Film-Tech Forum ARCHIVE: Cinemeccanica DolbyD reader

This is topic Cinemeccanica DolbyD reader in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Antonio Marcheselli (Member # 373) on 07-16-2002, 12:21 PM:

Hi everyone.

I've discovered that in the Dolby Digital reader that I have on my Cinemeccanica projector there are two jumpers that, if in one particular position, can double the ccd sensitivity. Is it true? What are their purposes? isn't it better to have them always on the maximum gain?

Bye
Antonio

Posted by Ken McFall (Member # 845) on 07-16-2002, 12:49 PM:

Yes they do double the gain..... and if possible you should run with them in the high gain setting. This will allow you to turn the led current right down and extend their life considerably.

The only thing to watch out for is that you don't start to introduce noise into the system.

I've re-set mine and the led current setting is now at its minimum, with error rates running in high 1's and 2's.

I'll do the others as time allows. I have all the equipment I need to realign fully but it does take time to get it at its best.

Posted by Richard Fowler (Member # 893) on 07-16-2002, 03:39 PM:

On the older style ( more than two years old ) the gain boost will help to get better LED life vs watching for signal to noise as noted. Cinemeccanica was one of the first to offer basement set-up and early units LED output recommendations where much greater than used today.
Richard Fowler
TVP-Theatre & Video Products Inc. www.tvpmiami.com

Posted by Antonio Marcheselli (Member # 373) on 07-16-2002, 06:36 PM:

thanks for your replies.

what are these jumpers? can i found a datasheet on the internet?

bye
antonio

Posted by Ken McFall (Member # 845) on 07-17-2002, 04:41 AM:

I've sent you two data sheets which should answere all of your questions.

Hope they help.

Posted by Antonio Marcheselli (Member # 373) on 07-17-2002, 05:11 AM:

Yes Ken, Thanks for your help!

Antonio

Posted by Antonio Marcheselli (Member # 373) on 07-18-2002, 04:26 PM:

I've set both of my readers to 2X gain, thanks!

A question: I've read that with a new LED you should stay between 2,5 and 4V. What is a "real" value? I mean, is it normal to reach 4V with a new led without overvolting the LED?

And what is the starting, or normal, voltage for a new led?

Bye!

------------------
Antonio Marcheselli
Florence, Italy

Posted by Ken McFall (Member # 845) on 07-18-2002, 04:40 PM:

Using an ocsilloscope the 'correct' range is between 2.5 & 4v. So provided you are getting a good 'image' on the scope and good consistant readings using the DRAS software, then you should be fine at about 3v.... however its very much a 'suck it and see situation'. Not all led assemblies will give exactly the same results so it depends very much on the situation at the time. The signal voltage should be between the range advised, the led current should be as low as possible to achive the correct signal range!

The actual current the led's are running at is not the same as the signal voltage. One is the result of the other and depends on acurate alignment of the whole assembly.

Its really a job for someone that...
1/ has the correct equipment, without it DON'T GO THERE!
2/ has the time to 'play' and try different alignments.
3/ Who can really be bothered!

If you can find such a person.... do everything you can to hold onto them (him)!!

It's an unfortunate fact that many engineers will walk away saying 'that'll do'! It's your theatre and you should insist on the best..... that's the ideal. Getting it is a very different problem!

Posted by Antonio Marcheselli (Member # 373) on 07-19-2002, 04:37 AM:

Ken,

Thanks for your reply.

I wonder that because our tech stayed half a day to calibrate our new led and was unable to go further than 3V (but led current was not at maximum and withh 2X gain on the CCD). I believe that with a new LED you could reach the 4V easily...

Moreover, our Cinemeccanica led's brackets are not very good, it is almost impossible to setup an iron arm that is hold by just ONE screw at one side.

Bye
Antonio

Posted by Ken McFall (Member # 845) on 07-19-2002, 05:04 AM:

With a brand new led I get 4v at 2X gain with minimum led current, in one screen. This is clearly ideal and gives some room to turn the current up slightly if the error rate gets worse with time as the led ages naturally.

In the other screen I can't get 4v at 2X gain with an older led. I will change it when the error rates climb and I have no head room to play with.

Looking at some of the postings on Test films and alignment issues, how are you ment to set up SRD perfectly anyway. Azimuth varies from reel to reel in most prints, focus seems to drift and nothing is consistent between prints. I have a new print of the SRD jiffy test film. I tried using that to align a system. It looked fine on the computer but when running 'real' film the error rates were very high. So it was back to using new release prints.

Bottom line is how the system operates generally.

In the real world 'ideal' may not be atainable so don't lose any sleep over it. Provided the optical side is aligned correctly, you get consistant low error rates and very few reversions don't waste too much time.

Posted by Gordon McLeod (Member # 33) on 07-19-2002, 09:13 AM:

Unless you know the information on the lateral position of the track the Dras software is not as good as using the scope and "putting the green grass between the goal posts" method

Posted by Antonio Marcheselli (Member # 373) on 07-19-2002, 11:28 AM:

Gordon and Ken,

Our tech used both oscilloscope and DRAS. On the oscilloscope, however, he was not able to set the led to have, without print, 4V of peak voltage. Maximum was 3V with 2X gain and 500mV (mV?) on power supply.
I thought that with a brand new led you should be able to have 4V easily...

Bye
antonio