Film-Tech Forum ARCHIVE: CP45 with low output levels

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Posted by Luciano Brigite (Member # 1104) on 05-21-2009, 09:47 AM:

Hello ,

I'm having some hard time with a CP45 putting low levels in the auditorium.. About 2 years ago I serviced this same theatre and re-did then entire A/B chain alignment and the processor had a bit of level left ( The output trims were at that time left between 1/2 to 3/4 of their setting) and sound in the auditorium was vivid and clean.
Then I got called to service it recently and found everything messed up, from sound reader to amplifiers and even the speakers! While redoing the reader alignment, I found out that the projector input being used had one of the channels with a very low level (turning up all the way the gain for htat channel would make any of the leds in the NR card to light, even the red led on the low level side) the cable was changed to the ohter input and things were ok, levels could be set properly and A-chain finished as it should. Things got ugly when came the time to do B-chain, all the output trims are at the maximum and the channels are hardly putting out the 85dB. I Checked the power amps and are ok. two fo the screen speakers had blown HF drivers and those were replaced. EQ could be done but sound isn't good.While the response is ok ,even at the low level, while the film is running, sound is muffled at the screen channels and surrounds are nearly dead ( even if the signal leds in the processor indicates a signal there).
The way I mention the problem will lead many to think that the reader has a problem, however it's properly set and working ( lateral,azimuth and response are all ok).

Posted by Marco Giustini (Member # 4544) on 05-21-2009, 07:36 PM:

Since everything was messed up, have you checked the phase of all the speakers?

Posted by Louis Bornwasser (Member # 3063) on 05-21-2009, 08:02 PM:

Feed high grade audio (cd player, etc.) directly to the power amps, one channel at a time. Test amps and speakers first; then insert CP-45. Louis

Posted by Luciano Brigite (Member # 1104) on 05-21-2009, 09:59 PM:

Hello,

All the speakers were checked during HF drivers replacement and are ok. Also re-did the surround speakers connections to make sure each of them is working and the proper impedance is set.
The amplifiers were checked too at the time by feeding pink noise and measuring SPL in the auditorium, levels reached the 110dB.
With the CP45 connected, SPL levels for each channel barely hits the 85dB for screen channels and 87dB for surrounds, and it happens with all the output trims inside the processor set to maximum.Fader is placed at 7 as usual during the tests.
Also checked the jumpers at the back panel and all of them are set to high.
A-chain was redone once more and nothing wrong with the reader was found. pre-amp levels are ok ,but any film that was run in this audiroium had poor sound with very little to nothing in the surrounds. the same films when played in the ohter auditorium performed ok.

Posted by Louis Bornwasser (Member # 3063) on 05-22-2009, 12:03 PM:

I would swap boards one at a time until your problem moves. If you set both auditoriums up, they should be similar so, for testing purposes, you could disregard any retuning.

Don't forget the front door which has much circuitry.

Also, on some earlier cp-45, it is possible that the large board could make contact with the nr board because the leads on the components are too long. Just raise the front of the large board. I have used a poker chip or a small piece of cardboard to stop this. Louis

Posted by Michael Schaffer (Member # 1204) on 05-22-2009, 09:09 PM:

Did you check your crossover settings, or that the crossover is set to "off" if not used? Do you have an external crossover?

Posted by Luciano Brigite (Member # 1104) on 05-22-2009, 10:59 PM:

I'll pull out the cards again and have a closer look. swap boards isn't an option there because the other auditorium has a Smart 7 processor ( wich is working way better than the CP) .

The crossover switchs are all off and no external crossovers are used.

Posted by Mark Gulbrandsen (Member # 72) on 05-23-2009, 09:12 AM:

If you're having troubles you must be using Ashley Power Amps....

Posted by Louis Bornwasser (Member # 3063) on 05-24-2009, 09:05 AM:

If so, then distortion would be unmeasurable. . . .nope; can't be that!

(They seem to work OK for me; what are you guys doing wrong?) 1900 in service in KY and Indiana. Louis

Posted by Mark Gulbrandsen (Member # 72) on 05-25-2009, 04:08 PM:

quote: Louis Bornwasser
1900 in service in KY and Indiana

My god... those poor people... and speakers!

Posted by Louis Bornwasser (Member # 3063) on 05-25-2009, 04:52 PM:

Haven't had a failure (on speakers) ever! Again, I cannot specify what is wrong elsewhere, but these amps do not blow speakers here. Louis

Posted by Luciano Brigite (Member # 1104) on 05-25-2009, 06:05 PM:

No Ashley amps here.. unless the sound rack is bought complete from a supplier in the US or elsewere, most of the amps used are made here.. but, yes.. there are many good and bad amps..the odd is that the major problem is with the rack that has the CP and well known amps wich rarely gave me any kind of problem..