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Author Topic: CP55 non-sync buzz Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-06-2009 09:28 PM                     Here is the situation: -CP55 has a buzz ONLY when in the non-sync format, but only when a signal is connected to the non-sync inputs -Signal is coming from a distribution amp -Identical processor, amps, distribution amp signal, etc. are being used in a second auditorium with no buzz -The only difference between the two systems is that the one with the buzz is 50 feet from the sound rack containing the distribution amp so there is a 50 foot run of shielded cable between the racks for the non-sync signal -Checked all wiring and grounds and there are no apparent problems with the wiring Not sure what else to check. Could there be a problem with one of the cards in the CP55? Perhaps there is another explanation. Any help would be appreciated. Thanks.  |  IP: Logged Elia Orselli Film Handler Posts: 42 From: Imola, Bologna, Italy Registered: Feb 2008 posted 06-07-2009 02:20 AM                        I have the same problem with aux input, but I'm sure that in my cinema the reason is that the cable has some shielding problem and it run from a side of the booth to the other where there's the audio rack. Because this cable is the link between a dvd reader and a surround processor, I'm going to change the processor with a digital one and the shielded cable with a toslink one. Bye Elia Orselli  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 06-07-2009 03:51 AM                     Try hooking a direct source near the CP to see if it goes away. Then work your way backwards  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 06-07-2009 07:00 AM                        Any cable can pick up hum or buzz depending upon what it is near. I would get another (much longer) cable and run it on the floor to see if it also has hum. If not, then you need to reroute the original cable. btw: most cinemas use the incorrect cable. If you are using a Smart distribution amp, a 2 conductor shielded cable is NOT correct; you are mixing l/r together under the shield. You either need 2 of these cables or its equivalent. Shield connected at one end only. Louis  |  IP: Logged Scott Christopher Film Handler Posts: 69 From: Adelaide, South Australia Registered: Apr 2001 posted 06-07-2009 08:26 PM                     I had this problem with the CP500 & CP650. It turns out it was a ground loop which was fixed by installing an ground loop isolation transformer. You can buy them already with male/female RCA's attached. This also fixed a problem of the play button on a DVD player not responding all the time on a CP500.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 06-08-2009 05:49 AM                        Of course it's always best to try to discover where wiring it faulty and what's creating ground loop hum in the first place, but that can be tricky in large, complicated systems. Barring that, try this in a pinch: Ground Loop Isolator - RCA Unbalanced from MCM Electronics. It's cheap enough to keep in your tool box so that you always have one handy to stick into an unbalanced circuit to see if a ground loop is the culprit. If it is and this box eliminates the hum, then you can try to find the loop and eliminate it; or, just leave the unit in place and buy another one for your tool box.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 06-08-2009 01:22 PM                     What isn't mentioned is what brand of distribution amp is used If it is a smart swap the auditorium feeds and see if the problem moves that would determine if it is the card If it doesn't move then I would suspect the wireing  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 06-08-2009 07:25 PM                     So I decided to purchase a $16 ground loop isolator from radio shack just to see if it would solve the problem. It did and I'm satisfied just leaving the isolator hooked up permanently. Thanks for all of the help. I'm still confused as to where the buzz was coming from. I have a second auditorium and lobby music all coming from the same distribution amp with no buzz or hum at all. I even swapped the outputs to rule out any problems with the output channels. But, like I said, I'm fine with having the ground loop isolator hooked up to eliminate the buzz. Thanks again.  |  IP: Logged Scott Christopher Film Handler Posts: 69 From: Adelaide, South Australia Registered: Apr 2001 posted 06-08-2009 09:52 PM                     We had an isolation transformer at every amp rack for the NS1 feed to eliminate possible loops between equipment - It works well.  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 06-09-2009 01:10 AM                     Sometimes when I have buzzing problems I connect a heavy gauge wire to the rear metal frames of all equipment involved. This usually takes care of the problem. This may not be good advice though. If it works; however, someone should be able to explain to you why this technique is working.  |  IP: Logged

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