Film-Tech Forum ARCHIVE: Analog Hum...

This is topic Analog Hum... in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Andrew Bangs (Member # 4938) on 10-01-2008, 01:31 AM:

Yes it is me again! (Today I nearly screamed!) One of my projectors (a different one than from before) Switched over to analog sound today for the first 15 min of the presentation with a dull humming noise. Once the Dolby Digital finally kicked back in the hum went away so I know it has to be something in the Analog Half. (As long as it stays in Digital this is not a major problem but still something that needs to be addressed and fixed as far as I am concerned). What could cause this "Hum" so I can start looking around. I already checked my Alignment and it was good, or at least the hum stayed consistent when I moved the beam. When the beam was moved out of the way (of course) all sound including the hum went away. So my thinking is it is either something on the camera lens on the beam or on the analog Soundtrack. I thought I cleaned both the Camera lens and beam emitter but I could check it again. It also sounds like it could be some sort of ground buzz. All I know for sure right now is it is not "whirr". Please Let me know if I am hot or cold on any of this. As always all input is wanted and helpful.

P.S. Does anyone know if their is a way to upload sound files here so that I could share this wonderful noise and perhaps get some better feedback. (no pun intended)

Posted by Monte L Fullmer (Member # 2797) on 10-01-2008, 02:01 AM:

Got a flourscent light nearby that the camera could be picking up the light from?

Did you try to shade any stray light from the reader area and see if the hum was reduced or disappeared?

Posted by Aaron Sisemore (Member # 145) on 10-01-2008, 02:06 AM:

If its 96Hz hum you are picking up sprocket holes with your reader.

An alignment would be in order, unless there was a tension problem in the soundhead film path causing the problem.

-Aaron

Posted by Jim Cassedy (Member # 4115) on 10-01-2008, 09:48 AM:

quote:
"When the beam was moved out of the way (of course) all sound including the hum went away." AND "It also sounds like it could be some sort of ground buzz."

If the noise went away when you moved the light beam off of the photosensor, I think that would eliminate the bad ground theory.

It would help to know what type of analog soundhead and/or reader you have.

And I also agree that a sound file of the noise would be some help in troubleshooting. One man's 'hum' is another man's 'buzz' if you know what I mean. It can be a subjective term.

Posted by Kenneth Wuepper (Member # 1174) on 10-01-2008, 02:53 PM:

Andrew,

Try placing a business card in the path from the light source to the "camera". If the noise goes away, it could be from ripple in the power supplied to the "beam source" in your system.

If you have an AC meter, you could measure the amount of AC that is present on the DC power to the "beam source". I assume that this "beam source" is an array of red light emitting diodes (LEDs).

KEN

Posted by Andrew Bangs (Member # 4938) on 10-01-2008, 07:51 PM:

I now have the same problem on another projector the one that was giving me problems before. In both cases the problem was preceded by the Dampening Sprocket freezing up.

Posted by John Wilson (Member # 269) on 10-02-2008, 06:48 PM:

quote:
Analog Hum...

...'cos he don't know de words. [Wink]

Posted by Andrew Bangs (Member # 4938) on 10-03-2008, 12:58 AM:

ha ha ha... Actually that helps only because I have had a night from hell and just being able to smile a bit makes a world of difference.

Cheers! [beer]

Posted by John Wilson (Member # 269) on 10-03-2008, 02:36 AM:

[thumbsup]

Posted by Don Sneed (Member # 955) on 10-25-2008, 11:26 PM:

(1) Is there hum in the sound without the proj. running ?? if not,
(2) is there hum in the sound with the proj. running without film?
if not, then it's your reader alignment,
(3) next question is what type of reader, what type of sound head ? (4) Final how did you check the alignment, with buzz track ?

could be a couple of things, the reader, tracking, sound processor,
or the system just can't learn the words so it hummmms !!!!