This is topic Non sync level on a CP50 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Tom Kroening (Member # 201) on 03-16-2002, 01:12 PM:
Hey everyone. We're currently having a few video projectors hooked up for ads. The guy thats doing the install can't seem to get the nonsync level down in one of the houses. I verified that the non sync pot is turned all the way down, yet the sound is still coming out really load. All I can think of is to get something to go inline with the preamp signal from the dvd player (like a volume adjuster on a set of headphones). I haven't taken a close look at it yet, but I will be tonight. Does anyone have any suggestions? Or maybe this has happened to you before? I don't think the CP50 was designed in mind with being hooked up to a DVD player to begin with 
but hopefully we can get it to work. Thanks!
Posted by Scott Norwood (Member # 30) on 03-16-2002, 01:19 PM:
Which switch card do you have? The cat. 113c "automation" card that uses a little screw to adjust the non-sync level or the regular cat. 113 with the mechanical pushbuttons that has a large knob for adjusting the non-sync level?
Posted by Brad Miller (Member # 2) on 03-16-2002, 03:04 PM:
Too much time has passed with me and CP50s for be of much assistance here from memory (and I don't have access to look at one for a memory refresher), but I do recall seeing that a LOT of CP50s had their non-sync wired through projector 2 of the optical preamp card for various reasons, others inputted the signal into the magnetic inputs. Can you verify which input is being used?
Posted by Steve Kraus (Member # 476) on 03-16-2002, 04:09 PM:
The standard CP-50 switch card with mechanical pushbuttons is Cat.112 and has no volume control for the non-sync/mag input. It simply switches this input directly to the amps. No volume, no EQ, no nuthin. If the source device does not have an output level control you must create one with a potentiometer mounted somewhere on the soundrack.I can't see any reason to hook up to the optical input unless for some reason the level is so low it can use the added boost. Perhaps people did this as a quick and dirty alternative to wiring up a non sync level pot?
Posted by Tom Kroening (Member # 201) on 03-16-2002, 04:24 PM:
It is the newer automation card. I'll have to check all the inputs on the back when I go in tonight. Does anyone know where I would get such a device that could lower the preamp signal before it gets to the processor?
Posted by Steve Kraus (Member # 476) on 03-16-2002, 05:09 PM:
Are you handy with a soldering iron? A 100K, dual gang (stereo) pot from Radio-Shack, etc. would do the trick. Wire it so that the "hot" signal lines from the source are connected to the ends of the potentiometers that the wiper reaches when turned to maximum clockwise while the counter-clockwise ends are each connected to the common / ground. Thus, the wiper sweeps across a range running from ground to full power. It's odd that you can't control it with the existing control but this should reign it in. 
Posted by Jon Bartow (Member # 241) on 03-16-2002, 08:58 PM:
Please don't be offended, but do you have the external fader connected? The CP50 needs a 100K linear taper pot connected to control the main "volume" (or one of Dolby's external fader boxes)
If you don't have the pot connected than IIRC the volume is at max and your 300mv+ signal from the DVD would be very loud.
Posted by Gordon McLeod (Member # 33) on 03-16-2002, 10:11 PM:
For the audio from the nonsync to be routed throught the fader the daugther board on the backplane is requried
Posted by Tom Kroening (Member # 201) on 03-17-2002, 04:42 AM:
I think you guys hit the nail on the head. The external fader might be hooked up wrong, although it works for the main volume. To solve the problem I just went to radio shack and got one of those inline headphone volume adjusters, put RCA cables on each side and pluged it into the audio output of the DVD player. 20 dollar solution that saved me from messin with that old dinosaur. Hopefully she keeps workin! Thanks everyone.
Posted by Gordon McLeod (Member # 33) on 03-17-2002, 12:00 PM:
Well I doubt the fader is wired wrong if it works as the main fader
One must remember how the processor was designed to be inserted into an exisitng 4 track mag system
Posted by Peter Hall (Member # 695) on 03-28-2002, 12:07 PM:
HI -The CP50 Cat 113C non sync level control is hopeless - a standard CD player blasts the audience out of their seats. But a CP50 even with a Cat113C does (from memory) not use thte main fader to control the non sync input. Assuming you're coming off DVD (as you said, the CP50 was not quite designed with a DVD in mind - in those days - I was still in school (!!) - CD's weren't in widespread use !) and using the LtRt outputs of the DVD wouldn't you want to utilise the matrix in a CP50 ? Once again from memory if you mod the CP50 as if it were receiving a SRA5, then hack into the return path from the SRA5 to the CP50 you'd achieve this. Select SR - return path would go thru the Cat150 with no NR. You'd still need to screw around with levels to get the ideal 300mV however.
Good luck
Posted by Steve Kraus (Member # 476) on 03-28-2002, 03:51 PM:
It is possible to introduce line level LtRt signals at a number of points on the CP-50 including at the stage of the 110L/160 slot just before the Cat.150. I'm not sure it makes sense to run this material through the matrix though, unless it was mixed with matrix playback in mind. Otherwise it may just bunch up on C. You'd have to listen to it and decide whether the normal, direct way is ok or whether it's worth the trouble to get it through the EQ cards (and fader).Are CD (and DVD) player outputs not line level?
Posted by Gordon McLeod (Member # 33) on 03-29-2002, 11:56 AM:
On the back plane one could connect to the preamp out terminals but the otpical preamp would have to be removed first or to the terminals marked external surround adapter but the before hand cards should be unplugged
Some electronic devices don't particularly like a signal flowing back into there outputs 
Posted by System Notices (Member # 2357) on 10-18-2008, 01:43 PM:
It has been 2395 days since the last post.
Posted by Dominic Espinosa (Member # 2122) on 10-18-2008, 01:43 PM:
I have a dumb question...
I'm currently going into a CP50 from a DVD players stereo out via the projector 2 input -- works pretty well.
But I wonder if perhaps I could take advantage of the free mag input/would it be worth the trouble?
Is there a cheapish way to control the volume for the mag input?
Posted by Tony Bandiera Jr (Member # 2365) on 10-18-2008, 01:55 PM:
See Steve's second post of 3/16/02 above.. and connect the outputs (on the right) to whichever channels of the mag input you'd like to sound to come out of.
Simple and cheap.
Posted by Marin Zorica (Member # 1716) on 10-18-2008, 05:53 PM:
SO problem is solved for controlling CP50 non sync....better is to use 10K LOG potmeter for controlling audio from CD/DVD to CP.
But why did dolby did such stupid non sync on it?? Is stupid when non-sync don't pass EQ and main volume controll. They might been for external (magnetic in that days) but even then is better to have central processor unit and all sources connected to it(CP50 in this case)and controlling volume along with EQ on it.
Posted by Sam D. Chavez (Member # 1841) on 10-18-2008, 07:44 PM:
The CP50 was designed in the mid '70s to be a retrofitted to 4 or 6 track mag systems. The Ampex system for instance, had a number of inputs on a motorized Ledex switching system. The original unit did not even have an internal VCA fader card and used the house 4 or 6 track mechanical fader instead.
Later units had a Cat. 117 fader card controlled by an external fader box which was a 100K linear pot.
The CP50 succeeded beyond expectations and a lot of mono systems were starting to be upgraded to stereo and this was the first choice of most.
A number of mods were made to the unit over time to help with its shortcomings and the CP50 was eventually superceded by the CP55.
Posted by Louis Bornwasser (Member # 3063) on 10-19-2008, 10:48 AM:
An OK processor.....change all the boards and you get a wonderful processor. It was, however, cheaper to just replace it. Louis
Posted by Dominic Espinosa (Member # 2122) on 10-20-2008, 02:51 PM: