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Author Topic: Audio Crackling DSS220 CAT745 Peter Maddock Film Handler Posts: 19 From: Benalla, Victoria, Australia Registered: May 2013 posted 02-12-2014 01:16 PM                    I have just installed the Odyssey 16 RJ-7.1-DDSY adapter board provided by our installer and it looks better than the original RJ45/D25 adapter and as yet no problems with crackling. Not set up for 7.1 yet but have a few extra cat6 cables ready in case we have more problems. Also waiting on installer to provide 7.1 test files. The DSS220 manual says ensure the rack is well earthed. Installer says < 3 ohm DSS220 chassis to projector chassis. We have yet to test this; perhaps if we have more problems. Cheers Peter.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 02-12-2014 04:03 PM                     Thanks Harold, I was looking for that information!  |  IP: Logged Peter Maddock Film Handler Posts: 19 From: Benalla, Victoria, Australia Registered: May 2013 posted 03-05-2014 09:48 PM                    We are still experiencing crackling problems after installing the Odyssey board. This is a very intermittent problem so it is driving us nuts. Steve, you mentioned wiring cat6 directly to DB25, do you have a wiring diagram for this as apparently Dolby has not published this?  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 03-05-2014 11:22 PM                        This could be a problem in the IMB, the cable, or the CP750. I know you're looking at swapping the cable, but is there other stuff nearby you can swap, perhaps between auditoriums, to see which piece the problem follows? I know that there have been problems with some content and forensic marking, but perhaps those issues have been solved. Also, I think you said there was an indication on the CP-750 that the AES was bad. I do not believe FM problems would show up as AES errors. Good luck! Harold  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 03-06-2014 02:24 AM                     I recently had a crackling issue with a similar setup. I replaced AES cable, connectors at both ends, replaced CP750->amps wiring, re-made amp output connectors, went over rack mains and speaker terminations and re-made all the loudspeaker terminations in the cinema. It sounded like typical crackle from bad connections. It was no better Eventually I traced it as coming from a hand dryer in the downstairs toilets!  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 03-06-2014 05:02 AM                     Peter - can you give a rough estimate on how often and for how long the crackling occurs? The question is - does it happen more or less 'on its own', e.g. due to bad cabling or IMB/CP, or is it strongly related to other gear, e.g. Freezers, HVAC operation, etc.? Do you have a chance to check the status/valid indicators on the CP750 when the crackling occurs? A good common ground between projector/IMB and audio rack is important, although I don't know wether both CAT745 AES outputs and CP750 inputs are transformer coupled. - Carsten  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 03-06-2014 07:12 AM                        I believe they are both transformer coupled. Harold  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-06-2014 07:25 AM                     They most certainly do. Look in the CAT745 installation manual (it is on line at Dolby's customer support web site...registration/authorization is required).  |  IP: Logged Peter Maddock Film Handler Posts: 19 From: Benalla, Victoria, Australia Registered: May 2013 posted 03-06-2014 12:45 PM                    Yesterday we had consistent crackling from the system. We did get some high resistances between the projector, audio rack and CP750; 20 + ohm. We have run some extra earth cables particularly between projector and audio rack and reduced to acceptable levels. After noticing the influence of movement of the CP750 DB25 input plug on the crackling our installer advised us to route the AES audio from the IMB to our Gefen Scaler which on digital bypass goes to the CP750 Multi Channel Analog input. This seems to have eliminated the problem. Our installer thinks there may be a problem with the CP750 input socket. We obtained this unit under warranty as a replacement for a unit which had a greyed display. This unit has the same display problem and our installer advises it may be a refurbished unit, not a new one. Matinee screening this morning so hope all goes well!  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-06-2014 06:16 PM                     What Gefen scaler do you have which decodes 4xAES? The "greyed" display is a known bug. If it's the one I'm thinking, just go to the contrast setting, move the value to whatever and the display will come back to life - till next time.  |  IP: Logged Peter Maddock Film Handler Posts: 19 From: Benalla, Victoria, Australia Registered: May 2013 posted 03-06-2014 07:02 PM                    We are using Gefen A/V Cinema Scaler Pro II. Yes correcting the display can be done by 4 presses of the menu button to the contrast screen. Slight adjustment of the contrast restores the display then 4 more presses of menu gets you back to the main display screen.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-07-2014 02:16 PM                     I did not remember the Cinemascaler pro II had an AES input, cool. Yes, the issue you have is "normal". I suppose they'll fix it at some point but we haven't seen a CP750 FW for a while now.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-07-2014 04:53 PM                     The Gefen Proscalers II and III have both analog and AES inputs...one could place it at the head of any film Cinema processor with 5.1 or 7.1 inputs much the same as a DMA8 Plus or ECI-60 or DAX602  |  IP: Logged Peter Hall Master Film Handler Posts: 314 From: London, UK Registered: Dec 2000 posted 03-10-2014 11:53 AM                        HI We've had similar crackling twice - 1. Where the original install had used Cat5 from a proprietary wall box to the CP. We replaced this with twin screened data cables x 4 earthed in the CP only and it worked a treat 2. A weird one, we ran a new set of screened AES cables from the DB25 adaptor through what was once the exciter lamp power supply conduit (now totally stripped and completely empty, and earthed to the rest of the building's containment). Channels 3 and 4 and 5 and 6 clicked and varied in level, sounding like something was charging up and breaking over (eg sound drops and drops and then CLICK and it is up full again). Measured it, played around to find the noise and eventually ran the cable externally and all was good.  |  IP: Logged Peter Maddock Film Handler Posts: 19 From: Benalla, Victoria, Australia Registered: May 2013 posted 07-03-2014 09:34 PM                    This is an update on this ongoing issue with intermittent audio crackling in our CP750, DSS220 system. In desperation sometime ago we bypassed the Digital 1 input to the CP750 and routed the Cat6 from the IMB to our Gefen Scaler. The Gefen Scaler on Digital Bypass to Multi-Channel Analog input on the CP750 has enabled us to screen without the audio crackle for nearly four months. Recently it appeared there may have been a problem with the 4XAES input socket on the CP750. To eliminate the RJ45 connection to the CP750, which has appeared to be some of our problem we soldered the Cat6 from the IMB to a DB25 plug. On initial testing the crackle returned, perhaps confirming a problem with the input socket. However further testing, before sending the CP750 for repairs the crackle is not occurring. I have uploaded a couple of short videos to you tube. The first one http://youtu.be/rlfqMNi13-0 is in our auditorium. The crackle comes through at the volume setting of the CP750 and the show playback audio is impossible to hear. In these two videos there is no show playback occurring. The second video shows the crackle coming through when the CP750 is set on Discrete on the Centre and LFE channels. When the decode mode is switched to Pro Logic the crackle stops. http://youtu.be/0bKGc7fmVa4 I presume this is because Pro Logic decodes the left and right channels only. So we seem to be back to chasing down a gremlin in our sound system!  |  IP: Logged

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