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

» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » dolby level in cp50

Author Topic: dolby level in cp50 Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 04-25-2007 11:00 AM                     A situation of a cp50 where I suspect the ballistics of the meters are completely off. Should the level on the preamp test points with dolby tone be 300 or 500mv for correct noise reduction. There is something written in the schematics that is unreadable. C.  |  IP: Logged Raphael Friedland Film Handler Posts: 37 From: Raanana Israel Registered: Nov 2005 posted 04-25-2007 02:50 PM                     Connect a voltmeter to Rt and ground and adjust level to 775mV and the same for Lt.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-25-2007 03:19 PM                        Most of those little meters (Cat 109 card) are worthless by now. Louis  |  IP: Logged Marin Zorica Jedi Master Film Handler Posts: 671 From: Biograd na Moru, Croatia Registered: May 2003 posted 04-25-2007 03:32 PM                     300mV RMS with Cat.No. 69T Dolby Tone!  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-25-2007 06:20 PM                     Yes, 300mV on the Cat 108 test points should correspond to Dolby Level on the Cat 109 meter. Mind you the Cat 109 was created to take advantage of existing technology, like many things in the CP50. So, the signal that feeds the meter in the Cat 109 comes from the Cat 22 (or Cat 280) from a different signal path than the actual signal itself. The voltage level coming from the Cat 22 (Cat 280T) is actually 1.85V that feeds the meter circuit. The signal that feeds the rest of the processor is at 500mV after it leaves the Cat 22 but it is at 300mV when it enters the Cat 22. Electrically, there isn't much to go wrong with the meter circuit...there are no caps to dry out but that does not speak for the line amplifier that feeds it from the NR card. There is always a chance of any component failure though I would find it odd if both meters failed at the same time. Mechanically, that is another story. I've seen them come unstuck from the PCB, the meters stick...etc. The meter movement itself was never precision...it has exactly one point of accuracy and it was calibrated when the PCB was assembled via resistors R121 and R123 in parallel with each other limit the current to the circuit prior to rectification. Using appropriate values of resistors for R121, R123, the technican would calibrate the meter at Dolby. Steve  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 04-25-2007 09:43 PM                     Silly point or perhaps more of a pet hate, Is the dolby tone loop in new condition? It amazes me how many loops from 1992 (exaggeration) are still being used for setting the levels. Obviously if its worn, you will not get the correct levels in the first place.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 04-25-2007 11:03 PM                     Wear will be more of an issue on pinknoise rather than tone  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 04-26-2007 01:55 AM                     300mv I'll do. Thank you all. Thank you Steve for the detailed explanation, when I'll have some time I will try tinker with the resistors on cat109. Asside the meter inconvenience the processor works perfectly, with upgraded cards and a SRA5 unit that I attached two days ago. C.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-26-2007 08:23 AM                     Again, make sure it isn't the Cat 22s throwing the meters off...try swapping the cards out or even transposing them to see if the levels change. Steve  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 04-26-2007 03:45 PM                     I already did that Steve, using three cat 22 cards. All of them at L & R position gave me with 300mv reference at cat108 test points: 1.84v at cat22 pin 2 that drives the meters and 504mv at Lt & Rt input of cat109. The left ch. meter always just below dot, while right ch. meter at middle of dot and upper end. Two more things. a. Where, at cat109, are the leads that power the meters' light bulbs? I know this consumes power, but its only just out of curiosity. b. I have a spare older cat117 that someone messed with it damaging two components. I want to replace them so the card can be functional, just in case. Again on the schematic its difficult to read clearly the values. So if you remember or have a large schematic on hand what are the values of C906 capacitor and R909 resistor. C.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-26-2007 04:36 PM                     C906 = 22uF/16V R909 = 8.2K The meter lights are powered by those two solder on tabs on the top side of the meter. They draw about 20mA at about 12VDC. Both +/- 12V are available on the card (and you probably only have about 10V or so on those rails in a typical CP50 unless you have the Cat 114C (it has a bit more juice to it). I suppose you could tag one meter to each power rail (to load them idetically so one isn't higher than the other). I looked at a Cat 109 On of the resistors that sets the meter calibration seems to be uniformly 3.3K and only a 5% resistor that that. The other resistor seems to be the one they varied. On the card I'm looking at...one has a 10K 5% resistor and the other has a 15.4K 1% resistor so there is a bit of a range there. If you really want to dial it in...mount a pair of 25K pots in place of the varied resistor and tweek as needed. Steve  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 04-27-2007 01:35 AM                     Thanks Steve. Its an upgraded processor with cat114C quote: Steve Guttag mount a pair of 25K pots in place of the varied resistor and tweek as needed. The best solution. I'll do. I meant should I connect the bulbs direct to the power rails or there is an outlet on the pcb for that purpose. C.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-27-2007 08:49 AM                     I'm unaware of any Cat 109s that lit up the lamps. I think they were only lit in the various 360 series frames. As such, I don't think there are specific tie points to light them up so you would need to tie them to the rails. Steve  |  IP: Logged Christos Mitsakis Expert Film Handler Posts: 242 From: Ag.Paraskevi, ATHENS, GREECE Registered: Sep 1999 posted 04-27-2007 12:56 PM                     Thanks Steve. I don't intend to leave the lights on during normal operation. just because I saw some pics of the cp50 with the meter lights on I presumed there would be a power outlet on the cat109. C.  |  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.