Dimming a Source Four

[Sean-1966]

I have a Source Four light that I'd love to bring down a few notches. I tried one of my router speed controls that work great with every other light I've tried. The Source Four gets a nasty hum to it. So I tried rigging a commercial 1000 watt dimmer to it. Same thing, nasty hum. Anybody have any suggestions?? I e-mailed ETC to ask them but no response yet.

[Baltimore Shooter]

I used the router speed control on mine once and also got a hum. I switched to the 1K dimmer that I made (parts purchased at Home Depot) and had no hum after that. I can't explain why you had a hum on your 1K dimmer.

Warren

[No half-days]

I bought a 1000W dimmer from a lighting outfit in Connecticut and it worked fine. It's probably not much different from something you can make with Home Depot parts, except you don't have to build it.

http://www.filmandvideolighting.com/di10horo.html

[Andy T.]

I have also notice noise from source fours when dimmed. I hear more of a buzz than a hum and it appears to be the filament making the noise. Buzz is a higher pitch than a hum. What wattage bulb are you using.

Andy

[Run&Gun]

I use homemade 1K dimmers from Home Depot. You are going to get some buzz/hum from almost any light you put on a dimmer like that. Some lamp brands are worse than others and the more you dimm it, the more it will buzz, most of the time you won't hear it on camera, though. Just don't cross the audio and power cables that you're putting the dimmer on. ;)

[Ed_Scott]

Save yourself the buzz hassle and buy a Magic Gadgets 2K dimmer. The best $250 bucks you will spend on your light kit!

[Andy T.]

I have still heard a buzz with a Magic Gadget 2K and a Source Four.

Andy


<<Save yourself the buzz hassle and buy a Magic Gadgets 2K dimmer. The best $250 bucks you will spend on your light kit!>>

[Run&Gun]

Save yourself the buzz hassle and buy a Magic Gadgets 2K dimmer. The best $250 bucks you will spend on your light kit!

No, the best $250 bucks you'll spend on your light kit is a Source 4.

MG dimmers are $250 EACH. I can make a lot of 1K dimmers myself for that. Considering I carry at least 8 to 10, I'd have over $2G's just in dimmers. I don't know a single shooter that has forked out the money for a Magic Gadgets dimmer. Everyone I know uses one's that they have built themselves or had built and I've never heard any audio problems on tape. If you have a lot of money just laying around that you need to get rid of and you've run out of useful things to buy, go ahead...:p

[Matt Box]

I'm with Run on this one. I build my own as well. I was just in a nice grip shop in LA and a guy was buying a few dimmers that were exactly the same as the ones I make and he was paying through the nose for them. Some of the Magic Gadget dimmers have some cool flicker effect features but it's just not something I'm ready to spend the dough on.

Wish I had an answer to the dimmer noise. I had a problem once with a frezzi camera light that made a lot of dimmer noise. Frezzi sent me some sort of little circuit thing (sorry, I'm not an electrician) and I soldered it in and the problem went away. I cant say I have ever had a problem with my home brew dimmers though.

[quicklad]

I'd go back to your bulb. Put a lower wattage bulb to start (500w or less).

Then - make a bunch of N.3 cuts and slap them in front as needed. no hum, no color temp change - just not quite as convenient as a dimmer.

[freedom]

Variac is the dimmer of choice for avoiding hum. But it's big & heavy. A 2k Variac is about as big as a football and weighs well over 10 lbs. But it's the way to go and is found on better grip trucks.
All the electronic dimmers can cause buzz. Here's a post I found on cinematography mailing list (CML):

"Variac’s take the 60 cycle sine wave at line voltage and reduce or boost the voltage without changing the sine wave - if you look at the wave on an oscilloscope, it will look the same as the stuff coming out of the wall or the generator but the voltage at the peaks will be higher or lower depending on where you spin the knob (and how the thing is hooked up - if you open the cover of the variac, you can see that there are several ways to wire it depending on what you want to do with it)

Electronic dimmers, such as the household type which use a triac, or theatrical dimmers that usually use Silicon Controlled Rectifiers (or SCR's) adjust the voltage on their load side by taking that line voltage sine wave and very rapidly switching it on and off at various points during the cycle...thereby taking a smooth wave and chopping it into shorter spikes which average out to a lower voltage.

So what are the differences in use?

Because the triac dimmers are rapidly switching the current on and off, they can generate radio frequency interference which sometimes affects the sound department. They can also cause certain lamps to buzz if the switch points at a given setting resonate with the filament's coils. This is especially prevalent with certain types of bulbs where the filaments run in a zig-zag pattern - the adjacent zigs take turns attracting each other magnetically and then ignoring each other as the dimmer switches the current on and off rapidly."
Mark Weingartner
VFX & Photography for Motion Pictures

[Canonman]

Wish I had an answer to the dimmer noise. I had a problem once with a frezzi camera light that made a lot of dimmer noise. Frezzi sent me some sort of little circuit thing (sorry, I'm not an electrician) and I soldered it in and the problem went away. I cant say I have ever had a problem with my home brew dimmers though.

Dimmer noise occurs because of the way electronic dimmers work. They use a thyristor or triac that basically 'hacks' off a portion of the AC sinewave. These dimmers don't reduce the amplitude of the sinewave like a rheostat to get a lower RMS value, they chop it. Same with the router speed controller. It's the rapid transition of the chopped current occurring 120 times/second that causes the 'buzzing'. Depending on the rigidity of the filament in the lamp, you'll get more or less buzz.

The little circuit thing that Frezzi sent you was likely an RC filter that will smooth the rapid transitions in current. Taken individually, the sound would be like a brief click. But what you hear are 120 clicks per second and they take on a buzzing sound.

BTW Warren, it's not a good idea to use a device made for inductive loads (speed controller) as a dimmer for resistive loads (lamps). Most devices are usually stamped as such.

cm

[Canonman]

There you go, Freedom and I posted at the same time. Absolutely agree with the Variac. It's essentially a large variable transformer and reduces the output of the AC sinewave without altering its shape and won't create buzz.

cm

[Run&Gun]

Freedom, Canon: Good info. Ed, I wasn't picking on your post, but just saying that the MG option isn't ultra practical or affordable(even though $250 isn't that much in the scheme of things in this business, it adds up when you have to have a lot of $250 things). We all like to use the best we can, when we can, but we all know that almost everything is a trade off to some degree to allow us to work within a given set of constraints(money, time, etc), but still gives us the best results we can get, given the constraints.

[Canonman]

We all like to use the best we can, when we can, but we all know that almost everything is a trade off to some degree to allow us to work within a given set of constraints(money, time, etc), but still gives us the best results we can get, given the constraints.

I kind of agree with Quicklad's advice. Go to a lower wattage lamp, scrim it, and/or ND gel it.

cm

[Ed_Scott]

Freedom, Canon: Good info. Ed, I wasn't picking on your post, but just saying that the MG option isn't ultra practical or affordable(even though $250 isn't that much in the scheme of things in this business, it adds up when you have to have a lot of $250 things). We all like to use the best we can, when we can, but we all know that almost everything is a trade off to some degree to allow us to work within a given set of constraints(money, time, etc), but still gives us the best results we can get, given the constraints.

No problem. I know some people who choose to make their own sand bags - who am I to say it's right or wrong.

[freedom]

FYI
I don't own a variac, it's too f'n big & heavy. I have 2 1k electronic dimmers. When the buzz in the dimmer gets bad, I run extensions for it to get it out of range of the sound & cover it if necessary. I find my dimmer makes more noise than the lamp.

[Nino]

Good timing for this topic because I just had some problems with dimmers this weekend.
I was doing two days of interviews at MGM Studios for the ESPN Weekend at DW, on the first interview we noticed that the lights were slowly dimming up and down by themselves, they were not doing it in unison, they were doing it individually. I had 8 lights on dimmers, this is nothing new on this type of set-up, I do it several times each week and I’ve been doing it for years with no problems. For the smaller light, 150 to 300w I use standard cheap Home Depot dimmers and for those up to 1.5K I made my own. I also have a few of the expensive electronic dimmers but I seldom use them for interviews because sometime they get noisy. We got around the dimming problem for the first interview but we had 22 scheduled in two days and this could have been a real headache. We changed outlets bringing power from other parts of the building but the problem persisted. The only thing that I could think was that something was affecting the electronics in the dimmers. I removed all the dimmers and used scrims and ND gels instead, (and BTW this should be the correct way to control the light outputs) and the problem went away. I’m not an electronic engineer but I would like to know what could have possibly caused the problem, dirty power or radio interference. We called the DW engineers and they showed up right away but all I could get out of them was that I was probably correct in assuming that something was causing the dimmers to misbehave, not much help there; any suggestions or previous experiences?

[Sean-1966]

I have also notice noise from source fours when dimmed. I hear more of a buzz than a hum and it appears to be the filament making the noise. Buzz is a higher pitch than a hum. What wattage bulb are you using.

Andy


I'm using 750 watt light. I've been sung ND to cut down the light but dimmers are so much easier.

[Matt Box]

Nino- I have had the same problem with my dimmers dimming by themselves. I only seem to get it with the little cheap ones and dont think I have had a problem with my home built 1000w dimmers. It has happened to me a few times and it can really screw up your day.

If anyone has any solution for this other than making 4-5 more 1000w dimmers let me know.

[Canonman]

Nino- I have had the same problem with my dimmers dimming by themselves. I only seem to get it with the little cheap ones and dont think I have had a problem with my home built 1000w dimmers. It has happened to me a few times and it can really screw up your day.

Sounds like you could be loading the dimmer to the point where internal heat build up causes a shift in the internal resistance of the components (cheap ones) which will alter their output for a given input. Since resistance tends to go higher with more heat, that would explain why the lights are getting dimmer and not brighter on their own.

Higher quality dimmers will use components spec'd beyond the dimmer's rated capacity (over engineered) so that you don't encounter this scenario.

cm

[henryj4123]

This message is from a guy on my fire department hope it answers your questions

All filament lamps have the tendency to vibrate
the amount is dependent
on the length of the filament. There are two
things to keep in mind when
discussing fixtures and dimmers. First, a
resistance dimmer like a
rheostat or the cheep Home Depot wall dimmer work
by changing amplitude,
electronic dimmers work by altering the waveform.
Using the Source 4 as
an example, dimming this with a good quality 1000
Watt rheostat will not
cause the filament to vibrate. The wall dimmer
will also not cause the
filament to vibrate but the dimmer itself will
produce a "buzz" due to
the work and quality of the components used. When
electronic dimmers are
used a whole new set of factors are introduced
into the process. An
electronic dimmer alters the waveform and works
on a time base instead
of an amplitude base. By altering the waveform
the dimmer shuts off for
a giver length of time then switches on for the
remainder of a cycle
this cause the lamp to be dim. What this does is
abruptly turn the
filament on causing it to vibrate, the longer the
filament the more
noticeable the buzz the lower quality of the
dimmer the more noticeable
the buzz. Consequently the lower quality
electronic dimmers will put
noise back into the source they get their power
from causing other
devices like sound equipment to pick it up making
the noise problem even
worse. The solutions are many and are different
for most every instance.
In a super quiet environment with sound involved
the trick is to not dim
our use an isolated service for the sound system.
When dimming keep in
mind that the dirtiest range is between 30 and 60
percent, this is when
the most noise is produced by the dimmer and
filament, and the most
noise is put back into the service. If you find
that you always need to
dim a Source 4 keep in mind that there are three
wattage lamps available
375, 575, and 750.

Patrick Stewart
Marketing Events Technician
Electronic Theatre Controls
Middleton WI 53562
patrick.stewart@etcconnect.com

[Canonman]

Yeah thanks, Henry. I believe we covered the theory of operation a few posts ago.

cm

[Sean-1966]

This is from Rick Wolff at ETC. He was great in helping me sort this out.


Sean - after doing some research, here is what I can say:

All triac and SCR dimmers cause filament noise when dimming as they
switch the power line 120 times a second. This causes the filament to
move in the envelope at 120Hz and the reflector efficiently collects
this sound and projects it out the front of the fixture.

Triac and SCR dimmer designers have included chokes to create rise-time
in order to reduce filament noise. Higher quality dimmers uses quite
large chokes and wall box dimmers have little to no noise reduction
designed into them for heat, size and cost reasons. Even Lutron
recommends a choke on their FAQ page to abate noise.
http://www.lutron.com/service/FAQ.asp

The only way to truly get rid of all noise is to use an autotransformer,
a sine wave dimmer, or neutral density gel. It may be possible to
reduce noise by going to a higher quality dimmer or adding a choke from
Lutron to the wall box dimmer.

[Matt Box]

Just wondering.....which are you all using; the regular or the Jr. source four?

[Sean-1966]

The regular Source 4

[Cameradude]

I built my own dimmers. You have to do some searching to find the 1000 watt dimmers at Lowes or HD.

Some advice, if you don't know anything about electricity I would suggest running up your liability insurance before making one.....LOL!!

One more piece of advice. Don't use them around union electricians on film shoots unless they are to code!!! I know of a shooter that had the fire marchall called on him because the dimmers were incorrectly built and an IBEW guy called the fire marshall!!