Film-Tech Cinema Systems
Film-Tech Forum


Post New Topic  Post A Reply
my profile | my password | register | search | faq & rules | forum home
  next oldest topic   next newest topic
» Film-Tech Forum   » Operations   » Film Handlers' Forum   » intermittent hum on optical mono (Page 1)

 
This topic comprises 2 pages: 1  2 
 
Author Topic: intermittent hum on optical mono
Anhtu Vu
Film Handler

Posts: 97
From: Montreal, Quebec, Canada
Registered: Jun 2013


 - posted 05-04-2019 12:20 PM      Profile for Anhtu Vu   Email Anhtu Vu   Send New Private Message       Edit/Delete Post 
I'm getting an intermittent hum when playing a 35 mm with mono optical send track.

I will do an azimuth and focus check of the soundtrack lens, anything else I should be concerned with ?

On a side note, my aging oscilloscope just died, are the sound card / software oscilloscope any good ?

Can anyone recommend a new hardware or software oscilloscope ?

Thanks

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9525
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 05-04-2019 12:22 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
I use the Rigol ds1054

 |  IP: Logged

Anhtu Vu
Film Handler

Posts: 97
From: Montreal, Quebec, Canada
Registered: Jun 2013


 - posted 05-04-2019 12:26 PM      Profile for Anhtu Vu   Email Anhtu Vu   Send New Private Message       Edit/Delete Post 
Hi Gordon,

The Rigol will be adequate for my calibration needs ?

I'm in Montreal, where did you buy yours ?

Thanks

 |  IP: Logged

Stephan Shelley
Jedi Master Film Handler

Posts: 846
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 05-04-2019 12:29 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
Check the lateral guide adjustment with buzztrack. Check for ware and play in the lateral guide assembly. I have had worn out assemblies where the film wandered back and forth getting sprocket or frame line noise in the system. If one side of the flanged rollers in the lateral guide is spring loaded make sure it moves freely so it keeps the film against the fixed side.

 |  IP: Logged

Dave Macaulay
Film God

Posts: 2314
From: Toronto, Canada
Registered: Apr 2001


 - posted 05-05-2019 08:19 AM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
The obvious suspect is light from a fluorescent or LED lamp getting to the pickup, have you eliminated that?

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9525
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 05-05-2019 09:28 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Electro-Meters Company Ltd.
Technology For All Your Measurement Needs



Ph: (905) 428-3413 x:206
Toll Free: (800) 617-3413 x:206

 |  IP: Logged

Anhtu Vu
Film Handler

Posts: 97
From: Montreal, Quebec, Canada
Registered: Jun 2013


 - posted 05-05-2019 10:13 AM      Profile for Anhtu Vu   Email Anhtu Vu   Send New Private Message       Edit/Delete Post 
quote: Dave Macaulay
The obvious suspect is light from a fluorescent or LED lamp getting to the pickup, have you eliminated that?
You mean an outside light source ?

The projectionist uses a small fluorescent light mounted on a pivoted arm to thread the projector, otherwise the booth is fairly dark. I will check.

 |  IP: Logged

Paul Finn
Film Handler

Posts: 41
From: Bay City, MI
Registered: Jan 2019


 - posted 05-05-2019 12:42 PM      Profile for Paul Finn   Email Paul Finn   Send New Private Message       Edit/Delete Post 
I second eliminating all sources of direct or reflected light, especially fluorescent light (the worst), into the solar cell pick-up area of the projector sound head. Even 60 Hz hum can be introduced from direct exposure to incandescent light. This precaution also applies for reflected picture light into the solar cell area from an incorrectly angled or unshielded window port glass.

Paul Finn

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9525
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 05-05-2019 12:48 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
What is the make of soundhead and reader and what is the processor
if it was worklight hum i would believe it would occur in stereo as well as mono tracks

 |  IP: Logged

Sam D. Chavez
Film God

Posts: 2147
From: Martinez, CA USA
Registered: Aug 2003


 - posted 05-05-2019 01:11 PM      Profile for Sam D. Chavez   Author's Homepage     Send New Private Message       Edit/Delete Post 
Back to basics here. Does it only hum in Mono format? Does the film need to be running to have hum? If so, cover the exciter lamp/LED light source with a piece of paper. Does it still hum? etc.

 |  IP: Logged

Anhtu Vu
Film Handler

Posts: 97
From: Montreal, Quebec, Canada
Registered: Jun 2013


 - posted 05-05-2019 04:22 PM      Profile for Anhtu Vu   Email Anhtu Vu   Send New Private Message       Edit/Delete Post 
quote: Gordon McLeod
What is the make of soundhead and reader and what is the processor
if it was worklight hum i would believe it would occur in stereo as well as mono tracks

Processor is CP650, century sound head, Kelmar reader.

According to the projectionist, the hum is only on Mono print.

I would be very surprise if it comes from outside light source as we have not change our ways of working for the past 8 years.

quote: Sam D. Chavez
Back to basics here. Does it only hum in Mono format? Does the film need to be running to have hum? If so, cover the exciter lamp/LED light source with a piece of paper. Does it still hum? etc.
Hum only on Mono format.

Yes film needs to be running to get the intermittent hum

Will try covering the exciter lamp when I have access to the booth

 |  IP: Logged

Gordon McLeod
Film God

Posts: 9525
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 05-07-2019 09:00 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
So it is a excitor not LED type of reader Is it a cinemecanica projector
If so sometimes i have had stray reflections inside the bells of the sound drum reflect perfs back into the reader

 |  IP: Logged

Scott Norwood
Film God

Posts: 8138
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99


 - posted 05-07-2019 09:44 PM      Profile for Scott Norwood   Author's Homepage   Email Scott Norwood   Send New Private Message       Edit/Delete Post 
Does it only hum in mono when playing a particular print? Or do you get hum if you play a Dolby print in a mono format? If the former, then it is possible that your print has shrunk to the point where the soundhead is scanning perfs.

What is the frequency of the hum? If 60Hz or 120Hz, then it's probably an AC or fluorescent light problem. If 24Hz or 48Hz, then it is probably reflected light from the lamphouse. If it is 96Hz, then it is probably perfs being scanned (or a soundtrack that ran off of a sprocket at some point).

One situation that I have seen is that leaving the soundhead door open is often an invitation to weird light reflections that affect the sound. Always leave the door closed when it does not need to be open.

One more thought: if you are using an exciter lamp instead of an LED reader, make sure that the power supply is putting out good DC and is not in the "AC/Emerg" position.

 |  IP: Logged

Stephan Shelley
Jedi Master Film Handler

Posts: 846
From: castro valley, CA, usa
Registered: Nov 2014


 - posted 05-08-2019 04:10 PM      Profile for Stephan Shelley   Email Stephan Shelley   Send New Private Message       Edit/Delete Post 
If it is a specific print check for damage in the optical soundtrack. Also I have seen prints made from shrunken negative where the sprocket holes get printed at the edge of the soundtrack area. May West films come to mind.

 |  IP: Logged

Anhtu Vu
Film Handler

Posts: 97
From: Montreal, Quebec, Canada
Registered: Jun 2013


 - posted 05-09-2019 06:51 PM      Profile for Anhtu Vu   Email Anhtu Vu   Send New Private Message       Edit/Delete Post 
Finally had access to the booth for an hour today.

Here's my finding so far:
- When I turn on everything (projector, lamp etc)...no noises
- When I run the projector with NO film, I hear noises...not necessarily low cycle hum but noises from the 35 mm running. Sounds like the noisy acoustic in the booth is getting picked up.

 |  IP: Logged



All times are Central (GMT -6:00)
This topic comprises 2 pages: 1  2 
 
Post New Topic  Post A Reply Close Topic    Move Topic    Delete Topic    next oldest topic   next newest topic
 - Printer-friendly view of this topic
Hop To:



Powered by Infopop Corporation
UBB.classicTM 6.3.1.2

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.

© 1999-2018 Film-Tech Cinema Systems, LLC. All rights reserved.