Film-Tech Forum ARCHIVE: CP-750 Analog Input Wiring

This is topic CP-750 Analog Input Wiring in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=16;t=001606

Posted by Jim Cassedy (Member # 4115) on 08-21-2013, 10:07 AM:

I wasn't sure if this should go in the FILM or DIGITAL forum, so I tossed a coin . . .
. . . . and it wound up here:

I've got a situation where a theater wants to get their 35mm projector running again.
(D'oh! I KNEW this was going to happen! I've been getting a lot of these requests lately.)

Fortunately, the digital installers did not follow the "scorched earth" digital conversion
policy I've seen so many times here in CA.

I'll deal with getting the projectorthingy running again, but my question has to do with
resurrecting the audio. The audio chain is intact from the 35 projector to their old CP-45.

I was thinking I could come off the outputs of the '45 and go into the 25pin analog input
on the back of the CP-750. I've already made up the neccessary cable & tested it yesterday.

I was able to get sound. . . sort of. Of course the EQ and levels were all over the place,
and as I walked around the auditorium I could here severe 'phasing'.

When I got home, I double checked the CP-750 documentation, and it appears that the
pin-out for the analog input connector is shown differently on two different pages.

Here's one diagram (slightly re-formatted to fit here). Page 15, Fig 2.2

But, on Page 69, Table 7.8 below shows totally different pin-ous:

Also, is it me, or does one diagram seem to show single-ended and
the diagram other balanced connections? WHICH ONE IS CORRECT ?

(Fortunately, I used a crimp-pin DB-25 instead of the solder connection one Dolby
supplies with the '750 so re-arranging the pins won't be too difficult! )

Posted by Sam D. Chavez (Member # 1841) on 08-21-2013, 10:23 AM:

I would go with the picture. I have done this before and it works. The list must be wrong or mislabeled.

I am doing a project with the same issue, connecting the 45 output into a USL-60.

Posted by Jim Cassedy (Member # 4115) on 08-21-2013, 10:33 AM:

Thanks, Sam.
I used the "table" when I made up my cable. I knew something was wrong!

I'm flying into Telluride on Saturday, so I guess I'll see 'ya there.

Posted by Alexander Alves (Member # 1746) on 08-21-2013, 10:50 AM:

The CP-750 analog inputs are balanced. The manual you are referring to may be old.

Posted by Carsten Kurz (Member # 5396) on 08-21-2013, 04:40 PM:

My CP750 rev4 manual shows the same discrepancy. The first diagram shows the 'old' unbalanced analog Dolby D25 pinout as used on previous processors, like the DA20 or the CP650 ext analog in. Maybe some sort of a copy/paste mistake or a late spec change.

Good to see Dolby finally acknowledged the benefits of full balanced connections in a high level listening environment. Took them quite a while.
Now only if it is true... [Wink]

- Carsten

Posted by Steve Guttag (Member # 268) on 08-22-2013, 05:22 AM:

I want to say we used the balanced wiring on the input of the CP750 without issue but I won't swear to that. But, generally, we look for the pinout tables when we make up our cables.

-Steve

Posted by Scott Norwood (Member # 30) on 08-22-2013, 07:22 AM:

It should be the same as the DMA8+ output (balanced). I have used a straight-through DB25 cable from the DMA8+ to a couple of CP750s and had no issues.

If I remember correctly, the channel assignments on the CP750 input are configurable in software (at least among common options).

Posted by Carsten Kurz (Member # 5396) on 08-22-2013, 07:52 AM:

There are multiple other parts in the CP750 documentation explicitly referring to balanced analog multichannel inputs and balanced multichannel analog outputs. Strange...

Did Dolby make a switch at some time, as with the DMA8 to DMA8+ to facilitate interfacing with the CP650/DMA8+ class of devices with 1:1 cables? Are there 'old' CP750 in the field and CP750+?

- Carsten

Posted by Jim Cassedy (Member # 4115) on 08-22-2013, 03:47 PM:

quote: Alexander Alves
The manual you are referring to may be old.

Exactly! -

The manual I was originally referring to came off of the Dolby extranet website,
and is apparantly very out-of-date. (D'oh!) I think it was an "Issue Vers 3".

I went down to a theater that recently 'went digital' & talked them into letting me
borrow the documentation disk that came packed in the box with their new CP750.

It's an "Issue 5" and they've changed the pin-out pictorial diagram so that it
agrees with the pin-out table elswhere in the manual.

I found one or two other discrepencies between the manuals too. I copied the
new manual offa the disk, & deleted the old one I had on my computerthingy.

Posted by Carsten Kurz (Member # 5396) on 08-22-2013, 07:22 PM:

Jim, could you make this rev5 manual available to me? I have a rev4.

Unfortunately I can not email you through the forum.

- Carsten

Posted by Steve Guttag (Member # 268) on 08-23-2013, 05:58 AM:

Issue 5 is on the Dolby Secure site AND a DA20-CP750 pinout table in a separate document.

Posted by Steve Moore (Member # 4753) on 08-23-2013, 11:18 AM:

I've just done the same thing with my CP750 and the output of a CP65.

The cabling for the analogue in (multi channel in) is the same pin numbers as the output ones... the plan being that if your CP 750 failed you could still plug the output of the CP(55/65) straight to the amps... (plug the male and female D25 together and bypass the 750) If you use the pin numbers for the output in the 750 manual as a reference for the pin numbers for the input that should be the same.