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Author Topic: IREM Rectifiers humming really badly Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 06-12-2009 12:24 PM                        Not quite sure what's going on here, but when we set up the projection tower this year, we did everything exactly the same (or so we think) as we've done every year with the IREM rectifiers down at the bottom of the tower. While they always had what I considered a normal level of 60hz hum, this year we fired up the lamphouse (4500A) last night and the hum from these babies was probably 3 times louder than usual. I mean, we could hear it all over the field. The lamps seem to be buring normally at the proper 160amps and voltage, nice bright light, no flicker. What is making me scratch my head is that BOTH units are humming loudly. The screws in the side panels are all tight -- anyway the hum doesn't seem to be coming from the metal on metal casing, it seems to be coming from the windings. Short of building a containment box around the rectifiers, any suggestions as to what could be the making these things hum so loudly? I am almost tempted to take a SPL reading a few feet away from them to see what I get and let you know. I know this can't be the normal operating noise because I would have balked about it years ago. This is new. And damn annoying.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 06-12-2009 01:20 PM                     The Irem rectifiers have adjustment screws inside you can tweeq to silence them and they do work! They are called Magnetic Shunt Adjustment. They are shunts between the toroidal coils or whatever you call them with two adjustment screws and one locking screw (middle one). You unscrew a bit the middle and then try screwing or unscrewing (jeez it sounds bad) the external screws until you can achieve the lowest of hum. Sometimes screwing them achieves a better result so don't hesitate to experiment. Don't worry about it. It can be fixed in no time. Demetris  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 06-12-2009 01:23 PM                       quote: Demetris Thoupis Sometimes screwing them achieves a better result I know that works for me.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 06-12-2009 02:01 PM                     pay GREAT attention when you put your iron screwdriver by the big coils while they're working. The magnetic field will attract the screwdriver toward the coils! Wear rubber gloves and guide the screwdriver with your hands while adjusting. You'd better find a plastic screwdriver, I heard that they can be found. Marco  |  IP: Logged Robert E. Allen Phenomenal Film Handler Posts: 1078 From: Checotah, Oklahoma Registered: Jul 2002 posted 06-12-2009 02:31 PM                     When I worked the booth at the local CineMark 15 we had one of the Christie units that hummed loudly when started. It eventually quieted down some but the tech said it was the windings on the transformer, said it was nothing to worry about and made no attempt to fix it. But it sure was annoying. I'm surprised the customers didn't hear it in the auditorium.  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 06-12-2009 05:27 PM                     There is a written procedure for reducing the hum with IREM rectifiers; I'm pretty sure it's in the manuals section. But, note it was written for the free-standing units, not when they are mounted sideways in a console. I never felt the screwdriver was going to get pulled in to the windings. It does 'buzz' in your hand when you reach in, but follow the usual precautions for working on live equipment will and you'll be OK. When I was working on several IREMs, I finally went and got a brass screwdriver which isn't affected by a magnetic fields. Note that some IREM just can't be made quiet. The hum will go down, but returns shortly.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 06-12-2009 05:54 PM                     I don't know, in my case I had to keep hard the screwdriver from being attracted by the coils. Perhaps I'm wrong and the screwdrivers wouldn't have been anywhere, just vibrating... Marco  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 06-12-2009 08:51 PM                     Frank, Just stand next to the Irem thats humming and along with it you hum out of phase and that'll cancel the hum completely... problem solved! Actually, be careful tightening the screws and tighten them in 1/8 to 1/4 turns... Don't get carried away, tighten just enough to calm it down. You want the same tension on all three cores. If I had a buck for each Irem I had to take apart and tighten I'd be two years closer to retirement! Not that far from it now actually... Mark  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 06-13-2009 12:09 AM                        Thanks guys. I'll give it a shot. And Mark, don't think it didn't cross my mind to put a subwoofer next to them and pump 60hz out of phase. And of course that would work with only 50% of the audience --the other 50% we'd have to give those Bose noice-cancelling headsets....and wash them after each show like the Dolby 3D glasses.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-13-2009 08:36 AM                        Remember you are shifting the shunt(s). (Loosen one side to allow the other side to "push.") "Tuning" really is the right word. I have never failed to get a 99% decrease in volume. Then go back to the other two and repeat. Finally be sure the shunt-adjusting-screw (knob) is not frozen as a result of misalignment of the 3 shunts. Louis  |  IP: Logged

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