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Author Topic: A Chain problem. Cant auto align. Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 08-22-2006 07:49 AM                     "Yes, C.E. LED arrays are just the single row variety." I understood that all the LED pips are made by Dolby, and are two rows of interleaved emitters, certainly all the CE, Kelmar, Kinoton, Cinemecannica and Dolby Cat70x I've ever seen use the same interchangeable LED pip. Once upon a time I carried spare heat sink blocks for all the different units in service, now I just carry pips and heatsink paste.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-22-2006 08:26 AM                     If you have any single array LED's then you have bad LED's. I had one the other day that only had a single row lit... one row was completely out. Aside from Dolby, USL Labs also supplies a red LED although its polarity is backwards from that of Dolby's, its prices a bit less than Dolby's and is very inexpensive when bought in quantity. Just reverse the LED leads at the power supply. Mark  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 08-22-2006 02:29 PM                        There is at least one source of these LEDs that no longer makes them for Dolby. I would be wary of stumbling on this sounce. Quality control was the issue. Louis  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 08-23-2006 07:55 PM                     quote: Mark Gulbrandsen For best A-Chain S/N I generally find the level bars end up at about 2/3 of the way up and then set the LED level inside it's power supply to achieve Dolby Tone. Then once the level is found always use the power supply adjust to get back to Dolby Level. When I install a new LED, I drop the voltage as low as it can go while still able to acheive Dolby Level. Then over the life of the LED, I will increase the optical gain to set Dolby Level, and only increase the power supply voltage if the level setting is maxed out. Mark, what advantage does your method offer?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-23-2006 08:02 PM                     Ken, We are doing exactly the same thing but I've also expereimeented with finding the best S/N of the cell preamps while still acheiving decent LED life. Running cell preamp at max. gain is not necessarily a good thing. The entire processing chain needs to work at its optimum S/N ratio from start to finish. The CP-500 level bars normally seem to fall at about 2/3's full to achieve a decent S/N level from the cell preamp. With USL you have to be even more careful with raising preamp gain too far.... or the result is hissssssssssss. People still do actually play back sound from the analog tracks ya know.... Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-23-2006 08:06 PM                     So Mark...Just what is the S/N level on a CP500 with about 2/3rds gain as opposed to at 50% gain or 100% gain?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-23-2006 08:18 PM                     Steve, I do remember that there can be as much as 4 db of difference in S/N between 2/3 and full gain but I don't remember the actual spec in db. It also depends on where the slit loss is set and what scanner you are using, cabling, etc. Back then it was C.E. or Kelmar and red was brand new. I would encourage you to measure one if you are interested in the exact spec. During set up at an install I measured a few 500's and settled on using 2/3's gain. The LED current is still reasonable this way, these LED's are still going today.... Have not done this with a BACP or CSP-1200. I suspect the CSP would be very good in that department! Mark  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 08-23-2006 11:46 PM                        Mark, if we are using CP-55s and CP-65s, and our 2 Mod-IIB houses, will your methid still work? I understand you don't have a neat little graph to set to, but you can tell the range of the trimpot, set it at around 2/3rds, and adjust the LED till both your dobly tone indicators light up. Would that be a relative equivalent?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-24-2006 12:13 AM                     Charles, I never measured any aspect of a mod-2 so I can't say where it might land. 2/3 of the way up might be a good starting place though. LIke an analog tape recorder I always believed analog film playback A-Chains need to be set up the ame way when it comes to levels so you end up with the best performance that is practical. In this case its a trade off for least amount of gain needed vs. LED life span. Mark  |  IP: Logged Charles Greenlee Jedi Master Film Handler Posts: 801 From: Savannah, Ga, U.S. Registered: Jun 2006 posted 08-24-2006 12:39 AM                        I see, so turning up your LED all the way, could possibly yeild better s/n ratio, but a sharter lifespan. While a lower setting gives you better lifespan, but worse s/n ratio. 2/3rds gives you a long life, with room to adjust if need be. Makes sense, now lets hope I don't have to use it for a while.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 08-24-2006 12:42 AM                     quote: Mark Gulbrandsen With USL you have to be even more careful with raising preamp gain too far.... or the result is hissssssssssss. People still do actually play back sound from the analog tracks ya know.... yea...I'm surrounded by USL analog stuff..and that is a definite truth - watching the preamp gain or you get a house full of snake hissing...I'm prob due then for some LED replacesments then. - Monte  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 08-24-2006 10:28 AM                       At this point Dolby is the only source of Red LEDs. Part # DPN 32075. USL manufactured a similar LED for a time mostly for use with the digital reader where the illumination uniformity is not as critical. It had the problem of being reverse polarity which de-standardized the plug and play combination LED/heatsink RSLH-2 used in both analog and digital BACP readers. They have now discontinued this product so with the exception of some dealer stock, the only Red LED for this purpose is the aforementioned one above.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 08-24-2006 08:45 PM                     And just how do you measure S/N?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-25-2006 12:24 AM                     You will be measuring the actual hiss and other noise genrerated by the electronics relative to the standard level of a test film. The meter is connected to the solor cell preamp card output, or LT/RT in a cinema processor. I use a Sound Technology 1701A Distortion analyzer, an older but still very good piece of test gear that has a very accurate AC RMS volt meter built into it. You can measure it refrenced to either 100% modulated film or to Dolby Level depending on the use of your A Chain. Run the film, set the analyzer to read a refrence level in db on the meter... say 0db... and then stop the film. Step the AC voltmeter range sensitivity up to measure the residual noise in DB of the electronics(combined with the reverse scan electronics and cabling. Read the S/N directly off the meter based on the meters range switch position. A simple definition is: The ratio of the amplitude of a signal to the amount of unwanted interference or noise that is mixed in with it. Measured in decibels (db), signal-to-noise ratio (SNR or S/N) measures the clarity of the signal in a circuit. Hopefully the above makes sense but if anyone else here is able explain it in clearer terminology please post away. P.S., I am not encouraging everyone here to go out and start measuring S/N ratio of cell preamps but one can learn something new if they have access to the tools. Also, the the same thing applies to measuring entire system S/N ratio..... It can help you optimize the output levels of a given processor for best system performance. Mark  |  IP: Logged

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