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Author Topic: intermittent hum on optical mono Anhtu Vu Film Handler Posts: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 05-04-2019 12:20 PM                     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: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-04-2019 12:22 PM                     I use the Rigol ds1054  |  IP: Logged Anhtu Vu Film Handler Posts: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 05-04-2019 12:26 PM                     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: 854 From: castro valley, CA, usa Registered: Nov 2014 posted 05-04-2019 12:29 PM                     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: 2321 From: Toronto, Canada Registered: Apr 2001 posted 05-05-2019 08:19 AM                     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: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-05-2019 09:28 AM                     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: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 05-05-2019 10:13 AM                     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                     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: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-05-2019 12:48 PM                     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: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 05-05-2019 01:11 PM                       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: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 05-05-2019 04:22 PM                     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: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-07-2019 09:00 AM                     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: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 05-07-2019 09:44 PM                        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: 854 From: castro valley, CA, usa Registered: Nov 2014 posted 05-08-2019 04:10 PM                     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: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 05-09-2019 06:51 PM                     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

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