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Topic: Dolby CP-50

Dave Williams
Wet nipple scene

Posts: 1836
From: Salt Lake City, UT, USA
Registered: Jan 2000

posted 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"

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 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.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

posted 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?

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Dave Williams
Wet nipple scene

Posts: 1836
From: Salt Lake City, UT, USA
Registered: Jan 2000

posted 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.

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"If it's not worth doing, I have allready been there and done it"

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Charles Lubner
Film Handler

Posts: 78
From: Milwaukee, WI USA
Registered: Sep 1999

posted 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.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 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.

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"Old projectionists never die, they just changeover!"

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 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

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 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

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Ari Nordström
Master Film Handler

Posts: 283
From: Göteborg, Sweden
Registered: Jan 2000

posted 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...

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Ben Wales
Jedi Master Film Handler

Posts: 602
From: Southampton. England
Registered: Jul 99

posted 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.

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 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.).

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000

posted 01-19-2000 11:02 PM

CP45??? I thought they converted all of those into SA10s

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Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 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.

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Ben Wales
Jedi Master Film Handler

Posts: 602
From: Southampton. England
Registered: Jul 99

posted 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.

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Stephen Jones
Master Film Handler

Posts: 314
From: Geelong Victoria Australia
Registered: Jun 99

posted 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.

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