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Topic: Sound interference from Strong Alpha Platters

Bill Hallsworth
Film Handler

Posts: 34
From: Loganville, GA, USA
Registered: May 2002

posted 05-10-2002 01:20 PM

We've been getting complaints about an intermittent popping noise in one of our houses. After checking it out, it seems to coincide with the payout switch on platter closing (but not opening). After looking at the other projectors, I found this problem on three more.

After replacing the switches, it only helped on one projector. Is there another way to fix this? Shielding the switch or the sound wiring?

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 05-10-2002 02:39 PM

This sort of noise is almost always indicitive of poor grounding on both the sound and equipment end. I would start with my grounds and work out from there. There are kludges to be done like putting capacitors across the switches or from the switch to ground (presumming it is a good one) to also kill switch related popping. Getting your grounds good is the first place though.

Steve

------------------
"Old projectionists never die, they just changeover!"

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 05-10-2002 02:55 PM

Sounds like your plaatter is running off on one of the sound system AC circuits. Try plugging it into another outlet and see if that clears it up. This may be the easy way out for a while but you still would have a grounding issue to deal with eventually.
Mark @ GTS

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Bill Hallsworth
Film Handler

Posts: 34
From: Loganville, GA, USA
Registered: May 2002

posted 05-10-2002 03:27 PM

Thanks for the tips, guys.

As far as where the platter is plugged in, I know for sure it does not come off of the sound. I'll definitely check into the grounding. Now that you mention the capacitors, I remember our tech saying that he put some on the switches at one time...but I haven't seen any these, so it must have been a while ago.

Thanks.

Bill Hallsworth
Regal Entertainment Group

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Dustin Mitchell
Phenomenal Film Handler

Posts: 1865
From: Mondovi, WI, USA
Registered: Mar 2000

posted 05-11-2002 02:24 AM

Unless they're on the same circuit then its not the platter. By plugging it into a different outlet Mark meant running it off of a different circuit. At my theatre every projector has four breakers, one for sound, one for the platter, automation, and projector head, one for the auditorium lights, and one for the lamphouse. If you theatre ever looks into new equipment for the booth you might consider having it rewired to a similar plan, makes things very easy to work on.

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Brad Miller
Administrator

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

posted 05-11-2002 06:12 AM

If you are not 100% familiar with the electrical wiring in your theater, a long extension cord always works nicely to ENSURE you are on a different circuit for testing purposes. Just get a 100 footer and run it to another auditorium and plug it in the convenience outlet on the console to run a test.

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Bill Hallsworth
Film Handler

Posts: 34
From: Loganville, GA, USA
Registered: May 2002

posted 05-11-2002 09:51 AM

Everything is wired to the console. The platters, sound, etc. don't have their own breakers (in other words, when the console is turned off, everything except the house lights is turned off). As far as grounding goes, I haven't had much of a chance to look at it yet.

Bill

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Ian Price
Phenomenal Film Handler

Posts: 1714
From: Denver, CO
Registered: Jun 99

posted 05-11-2002 12:18 PM

If everything is plugged in to your console then that is your problem. Just plug the platter in to somewhere else. That should clear up your sound problem.

Even in my underpowered, poorly wired theatre. There are 4 circutes per booth. Sound is on one. Projector and console 110 is on another, then there is the 3-phase and lastly is the circuit for everything else like platters, booth lights, make-up table and so on.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 05-11-2002 12:52 PM

I had that problem with a Potts platter. The contact points in the platter feed created a "snapping" in the sound. This booth was installed by former owners in a manner which in no way could be called professional.

I am sure that had the Ontario Fire Marshall visited that booth, they would have been shut down immediately. (It has since been brought up to safety code standards).

To clear the problem, I wired .05uf/600-volt capacitors in parallel with the feed contacts.

A word of warning on this however. Do NOT use ceramic capacitors with 110-volt control where inductive circuits (such as motors or change-over coils) are involved. They have a nasty habit of blowing up and shorting.

My favourite item had been the Centralab DD-104 (.1uf/1KV) ceramic disc capacitor. I mean, ya gotta figure, 1000-volt rating, what can go worng? I found out that these are NOT good on 110-volt inductive circuits.

They blowed up real good.

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Bill Hallsworth
Film Handler

Posts: 34
From: Loganville, GA, USA
Registered: May 2002

posted 05-11-2002 02:57 PM

I know what you mean about things being poorly wired. Even though each auditorium has its own breaker box, platters and sound were still wired to the console (which kind of makes sense, because originally, all the sound equipment was mounted in the console). We have plenty of other circuits, though, for fans, house lights, and that sort of thing. I'll see about getting some more breakers added, with outlets for sound and platters.

Rick, thanks for the info on the capacitors. I wouldn't think that it made any difference if you were using ceramic capacitors or not. But hey, since I want to keep explosions in the booth to a minimum, I'll go with something else.

Bill

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Pat Moore
Master Film Handler

Posts: 363

Registered: Mar 2000

posted 05-11-2002 05:04 PM

Good suggestions, all. Sounds like you have an early Strong booth with X90's or Super Highlights, but a lot of consoles supplied the platter power and that is probably where the noise is getting in.

Poor grounds can be a tough thing to chase down, but if you're getting noise from the platter, chances are there's noise from other sources too. Good grounds are the way to clear that up. Changing phases is good, might be a challenge in the console depending on how it's wired. Hopefully there's a wall plug or an extension cord that can prove the source of the problem. The capacitors are probably the end-all fix and will also have the benefit of redicing pitting on the switch contacts and improving their life.

Good luck!

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 05-11-2002 10:44 PM

In our little projection booth, here at the college, the entire sound system is on an isolated ground from everything else.

Try getting one of those three prong adaptors that you use to plug three pronged cords into two pronged outlets. Then take the green grounding lug and connect a wire to it. Connect the other end of that to something that you KNOW is a seperate (and safe) ground like a cold water pipe.

It's a cheap, 10 cent solution to see if that's what your problem really is. If that does work you know you need to get an electrician in there to redo your grounds. Tell your boss that, not only is this annoying to customers, it could eventually cause the sound system to fail prematurely. In other words, he can spend a couple hundred bucks now or he can spend a couple THOUSAND dollars later when he has to replace a sound processor... or two.

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Jesse Skeen
Phenomenal Film Handler

Posts: 1517
From: Sacramento, CA
Registered: Aug 2000

posted 05-12-2002 11:25 AM

Does your sound system have Afterburners (AKA Bastardburners) hooked up? I had this exact same problem where I used to work and bypassing these things cleared it all up, as well as eliminating some hissing that was going on in one auditorium. These have to be among the silliest things ever invented; if the sound is too loud just turn the volume down but don't mess with the dynamic range!

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 05-12-2002 12:57 PM

The problem with just turning it down is that the dialogue can become to low
In many locations where the rooms have turned out to be underpowered or there is bleed through problems I have installed them and never had a problem with noise hum or interference.
If they are doing that then they are installed incorrectly
As a side note I only install them in between the digital adapter and the main processor so they are only on line for digital tracks

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