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Topic: Audio Popping on Change-Over

Joe Beres
Jedi Master Film Handler

Posts: 606
From: Minneapolis, MN, USA
Registered: Nov 2000

posted 11-06-2002 07:09 PM

When changing over from projector 2 to projector 1, there is a slight, but audible pop that comes through both the booth monitor and mains. It is slight, but still a problem. It seems to have developed, or at least become more pronounced recently, but nothing really has been changed in the booth. I am hoping to get some advice on where and how to start chasing down this problem.

Here is the equipment we have:
Century (Westar) SA heads
Century (westar) R3-Optical soundhead
Kelmar ECC-35 Changeovers
Dolby CP-55 Processor
Xetron XTN 4000 Lamphouses (soon to be changed out for Ultra 80s)

I know it could probably be any number of issues causing the popping, but any advice would be appreciated. thanks!

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 11-06-2002 07:18 PM

It could be the changeover shutter coils causing the noise.
Does it happen when the picture changes or when the sound changes (or do you do both at the same time?).

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Matthew Bailey
Master Film Handler

Posts: 461
From: Port Arthur,TX
Registered: Sep 2000

posted 11-06-2002 07:19 PM

Could use a potentiometer or a miixer to cross fade between the soundheads of the outgoing & incoming projectors.

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Joe Beres
Jedi Master Film Handler

Posts: 606
From: Minneapolis, MN, USA
Registered: Nov 2000

posted 11-06-2002 07:24 PM

Daryl, Thanks for the quick response. I hadn't remembered to add this information. I have seperate controls for picture and audio, and the pop is only heard when changing over the image, regardless of which projector is set for audio.

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Daryl C. W. O'Shea
Film God

Posts: 3977
From: Midland Ontario Canada (where Panavision & IMAX lenses come from)
Registered: Jun 2002

posted 11-06-2002 07:34 PM

It sounds like it's the Kelmar changeover causing the problem.
Check out this thread here for some solutions.

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Steve Kraus
Film God

Posts: 4094
From: Chicago, IL, USA
Registered: May 2000

posted 11-06-2002 08:40 PM

That was primarily about hum problems.

The question is why would he start having this problem if he didn't before. There's probably not too much that can change on the changeover solenoids outside an actual failure. Does the pop occur as you make contact (push the button) or break contact? Yes, it's hard to tell but try holding it on briefly (very briefly) to see. Could wear on the button contacts cause a bit more arc than you had originally and make more RF? Are there capacitors across the buttons--there should be--a .1mF disc or something like that with voltage rating of at least several hundred volts.

Maybe this has nothing at all to do with the changeovers and everything to do with interference pickup. Check the shields on your solar cell leads--they should be grounded at the CP as you see in the manual but isolated at the projector end. Maybe something is touching. Check the grounding of the sound rack and look for something amiss with the wiring behind it. Do you hear the C/O pop if you are in non-sync? How about with the CP off (amps on of course)? It's getting picked up somewhere and it didn't before or at least to a much lesser degree so your answer is in there someplace.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 11-06-2002 08:58 PM

I would also try the capacitor across the switch idea. Be sure the capacitors have a high enough working voltage or you'll have more trouble.

Joe, which theater do you work at down there. I have been known to drop in on the Heights from time to time.

Josh

------------------
"Film is made of silver, video is made of rust"
'nuf said

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 11-06-2002 10:15 PM

Check your equipment grounding. See if you can detect if it is coming in through the front end, mid-stream, or whatever. Once you establish the point of detection, it is usually very easy to swamp out.

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 11-07-2002 07:12 AM

I agree with Steve that if the problem has recently developed without any other changes in your wiring or sound system, it's likely that there is just some increased arcing at the contacts that control the power to the changeover solonoids. Clean the contacts and use a snubbing circuit (capacitors) if necessary.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Joe Beres
Jedi Master Film Handler

Posts: 606
From: Minneapolis, MN, USA
Registered: Nov 2000

posted 11-08-2002 01:10 PM

Josh Jones, and his Dad, happened to be blowing through the Twin Cities today. I got a call from Josh's Dad, and he told me that Josh brought all of his parts and tools to check out the problem with the popping. (An unbelieveably pleasant surprise)

First, Josh tied a cap into the switch, but that didn't fix the problem, but will probably prevent the same problem down the line when the switch starts to go. Then he found a cap that had been tied in between the switch and changeover on the other projector. One leg of that capacitor had come loose. He put it back in place and voila! No more popping!

Thanks everyone for all of the advice, and thanks to Josh for being the whiz kid he is and his Pop for being so damn supportive. (And Paul for providing Josh with all of his toys and much of his expertise)

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 11-08-2002 02:56 PM

Just wait until you get the bill!

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 11-08-2002 03:37 PM

Well, hearing that made my day.

Thank you for the plug, Joe. Maybe I am doing something right after all.

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Josh Jones
Redhat

Posts: 1207
From: Plano, TX
Registered: Apr 2000

posted 11-08-2002 08:12 PM

Glad to have helped

Josh

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Bill Carter
Expert Film Handler

Posts: 162
From: Minneapolis, Minnesota
Registered: Sep 1999

posted 11-08-2002 08:22 PM

Hey Josh...

Any time you want to come back and do a couple of (paid) days work at
St. Anthony Main... give me a call!

Bill

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 11-09-2002 09:36 AM

<raising an eyebrow> And just where was this capacitor again? (Just trying to visualize what capacitor came undone and where it was in circuit).

Steve

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"Old projectionists never die, they just changeover!"

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