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Author Topic: Refersher on A-Chain Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 07-31-2012 11:32 AM                        The outboard EQ sounds like it may be the cure for my problems with mono tracks. How does one go about installing it?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-31-2012 11:38 AM                        Most Dolby processors have a "mono EQ" setting. (I can't remember if this is so for the CP650). A tweak of this may be all you need. Louis  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 07-31-2012 01:09 PM                     Louis, while you are technically correct many mono tracks can benefit from more comprehensive EQ than that limited function can provide. That is one reason why the install I mentioned did what they did. And why Victor followed suit. Martin, the EQ I suggested is simply installed in the center channel output line of the processor, between the processor's output and the input to the center channel amp. Any tech can do in in less than 1/2 hour. I recommend the DBX unit I linked to as it is high quality and inexpensive as well as rack-mounted. EDIT: Sorry, I sent the link to Victor by email, so everyone here this is one place to get it: Markertek  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 07-31-2012 02:18 PM                        Louis: Yes, I've played with the Dolby mono EQ, and the results were about the same as Victor's. Every mono print we've run in the last few years has been incredibly shrill, no matter what I do with the Dolby unit. As I mentioned earlier in a different thread, I have a 1950's sound test reel that sounds perfect with no adjustments, but a modern print just sounds like crap. Tony: thanks, I'll look into this.  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 08-06-2012 08:59 PM                     I ended up swapping the new PR 1014 head with my main projector and then swapped that in place of the other projectors flat gate old xl head. I will now use that head for parts. Sound align remained perfect on the main projector 1 but trailer projector 2 has lost it! Tried adjusting the position of the head but cant get Dolby level on the left channel. In fact almost no sound is coming from the left or center while in SR. So swapping heads can effect A chain align. Its mono only for that machine until a new A chain can be done. Picture quality is fantastic on both machines!  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-06-2012 09:43 PM                     Martin...are you using red leds with older prints (non-cyan or high-magenta)? This can cause a shrillness (really cross-mod distortion).  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 08-06-2012 09:59 PM                        yes, we are using red leds. Anyway around this other then reinstalling the exciter lamps (not likely for single show). Hoping the above EQ trick will help. OTOH, we had a print of Goldfinger which came with a digital track and it, too, was shrill. I suspect they didn't do a remix for digital.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 08-07-2012 06:01 AM                     IR LEDs play the older tracks best. The IR leds will NOT play back cyan tracks though.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 08-07-2012 06:25 AM                        So, why is it that the CP650 does not seem to give a very clear trace on the scope when doing an A-chain? (No, adjusting the CRT optical "focus" control on the scope does not help.) I have seen this on two CP650s in two different theatres using the same scope, same pin-tip probes, etc. It's as if there is a bunch of digital background noise in the signal. By contrast, I can get a perfectly sharp image on the scope from a CP65 or CP500, using the test points on the preamp card. This isn't really a problem...I'm just curious. And, no, I don't do A-chain alignments very often, and when I do it is typically with older equipment.  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 08-07-2012 12:05 PM                        Just ran a test of Dr Strangelove and it did not sound shrill even without tweaking. I does sound cavernous, but as I recall, that's how it is supposed to sound. So some mono's are better than others.  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 08-07-2012 12:57 PM                     Victor: You have another problem rather than physical misalignment. You have lost a connection from the reader in the process of the head swap. To move the film far enough out to lose one of the SVA tracks you would have a very visible deflection of the film as it threads through the reader. So double check the cabling to the reader and make sure nothing got pulled out or cut. Scott: I have noticed the same thing on CP650s...it doesn't really affect the adjustment but it is annoying. If I had to guess, what that "noise" is from would be the digital chips in the processor. (Not the Dolby Digital system.) Try to ignore it.  |  IP: Logged Rob J. Buskop Expert Film Handler Posts: 111 From: Rotterdam, the Netherlands Registered: Aug 2005 posted 08-10-2012 02:10 PM                     Interesting to read all this..... About 27 years ago I realised that all theatres, including my own private home cinema sounded worse on academy mono optical films after full modification of the sound system to Dolby. This was the logical result of speaker replacement and B-chain equalising as per Dolby instructions. So what I did, to anniliate this problem was the following: On my (modified) CP-100 I installed some extra circuitry that, whenever mono-opt. is selected, takes the input and output of the Centre Cat.64B and switches these connections, via a relais, over to and external Cat.64 in it's original early Dolby housing. With this equaliser I apply the necessary corrections to emulate the original sound character and quality of the well mixed mono soundtrack. There's also a small switch on the front of the CP-100 that allows you to choose between the internal Cat.64B or the external Cat.64. All other formats automatically switch to the internal equalisation. Works like a dream and I like to consider this a very neat modification. Must say that I've never ever been able to get a proper and excitingly good result with the extremely limited and poorly designed facility that Dolby supplied for mono tweeking on their later processors.  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 08-10-2012 02:34 PM                     Yeah it's like the playback of mono films from the past was given little consideration. Tony,Jarret brought in his scope and we verified that the left channel was still present but weak.The film looked to the naked eye to be running straight from the sprockets through the sound drum. We adjusted laterally to regain the left channel but now the B.A.C.P LED seems to be weak and while balanced,both channels only get to one green light on Dolby level running the cat 69 loop. Thing is LED strength was fine before the head swap? We already cut the resister wires a while ago. Anyway sound for trailers on that projector now sounds decent in SR. Need to get new LED units before the next A & b chain. When digital is installed...  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 08-10-2012 04:15 PM                     Victor: How far out was the lateral? I am suspicious of why that was necessary, if anything more than say one full turn was required. If the levels are even but very low then the LED position needs to be checked and tweeked. Loosen the LED base mounting screws slightly and while running CAT 69T (Dolby tone) twist the mount up and down for maximum level. Tighten the mount when you get max level. Be careful to get the LED itself as close as possible to the film, but not touching it. You also need to check Illumination Uniformity with a CAT 566 loop and an RTA. You will have 6 tones, three per channel, that need to read within 1db of each other all the way across.  |  IP: Logged Victor Liorentas Jedi Master Film Handler Posts: 800 From: london ontario canada Registered: May 2009 posted 11-13-2012 10:47 PM                     Been so busy with our recent booth modifications(Christie 2220,Doremi Showvault IMB and CP750)! The 35mm machines got spread apart a bit, our CP55 eq disabled and connected to the CP750 inputs. Also replaced both analogue leds or rather Rick Long Jr of Cinematronix did! Anyway all our formats sound fantastic now! I still don't know what happened to the left channel on the problem machine after the xl head swap? If I were reading the above posts,I would assume Mr Victor screwed something up when swapping heads But I swear I was insanely careful! I think Tony is right that a connection was lost or led alignment got out of whack.  |  IP: Logged

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