Film-Tech Forum ARCHIVE: Christie soundhead alignment problem

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Posted by Jean-Michel Grin (Member # 1360) on 05-14-2007, 02:52 PM:

Hi everyone,

Recently my boss asked me to align some dolby digital basement reader on various Christie P-35GPS.
For this, I used the famous alignement tool from Christie “SK 1994-3”, Like explained by Brad Miller in the “Christie 35mm P-35GPS projector (re-review) “ an oscilloscope, a pc running the DRAS Software, and a Dolby Cat 530 film test loop.
All the bearings on the soundrum shaft was replaced few weeks ago and all readers was perfectly clean.
So I performed the alignement as usual, (I’m more familiar with Component Engineering basement reader on Simplex / Strong Cinema projectors by the way) The result on the scope an on the PC was perfect. [Smile]

The error rate was dramaticly low on the Dolby CP500 processor (3.5 – 4.0 ) Before it was on 6.5 – Fault. All seems me perfect at this time, but when I played the main feature again, the result was a disaster ! [Eek!]

The error rate was ever on “Fault” I tried to re-align the reader with an another test loop, the result was fine, but when I played again the movie: same problem again. I suspected that the print had a bad digital sound track, but I tried with a another print and the result was deceiving too.
On some other P35GPS projector that I aligned the result was fine for one day, and the day after with the same print, the error rate was on “F” again. [Mad]

I have no more idea to solve the problem, but if someone could give me some advice, it will be thankfull
I’m realy deceived with these readers, and I think that the better solution could be to install on each projector a Dolby Cat 702 Digital sound reader. I saw that few years ago in a brand new multiplexe owned by Cinemark in Lima (Peru) when I was there for vacations: They running Christie P-35 projector and penthouse dolby digital reader...

Thanks for Your help and appologyses for my really weak English ! [Roll Eyes]

Posted by Brad Miller (Member # 2) on 05-14-2007, 07:29 PM:

If I recall I got the best result by setting those up with something like 101% or 102% zoom. I know Dolby says not to, but I was able to achieve solid 0s and 1s by doing it that way. It's been 7 years since I messed with them though, so I am very rusty on remembering the specifics.

Also, don't align to the Dolby loop. They are a joke for aligning SRD. Since I am pretty sure you don't have an official Dolby reference loop, assemble a full reel of brand new trailers and run them. Watch the WinDras program and note the alignment settings for each trailer (do not adjust things during this). Afterward look at your notes and find the most "average" trailer in terms of lateral position, jitter, etc. Then use that trailer to cut into loops to do your alignment with. It may not be "Dolby perfect", but it'll get you a lot closer than using that Dolby loop.

Don't forget to adjust your led brightness!!! That is crucial.

Posted by Scott Christopher (Member # 834) on 05-14-2007, 07:59 PM:

I've got a Christie P-35GPS and have had excellent results with the Dolby 69t reference loop. Average readings (used print) 4 - 5.5. New prints have been seen to go down to '0'.

Also check your belt tension, as too much 'slap' in a belt will transfer to the sound head as vertical jitter.

Posted by Mark Gulbrandsen (Member # 72) on 05-14-2007, 10:55 PM:

FWIW: Christie is comming out with a revised belt kit that will include metric type round tooth belts and pulleys as used in the Cine X-35. This should take care of most of the verticle jitter problem that is so common on Christies. The Cine X-35 tracks as good as a penthouse reader. They have promised that this "kit" is going to be inexpensive. I told them there is nothing left to re-design in this projector..... [Confused]

.

Mark

Posted by Monte L Fullmer (Member # 2797) on 05-15-2007, 01:27 AM:

quote: Brad Miller
assemble a full reel of brand new trailers and run them. Watch the WinDras program and note the alignment settings for each trailer (do not adjust things during this). Afterward look at your notes and find the most "average" trailer in terms of lateral position, jitter, etc. Then use that trailer to cut into loops to do your alignment with. It may not be "Dolby perfect", but it'll get you a lot closer than using that Dolby loop.

..that's an interesting, yet practical trick. How'd you come up with this alignment practice version - just a trial and error sort of thing?

Posted by Brad Miller (Member # 2) on 05-15-2007, 02:31 AM:

Ideally you need a piece of reference film from Dolby. At that point you can run it on a reader, tweek the reader to line up perfectly to it's specs, then simply run other reels and find the one that matches up the closest and write down the "offset" from that.

In this guy's case he doesn't have the luxury of an actual calibrated Dolby loop, so finding an "average" is the best route.

Posted by Louis Bornwasser (Member # 3063) on 05-15-2007, 08:32 AM:

If you know anyone at Dolby, you can have a loop "calibrated." This should be locked away as a way to calibrate a system which will be used to "calibrate" any other film loop.

We have not found this set up to be so touchy. Maybe that's because we only do digital alignment with a scope and do not use the dras-10, except for minor touch up.

In fact, we are able to get reliable operation using only the scope and no film. Later using the film to verify and fine tune the system. Louis

[ 05-15-2007, 03:15 PM: Message edited by: Louis Bornwasser ]