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hi everyone.


currently I am pulling my hair out with some new (old) lights. We have bought 4 antique film lights as part of a set design. Each are running a 1k lamp with a massive edisson screw fitting. These lights were originally designed to be either on or off. This is where we come to a problem... I need to run them at about 40%. As soon as they are dimmed (using pearl 2000 with lightprocessor paradim) they are producing a loud ringing noise and understandably the noise boys are not happy as it is ringing through most mics. Ordinarily this wouldn't bother us because its probably loud enough in the venue to mask out the ringing but we will be doing a live recording at the event and it can be heard clearly in the studio on several of the tracks.


So the question is how do I stop the buzzing(ringing or whatever you want to call it). I know this is a long shot and the answer may be put up with it and take it out with pro tools after but I thought you fine people may have a better solution. Just to help, here is what I have tried already


run at 100% with some diffusion over the lights to bring them down a bit. Unfortunately this loses the aesthetic of the 40%. these lights are being used purely for their aesthetic quality not for their light producing ability. because they are 2800k at the 40% they give a nice warm glow


put in 300w lamps and run at full. again, this loses the nice glow as they just throw white at 100% (understandably as this is what they are designed to do)


add a second generic to the lamp using a y split to take some load. This was suggested to me by a local company but seemed to make no difference whatsoever


add a ferrite ring - clearly this was never going to work but I was getting frustrated


the other suggestion that I have had is that it is thyristor noise. I have to admit that my knowledge falls down at this point. From some Internet hunting I have a vague understanding but I cannot work out what I would have to buy to solve this. Understandably finance are not happy throwing money at the problem unless I can justify it and guarentee it will solve the problem. This set will be used for a long run so hiring isn't really financialy common sense for us.



sorry for the long post but I figure the more info you have the better


any help would be much appreciated



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thanks for the quick responses


unfortunatly, with the 300w with colour correction, although it gives the right colour, it loses some of the aesthetic, it becomes very obvious that there is something over the light rather than it being completely open to the bulb and since there will be a full camera rig in we can't rely on the distance of the audience to hide this.


It is a suggestion that we would probably go with if no other solution can be found so thanks for sharing itg


as to sine wave dimming consider me to be googling it right now!!!!

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Older theatre bulbs were not designed for phase angle (thyristor) dimmers. The chopping of each half cycle of the mains results in the filament heating and cooling, the expansion and contraction results in mechanical movement hence sound ( the main source is the thermal one but magnostriction also plays a part). Later lamps supported the filament better.


I can suggest four possible solutions:


As Jim suggests try another dimmer, ideally one designed for TV dimming. This is unlikely to get rid of all the noise.


Add an inductor in the lead to the lamp, this will slow the rate at which the lamp receives power and make the noise less (TV dimmers have larger filtering inductors)


Buy or rent a sine wave dimmer, there are several 2 channel units on the market rated at 1KW per channel aimed at commercial dimming.



Lastly, put a dummy load in series with the lamp so the dimmer has to be run nearer full. Putting a 500watt lamp in series (back stage somewhere) will run the lamp at about third output. A 500 watt with a 250 watt across it will result in more output. Messy in cabling and needing some experimentation to get right output this approach will be the cheapest solution. ( I take it your from your Y lead test you put the second lamp in parallel not in series).

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Which dimmers are you using?

The console doesn't make any difference.


Many dimmers (especially at the cheap end) have very small chokes, leading to short dimmer rise times and very loud 'ringing'/'buzzing'

The Sensor+ Extended Rise Time (600uS to 650uS) modules may help reduce the noise, but cannot eliminate it.

(Other manufacturers of long rise-time dimmers exist!)


If you need to make them truly silent, you will need some form of Sine-Wave dimming.


We do some 1, 2, 4 and 6-channel sine-wave 2.5kW power modules - I suspect that hiring one or more of those (choose number of channels to fit) will be your best bet.

ETC/IES Sinewave Power Modules


For hire, try the usual suspects - I'm fairly sure that Whitelight and SLX have some.


Running the lantern from your dimmer through a fixed transformer won't really help you - it will still buzz as you fade it out, and you run the risk of damage to the transformer due to 'imaginary power' losses.

(You'd need to find a transformer rated at least double what you'd expect, again at 100% duty cycle.)


Some cheaper alternatives:

Variac or Resistive dimming - give it hard power, needs an operator backstage to run the dimmer, and may be hard to find. But does work!

Variac is the better of these two - resistive has a funny dimming curve and obviously gets very hot.


Obviously you would need to choose ones rated at or above 1kW

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thanks people. great description of thyristor noise madmac it now makes a lot more sense.


dimmer being used is the lightprocessor paradim currently. I think the best approach is probably the sine wave dimmer. I suspect the bottom line is I'm not going to fully get rid of the noise without changing the fittings and lamps so something that gets rid of most of it will be great

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Use your 100W lamps run at full then use a gel to get the colour you want then add neutral density till you reduce the intensity to your liking, no problem.


unfortunatly, ... [snip] it becomes very obvious that there is something over the light rather than it being completely open to the bulb and since there will be a full camera rig in we can't rely on the distance of the audience to hide this.



You must have missed that bit, David!

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Excert from Rank Industries Australia Sound Interefrence Problems With Thyristor Dimmers:

6. Lamp Sing

Some lamps may sing when used with thyristor dimmers. This sing is less likely with the better "TVC" and "HL" C core filters fitted in JTM and PAM modules. In practice, lamp sing is not normally noticeable except with open fronted lanterns such as floods or scoops close to audience or microphones.

Colour medium considerably reduced the sound level.

Only some lamps are susceptible to sing and usually the simplest solution is to change the offending lmap. Special low sing lamps are available for critical applications.


The colour medium they are referring to is Cinemoid, which is very thick, hence the soundproofing characteristic.

The C core chokes used ferrite cores, not iron cores so rise time was reduced.


Your search for authenticity of lighting has brought with it the old problems. At least you have the option of sine wave dimmers to solve the noise problem.


The "Good old days" werent always that good, we just like to think they were.

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thanks again people. currently we are looking into the etc sinewave dimmers as probably the best option. as for whether it is better to have the lights singing than the in show talent I couldn't possibly say!!!!!
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You could modify the fixtutes to take a more modern bulb. Depending on the layout of the fixture this might not be very hard. Just bolt a new 1kw base in and then you can use a modern bulb with no sing.

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