Film-Tech Forum ARCHIVE: How to improve optical sound on a DP70 for a couple of bucks!

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Topic: How to improve optical sound on a DP70 for a couple of bucks!

Thomas Hauerslev
Master Film Handler

Posts: 451
From: Copenhagen, Denmark
Registered: Aug 2000

posted 08-09-2000 04:16 PM

Newly developed photographic slit masks for the DP70 optical sound head enable the DP70 to faithfully reproduce audio up to 12.5 kHz at 0dB with little slit loss compensation added in the pre-amplifier stage. This is equivalent to a half-mil slit or less in a forward scan sound head.

Check this out:
http://hjem.get2net.dk/in70mm/dp70/projector/mask.htm

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-09-2000 04:37 PM

Thanks Thomas
I have contacted them and have one on the way

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-09-2000 05:08 PM

Hey guys,
Thats a great idea but what about Cyan tracks? The only other option right now is the JAX light with the new Todd-AO slit if the JAX light can provide enough illumination. If you intend to stick with exciter lamps, and some theaters that run a variety of older films should, expect to go through a bunch of exciter lamps as the voltage will have to be cranked up. You also may have to replace the light tube to acheive a high enough light level on the film. This brighter spot may also cause the film to get very hot at that point and actually melt through. All systems have trade offs, you just have to look at whats best for your operation.
I'm almost done developing a RED LED reverse scanner retrofit that will improve it beyond that. It uses the short Christie Analog reader assembly as this is the only analog reader small enough that will fit in the DP-70's space alotment. It does require some re-machining of the sound head casting, and the incandescent exciter will no longer be able to be utilized. However,it does use the original rotary stabilizer. If enough people are interested in them I could have new castings made for the optical so the original can be maintained in as is condition. This gets quite expensive however and will drive the price way up. My target price to do the modification is under 1500.00 U.S. including the Scanner and LED assembly, and necessary machining of the casting.
Personally, for those that run DP-70's on a day to day first run basis the RED LED- reverse scan is the better way to go. A basement digital pickup is also possible with this modification.
Mark

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-15-2000 01:04 PM

I got my new and improved masking today from Todd-AO. It's a piece of film!. I'm going down to install it now.

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 08-15-2000 02:52 PM

what was the cost

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-15-2000 11:15 PM

Hey this is starting to look pretty good. Listen I'm no tech, and I sure could use some pointers, but my RTA says I am getting out to 12.5k flat. I have some more tweaking and cussin to do. I'm having to go by the CP65 manual as I'm real green at this. I wish it could talk so I could ask it some questions

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-16-2000 02:33 AM

Greg,
Is this with the standard exciter in there or a JAX light?
Mark

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Alan Lyman
Film Handler

Posts: 13
From: Copenhagen, Denmark
Registered: Aug 2000

posted 08-16-2000 07:12 AM

We have both the new slit and the Jaxlight,and
are very happy with both.
I have seen pict. of a rev/scan-digital on the web of the american kinoton dealer.
We also have a laser,but haven´t installed it yet.

Alan Lyman
Denmark

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Martin Frandsen
Master Film Handler

Posts: 270
From: Denmark, Europe
Registered: Jun 99

posted 08-16-2000 07:27 AM

Alan, do you use the JAX lights on the DP's at the Imperial Bio in Copenhagen, Denmark?

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-16-2000 08:29 AM

Mark
So far it's the standard lamp.

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-16-2000 10:55 PM

Well there's good news and bad news. The good news is yes it does work, kinda. I can get flat to 10k without any hf adjustment. I can get to 12.5k with a 1-2db drop. I can flatten it all out within tolerance beyond that with the hf adjust. The bad news is I can't get Dolby level unless I crank up the exciter to 9.6 volts. I guess that narrower slit takes it's toll on the output. I guess the guys with the jaxlight and little slit gizmo, are getting the advantage of the little built in preamp to jax up the level before it gets to the CP. The good news is I can change test loops on a DP70 like a mother f. The bad news is I've taken the sound head apart 3 times to check everything physically and run through the "Tuning the "A" chain" routine about 6 times. I guess this will work till I can come up with somthin better. Any suggestions?

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Alan Lyman
Film Handler

Posts: 13
From: Copenhagen, Denmark
Registered: Aug 2000

posted 08-19-2000 05:47 AM

Martin
Yes we are using the Jaxligt at Imperial.

Before installing the Jaxlight we also had problem with enough light to reach Dolby-level,with the new slit.
That also happend with the Jaxlight,but I found out,that I could move the mirror,to hit the slit better,and now we have plenty of
level.

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-19-2000 08:31 AM

I found out that my little light pipe was in pretty poor shape so I stuck in a spare, which is not the best, but at least better. I was able to lower the voltage to 9.3 vdc. While I was monkeying around in there I got to looking at the problem with the light from the exciter lamp spilling toward the screen. I tried a little experiment and held a mirror so that it reflected the light back in and it increased the levels significantly! So I am going to get a little concaved mirror and build a bracket to hold it so that it gathers the wasted light (and blocks the spillage) and focuses it back to the inlet of the light pipe. I'll mount the mirror so that it lets the heat out but reflects the light. After a complete a-chain, b-chain tune up it sounds pretty good in there. More to come...

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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Stefan Scholz
Expert Film Handler

Posts: 223
From: Schoenberg, Germany
Registered: Sep 1999

posted 08-19-2000 09:55 AM

Why do you stay with the original bulb. I once used 50 W 12V halogen bulbs on my AA's, which, cleaning and maintaining the light guides worked well with the new slit we used some 9 years ago. Another advantage was the longer service life and reasonable cost of this bulb, compared to the original types.
Jaxlight, is my current solution, but it requires the preamp, and is less efficient than even the old XCTR bulb. Good thing, JAXlight came with a new and very nice light guide.
Another conversion I have seen was a defocused 3 mW laser directed on the little light guide. It worked well and was a reasonable solution. THe light output was high enough to use a narrowed slit. This I have seen in a preview studio application.

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Greg Mueller
Phenomenal Film Handler

Posts: 1687
From: Port Gamble, WA
Registered: Jun 99

posted 08-19-2000 10:11 AM

I'm real interested in the Laser light thing especially since most of them fall in the 640-670 nm range, which is the same wavelength as the red leds. Only 3mw, eh? That would be worth an experiment. Did they use the light pipe or just shine the laser right on the film?

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Greg Mueller
Amateur Astronomer, Machinist, Filmnut

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