Film-Tech Forum ARCHIVE: Arc 'Splash' Muting Relays

This is topic Arc 'Splash' Muting Relays in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by David Graham Rose (Member # 1450) on 10-25-2005, 03:02 PM:

Greetings All from what can only be described as a miserable evening.

Unfortunately, my pet cat, Horace passed on this evening at the grand age of 14.

And so to business.

I have recently been evaluating various UK theatres for suitability for digital cinema installations. Mark my words, I am not impressed with what I have witnessed.

In one theatre, which will remain nameless, I encountered a bizarre phenomenom - namely the installation of relays on the output of the power amplifiers.

When one strikes the arc lamp, these relays operate such as to cut the stage lines to the speakers.

The only reason I could see for this is to mute the sound of the ignitor on the audio.

Would anyone care to explain this lame idea and why other methods of suppression could not be utilised.

Goodnight from Cambridge

David

Posted by Steve Guttag (Member # 268) on 10-25-2005, 03:59 PM:

That is a rather old practice that has been around for as long as I can remember. Most 16mm pedestal projectors that came from the Asian area also used this technique.

Are there alternatives? You bet but you have to watch how you ground things and how you isolate things.

It isn't a practice I use but I've seen it right from the manufacturer.

Posted by Clive Carmock (Member # 2882) on 10-25-2005, 04:06 PM:

On a slightly related note I remember at the ABC Cinema, screen 1 in Cardiff in Wales (now demolished sadly). When the Arc was struck, which they usually did about 2 mins before the start of the show, there would be a VERY loud splat sound from the stage and surround speakers. It was loud enough to make people in the auditorium jump.

In the 4 or so years I used to go to that cinema as a student they never fixed that.

Posted by Pete Naples (Member # 761) on 10-25-2005, 05:03 PM:

That wouldn't be a wall mounted, blue rack, containing a Cp55/65, anda few re-badged Quad power amps, would it? Didn't think there was any of those left!

It's a cheating way to stop ignitor splat being audible, there are better ways! Fit newer type Irem ignitor for one, or fit some polyprop HV capacitors to whisk the splat down to deck.

Older Cinemecannica lamphouses had an extra pole on the striker switch, for this purpose. Double bad, as it means you have mains in side the lamphouse, which could be on a different phase from the lamphouse fans etc, and live when you thought you'd isolated the lamphouse/rectifier. Don't ask me how I know this, I still have the twitch...

Posted by David Graham Rose (Member # 1450) on 10-26-2005, 01:29 AM:

Greetings Peter

Yes indeed. The rack was blue with a CP55. However, I failed to notice the amplifiers.

From a cold Cambridge,

Good Morning