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This topic comprises 2 pages: 1 2
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Author
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Topic: New Analog Sound Readers
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Mark Gulbrandsen
Resident Trollmaster
Posts: 16657
From: Music City
Registered: Jun 99
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posted 07-30-2000 03:12 PM
Gord, Are you sure its not a current converter? I seem to remember Sam Chavez saying that it was ment to be used that way.Bob,
Thats what Christie does for their projector scanners. The Preamp is removed from the scanner assy and is attached by a short length of shielded cable. The preamp is mounted on the frame of the projector right behind the scanner.
I am making an analog scanner for a AA_2 right now that will utilize a Christie reader cause it has a short focal length lens that allows it to fit on the original casting...although the casting requires some re-machining to mount it. I also have to make a new LED mount as well.
Mark Mark
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Bill Purdy
Expert Film Handler
Posts: 139
From: Seattle, WA
Registered: Oct 1999
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posted 08-01-2000 12:06 PM
Gordon, you are correct about the photo-cell and this is why the pre-amp in the sound head does just what you are asking for. I am not enough of an electronics theoretician to be able to explain it fully, but the net is that the cell looks into the (-) input of an op-amp and the feed back network holds that node very close to ground so that there is no effective voltage----just current. As the circuit of the pre-amp is Dolby's, I am reluctant to publish it without their permission. I think, note that "think", that the distortion you refer to is a function of cross mod artifacts which is one to the purposes of the "High Magenta" tracks.As to the matter of the removeability of the photo cell etc., Our design philosophy from the beginning has been that it was our responsibility to provide an assembly that has been properly adjusted for magnification, track placement and all that sort of thing. Yes, there are those out there who are fully capable of doing this properly, but there are a lot more who are not aware of all of the factors to be considered. So, we build them as an assembly that is clean, dark and not easily damaged. ------------------
Bill Purdy
Component Engineering
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