Buzz when projector is idle

[Jesse Crooks]

Today I experienced an issue at a theater where I’ve been filling in to run 35mm shows for the last three years. They have Simplex X-L soundheads with Component Engineering readers, and a CP65 processor. Their changeover system requires one projector to be selected at all times (dowser open, audio live). Perhaps I’ve been spoiled by my Kinotons, but there is no “dowser close” option in which both projectors have their changeover dowsers closed and audio muted. As such, in preparation to start a show you have to first change over to the projector that will NOT be starting the show. This has never been a problem in the past, but today I noticed that when Projector 2 was selected while idle, it produced a loud buzz. There was no buzz when actually running film. When starting a show with Projector 1, we had to switch the CP65 to a different input to hide the buzz, change over to Projector 2, and have a second projectionist switch to the 35mm audio input when they heard the dowser open on Projector 1.

It seemed odd to me that the buzz only manifested when the projector was idle, and not when the reader was scanning film. And this occurred during a 35mm marathon, so I had the chance to observe it multiple times. As far as I know there have been no changes to the projectors or sound system.

I’m curious whether anyone knows what may be going on here.

[Steve Guttag]

I'd be curious as to how the noise behaves in the background when it is showing the movie as I suspect it is still there, at some level. Since it only affects one projector, you are down to half of the Optical Preamp card (CAT240A) and the preamp on the reader itself, plus the wiring between the two (including the ground, if you have a gearbox soundhead...the part that floats for vibration reasons needs to be grounded too).

Does the noise go away when the reader power supply is turned off?, how about if its cell cable is unplugged (to isolate is it in the CP65 or the reader)? In any event, you have the connections, solder joints capacitors and even resistors that can change over time.

Note, on a Simplex, there is nothing that stops you from manually closing the changeover douser. As for the sound...that is intrinsic into a CP65...it is on either 1 or 2 (and this is true on every cinema processor that caters to just 2-projectors). There is no "neither" so even if you had your Kinoton machines, one of the preamps is always "live." Many would use a "Mute" button to kill the sound. What you also have on your Kinoton machines is our Cardinal interface that monitors your motor and changeover button presses to ensure that you are always on the opposite preamp when starting up. It is just working in the background. By virtue of pressing the "FWD" button, it switches the optical preamp to the other projector and then switches back when you press dowser open. That isn't factory. Most installers just use an available relay contact on projector 2 to monitor when its dowser is open...so you HAVE to start on projector 1...alternately, they switch the LEDs on/off and don't mind the "thump" of that action (which is attenuated with the film in the light path).

[Mark Gulbrandsen]

Sounds like you have a ground loop of sorts. Check and be sure the shield in both channels of the scanner cables only have the shield connected to the processor input.

[John Eickhof]

what about ambient light? does it quiet down if you close the soundhead door? turn off the lights in the proj door? turn off all booth lights? do you have incandescent or fluorescent lighting? try and keep it simple!

[Jim Cassedy]

"Buzz when projector is idle"

Ya know, I used to get a get a buzz when I was idle too. . . but that's a different story.

Like John said- - ambient light can sometimes cause this. Have any lighting changes been made
in the booth recently? In one old booth, you HAD to have the soundhead doors closed or it would
pick up room light, or I've seen booths where the light bounced off the port glass & into the sound
head area. Just for fun, try turning off all the booth lights & see if the hum goes away. Or better
yet, try completely blocking the light from the soundhead LED. If the hum is still there, you might
have a problem in the power supply for the LED. I've seen something like that once.
Is what you're hearing a hum or a buzz? There IS a difference!

One of the really ancient theaters I worked at was a ground loop nightmare. Parts of the building
had upgraded AC power wiring, but there were still some of the original 2 wire1926 circuits in use
throughout the building and in the booth.
Once, they had to replace about 6 or 8 feet of the old cast iron sewer outflow pipe under the
sidewalk out front that had sprung a leak. The replacement pipe was made out of fiberglass or
something - - and that threw the whole building grounding out of balance. It took me about a
week before before I finally got rid of all the the ground hum. (I worked really hard to fix it
one afternoon before a big show that evening- - I thought I had finally fixed it, - - and then the
big neon marquee came on at dusk and created a whole new set of noises!)

[Ryan Gallagher]

I thought I had finally fixed it, - - and then the
big neon marquee came on at dusk and created a whole new set of noises[/I]!)

Haha, I've heard tale of stories when our older marquee contactor motor used to cause a clicking interference on the live PA system for similar reasons.

[Tony Bandiera Jr]

Well Ryan? Did you find the issue? Inquiring minds want to know....

[Ryan Gallagher]

Well Ryan? Did you find the issue? Inquiring minds want to know....

For once in recent history I did not start this 35mm thread. ;-) Jesse is the OP.

[Tony Bandiera Jr]

For once in recent history I did not start this 35mm thread. ;-) Jesse is the OP.

LOL sorry...been a very long week with track work and racing so I forgot to look at who the OP was....

[John Eickhof]

talking about sign noise, the 1955 vintage ACE neon sign on my building was terribly noisy! it has two motorized flashers, one makes 12 stars blink randomly and the other cycles A-C-E...A-C-E...and then ACE-ACE-ACE with big stars around each letter flashing at the same time, it was causing horrible hash and pops in my non-synch in both theatres...I pulled the old ACME Sign flashers out and dressed up all the contacts and installed AC filter caps across all contacts, from then on its been quiet as a mouse! On a side note, those who may remember Robert M. Dominic of the SF Bay area, it was his father who designed and patented the ACME brand sign flashing mechanism! They were used world wide! When I first met him in the mid 1970s, he still had his dad's full neon shop in a storefront on E14th st in Oakland right next door to his film lab and screening room!

[Mark Gulbrandsen]

LOL! Bob Dominick... Only ever bought one thing from him (even though I was previously warned) in my life because everything that came from him sparked, flashed or buzzed. In my case it was his pair of Crown 35/70's. The Japanese DP-70 look a likes... He was a hoot!

[John Eickhof]

OMG! Thats funny, I was there in the mid 80s when he installed them in his theatre on 14th ave...it was a beat up old house had no seats and part of the roof had become a sun roof! he cobbled it together and a couple guys out of the local and i horsed those monsters upstair s!he pu super core lights behind them,,,first time he started the Film-Tech Forums it broke a taper pin on the int drive gear...so he slid a 4 penny nail in and bent it over! he opened with a nitrate silent print of Birth of a Nation! the locals had picket lines in front of the theatre! his plan was to run kung-fu and exploitation films...only lasted about 6 months before he went broke! where did the nichao crowns end up? i was there opening nite, he still had no seats but borrowed a bunch of folding chairs and lashed them together in rows! the only fun feature of the theatre was it had a 40ft billboard on the roof advertising 'COLT 45 MALT LIQUOR' ! that was Bobs favorite beverage! he got the crowns from Jack Craig at United Artists Theatres out of their warehouse at the Geneva Drive In!

[Mark Gulbrandsen]

OMG! Thats funny, I was there in the mid 80s when he installed them in his theatre on 14th ave...it was a beat up old house had no seats and part of the roof had become a sun roof! he cobbled it together and a couple guys out of the local and i horsed those monsters upstair s!he pu super core lights behind them,,,first time he started the Film-Tech Forums it broke a taper pin on the int drive gear...so he slid a 4 penny nail in and bent it over! he opened with a nitrate silent print of Birth of a Nation! the locals had picket lines in front of the theatre! his plan was to run kung-fu and exploitation films...only lasted about 6 months before he went broke! where did the nichao crowns end up? i was there opening nite, he still had no seats but borrowed a bunch of folding chairs and lashed them together in rows! the only fun feature of the theatre was it had a 40ft billboard on the roof advertising 'COLT 45 MALT LIQUOR' ! that was Bobs favorite beverage! he got the crowns from Jack Craig at United Artists Theatres out of their warehouse at the Geneva Drive In!

Paul M. told me Bob ran X rated stuff there.. But anyways, both found their way to the Chicago Cinema Museum....

[John Eickhof]

the only othert pair I had ever seen were the ones that Larry Little had in his warehouse in Vegas years ago! they were a slightly newer model nichon crown 35/70 than Dominics were.

[Mark Gulbrandsen]

Well, they ran... Emil Varga in Sun City who was a big film collector had a pair of the JJ style Crowns by his swimming pool. I bought a lot of films from him, but not those Crowns... The pair I got from Robert ran ok, but they were just not very well made. The bent over nail was also still in place.

Speaking of Emil Varga, he also had a complete Cinerama system in storage in his garage. Not sure what ever happened to all that stuff though.