The peaks of Cat 97 shown on the scope shouldn't be round they should be fairly sharp, look at the illustrations in the early Dolby manuals (CP50) for guidance. IIRC those are actual oscillographs, not drawings.
Back to your predicament.
It's possible that the lens is full of oil and dirt, but I'm a little concerned by your use of Cat 97 to adjust the lens position. You should use buzz track to adjust the laterl relationship between the lens and the film path, then use Cat 97 to adjust the cell relative to the film path. The two adjustments do tend to play off against each other, so you check and adjust each one until you can make no further improvement. Then you set the scanning width accurately.
It's not unconceivable that the cell is damaged, they are fragile and do actually wear in use, especially if static is prevalent.If you really need I'm pretty sure we can supply a
cell and block for a Prevost, but I've no idea at what cost.
Posted by Sam D. Chavez (Member # 1841) on 05-18-2005, 07:50 PM:
I am not certain whether the Prevost lens slit width is adjustable, but it could account for the problem you are having.
The only problem I have wth Pete's procedure is that the Cinemeccanica's lens "iris" closes down unevenly giving you the impression that the lens is over the center of the soundtrack when its not. The best way I have found to get optimum adjustment of the the front scan Cinemeccanica readers is to splice a loop of half Buzz and half 97. This way you can keep working back and forth until slt width and cell postition are both optimized.
I do make a reader for the Prevost P55, P60, P70, P 90 as long as you have your original Prevost film guard and solar cell holder. I also make a reader for older P93's as well.
Commercial message aside, the cell should be pushed as close behind the film as practical.
Posted by Pete Naples (Member # 761) on 05-19-2005, 04:15 PM:
Sam, that's pretty much what I do, although I don't splice together a loop of buzz and Cat97, I run buzz, then left-right, then buzz, then left right, then buzz....., until no further improvements can be made.
If you want to see a slit lens that adjusts width un evenly, try a Projecson laser unit! It adjusts from one side only, which actually isn't that much of a problem. One adjusts lateral scan to get quiet one one side, then adjust the width until the other side shuts up.
Posted by Sam D. Chavez (Member # 1841) on 05-19-2005, 09:39 PM:
Pete,
All my method does is speed the process up as you will eventually break the film rethreading it or run out of patience and choke down the iris wen you get close enough.
I do the entire procedure in X/Y as you can clearly see buzz track modulation as well as the Cat. No. 97 vectors.
Posted by Marin Zorica (Member # 1716) on 12-18-2005, 01:53 PM:
It would be nice that somebody upload good pictures how oscilloscope and spectrum traces looks like when a chain is aligned, because manuals pictures are drowning, so if somebody got real picture from scope and spectral analyzer for A and for B chain as well!
Posted by Marin Zorica (Member # 1716) on 12-20-2005, 05:22 PM:
I got another question.
Should i with cat 69T (Dolby tone) set gain of preamplifier/processor to 0dB reading?
Because i got here equipment what don't have calibration, manual or any kind of documentation, but have VU meter from -25 to 6dB.
So is it Cat 69T 0dB level in movies or Cat 97 (100% modulation)??
Posted by Louis Bornwasser (Member # 3063) on 12-20-2005, 07:49 PM:
My understanding is that Dolby reference level is 50%modulation. Louis
Posted by Gordon McLeod (Member # 33) on 12-20-2005, 08:01 PM:
i guess i will post the question
quote "I got another question.
Should i with cat 69T (Dolby tone) set gain of preamplifier/processor to 0dB reading?"
the cat 69 is the 50% level as such typically 300mv
"Because i got here equipment what don't have calibration, manual or any kind of documentation, but have VU meter from -25 to 6dB."
the manual for all the olby products is on this site what more documentation does one need
So is it Cat 69T 0dB level in movies or Cat 97 (100% modulation)??
RTFM ![[Smile]](smile.gif)
Posted by John Hawkinson (Member # 1135) on 12-20-2005, 10:08 PM:
I think Marin has a non-Dolby processor.
--jhawk
Posted by Marin Zorica (Member # 1716) on 12-21-2005, 02:48 PM:
Yes it's non-dobly processor!
What's RTFM??
Posted by John Hawkinson (Member # 1135) on 12-21-2005, 02:57 PM:
RTFM is a crude way of telling you to "read the instructions."
It would help if you could tell us more about the processor. What model and brand?
The discussion in the other thread about setting levels with Cat69T is about setting the preamplifier levels for proper Dolby A and Dolby SR decoding (300mV). But you seem to be talking about the main output level when you discuss a VU meter from -25dB to 6dB.
This makes it quite confusing. We do not understand your question.
The preamplifier gain needs to be set properly so that Dolby decoding can take place, and that voltage is internal to the processor. If you do not have Dolby decoding, then the preamplifier gain is less critical. Others may have better advice, but I think you probably want to set it to the middle of the range between the minimum sufficient to hear the track and the point at which clipping is noticable.
As for the master output gain of the processor:
When you calibrate the processor, you should set it to a nominal level (probably does not matter much what exactly it is) and inject pink noise into the processor, and adjust for 85dBC from the speakers. Do this once for each channel.
When you play a film, start at the nominal volume level to which the process has been calibrated, and adjust "by ear."
If your question is what nominal level to choose, in your case I would use 0dB, but it is arbitrary (as long as you have sufficient headroom to make soft movies louder and loud movies softer).
--jhawk
Posted by Brad Miller (Member # 2) on 12-21-2005, 03:45 PM:
John, you have never installed a Dolby processor, have you?
First, he has a CP50.
On the CP50 is a card (cat109) with analog meters on them that are used to quickly calibrate dolby level with a dolby tone loop running (make sure you are in MONO when you do that Matthew.) That is what he is referring to.
Remember also he has cat64 cards, not cat64B cards. The levels must be set properly on those or even if everything else in the processor is spot on, he can have distortion.
Also it is important to calibrate the processor with the fader at 7, as it is "stepped" and calibrating at say "4" would end up with slightly skewed balancing between channels (levelwise) and also because 7 is the point in the fader where the lowest noise floor resides. This is why I always laugh when I walk into a theater and find the faders between 4-5. Properly calibrated, the fader should sit at 7 for most features and never go lower than 6, and yes this is without customer complaints. Any machine that has to run lower than 6 either has crappy speakers, poor aiming or was over-EQ'd by a tech looking for that perfect X curve (which causes the end result to sound like ass).
Marin - upload a picture of what the image looks like on your oscilloscope and we can tell you what's wrong. Just seeing a bench perfect alignment image won't help you figure out WHY yours doesn't look like the manual.
Posted by John Hawkinson (Member # 1135) on 12-21-2005, 04:15 PM:
Yes, Brad, of course I have. Though never a non-Dolby processor, which Marin said he had. Perhaps we're confusing Marin and Matthew.
The CP50 doesn't have a built-in fader, though, and any external fader is probably not marked from 0-10.
--jhawk
Posted by System Notices (Member # 2357) on 06-08-2009, 05:38 AM:
It has been 1264 days since the last post.
![[Big Grin]](biggrin.gif)
) but it is depending on your preamp .... The ideal solution is to use transformers as CP-50 do !
