my profile | my password | search | faq & rules | forum home

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Harmonic Buzzing Noise in Analog

Author Topic: Harmonic Buzzing Noise in Analog Danial Simmonds Expert Film Handler Posts: 107 From: Kota Damansara, Selangor, Malaysia Registered: Jan 2008 posted 06-25-2009 03:36 AM                        Hello again, I have came across a very weird problem. I guarantee it is nothing to do with A-Chain. From the front channel speakers, subwoofers and surround there is this buzzing noise that is like the electrical harmonic noise coming from them. I have literally tried almost everything. I have done the A-Chain and B-Chain alignment, swapped all the cards of the CP500 and even swapped the QSC Amps... This problem only occurred after a huge renovation was made opening an IT center above the cinema. If you guys got any ideas please let me know. Thanks alot... Regards Danial  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-25-2009 03:08 PM                     Disconnect all sources that fed the cp and see if it is still there if not then add one source at a time till it reappears and then start looking at it. If it is still there with the cp with no sources connected then try disconnecting the cp output and see if the noise is there  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-25-2009 08:09 PM                        CP-500: there is supposed to be a small jumper from one of the LOW on the output plug to the chassis. (I use the sub woofer LOW.) This is not in the older manuals and is quite often missing. Hope it helps. Louis  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 06-29-2009 10:07 PM                     Yes...follow Gordons advice. Also, you can hook an oscilloscope up to the output of one of your amps far a visual of the buzz. This way you can see when you have eliminated it.  |  IP: Logged Danial Simmonds Expert Film Handler Posts: 107 From: Kota Damansara, Selangor, Malaysia Registered: Jan 2008 posted 06-30-2009 01:02 AM                        Hey guys, Thanks, i found that the problem is definitely from electricity. The noise will only go away after i disconnect the power for the analog pre-amp card located at the projector or disconnect the optical input behind the processor... The projector is V5 Cinemeccanica... I got a power converter 240VAC to 24VDC and took a different power source and the noise disappear. The noise only happens in Analog. Digital and other sources is okay. However this problem only started after a new floor (Computer shops and mobiles) was opened above the cineplex. What you guys think? Thanks Danial  |  IP: Logged Hugh McCullough Expert Film Handler Posts: 147 From: Old Coulsdon, Surrey, UK Registered: Jan 2003 posted 06-30-2009 05:07 AM                        Danial. Had a similar problem in the 1970s. We suddenly started to pick up a low buzzing on both optical, and magnetic sound. No digital in those days. We eventually traced the problem to the Underground station next door. They had had the station refurbished, and a new escalator installed. It was the motor of this escalator that we were picking up. We contacted the underground people, and within about two days they had cured the problem at their end. Has this new floor above the cinema got an escalator, or some other motorised machinery that could be causing the trouble?  |  IP: Logged Danial Simmonds Expert Film Handler Posts: 107 From: Kota Damansara, Selangor, Malaysia Registered: Jan 2008 posted 06-30-2009 09:48 AM                        Well ya, they had placed a total of 2 new escalator's right in front of the cinema, and also they tapped in the electricity just right before the cinema termination... But the shopping mall doesn't want to do anything.. would there be a solution around this?  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 06-30-2009 12:55 PM                        Years ago, I had an intermittent whining sound in an audio studio I ran. I eventually traced it to a building next door. The owners had upgraded their elevator, including a new hoist with an electronic power supply. The problem was similar to the interference you can get when cheap light dimmers are hooked up nearby. In this case, the SCRs in the motor's variable power supply were not filtered. It only took some capacitors across the input power to fix the problem. Something along those lines might be what's happening to you, and filtering at the offending equipment could take care of the problem.  |  IP: Logged Danial Simmonds Expert Film Handler Posts: 107 From: Kota Damansara, Selangor, Malaysia Registered: Jan 2008 posted 06-30-2009 09:37 PM                        Hi Jack, Thanks for the reply... So i should try to put capacitors at the power input to the analog pre-amp? Thanks Dan.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 06-30-2009 10:24 PM                        If your situation is similar to mine, the best place to install filters is where the power goes into the offending equipment. That prevents the interference from going into the power system in the first place. I wasn't able to eliminate the problem until I did that. Jack  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 06-30-2009 10:33 PM                     I had a similar problem when I installed a screening room in Houston. There was a factory about 100 yards from the office park and the company made railroad tank cars. You can imagine the types of welding equipment they had over there... the stuff threw back so much garbage onto the power line that you could see it in the projected light on the screen. The only cure there that worked was to install switching power supplies for the lamphouses. Mark  |  IP: Logged Justin Gorka Expert Film Handler Posts: 174 From: High Wycombe, England Registered: Apr 2006 posted 07-03-2009 05:59 PM                     Deaf loop? I had it a few years back. Do you have deaf loop? If so check all the cables in the trunking. One minor short will do the job(Coke normally is good at it!)  |  IP: Logged Danial Simmonds Expert Film Handler Posts: 107 From: Kota Damansara, Selangor, Malaysia Registered: Jan 2008 posted 07-03-2009 09:47 PM                        Now the offending supply to the projector is a 3 phase power input, were using cinemeccanica machine's here and the power for the analog is taken from one of the 3phase lines... However what i did was this; I took the power source "single phase" from another power point in the projection room, hooked it up to a 230VAC Step down 24VDC for the analog pre-amp power and it did got rid of the noise for 2 halls but the rest it only reduced it... Any suggestions on where and what filters to install? Thank you all for your kind advice :-) Regards Dan.  |  IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

Hop To: Select a Forum: Category: Operations -------------------- Digital Cinema Forum Film Handlers' Forum Large Format Forum Ground Level Feature Info, Trailer Attachments & REAL Credit Offsets Category: Community -------------------- Film-Yak Film Handlers' Movie Reviews The Afterlife Bob Maar's Joke-A-Thon Category: Classified -------------------- Equipment and Supplies Wanted/For Sale Help Wanted/Seeking Employment Category: System -------------------- Software Beta Testing Forum

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.