This is topic Dolby CP-50 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Dave Williams (Member # 299) on 01-18-2000, 10:57 PM:
One of my auditoriums is powered by the great and all powerful Dolby CP-50 (please dont laugh, I dont find it funny at all, haha). Problem is it is NOT and I repeat NOT doing a very good job of separating the sound. It sounds as if the Left and Right Channels are mixed together to create the Center Channel and the Surround Channel. Has anyone had any problems of this nature with the CP-50? If so what was the solution?
For information, this unit had failed and was totally changed out with spare parts, and I mean all the parts eventually were changed including the main board, so it is actually a different unit but still does the same problem of not separating the sound.
Any help is greatful...
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"If it's not worth doing, I have allready been there and done it"
Posted by John Walsh (Member # 168) on 01-18-2000, 11:16 PM:
Remove the Cat. 110 card and see what revision it is. I wouldn't be surprised if someone had switch out any newer rev cards that were in it and replaced them with older revs.Dolby has a list somewhere that tells you what the current rev is of the boards used. If they are really old then you might want to upgrade.
I'm assuming that you have run some tests like crosstalk and Dolby level film, and have ruled out bad cards or alignment, etc.
Posted by Richard Hamilton (Member # 321) on 01-19-2000, 12:04 AM:
it sounds like the a-chain is bad. I would be curious what kind of sound head you have, and what kind of slit lens? It's obvious you don't have a reverse scan, right?
Posted by Dave Williams (Member # 299) on 01-19-2000, 01:37 AM:
Well if I am reading it right it would be revision L, but don't quote me on that. But correct me if I am wrong here, but shouldn't there be only THREE wires coming from the pickup cell? Then why do I have eight? I think whomever wired this thing has crossed the lines over and I am probably only getting Mono on all channels. I am going to tear into it Thursday night and rewire it. Will let you know if that solves the problem.------------------
"If it's not worth doing, I have allready been there and done it"
Posted by Charles Lubner (Member # 157) on 01-19-2000, 02:12 AM:
I've got a complete set of CP-50 cards at my theatre. I had to throw the actual processor out, but I kept all of the cards cause I collect stuff like that! I have no use for them, so if you need anything let me know.
Posted by Steve Guttag (Member # 268) on 01-19-2000, 10:08 AM:
From the decoding side, the Cat. 150 is the most likely suspect. But don't forget to make sure that the A-chain is tuned up right and then there is the B-chain wiring...I've seen people in the attempt to wire their booth monitor short the various outputs together and get the equivalent of mono out of all the channels.------------------
"Old projectionists never die, they just changeover!"
Posted by Gordon McLeod (Member # 33) on 01-19-2000, 11:31 AM:
It is possible that your CP50 has the original cat 110 and 116 cards still installed and there maximum seperation is 4db per channel of gain control
If they are still installed replace them with a 110L link card and a 150E
If that isn't the case check the usuall list of suspects a and b chains
Posted by Aaron Sisemore (Member # 145) on 01-19-2000, 01:54 PM:
EIGHT wires?From the solar cell head? or from the terminal block? What soundhead are we talking about here?
Aaron
Posted by Ari Nordström (Member # 288) on 01-19-2000, 05:14 PM:
I experienced a similar problem a couple of years ago. The solution was to replace the Cat 150 matrix card. It fed the left and right channels with the center channel, in addition to the actual left and right signals...
Posted by Ben Wales (Member # 92) on 01-19-2000, 05:46 PM:
If the stereo Cell is aligned and other items have been checked over as suggested.
Perhaps upgrade the Dobly Matrix Card with a Cat 150E and replace the pre-amp cards as well.Most of the the old Dolby cards along most old CP50's are well out of date, Dolby Labs in fact will not repair cards for these any more.
The CP50 is well suited for home use and perhaps mobile work etc, but it would be worth upgrading to either a CP45 or CP65 or take a chance with a CP500.
Posted by Scott Norwood (Member # 30) on 01-19-2000, 10:46 PM:
Why would anyone consider a CP-45 to be an "upgrade" from a CP-50? Sure, it has newer a newer matrix and SR decoding out of the box, but the one that I saw recently just looks and feels "cheap" in every possible way. The CP-50, by contrast, feels pretty solid and can sound just as good as the modern processors with the upgrades (A and SR NR cards, 150E or F matrix card, 64B EQ cards, subwoofer card, etc.).
Posted by Richard Hamilton (Member # 321) on 01-19-2000, 11:02 PM:
CP45??? I thought they converted all of those into SA10s
Posted by Tim Reed (Member # 137) on 01-20-2000, 01:44 PM:
The CP-45 was Dolby's answer to the low-cost el-cheapos out there, which were getting the lion's share of the independent market.In other words, since many theatres were buying rinky-dink crappy processors, simply because price was the only consideration to have stereo, Dolby figured it might as well be one of theirs.
Posted by Ben Wales (Member # 92) on 01-20-2000, 04:33 PM:
The Rank Cinema Circuit Odeon Cinemas in the UK did infact install a load of CP45's in some of it's older high streets sites upgrades, I think this practice has now stopped as more CP500's are being installed now for digital sound.
Posted by Stephen Jones (Member # 16) on 01-20-2000, 10:58 PM:
I have used the c.p 50 once so cant really comment on it but the short time I did use it I found it to be a good unit.Used the dolby 55's ,65,s 500. and Panastereo (late model)I find that the c.p 65 is still the best that Dolby have put out, it's the most versatile processor on the market in my opinion.The Panastereo beats the c.p 500 hands down a great unit and a lot cheaper than the 500,and dose exactly the samr thing as the 500.------------------
Posted by Gordon McLeod (Member # 33) on 01-21-2000, 12:08 PM:
Rank also made two attempts at building there own processors as well with out much success.
There are two of the units with the horizontal boards in Ontario still any schematics would be appreciated as they only got an instruction book with them
Posted by Ari Nordström (Member # 288) on 01-21-2000, 04:41 PM:
>>"The CP50 is well suited for home use and perhaps mobile work etc, but it would be worth upgrading to either a CP45 or CP65 or take a chance with a CP500."<<Why should getting a CP500 be "taking a chance"? I've had no problems with them so far. A CP45, on the other hand, is a piece of junk, and I agree with the comments stating that a CP50 with upgrade cards is a much better processor. It is.
Posted by Dave Williams (Member # 299) on 01-22-2000, 02:44 AM:
Ok as promised I would follow up and let you know how my rewiring went and if it solved the problem of same sound in all four channels.All of the wiring was correct if you are a psychopath, however for us regular folks it was whacked out man. First I traced the wiring from the cell to see what the hell they were doing. They had it wired all to hell but the main important thing is that it actually should have worked if not for one thing.
You see they hooked up a CD player to the projector 2 inputs. That is correct. However for some damn reason they also hooked the same line from the CD player into the cell inputs through a standard light switch, this was so they could switch between CD player and projector and have it wired right there, instead of actually wiring the sound unit there (it is wired 15 feet away, go figure.
This in and of itself shouldn't pose a problem, but I inspected the hookups a little closer. On the Cd hookup to projector 2, they did in fact crosswire left and right channels. This caused all of it to go mono as it was wired into the cell as well. I took out my trusty wire cutters and waited for the show to start. Cut the wires and DAMMIT we have stereo all of a sudden.
My next project is to tear that whole damn thing apart and rewire the entire thing. Wires everywhere I tell you, its a mess.
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"If it's not worth doing, I have allready been there and done it"
Posted by Stefan Scholz (Member # 147) on 01-22-2000, 07:04 AM:
With CP 45's I had 3 main decoder boards fail within less than two years, at the same site. Now we have another board failiure, and the owners get upset, what a poor home theatre type of equipment.
Posted by John Walsh (Member # 168) on 01-22-2000, 09:21 AM:
They used a regular light switch!? That is wacked-out job. It's serious enough that I would never not only never call them again, but charge them for someone else to come in and fix it.There's a lot of techs who really don't know that much. I used to do a little 'test' to grade a tech while he would do an A chain aligment. First, I watched if they cleaned the optical lens by licking a Qtip rather than using lens cleaner. Lick=Slob. Next, I would see if they would measure the dB difference between L and R (at the time, Dolby specified more than 20dB.) If they tried to skip it, I ask that it be done. If he didn't know the formula= inexperinced.
Posted by Dave Williams (Member # 299) on 01-22-2000, 11:39 PM:
The person responsible for this wiring job is actually dead from what I understand. It was done 19 years ago, when they hooked up a tape player to the thing and they just wired in the CD player when they upgraded to the 20th Century.I used to do sound for concerts and bands and have tried to move that into the theatrical arena, but for some damn reason people just cant stand the sound at 200 Db. It sounds fine to me. (previous remark intended as satyrical for the uneducated).
I have hired my brother who is the sound engineer for a local play house and considered one of the best at his game. He has my DTS POS theater sounding almost good (actually we redesigned the sound so now it actually fills the entire auditorium, once again exceeding the sound a jet engine cranks out but who needs eardrums?)
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"If it's not worth doing, I have allready been there and done it"
Posted by John Walsh (Member # 168) on 01-23-2000, 10:52 AM:
Yeah, we have a guy like that here, too.This guy used to own a recording studio near here (did several early Deep Purple videos.) He made a ton of money, sold his studio to spend more time with his kids. He came to the theater one day and was just asking questions. He thought we just set up a speaker behind the screen, and that was it. When he found out that we actually try to really EQ the place, he got real interested. He went out and bought his own R2 unit. We let him come in whenever he wants (during off hours) and play. He spends hours EQ'ing this way and that, many times for free. He has got some fantastic sound out of some auditouriums, especially 'problem' or odd shaped auditouriums.
He sometimes forgets to put everything back befor the show that evening, but I usually catch it while threading. It's a small price to pay for such great sound.