Film-Tech Forum ARCHIVE: How To Eliminate Buzzing?

This is topic How To Eliminate Buzzing? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Demetris Thoupis (Member # 833) on 10-04-2005, 01:20 PM:

I've almost retroffited all projectors with RED LED Readers. 2 have not been retroffited because of budget for now and I always had this problem. Humming/Buzzing!

Case No.1:
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Smart MOD6 processor
Cinemeccanica V4 projector
Kelmar Stereo Sollar Cell

When lamp is on, even if no film is on projector I have humming and buzzing from the speakers. I have checked for grounding and both the rack and the Projector are grounded properly. Also the processor is grounded properly. I have tried "ungrounding" the processor, rack, projector in several combinations but I was never able to eliminate it completely just reduce it a bit. Any ideas?

Case No.2:
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Unknown Brand Mixer-Preamp with Phono Capabilities
Lexicon Home Theater Processor
Several Amps!
Cinemeccanica V8 Projector
Kelmar Stereo Sollar Cell

Same situation as Case No1. When exciter lamp is on, humming is heard. Tried several ways of grounding the components and checked for proper grounding and it appears ok. I was never able to eliminate the humming again but just lower it. The Sollar cell is connected on the Phono Inputs of the mixed (phono 1).

So. Any ideas?

Posted by Bruce Hansen (Member # 281) on 10-04-2005, 06:39 PM:

Have you checked the filter cap in the excitor power supply?
Block the light from the cell, and see if the hum goes away. If so, try swaping the supply with a known good one.

Is there stray light getting into the cell from the room, or a threading lamp?

Posted by Floyd Justin Newton (Member # 1316) on 10-04-2005, 06:44 PM:

Ground loops?
[Confused]

Posted by Ron L. Funderburg (Member # 3325) on 10-06-2005, 12:35 PM:

If the red LED is not in the right alignment, you can buzz or hum from that as well. The light to high or low will give you a stray light buzz not sure if left or right can affect that. I had a reverse scan problem that was driving me nuts (because an employee must have tried to adjust it) we had a popping in perfect rhythm. It was the sprocket wholes but at the time I found it (after midnight and several complaints) my mind wasn’t working right so I didn’t jump on it right off. Well I looked everything over for a good hour before it dawned on me. When I pushed the light side back in a fraction of a fraction the volume jumped up and the popping dropped out. I then put the oscilloscope on it and made the proper adjustments and it is fine. At least until some over curious projectionist plays again.