by the dimmer (of course the voltage drops a lot!). For a quick overview of these dimmers see the latest Theatre Crafts magazine. There is a good article in it (April, I think). These new dimmers are still more expensive, but it seems a safe bet that the new technology will replace the SCR before too long. Randy Brumbaugh rando@skipper.dfrf.nasa.gov
jon@inqmind.bison.mb.ca (Jon Chesnut) (04/17/91)
> > In article <1991Apr2.162037@maximo.enet.dec.com>, ajf@maximo.enet.dec.com (Ad > > [ . . .] annoying buzz when dimed. Is there a better circuit for dimming > > the bulbs that will prevent that !@#$%^&*&^%$# buzz? > > > The buzz is caused by the SCR/TRIAC type dimmers which are found in > many low cost dimming circuits today. These work by switching the > AC waveform on at some point in the cycle. This creates a nasty > high frequency spike which is both audible and can cause interference > for nearby audio equipment. This is especially bad for theatre light > dimming, which have many dimmers and lights over the audience. > You're right - in low-cost dimming circuits, this can be a problem. But, as you go on to say, torroidal chokes can, for all intents and purposes, eliminate this problem. Having just completed THE PHANTOM OF THE OPERA CANDADIAN TOUR lighting and sound system supply, as well as supplying all the lighting and sound equipment for the production currently playing in Toronto, I would suggest that in the better systems, SSR's rapidly switching cause no problems whatsoever. By matching chokes to loads (as you said) the noise can be effectively eliminated. Metal dimmmer chassis also help, and shielded multi-conductor power distribution also lends a hand. I would suggest that it is only the cheapest SSR based dimmers that are prone to noise, and that even the most cursory attention to design makes these devices practically silent. Getting back to the original point, I have seen MANY mechanical dimmers that generate HUGE amnounts of noise, and especially RFI - and would go so far as to suggest that these devices are MUCH noiser than any SSR (SCR/TRIAC) setup. Jon Chesnut formerly with WESTSUN - Technical support to the entertainment industry!
tom@syssoft.com (Rodentia) (04/22/91)
I posted this question before, but the news feed has been very sporadic here, so please reply by e-mail even if you followup (my Reply-To: should now be tom@syssoft.com (even that was broke)). To summarize: If dimming by chopping cycles or half cycles of the 60Hz waveform causes audio noise based on these 60 or 120 Hz fundamentals, couldn't the noise be made inaudible by doing the chopping at some inaudible frequency such as 20KHz? Would this be less efficient or more expensive than the other (transformer based, I believe) approach mentioned in this forum? Or would it just not work? Thank you for your attention. -- Thomas Roden | tom@syssoft.com Systems and Software, Inc. | Voice: (714) 833-1700 x454 "If the Beagle had sailed here, Darwin would have | FAX: (714) 833-1900 come up with a different theory altogether." - me |
ajf@maximo.enet.dec.com (Adam J Felson) (04/23/91)
I'm considering trying to add a filter between a light dimmer and a set of floor lamps. Anybody know any suitable circuits? __a__d__a__m__
del@fnx.UUCP (Dag Erik Lindberg) (04/27/91)
In article <1991Apr22.161357.23840@syssoft.com> tom@syssoft.com (Rodentia) writes: >To summarize: If dimming by chopping cycles or half cycles of the 60Hz >waveform causes audio noise based on these 60 or 120 Hz fundamentals, >couldn't the noise be made inaudible by doing the chopping at some >inaudible frequency such as 20KHz? Yes > Would this be less efficient or >more expensive than the other (transformer based, I believe) approach >mentioned in this forum? Or would it just not work? Well, it wouldn't work using the inexpensive technology most of the dimmers available are based on. That being the SCR or TRIAC. These devices can be triggered, or 'fired' at an arbitrary time, but can not be turned off, period. They are essentially 're-armed' when current stops flowing in them, or every time the AC reverses direction. This means that no matter what frequency you modulate the triggering, they can only be turned off 120 times a second. In order to do what you want, you would need to use high voltage power transistors, at considerably greater expense, not only for the transistors themselves, but for the triggering circuitry. The triggering circuitry is not inherently more expensive, but high volume demand exists for SCR trigger circuits and a wide variety of packaged solutions exist at low cost. -- del AKA Erik Lindberg uunet!pilchuck!fnx!del Who is John Galt?