Film-Tech Forum ARCHIVE: SR cards in CP50

This is topic SR cards in CP50 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Tom Wienholt (Member # 1510) on 03-15-2003, 04:11 PM:

When using SR cards in a Cp50, should dolby levels be set with the SR cards in the system or the A-type noise reduction cards?

Posted by Scott Norwood (Member # 30) on 03-15-2003, 04:14 PM:

Would it even matter? The processor should be in format 01 (mono) when setting Dolby levels.

Posted by Mark Gulbrandsen (Member # 72) on 03-15-2003, 04:23 PM:

I was taught by Dolby to use the Type A cards to properly calibrate for SR playback in a CP processor. Now that was long ago when it first came out but it still seems to work just fine.
Mark @ CLACO

Posted by Christopher Seo (Member # 7) on 03-15-2003, 05:10 PM:

According to a (probably very early) Dolby bulletin on the use of the Cat. 280T as a direct replacement for the Cat. 22 in the CP50, CP100, and CP200, the procedure is:

1. Make sure the A-chain is in the proper alignment. Thread Dolby tone loop Cat. 69T and set Dolby levels with Cat. 22s in place.

2. Leave loop threaded. Shut off processor. Replace L,R Cat. 22s with Cat. 280Ts.

3. Restore power, run loop again, and verify Dolby level with the Cat. 280Ts. If the level has changed significantly, there is likely a problem with the Cat. 22s or the Cat. 280Ts.

4. Increase the fader 3 dB (just about one step) to run Dolby SR films.

Presumably once the levels are initially verified to match, then Dolby level can be set with either NR in the CP. In the case of the CP50, I think it's been stated that the meter cards are before the NR anyway in the signal path, so you could probably get Dolby level even with no NR cards in. The 3 dB fader increase is because "the overall program level on the Dolby SR encoded print is about 3 dB lower. (This is done so that the lower noise achieved with Dolby SR is partially exchanged for increased headroom)."

Posted by Gordon McLeod (Member # 33) on 03-15-2003, 07:36 PM:

" I think it's been stated that the meter cards are before the NR anyway in the signal path, so you could probably get Dolby level even with no NR cards in"
The NR cards affect the meter reading as such that is why it must be in 01

Posted by Steve Kraus (Member # 476) on 03-16-2003, 12:01 AM:

Christopher, except for a few resistors, a couple of diodes and the physical meter movement itself (times 2 channels) which are located on the Cat.109 card, all of the meter drive circuitry is part of the NR card, so with no card in place there would be no reading.

The rest of the circuitry on the Cat.109 is the Academy filter that kicks in when NR is off.

Posted by Christopher Seo (Member # 7) on 03-16-2003, 08:47 AM:

Thanks for the clarification.

Posted by Alan Lyman (Member # 557) on 03-17-2003, 07:48 AM:

When using CAT280T´s in A CP50,the millivolt output should be adjusted,due to the old VCA´s,and the higher levels in SR.
connect a loop on the CAT109,with CAT22 inside,and take out one of them.Put the CAT64 in the opposite slot,and adjust to 150mV.Do this with all three 64´s in the same slot.Then reinstall CAt280´s and the 64´s in their right possition.

Posted by Sam Hunter (Member # 1119) on 03-17-2003, 11:57 AM:

What does a CAT280 do?

Posted by Stephen Furley (Member # 1277) on 03-17-2003, 01:03 PM:

Single channel SR type noise reduction, can be installed as a direct replacment for the Cat 22 A type modules in the CP 50 and 200, and is also used in the SRA5. I'm not sure how it differs from the later Cat 350 cards used in the CP-55 and 65.