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Another possibility is that one of the cards is either bad or not seated properly. The output card could have the levels set too low, also.

SR is not the same as SRD. SR is a newer noise reduction scheme; it's like Dolby A, but better. Since you have the cat 280T cards, you can play SR prints properly. IF you want to play older Dolby A prints, you will need a set of cat. 22 cards. SRD is Dolby's digital sound system; all (well, most) SRD prints also have an SR optical track.

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On a CP-50 though the power supply is barely big enough to power the unit with the 113C card and a pair of CAT 280T's. If U plug in a new 108C preamp card it will lower the B+ to the point that some of the cards cease to function properly. If it seems that the level cannot be achieved or if it comes up sounding ok and then fades out, check the B+ lines and you'll probably find one of them quite a bit lower than it should be. On a unit this old its also a good idea to replace the power supply caps inside the power supply. I've found many of them actually leaking electrolyte. Several have had hum problems stemming from aged power supply components. Ya have to stop and consider that most electrolytics have a rated life of 5 to 10 years and many of the 50's out there are far older than that!

On another note replacing the caps will not correct a sagging power supply problem either. There are two options for this problem. The forst and expensive way out is to buy the newer uprated power supply fomr Dolby at about 450.00. The second way which is cheaper and actually better is to build a whole new supply for it and can the original which is way to under rated for an upgraded 50. I ahve a completely upgraded 50 in my screening room and the supply I built is competely regulated on all lines and cost under 75.00 to build with all new parts, including a new toroid power transformer. The supply is now outboarded as well. The CP-50 can be a great sounding unit, easily surpassing the sound quality of the newer digital processors quite easily. For best performance you should also have the new cat 417 fader card in there as well to handle the higher playback levels of SR tracks.
Mark @ GTS

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As Mark has pointed out...the power supply (Cat. 114) was a very simple brute force supply that had just enough current to handle a stock CP-50. I've seen the +/- 12 volt rails dip down below 10 volts! (they start out at around +/-15 volts).

Ideally, you would want a good +/- 15 volt supply and +24 volt supply...the +/-15 volt rails are the ones that take the biggest hit when you upgrade. I believe the NR cards use only the +24 volt rail since they must be backwards compatible to old pro-audio systems.

Steve

How do I know? because we had down and dirty setup in one booth where we were just going directly from the cells directly into a standard Shure mic preamp with no EQ at all and the thing sounded great -- plenty of high-end. I remember the first film we ran on that setup was YELLOW SUBMARINE and it sounded almost like the kind of response you got with mag. I remember being very impressed. We added an outboard EQ and only had to give the bottom end a bit of a boost but other than that, the high-end was very smooth.

One big difference though between your Shure preamp and the CP50 is the slit compensation circuit which adds about 16dB of boost at some frequency in the region of 10 to 20kHz, depending on your slit size. This would most likely make your unfiltered mono films sound very brittle and crackly. Add to this the effects of any high end boost in the room eq and your unfiltered mono films may sound really awful.

A more preferrable alternative may be to modify the Academy filters for a more gentle roll-off, say 6dB/octave rather than 12dB/octave. This could probably be done simply by shorting out inductors L101 and L201 on the Cat109 card. This should give a 6dB/octave rolloff with a 3dB down point at about 5.4kHz. If you want to try this let me know and I can look into it further for you.

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Frank,
I don't think turning the NR on and running that way is a good idea as the NR may add its own artifacts to an un-encoded audio program. This is further complicated in units that have a CAT 113C automation switch card. On this card there is no NR off and on button, its patterned after a CP-55/65 processor that only allows certain pre-selected formats that are designed into the 113C card. Fortunately there is a mono(01) select button on this card.

Adding a switch for disabling the academy filter is easy and there are two ways to do it. The quick and and easy way is to lift the junction of R102(R-202) and L-101(L202) and insert a spst dip switch there to open , or close this junction. There is plenty wide open space to add one of these into the card quite easily. You could also add a DIP switch to the rear of the backplane as well just by opening up the pin 10 trace of the meter card and inserting the same DIP switch there. This is labeled + for NR off on the drawing(there's that darn refernce to b+ again right on the CP-50 schematic Steve, courtesy of none other than Dolby!)Either way is good but I prefer the switch installed on the meter card as its out of sight and out of mind from other operators curiosity. The final option is to pull L101 (201) off the pcb entirely to disable the darn thing all together. I always felt it had bit to steep of roll off and perhaps Dolby intended it to be that way. Only poor mono tracks with lots of over modulation, or very worn tracks will be more noticable. Clean mono tracks sound lots better IMHO without the filter in place. Even old variable density tracks can sound great with the filter removed, although there will be a bit more noticable background noise on these.
Mark @ GTS

Boy do you like to use things out of context! The "+" in this instance is for a logic input such that it is active high or high for on. The "+" merely refers to "high". There is no mention of "B" in there.

Now back to the subject...personally, I think you are dead wrong on the Academy filter. It is proper to be in there for mono film, even recent ones. While I don't doubt that there may be SOME films that did not have a pre-emphasis, that wouldn't be the norm. Mono films were mixed with the presumption that you had the typical sounding theatre from the '30s or so (before equalization in the current sense was used). With a modern cinema processor, one can tune a theatre for "flat". This equalization does not make your theatre look like one from the '30s. The Academy filter does and thus makes your theatre sound closer to what the director/mixers heard when they mixed the film.

As to not running with the filter making the films sound "better" or brighter..., perhaps, subjectively but it isn't they way they were supposed to sound. Your position is similar to that which I heard back in the '70s when using cassette recorders...encode with Dolby-B and playback without...after all, using Dolby-B on the playback kills the highs! No it really doesn't (unless your recorder was rather poor) but most people tend to boost the treble to make it crisp....if that is the case, then use the treble control, not the filter or NR.

Now, if you insist on having a switchable filter, I'd vote for putting the switch on the rear and switch pin-10 (open for filter off, closed to follow normal CP-50 logic)

Steve

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