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Author Topic: CP-500/70mm Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 01-12-2018 05:38 PM                        That makes perfect sense. Thanks, Sam.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 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.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 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.)  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 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.  |  IP: Logged

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