Film-Tech Forum ARCHIVE: CP50-problems with output levels.

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Posted by Luciano Brigite (Member # 1104) on 10-30-2004, 11:54 PM:

Hello,
I'm having a bit of trouble with two CP50 lately about their output levels and internal level settings.
Whensetting the input/output trims in the Cat64 for the levels indicated in the manual,I can't get the 85db from any channel in the auditorium, even with all the trims in the output card and the fader at maximum. it's happening on both units ( it's a twin theatre) the CP's were all messed up regarding level settings and took me a full day to have them aset properly.Now when it comes time to do the EQ'ing, and finish the B-chain, I get no level from it.the jumpers in the backplane are all set to maximum,output levels set per instructions in the manual(dolby tone running in the projector,150mV output at hte test points for L/R channels and 210mV for center.)
The only way to get the 85db is turning up the output level from the cat64 to 1Vpp or more,with levels that way, the output trims will be open at 8/10 of their turns.However when set that way,the fader cannot be advanced past the 5~6 mark or the sound will crack and become a mess no one can understand. sampling the signal in the oscilloscope,shows a severe clipping when the fader reaches the 6 mark and goes beyond it. What am I missing in all this? already checked power amps,speakers,drivers and frequency dividers(?) what was found messed up was replaced.
Also, with levels set that way is about impossible to do a decent Eq'ing in the auditorium because each step the fader is turned up,more the mid-highs "scream" and I got to the point where I set those bands in the cat64 about all way down and it still screams.
One thing,for what purpose the internal dolby tone generator is used in the CP? at one time after getting tired of hearing a loop clicking in the projector all the time I closed the link in the meter card and used it to set the output levels.. Did I do it wrong?
Not mentioned before,but power amps are Brazilian made and I don't know if they're known elsewhere.they're very good units and a lot of theatres here uses them without problems. also the Cat150 seems to be one of the recent ones, a Cat150E or F,don't remember the letter right now ( it's a single board now with large IC's and peak leds.) output card is Cat117.

that's all for now..
Thanks!

Posted by Mark Gulbrandsen (Member # 72) on 10-31-2004, 10:03 AM:

Are there gain controls on the power amps and where are they set? Sounds like they are turned down....

Mark

Posted by Edward Jurich (Member # 1787) on 10-31-2004, 11:05 AM:

I'd start from scratch. Set all the level pots to mid-rotation and all EQ's to flat (center rotation). Turn the power amp levels down at first so you don't chance blowing a speaker. Get the levels set right first, then EQ. I believe there is more than one place to control levels in the CP-50 besides the output level controls.

Posted by Luciano Brigite (Member # 1104) on 10-31-2004, 11:26 AM:

The power amp's gain controls were set at maximum in the first try, with the settings in the CP done the way it's written in the manual and the 85db level couldn't be reached.They were left that way since then since turning it down when the cracking in the sound started,at first thought it was the amplifier's input saturating,but checking the signal with the scope showed it was comming out clipped from the processor.
For now the theatre is running with all the 3 EQ's with all controls,except bass and treble in the middle position.
I don't know of any other level setting in the CP other than the trims in the output card and the in/out trims in the cat64.
other than these, the only other level trims in there are the pre-amp gain and hf.( wich are set properly for dolby level) and again, the jumpers in the back of processor are all set to hi level.

Posted by Sam D. Chavez (Member # 1841) on 10-31-2004, 11:35 AM:

Luciano,

I would suggest the following procedure which is simpler than the one described in the manual.

Turn the Cat. 64 input controls all the way down.
Use the Cat 85 generator to set the Cat 64 output controls as measured on the Cat 117 or 111 test points which are actually on the input to the card. The actual exact level is not critical but it should be in the 200 mVolt area.

If you can achieve this level, the fault is in the output card or power amps.

The internal Dolby tone level generator is of no value in cinema applications as the phase between the two tones is random and throws the Cat. 150 matrix all over the place.

Posted by Luciano Brigite (Member # 1104) on 10-31-2004, 08:28 PM:

Uh.. I don't have the Cat.85 generator and I believe the person that has one won't let me borrow it [Frown]

The output card is the Cat.117 and the levels of 150mV for L/R and 210mV for center can be easily reached. I could even get a level of 1 volt peak-to-peak when measured in the oscilloscope at the tests points.
Setting the levels around the 200mV like you said,Sam, won't give me more than 68db in the auditorium with all the trims in cat.117 set to maximum.The only way to reach the 85db mark was turning the output level of all the 3 cat.64 way up from the 200mV point.then the sound starts poping and cracking,specially in the center channel with the level set that way when the fader goes past the center mark.
I asked the theatre's owner for other power amps,I'll be back there now only when he gets the amps plus some other parts and agrees in not opening the theatre for an entire day so I can do the work properly and not in a hurry. I got really pissed when an old man entered the booth and asked when all that noise would end and the movie start.. [Mad]

they knew the theatre was being serviced and sold tickets to people!! [Mad]

In case the problem lies in the cat.117,can it be serviced easily without the need to have it sent to a dolby rep for repair? ( as in component availability,no esoteric Ic's and so on in it)

Posted by Gordon McLeod (Member # 33) on 10-31-2004, 08:33 PM:

What level and source of pink noise if you didn't have the 85c card did you try to use

Posted by Luciano Brigite (Member # 1104) on 10-31-2004, 09:43 PM:

Pink noise was generated by the same computer I was using with PCrta,with output level set for 600mV and fed into the CP tru a modified link card.

Posted by Luciano Brigite (Member # 1104) on 11-10-2004, 03:48 PM:

Got back to the theatre yesterday and spent the entire day "having fun" in there, good thing is that rom hte 4 shows of each theatre, only one happened in one room and first two in the other. could do everything that was needed in there even if it took some good 12 hours.
The low level problem I had in one theatre is gone, turned out to be a power amp with a bad input,switched amps and got levels ok with the CP set as per manual.However,after doing the EQ'ing ( I did borrow the Cat85 from someone and alsoenjoyed my new toy, the PAA2) the sound in the auditorium became too "hissy" ,specially from middle to end, it's fine in the fisrt 5~6 rows starting from the screen, fired pink noise again and the curve is ok to me, going flat to 8k and then falling from it until the 20K
What'd be happing now?

Now in the other theatre,the level problem is still around,outputs from Cat64 where set as Sam told in his post (Set L/R at 200mV and C at 350mV) and still couldn't get more than 72dB from the center channel while the L/R easly reached the 85dB. changed the monoblock amp for the channel with no result.
I didn't check the speakers in this room before and when did so, turned out that the center channel has a different setup than L/R. it is a woofer cabinet with a 15"driver in it and a Horn on top of the cabinet (one of those wide-mouth horns,about the same style of the altecs,but has nothing to do with one) while the other two speakers,for L/R are smaller cabinets, also with s 15" woofer and a much smaller horn mounted inside it. all the 3 speakers have crossover networks and they're the same for the 3 channels. Could be this different speaker for the center channel,the problem regarding the level? while behind the screen,I checked the driver's coils for shorts or altered resistance but both are ok.
The output level trims in the Cat117 are set all way down for L/R and all way up for center,and the center still sounds low

(made another post because I thought that editing my last one wouldn't bring the topic back..)

Posted by Gordon McLeod (Member # 33) on 11-10-2004, 04:00 PM:

"too "hissy" ,specially from middle to end, it's fine in the fisrt 5~6 rows starting from the screen, fired pink noise again and the curve is ok to me, going flat to 8k and then falling from it until the 20K" it should be flat to 2K not 8K

Posted by Michael Schaffer (Member # 1204) on 11-10-2004, 04:54 PM:

You are probably aware of this, but I just wanted to mention that many crossover networks have a HF gain control. If that is all the way down, it will give you problems achieving the proper level (among other things).

Posted by Luciano Brigite (Member # 1104) on 11-10-2004, 05:45 PM:

Uuuuhhhhhh.. flat up to 2K.. [Embarrassed]

I bombed all the EQ [Frown]

was sure it was up to 8K ....

The crossovers are passive, the kind someone will find inside a speaker cabinet or in a small box attached to ouside of it, It has no level controls.

And I thought I had done the eq right.... *sigh*
better I consider selling hotdogs or whatever somewhere inna corner .. [Embarrassed]