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

» Film-Tech Forum ARCHIVE   » Operations   » Digital Cinema Forum   » audio buzzing: Doremi IMB HDMI

Author Topic: audio buzzing: Doremi IMB HDMI Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 09-18-2011 05:18 PM                     This has been my month for ground loop problems. This one has me stumped though. Here is my scenario. I have a BluRay player which is connected to my Barco Series II DP2K projector with integrated Doremi media block (IMB) via an HDMI cable from the BluRay out to the IMB in. The BluRay analog Left Right audio outputs are connected to a CP500 non-sync 1 input. When the HDMI cable is unplugged, there is no hum on non-sync 1 when connected to BluRay analog audio outputs. The moment that the HDMI cable makes contact with the IMB, a hum is present. So far I have reduced the hum by: 1) Connecting the IMB gound plane to the CP500 frame with a very thick wire (10 gauge) 2) Connected the CP500 output grounds to the frame ground of the 500. Nothing else I do seems to reduce it any further. I also tried an experiment in which I reversed the tip and ground of the non-sync cable on one side (made hum worse.) 3) I also tried connecting to non-sync without the ground wire by clipping the ground/shield wire midway through the cable, I still got sound but there was still hum. To top it off, I have this same problem on every projection system. The BluRay player has been substituted by several different devices. Thoughts?  |  IP: Logged Bajsic Bojan Expert Film Handler Posts: 190 From: Ljubljana, Si, Eu Registered: Aug 2008 posted 09-18-2011 05:31 PM                     Try putting a transformer isolator (we use a fairly inexpensive ART T8) between the bluray player and the cp500. Usually does away with most of our grounding problems.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-18-2011 07:14 PM                     Yep. Two-Channel passive DI-Box will most likely solve the issue. - Carsten  |  IP: Logged Phil Ranucci Expert Film Handler Posts: 236 From: Carpinteria,CA, United States Registered: May 2006 posted 09-19-2011 02:51 AM                     Grounding is a pain. The best idea is one path to ground. How is the Barco powered? Does the pedestal have a circuit breaker panel for distribution, or did they run conduit directly to the machine? Did they run a ground back to the breaker panel? Does the series 2 have a separate 110VAC power input for the electronics? If so, have you tried powering the blu-ray from the same source? Does your audio rack get it's power from the same panel as the Barco? A direct box will probably clear it up. But it's interesting that you have this problem on every screen. Sounds like an issue with the electrical system in the building. Have you measured with a VOM AC to ground and between the CP 500 chassis and the blu-ray chassis?  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 09-19-2011 01:02 PM                     quote: Phil Ranucci How is the Barco powered? Single Phase 220VAC - 2 hots / one ground quote: Phil Ranucci Does the pedestal have a circuit breaker panel for distribution? No direct line to breaker. quote: Phil Ranucci Did they run a ground back to the breaker panel? Yes. quote: Phil Ranucci Does the series 2 have a separate 110VAC power input for the electronics? Yes. I have used this one for the BluRay and I have used the soundrack outlet with no difference. The 120V circuit in the Barco base is a separate circuit from the Barco 220V circuit. FYI quote: Phil Ranucci Does your audio rack get it's power from the same panel as the Barco? Yes quote: Phil Ranucci Sounds like an issue with the electrical system in the building. Yes possibly. Note also that when the house lights are dimmed and raised, you can hear the humm frequency change. If the house lights are just shut off completely, there is just a lower steady hum. quote: Phil Ranucci Have you measured with a VOM AC to ground and between the CP 500 chassis and the blu-ray chassis? Yes 25mV AC.  |  IP: Logged Phil Ranucci Expert Film Handler Posts: 236 From: Carpinteria,CA, United States Registered: May 2006 posted 09-19-2011 02:34 PM                     possibly running a ground wire between the blu-ray chassis and the CP500 would help. The dimmer noise might be a clue,also. Any chance the neutral and ground are tied together and your ground isn't really grounded? I think that 25mv is a lot of potential, especially when dealing with a -10 RCA signal  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 09-19-2011 04:26 PM                     The ns input of the cp500 is unbalanced so you will need a pair of transformers to isolate it from the audio system you can get transformer direct boxes from most music rental places avoid the active ones or buy 2 txmr from jensen that are 10k:10k  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 09-19-2011 04:53 PM                     It looks like the Jensen JT-11P-1 would be a good choice. I'll give it a try. The unit from Art looks nice too, I may try one of those at another theatre. Thanks for the tips :-)  |  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.