CP750 8ch analog input connector pinout

[Marty Brenneis]

I have a CP750 that has been running in my screening room for more than a decade. I have an analog input cable that I wired up from the chart on page 69 of the CP750 manual. (I do RTFM)
Things have been fine because I just use that input for LCR from a mixer so I can do things like feed Zoom audio to the screen speakers.
Now I have a client that is handing me 5.1 as 6 discrete lines, okay I feed them into the 6 inputs. We see that Screen R comes in a few db lower than the other channels. Said client's tech then RTFMs and finds the pinout on page 15 of the friendly manual and takes my cable and rewires it. it does not seem to work well, but it also does not not work.

The question for this grand brain trust of cinema tech wizards, which pinout is wrong, page 15 or page 69.

Bonus if you can suggest why the R channel would show a lower level than the other inputs.
Extra bonus on how I might get the dolby decoder to not try and decode 5.1 from the 6 discrete channels.

Thanks
Marty Brenneis
StudioDroid
32Ten Studios

[Jim Cassedy]

I know this isn't going to help you much- - but I seem to vaguely recall running into the same problem about
7 or 8 years ago when wiring up a cable and discovering that there ARE two different wiring diagrams in the
CP-750 manual on FT, and that, yes- - they are different. Unfortunately I don't recall which one was correct.

I once mentioned this to someone at Dolby, and was told that the error was corrected in later versions of the
manual. I don't know what "Issue" version of the CP-750 Manual you have, but in "Issue 5", which is the most
current version I have, the diagrams match, and I think this is the diagram I used.
(It's also the most recent and only issue available on the Dolby website- -so I sort of assume it's correct)

(Page 15 / CP-750 Manual #5)

Dolby15.jpg

Page 69/70 (combined ) - CP-750 Manual #5
DolbyChart2.jpg

[Marty Brenneis]

Thanks, I'll try that out.

[Steve Guttag]

The CP750 uses the THX pinout on both connectors. Earlier versions of the manual also labeled Bsl and Bsr as Le and Re, in error. I believe that the original multichannel input connector was, incorrectly, labeled according to the CP200 (unbalanced) pinout. That pinout was derived by taking the JM21 ribbon cable and merely squeezing it onto a DB25 connector and then adding in the subwoofer (JM21 only had 20 conductors). This is why the channels seem so disjointed on that pinout. Conversely, the THX pinout is uniform through the screen channels and has the surrounds through the subwoofer in sequence.