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Author
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Topic: Dolby processors' Non-Sync Input Specs
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 10-13-2001 11:27 AM
Often, people rent out our theaters for private video and 16mm showings, conferences, etc. So we have a small project going to provide a plug on the front rack to allow an external input (from, say a microphone.) It will connect to the non-sync inputs.We have chosen to use the "insert plug" idea, where there will be a female 1/4" stereo phone jack on the front panel. Also, there will be a seperate cable with a male 1/4" stereo phone plug on one end and two RCA-type connectors on the other. When the cable is pluged into the front panel, the contacts in the female 1/4" stereo phone jack will disconnect the CD player, and connect the RCA inputs to the processor. We chose this because it seemed like the best "cost-effective" way to do about 160 screens. So, two questions: Does this seem like a good way to do this? (Remember, we can't spend too much time or money: there are too many screens.) It seems OK to me, but someone may have a better idea.
Second, I'd like to put a label on the front panel describing the input spec, so people will know what the non-sync input impedence is, etc. I can only find the spec for the CP650. Are all Dolby processors the same? The CP650' is (for non-sync input #1) 21k ohm .2-4 volt.
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Bob Peticolas
Film Handler
Posts: 73
From: Mesilla, New Mexico
Registered: Jan 2000
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posted 10-13-2001 04:38 PM
I installed a small (1 RU) panel under our CP-50 with three 1/4" phone jacks and audio pots. These are wired to the left, right, center, and surround non-synch inputs.The first two are labeled "center" and "surround" respectivly. The center" is used for a hand mike when we have speakers. (I use a Nady wireless mike whose reciever output matches the input to the Dolby very nicely.) This eliminates any wiring problems and allows full freedom for the speaker to move around the house. The "surround" input is just there. Sometimes I'll plug the mike into it just for the "fullness" it provides to a speaker wandering all over the house. The third is a TRS jack with a ganged "stereo" pot connected to the left and right inputs on the Dolby. The jack is normalled to our CD player. (That is whenever nothing is plugged into it, it connects the CD player.) Whenever we have a video show, a simple 1/4" TRS plug to RCA "red" and "white" plugs (like John described) works just fine from any VCR or DVD player. This gives us independent control on the VCR/DVD playback level and the microphone level. Plus, any stereo tapes or disks are fed into the stereo screen speakers while the voice is from the center speaker. As far as playing back 5.1 or whatever, for the few times we do a video show, no one notices that its just plain "old fashioned" left-right stereo. Whenever we have a 16mm show, I just run a 1/4" to 1/4" patch cable from the speaker out jack on our B&H to the "center" jack. The difference in impeadance (4 ohm speaker to 20k+ ohm Dolby input) drops the level enough to make it work just fine. (I tried an inline 20db pad from Radio Shack, but didn't need it.) For purists, you may note that this does not give any "tone" control to anything (other than the Bell & Howell, which has a tone control). Well, we are a movie house not a concert venue. On the very few times we needed some equalization on the audio from a professional tape playback (along with the owner of the tape and his "golden ears") , I brought in a small pro audio mixer board and ran the mike(s) and tape through it. It's output went to the "left-right" jack. This gave us a lot of mixing options with full EQ on every channel. But, this is an exception, and happens about once every five years or so.
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