Film-Tech Forum ARCHIVE: A Chain problem. Cant auto align.

This is topic A Chain problem. Cant auto align. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Dubrois (Member # 3042) on 08-19-2006, 06:52 PM:

We have a Cat 701 reader and Cp500 processor. The problem just happened yesterday where I tried to use the Auto Align OPU function. I dont remember the exact error message, but it was something like Out of Range (while running the 69T loop) Did I just not have something set right or is there a problem somewhere? I made sure I had the right loop in and pushed the right buttons. It seems that nothing can auto-align with that projector. It can't auto set the levels or anything. Bad parts somewhere? Thoughts?

Posted by Alan Gilbertson (Member # 242) on 08-19-2006, 07:19 PM:

This is not uncommon at all especially if you have a older loop. If the loop is new and in good shape make sure the sound drum is up to speed before hit the button to auto align. You will also get the error if LED has low voltage. If all this fails just set Dolby Tone manually and everything will be ok

Posted by Louis Bornwasser (Member # 3063) on 08-19-2006, 08:39 PM:

The auto align has always been problematic for me, too, on cp-500. Louis

Posted by Gordon McLeod (Member # 33) on 08-19-2006, 08:45 PM:

I don't believe in auto aign anything If you are competent engineer then aligning it should not be a problem
Often the LED is either faded or out of alignment so it can't get enough gain

Posted by Mark Gulbrandsen (Member # 72) on 08-19-2006, 08:49 PM:

quote: Gordon McLeod
Often the LED is either faded or out of alignment so it can't get enough gain

Also check that both the jumpers are cut on the small reverse scam board. We got a mothafuckin autoaligner on this thread..... [Eek!]

Mark

Posted by Steve Guttag (Member # 268) on 08-19-2006, 09:01 PM:

The CP500 came out prior to the dreaded stupid red LEDs...back when superior S/N was more important (a good thing since it is not the quietest processor)...

Anyway...the Auto Align only works if the levels are around the middle of the range. If they are above about 2/3rds -3/4 the way up, it will complain about being out of range.

With red LEDs, the goal is to keep them running as dim and noisey as possible...as such the level bars are going to tend towards the upper part of the CP500s range.

Posted by Frank Dubrois (Member # 3042) on 08-19-2006, 10:51 PM:

Steve,

The levels are near the bottom. The LED is new (about 3 months old). If I manually raise the levels then try to autoalign, it should work?

Posted by Scott Norwood (Member # 30) on 08-19-2006, 11:00 PM:

You do realize that there is more to an A-chain than simply setting the Dolby levels, correct?

Have you read the installation manual (not just the operator's manual) for the CP500?

Posted by Mark Gulbrandsen (Member # 72) on 08-19-2006, 11:19 PM:

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. The LED will last longest this way. This is also the main reason for not using the auto level align feature. With the 500 there will always be somewhat of a trade off for noise vs. LED life span. I maintain a gob of 500's and this has worked well in the majority of them that have Kelmar or C.E. scanners.

Mark

Posted by Frank Dubrois (Member # 3042) on 08-19-2006, 11:28 PM:

quote: Scott Norwood
You do realize that there is more to an A-chain than simply setting the Dolby levels, correct?

Ummm...yes...I do.

Posted by Tim Reed (Member # 137) on 08-19-2006, 11:59 PM:

quote: Gordon McLeod
I don't believe in auto aign anything

Amen, brother! I never used that feature, either.

Posted by Charles Greenlee (Member # 3856) on 08-20-2006, 12:35 AM:

When I was at the Wynnsong, our CP500s wouldn't autoalign for crap. I'd maybe get one or 2 to. I'd almost always have to manually align. Good point on adjusting the power on the LED, I'll remember that for later. The aligning on the processor is more for fine tuning. If you are not already in the ballpark, you need to check your other adjustments. Like the LED power, or life, or physical alginment. If you are just a slight bit off, then aligning in the processor is fine, but you should get as close as possible prior.

Ours, BTW, did suffer the problem of being to high to auto align, but were aligned real well left to right, so adjusting the LED juice would have fixed that at the source.

Posted by Monte L Fullmer (Member # 2797) on 08-20-2006, 03:52 AM:

...even though the LED's are not that old..are all of the arrays within the LED lit up being that there is a good dozen arrays per row and two rows of arrays..

Found this out the hard way as well..tried to do autoalign and got the "out of range" flag, so did the manual but couldn't get the levels where I wanted them to be. Thus, took a piece of tail lead from a trailer that is black to use as a viewer to look through at the brilliance of the LED and not expose my vision to the brightness, and I saw 5 arrays burnt out-3 on top row and 2 on the bottom row.

Time for the change.. - Monte

Posted by Eric Robinson (Member # 2966) on 08-22-2006, 01:18 AM:

As far as I knew there was only one row of LED's. I have only been exposed to Component Engineering, Simplex basement readers though. Are there other LEDS with more than one row?

Posted by Monte L Fullmer (Member # 2797) on 08-22-2006, 05:20 AM:

the Dolby Optical LED units in the newer Simplex 5-star units are in a two row array setup.

Yes, C.E. LED arrays are just the single row variety.

Posted by Pete Naples (Member # 761) on 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.

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Louis Bornwasser (Member # 3063) on 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

Posted by Ken Lackner (Member # 1002) on 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?

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Steve Guttag (Member # 268) on 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?

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Charles Greenlee (Member # 3856) on 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?

Posted by Mark Gulbrandsen (Member # 72) on 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

Posted by Charles Greenlee (Member # 3856) on 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.

Posted by Monte L Fullmer (Member # 2797) on 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

Posted by Sam D. Chavez (Member # 1841) on 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.

Posted by Ken Lackner (Member # 1002) on 08-24-2006, 08:45 PM:

And just how do you measure S/N?

Posted by Mark Gulbrandsen (Member # 72) on 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