Film-Tech Forum ARCHIVE: CP-500/70mm

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Posted by Sigurd Wik (Member # 6131) on 01-08-2018, 05:46 PM:

I'm looking into using a Dolby CP-500D for processing 70mm magnetic soundtracks in combination with an old MPU-1, and I wonder if I have understood everything right. Maybe someone can help clarifying if not?

Having a CP-500D, as I undestand it I will need two Cat. 222A modules in addition to the Cat. 222SR/A for getting six channel noise reduction capabilities. Also I will need Cat. 669 adapter card and Cat. 685. And I haven't found the pin configuration of the magnetic input connector on the CP-500.

Posted by Axel Fransberg (Member # 5630) on 01-09-2018, 06:17 AM:

I'll trade you a CP500-70 with all the cards for a MPU [Smile]

Posted by Axel Fransberg (Member # 5630) on 01-10-2018, 12:37 AM:

The pin configuration should be in the install manual, it's the analog accessory connector.

Posted by Sigurd Wik (Member # 6131) on 01-10-2018, 03:59 PM:

Thanks! Sent you a PM.

Posted by Stephan Shelley (Member # 8587) on 01-10-2018, 11:10 PM:

another way is two cat 300 sr/a and one cat 222. If you ever want to do optical that will give you real sr.

Posted by Gary A. Hoselton (Member # 3447) on 01-11-2018, 12:29 AM:

The CP500 does not supply power for the MPU1, so you will need an 18V to 24VDC power supply for it. I use a Phoenix Contact 24VDC supply mounted on a DIN rail on side of rack.

If you do changeovers, you must supply a contact closure for each of projector 1 and 2 to the MPU1, to energize output relay for each of two channels on cat92 preamplifier boards to put correct projector's outputs on conductors that go to Analog input connector on CP500. I use two Schneider 24VDC relays on same DIN rail, powered by above 24VDC supply routed thru Douser relay on each projector.

From what I've seen, the cat92 preamplifier cards in early MPU1s have trimpots on front for low and high frequency gain and most have a third pot glued on for mid frequency gain. Later cards have low and high frequency trimpots on front and a round pot for midrange in middle of card so need a proprietary extender card to get at it. The last cards, cat92C I think, have three trimpots for each channel on front but no relay to switch outputs so must have solid state switching of some sort--I've not seen a schematic. The few cat92C's I've encountered did not work, they were used ones of course.

Posted by Sam D. Chavez (Member # 1841) on 01-11-2018, 01:45 AM:

quote: Gary A. Hoselton
If you do changeovers, you must supply a contact closure for each of projector 1 and 2 to the MPU1, to energize output relay for each of two channels on cat92 preamplifier boards to put correct projector's outputs on conductors that go to Analog input connector on CP500

There is a way to wire the MPU so it makes an internal changeover where projector one is normally active and you use maintain ground for projector 2.

Posted by Gary A. Hoselton (Member # 3447) on 01-11-2018, 12:15 PM:

Want to improve my description of relay connection that I posted 11 hours ago, but message says time limit for editing post has expired. Here is complete post, improved:

The CP500 does not supply power for the MPU1, so you will need an 18V to 24VDC power supply for it. I use a Phoenix Contact 24VDC supply mounted on a DIN rail on side of rack.

If you do changeovers, you must supply a contact closure for each of projector 1 and 2 to the MPU1, to energize output relay for each of two channels on cat92 preamplifier boards to put correct projector's outputs on conductors that go to Analog input connector on CP500. I use two Schneider 24VDC relays on same DIN rail, wired as an RS flipflop, powered by above 24VDC supply and switched by above 24VDC routed thru Douser Pulse relay in controller (Components Engineering TA-10) for each projector.

From what I've seen, the cat92 preamplifier cards in early MPU1s have trimpots on front for low and high frequency gain and most have a third pot glued on for mid frequency gain. Later cards have low and high frequency trimpots on front and a round pot for midrange in middle of card so need a proprietary extender card to get at it. The last cards, cat92C I think, have three trimpots for each channel on front but no relay to switch outputs so must have solid state switching of some sort--I've not seen a schematic. The few cat92C's I've encountered did not work, they were used ones of course.

Posted by Sigurd Wik (Member # 6131) on 01-11-2018, 12:48 PM:

Thanks guys, this is very useful.

Anyone have a Cat. 222A and a Cat. 669 laying around that you are interested in selling/renting? Or do you know of someone I can contact?

Thanks,
Sigurd

Posted by Steve Guttag (Member # 268) on 01-11-2018, 12:59 PM:

I'm unaware of ANYONE supplying both projector 1 and projector 2 commands to the MPU-1. It defaults to 70mm projector 1. If put the link on the switch card to "Normal" both Projector 1 and Projector 2 outputs are hot at all times. The switch on the front or a remote contact closer can be used to select between 35mm or 70mm. If you move the link from Normal to Remote, then EITHER projector 1 OR Projector 2 are hot. To switch to projector 2, ground (E) the C/O terminal on the rear. For remote 35/70 selection, the 35/70 terminal on the rear selects 35mm.

I suppose, if you remove the switch card, you could use the discrete terminals to select which cards you want on line...but why? I've never seen anyone do that!

As for the various preamps. The CAT92 up through CAT92/4 had level and gap loss on the front via trimmers. They label it as HF but it is just for the head gap, not treble. It is set like a slit loss correction on an optical preamp. The MF and LF controls are single turn pots and one does need the extender to get to them.

the CAT92C moved it all to the front with LF and MF still single-turn pots. The CAT92C also has a fringing connection filter if you are running old tracks (pre-1983) with a narrower recording width but with later heads (post-1983). The CAT92C also is direct coupled (no transformers) and has a bit better range of accommodation with a high/low level link.

I'd suggest a 24VDC suppy rather than being near the bottom of the range.

Posted by Sam D. Chavez (Member # 1841) on 01-11-2018, 03:07 PM:

I was waiting for Steve. He's right on point as usual.

Care to comment on why the 92Cs don't work? Gary, I can get the cards repaired by the person who designed them if need be.

Posted by Gary A. Hoselton (Member # 3447) on 01-12-2018, 02:00 PM:

Sam, Joel Miller has the non-working cat92C cards. He'd left 3 or 4 of them here for me to see how they worked, and none did, so he has them back. Sounds like an improved design. I'm running 35mm changeovers, not 70mm. I suppose Bob Leader has this working for 70mm, I haven't talked with him about it.

Steve, looking at my drawing, I see my problem was I had only douser pulse signals to work with, so built a flipflop relay to provide constant E (earth) to C/O CONTROL for MPU-1. Works fine, just have to switch dousers from one projector to the other and back at power up to synchronize flipflop and MPU-1 to CP500 initializing on projector 1. Could have put a delay on one relay coil so FF would initialize with C/O CONTROL open, but didn't seem worth doing, given tight spacing of relay socket terminals.

Posted by Sam D. Chavez (Member # 1841) on 01-12-2018, 02:38 PM:

The 92C was the last version of the Dolby Mag preamp and used an active, balanced, transformer-less design. Failures are pretty rare and I'm thinking they may work but theres an issue with the circuit that turns the output on.

We used to use a mechanical latching relay coil across the douser wiring to convert a pulse to latch and then used one on the dry contacts to do a sound changeover.

Posted by Scott Norwood (Member # 30) on 01-12-2018, 02:41 PM:

This might be a stupid question, but what could possibly be the use of having both projector 1 and projector 2 inputs active at the same time? Why is this even a possible configuration?

Posted by Sam D. Chavez (Member # 1841) on 01-12-2018, 04:41 PM:

Scott,

I think you mean MPU outputs.

I think Dolby may have designed the MPU that way to be compatible with the 70mm sound systems of the day. For instance, Ampex used dual Ledex switching for changeovers; so to be compatible with that arrangement, you needed to feed both Ledex projector one and two inputs. FYI, Ledex was a multi channel motorized wafer switch. Quite a nice device for its time.

Posted by Scott Norwood (Member # 30) on 01-12-2018, 05:38 PM:

That makes perfect sense. Thanks, Sam.

Posted by Steve Guttag (Member # 268) on 01-12-2018, 06:05 PM:

Yup. The MPU-1 stood on its own and predates the CP200 by a bit. Even the CP200 could work with both outputs live at the same time. You hooked Output 2 to Mag B and set the CP200 so it switched the CAT201 to make the magnetic changeover. An argument could be made: Would you rather switch 6 relays (3 on and 3 off) or have 12 JFETs switch the audio that won't ever wear out or get noisy due to oxidation. (Mind you, they can and do "pop" a bit, which is why Dolby had a clever slow switch to them (it would slowly change the voltage gate...all discrete components back then.

Mind you, most of us CP200 types (that worked with them seriously) had/have many uses for "Mag B" than for merely projector 2! Most people used it for Pro-Logic decoding. I use it for all sorts of stuff that needs to or makes it easier to go through the full audio path. And, the realities are the reed relays used on the CAT92s were quiet and reliable. I forget what the CAT92C used but they too were not problematic.

Posted by Louis Bornwasser (Member # 3063) on 01-19-2018, 10:16 AM:

Sam: the Ledex was almost bulletproof. Emblematic of MY era. Not so old you used #12 wire to control it, but not so new you used cat 5. LOTS of multicore wire!! Lots of IRON and heavy racks.

One of the "reasons to install Dolby" in small booths was to move out 5 racks of tubes and Ledexes, and install one rack with CP-100/mpu/transistorized amps; in those days Crown DC300. ( wonderful amp for its day.)

Posted by Sam D. Chavez (Member # 1841) on 01-19-2018, 03:54 PM:

Hi Louis,

I agree but a lot of early CP100's and 50's were installed with aging Ampex systems. Since Dolby had only one unbalanced output and there were two Ledex inputs in changeover houses, you had to parallel or bridge the inputs. Problem was the outgoing Ledex would short its outputs to mute them including the incoming Dolby ones. Learned that the hard way like most things.