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Ian_p

Get lights to fade up / down more linearly

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All,

 

Perhaps this isn't a Frog issue, but I have noticed that the lanterns don't fully follow the sliders on the Frog. Ie, they come on suddenly when the slider is pushed on past 45%.

The DMX is terminated in a Strand S72 demultiplexer, and I wondered if this is to do with dimmer 'laws'. I notice the Zero 88 demux has laws and the Strand doesn't seem to.

 

What do you reckon?

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This sounds like it could be the law set up in whatever dimmer is connected to the desk. If the lamp does nothing until around 45 - 50% and then suddenly comes on full - this sounds like the dimmer has a switch law.

 

If you check the outputs screen on the monitor you can see if the DMX output from the desk is changing according to the fader position. If the DMX values are rising/falling smoothly as you move the fader up/down then it is almost certainly the way that the dimmer has been set up.

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What kinds of lanterns are you talking about if I may ask? With intelligent fixtures this is rather common... our MACs seem to be at 90% output while the fader is still around 50 or so. But that's got more to do with the shuttering I think.

Check the curves on your dimmers.

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The lanterns are all generic, source fours, selecon, tatty old battens etc etc.

 

I believe the issue IS the DMX demux, but this cannot change its dimmer curves, nor can the dimmers themselves. The dimmers are 15-18 years old and the company that made them is no more!

 

So, I guess I am stuck with the fade characteristics I have got. Oh well, I won't worry about something I can't change!

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Big bucket of water, throw it over the dimmers " WHILE OFF!!!" turn on power biggest pyro bang ever, ring insurance company and buy some zero dimmers :lol:

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biggest pyro bang ever

8O

I´ve seen such a mess looks very evil.

 

Before killing the dimmers you can change the Demux unit -

I think that your problems are made by bad Demuxing.

 

What dimmers do you use exactly ?

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A new demux isn't that expensive I think; just buy one that alters the dimmer curves (if such a demux exists?) and your problem should be solved I gues...

 

To check if the demux is the problem, simply find/rent a analog desk and test it directly onto the dimmerunits.

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There are old analogue dimmers with CURRENT INPUT. Apply a 27k/1/4W resistor in series with each channel in the dimmerpack.

Yes, sudden brightness at somewhere between 30 - 60 % and full between 50 - 80 %.

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The dimmers were made by an a small company which are no more called PLS Lighting (I think). This was a one man band which meant the cost was extermely keen (about half of anything else available at the time). I think I bought them about 1988!! So with 4 shows a year and all tech rehearsals they are used about 40 times a year (640 times in total)

 

He decided however that he couldn't compete with Anytronics etc, so packed in. He has repaired one for me once (Thanks - I'd plugged a motor into the dimmer - didn't understand inductive loads etc then...), but the units are standard 5amp dimmers with no ability to change dimmer laws etc.

 

As they fail I will replace them, probably with Betapacks or similar, but they still work OK, and the fade characteristics were only noticed since we got a Fat Frog and a demux to run them. I guess this proves the issue IS the demux (Strand S72) but its not so bad, I hadn't noticed myself until a keen eyed operator pointed this out.

 

The things we amateurs have to put up with ehh?

 

SO I won't be killing the dimmers, we continue but start looking for replacement over the next few years

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Hi Ian,

 

the demux you described is not too bad I think but....*LOL.

 

I have a few questions about the dimmers.

 

Do they work with standard 0-10V? Some work with negative voltage (Strand!!!) or higher voltages (older german products 0-18V)

Have you tried different voltages at the demux?

 

Are the Sub D connectors pinned right? pin 1 of socket is pin 1 of plug?

 

Perhaps silly questions but do help checking your problem.

 

cheers

 

Sven

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No, the dimmers are defintely 0-10v, and worked OK with the analogue board. They still work OK with the demux, but the way they dim in is not linear, and by deduction this must be the Demux.

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