Film-Tech Forum ARCHIVE: Strange connections to CP-65

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Posted by Stephen Furley (Member # 1277) on 07-08-2007, 04:57 AM:

I had cause to download the CP-65 installation manual yesterday; I just needed to check a jumper setting on the exchange Cat.441 card that had just arrived. This card seems to have solved the last remaining sound problem that we had with the digital system, but we don't have any films on digital in the next few weeks. I don't have the equipment to set up the EQ, but it sounds ok, and they are putting in new amps next week, so a full B chain alignment will presumably be done then anyway.

While I was waiting for the last show to finish last night I was looking through the manual, and saw something strange which I hadn't noticed before. Its on page 2-5, the wiring diagram for the CP-65 300 configuration for running format 42. There are two outputs on the CP labeled pre amp outputs Lt and Rt. These are unused in the standard configuration, but are marked 'To Switching in Mag Pre-amps' in the CP-65 300 configuration. I cannot think of any possible reason for this. There are three things which are switchable in the MPU-1, the use, or otherwise of the 12kHz. surround switching system, controlled only by a local switch on the Cat.93 card, and the projector changeover and 35/70mm selection, which can be controlled remotely, by grounding a terminal to switch to projector 2, or to 35mm. Lt and Rt pre-amp outputs seem to have nothing to do with either of these, so what are these connections for? I suppose it's just about possible that you could use the presence of the pre-amp signals to indicate that a 35mm print is being run, but you would need external circuitry to operate a switching relay, and it would only work with a mag-optical print, in which case only one channel would have any output, so why connect both? It wouldn't work at all with a pure magnetic print, and there have got to be easier ways to get the CP to tell you when it's running format 42 anyway, so I don't think that can be the reason. Did many places ever run this configuration? 70mm houses always seemed to have a CP-200.

It's highly unlikely that I would ever want to do this; I'm just curious.

Posted by Ben Wales (Member # 92) on 07-08-2007, 05:51 AM:

quote: Stephen Furley
Did many places ever run this configuration? 70mm houses always seemed to have a CP-200.

Yes, I know of a CP65 that was installed at Harbour Lights in Southampton.

When I was there (1995) the 70mm mag was selected through the Aux imput (CP65) and a additional external format selector switch for the 70mm formats,the 70mm format 42 & 43 signal path was routed back into the Cat22's, this was a 3 + sub channel stage speaker system.

I recall you could not check the Dolby Levels for 70mm without a RTA, so it was only done on a few occasions by our service Tech.

Posted by John Hawkinson (Member # 1135) on 07-08-2007, 09:29 AM:

On the CP65, TB2 positions 11 and 12 are the optical preamp outputs (left and right) from the Cat. 240A before noise reduction. They are quite handy to have available on a booth monitor selector, particularly when playing old or noisy prints, to listen to the nature of dirt and scratches if you're wondering why the NR'd print sounds strange. They are also handy for, say, listening to buzz track while doing A chains. (Of course there are other ways to do these things, too.)

--jhawk

Posted by Stephen Furley (Member # 1277) on 07-08-2007, 10:50 AM:

Yes, that's the connections, TB2, 11 and 12; should also be useful, along with the mag/aux inputs, as send and return for other external processing for special formats, like Perspecta, or dbx noise reduction. But why does the CP-65 300 wiring diagram label them as going to 'Switiching in mag pre-amp'?

I did wonder if I had mis-understood it, and it meant that these signals were being sent to the MPU to be switched, rather than being used to switch something in the MPU, but that wouldn't seem to make any sense either.