Film-Tech Forum ARCHIVE: Dolby Analog sound track reader to L+R line level outputs

This is topic Dolby Analog sound track reader to L+R line level outputs in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Gavin Lewarne (Member # 5397) on 05-04-2013, 04:51 AM:

Is it possible to convert the output from a dolby analog reader to basic L+R line level outputs to feed into another processor?

Basically we have a 35mm machine and a CP45 that is currently tied in to the analog inputs of our CP750.

Since we haven't played a 35mm film in over 6 months now I dont think that spending money on repairing or replacing our CP45 (center channel gone) is really viable for us, so was wondering if I can somehow convert the output of the reader into basic line level L+R to feed into the non-sync input of the 750. I dont see us playing anything other than restored or archive prints of really old films on the 35mm any more - and most of the ones we have had have been mono anyway.

Do i just need a preamp and a bit of soldering? I believe that the dolby reader outputs are balanced (red,black and shield on each channel)

is this even possible? I am aware we would lose channels but am not really sure if the L+R tracks on the film itself make a viable sound themselves without going through a processor...

Thanks!

Posted by Bajsic Bojan (Member # 4928) on 05-04-2013, 05:22 AM:

you can, it is always 2 channels that go to the CP, they sound decent, this has been done alot so don't worry.

you can solder on som xlrs or 1/4" and feed a mixer if need be. there is no processing or noise removal tho, so it will sound a bit harsh (as in agressive, with pronounced highs), and older prints with scratches to the track will sound full of hiss and pop, just like playing vinyl.

Posted by Sean McKinnon (Member # 612) on 05-04-2013, 09:43 AM:

If you had a decent reverse scan led reader and a decent pre-amp where you could set the output to the correct level using Dolby tone (300mv?) would the non-sync input decode 2:4 if you set up the format for it?

Posted by Louis Bornwasser (Member # 3063) on 05-04-2013, 01:23 PM:

I'm with Sean. Please consider how much noise reduction helps your quality if not in Mono. I would consider either repairing the cp45 or just buying another on ebay or used; should be cheap. louis

Posted by Alban Birch (Member # 4121) on 05-04-2013, 03:39 PM:

Or get a CP55/SRA5 or CP65, they have a post-NR output which you can hook to the NS-in of your CP750 with Pro-Logic decoding

Posted by Scott Norwood (Member # 30) on 05-06-2013, 10:13 AM:

Another option would be a standalone NR unit (e.g. Dolby 363 with cat. 300 cards).

Posted by Richard Hamilton (Member # 321) on 05-06-2013, 12:24 PM:

What about just putting the CP45 in bypass, then you get a summed mono mix to all three stage Channels. If you have no center output from the CP45, then just take left or right output and send it to the center analog input of the CP750. You'll have a mono signal which it sounds like is all you want.

Rick

Posted by Gavin Lewarne (Member # 5397) on 05-06-2013, 12:32 PM:

Thanks for the replies everyone. I will speak to the boss and see what money (ha!) is available, but now I know there are other options that can be explored.

Ta!

Posted by Gavin Lewarne (Member # 5397) on 05-07-2013, 08:41 AM:

Ok had another thought before i write off the center channel on the cp45 as completely gone.....

Curently the cp750 is getting the signal from the phoenix connector ouptuts on the back of the 45. Is the 25 pin D-Plug "Booth Monitor" output on the back an exact replica of the phoenix connector outputs? as in level is adjusted by the fader and EQ dials on the front panel?

I might solder up a temporary cable to see if the center channel works on that connector.

I have the schematic and output diagram but it makes no mention of whether the signal going through it is the same as the phoenix connectors.....and I dont want to waste my time soldering if that is completely not going to work

Posted by Louis Bornwasser (Member # 3063) on 05-07-2013, 01:01 PM:

Probably. A used cp45 is prob 4-600 dollars in the USA. The offending board might be in an SA-10 adapter which should be even cheaper. (CP45s were scuttled into the SA-10 initially so a lot of the boards are the same.) This means repair could be very cheap.