This is topic Amplified Power into Non-Sync in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Adam Fraser (Member # 1074) on 06-06-2002, 10:12 PM:
Is it safe to put an amplified source into the non-sync input of a CP55? (Amplified A-B selector with a volume control) This would be to switch between digital audio of our slide projectors and satellite music.------------------
Adam Fraser
www.pinestheatre.com
Posted by John Walsh (Member # 168) on 06-06-2002, 10:14 PM:
No. You could easily blow out the input preamp.
Posted by Adam Fraser (Member # 1074) on 06-06-2002, 10:16 PM:
Thats what I was thinking and why i asked, does anyone know of an unamplified A-B selector with a volume contol on it?
------------------
Adam Fraser
www.pinestheatre.com
Posted by Frank Angel (Member # 248) on 06-06-2002, 10:48 PM:
Unless the LINE output of the two sources are very different i.e., one much louder than the other, there really is no reason to use a volume control. A simple toggle switch that will select one or the other, will do just fine. The non-sync inputs on most cinema processors will accept consumer level outputs. If you find that the level is too hot going in, i.e., you need to turn down the main fader lower than when playing film (not likely), then you may want to put a stereo pot between the toggle switch and the cp input. BUT if the level is significantly lower than your film playback level, then you will need find out if your cp has a seperate gain for the non-sync input or if not, you will need to buy a cheap preamp to boost the level. But as John has already said, never EVER ever apply the output of an amplifier into the line level inputs of a cinema processor, or to any other line level device.
Posted by Paul G. Thompson (Member # 655) on 06-07-2002, 02:03 AM:
No. You can go to Radio Smack and pick up a simple rotary switch to select your input feed to the CP-55. However, the output level of both sources should be the same. If you have only two sources, a toggle switch would work very nicely as Frank suggests.
If the output levels of the two sources are different, build a "T" pad to attenuate the strongest of the two to match the weakest one.
There is a website you can download a neat program that will calculate the size of the resistors needed to make a "T" pad to attenuate the audio signal. To be accurate, you have to know the input impedance of the CP-55, and the output impedance of your signal source. I think the manuals will tell you that.
http://www.rfspec.com
Of course, it is possible to create a separate format for one of your additional audio sources if you so desire.