Film-Tech Forum ARCHIVE: CP50 Historic Question

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Posted by Steve Kraus (Member # 476) on 03-13-2019, 01:14 PM:

I was rereading some old posts about the decoders in the CP50 and while I am familiar with the old Cat 110 LCR - Cat 116 Surround two card solution, what variant made use of the surround adapter connection on the backplane and did that predate 110/116? What was the original configuration of the very first 50s?

I know that somewhere along the line in the gestation of the CP100, LCR was handled by the card that plugged into the format slot and surround was outboarded. Then along came the Cat150 and the whole operation was outboarded with the card in the format slot just something that switched signals along.

Posted by Sam D. Chavez (Member # 1841) on 03-13-2019, 04:26 PM:

I go bak quite a ways but I don't recall an external adaptor for the CP50. It would have been an SA2 if anything. I'm stumped. There was a Cat. 110 that did LCR and then a 115 in what now is the 150 slot. Later a Cat. 116A took care of surround channel plus delay. Ultimately the Cat. 110L/Cat 150 did all 4 channels, LCRS. The Cat. 160 came later to did the subwoofer channel and fit into the 110L which was a blank bypass card. Let's see what others recall.

Posted by Steve Kraus (Member # 476) on 03-14-2019, 08:43 PM:

Ah, it must have been something they allowed for in the CP50 design but never made use of. Maybe the thinking was that stereo decoding might evolve into a level of complexity beyond what would fit on two cards.

The labeling is "Output to Surround Adapter" and "Input from Surround Adapter." It's four out and four back so maybe it could have been a LCR card internally and just surround being handled externally.

Posted by Steve Guttag (Member # 268) on 03-15-2019, 06:53 AM:

It, to the best of my knowledge, was never used with any form of surround adapter.

The CP50 came out AFTER the CP100. The CP100 used surround adapters so I would suspect that when the CP50 was designed, it was likely designed in kind by providing a signal path for Lt/Rt and return from the surround adapter that never came to be whereas technology allowed for surround decoding internally as well as improvements, like the CAT150 to put it all on one card slot. (Sometime in 1978).

They eventually got hijacked for the SRA5 (after some modifications, that were safe because there was no surround adapter and even if there was, one would be on the CAT150 by the time they were considering the SRA-5).

The Center out did get used with the CAT160 for those with OBE.

Posted by Sam D. Chavez (Member # 1841) on 03-15-2019, 04:13 PM:

Might have had some early use as part of the encoding/decoding loop like an EPL, i.e, external process loop in a dubbing situation. Don't recall as it was a little before my time. Dolby developed the DS4 Encoder/decoder/monitor which became the official unit and could patch into the consoles of the day. This had outputs for an audio meter bridge as well as normal audio outs so the dubbing engineer could hear the audio as it would be heard in a cinema vs., off the recorder/dubber and if there were significant differences in quality/level, etc., could be worked on some more to make it more compatible. There would have been no more use for a modified CP50 once the DS4 became the standard.

Posted by Steve Kraus (Member # 476) on 03-17-2019, 03:05 PM:

As labeled, it does not appear that the external unit would have access to Lt/Rt but since, per the diagram, the output connections are between the two card slots, it will all depend on what is put in that first slot. If all decoding was done externally then a 110L or equivalent should put Lt/Rt on the L & R connections going out to the hypothetical external box.

Which leads to another, related question. If one is using the old pre-150 two card solution, the first card is passing along LCR, right? How does the second card derive surround from that? Doesn't it *need* access to Lt & Rt? It looks like it does not.

Posted by Steve Guttag (Member # 268) on 03-17-2019, 05:04 PM:

It would be incumbent on the first card to pass Lt/Rt along, if it is needed. For instance, the CAT160 does send Lt/Rt down to the next card (CAT150). The 110L does this for the CAT150 if no CAT160/560 is present.

The same would be true on the 110/116 dual card solution. Note, if you had the CAT110 (or CAT82, if memory serves), you could omit surrounds by putting a CAT115 in the second slot to let L/C/R pass through.

Posted by Sam D. Chavez (Member # 1841) on 03-17-2019, 08:03 PM:

This is way back but the 110 and 82 were the same except for the need for circuitry to choose the 82 in the CP100 format slots. I don't recall an 82 in a CP50 though but it should work. Cat. 115 card function was just a surround decoder line. I believe the 82 /110 did all the LCR decoding so I don't recall how it passed a true Lt, Rt along down the backplane. Dual pins on the edge connector perhaps. My, what a long time ago. only 37 years.

Posted by Steve Guttag (Member # 268) on 03-18-2019, 07:17 AM:

The CAT115 was a straight up bypass card (shipped with the CP50. My guess if you had the CAT160 and didn't have a 110L, then the 115 was necessary to let the CAT85 PN card have access to all four channels.

I haven't looked at the CAT116 schematic (at least not in a VERY long time) but I suspect that it passed the L/C/R through it.

Posted by Sam D. Chavez (Member # 1841) on 03-18-2019, 04:32 PM:

The other end of the dual edge connector 110L is a version of the 115 bypass card. Thanks for the reminder.

Posted by Steve Kraus (Member # 476) on 03-20-2019, 07:24 AM:

I have a two card set somewhere. Hacked up because when I once could not find my 110L I cut & jumped traces to create one. I will have to look to see if the 110 or whatever that LCR card was passes Lt/Rt.

Posted by Sam D. Chavez (Member # 1841) on 03-20-2019, 10:53 AM:

I have a couple of CP50's at the warehouse. I will take a look when I'm there. It could be the Lt, Rt, post NR, are hard wired on the backplane to the Cat. 115/150 card slot on different pins.

Posted by Steve Kraus (Member # 476) on 03-20-2019, 09:00 PM:

Perhaps but you'd think the 150 would make use of those and then the 110L would not be needed (except for 150 bypass with the Cat85C). The pre-amp outputs on the back are post-NR and I cannot find any continuity to the 115/150 slot unless the 110L is in place.

Posted by Steve Guttag (Member # 268) on 03-21-2019, 08:20 AM:

The second slot doesn't get Lt/Rt on its own, that is correct. In the original design, the first slot was the L/C/R decoder so it would get it.

Again, a CAT160 was designed to send Lt/Rt to slot 2 (not on the same pins either) so one would presume that a CAT110 would do likewise.

Posted by Tony Bandiera Jr (Member # 2365) on 03-21-2019, 10:48 AM:

The Warehouse has the CP50 circuit diagrams, and the answers all appear to be there. See page 8 of the pdf for what the 110L pinout is in particular.

Posted by Steve Kraus (Member # 476) on 03-21-2019, 03:02 PM:

Well, no, the diagrams in that manual are for the 110L / 150 version. We know the 110L passes Lt/Rt! But Steve is probably correct that the 110 LCR card does send along Lt/Rt.

Posted by Gordon McLeod (Member # 33) on 03-23-2019, 05:05 PM:

The original 110/116 combination work like this
The 110 received the LtRt and decoded LCR of which the decoded L and R were passed on to the 116 card to be reprocessed
I suspect this was done to keep less crosstalk in the surround channels
Some of the first CP50 did use the SA adapter