Film-Tech Forum ARCHIVE: RCA Photophone Laser Conversion

This is topic RCA Photophone Laser Conversion in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=004435

Posted by Paul Trimboli (Member # 1509) on 01-14-2003, 08:13 AM:

I will hopefully be getting an RCA Photophone soundhead and would like to fit Stereo sound as well as a RED laser in place of the exciter lamp. What problems will I face? I plan on installing this into a theatre so am going to make it professional! If I install stereo cells, how can I test to see if I have them set propoerly? Where can I obtain stereo cells? Can I just cut some solar cells down to size? Do I need to install a slit lens, or take it out and just use the laser with it lens and focus system? How many Watts should the laser be? I was think of using lasers off this site http://www.oatleyelectronics.com/lasers.html Probably the 10mw module I was thinking. What kind of power supply would I need? What kind of adjustments should I make avalible or either the Laser or stereo cell mounts? What test equipment will I need to test it? I know some will say it is not possible, it has to be possible! Thanks for any help you can offer me.

Posted by Scott Norwood (Member # 30) on 01-14-2003, 10:19 AM:

You don't need the LED reverse-scan modification if you just want stereo. Kelmar sells the brackets and solar cells that you will need. You might want to upgrade the sound optics as well if they are old or damaged.

The Dolby manuals spell out the alignment procedure quite nicely, though it would probably cost you more to buy the test films and oscilloscope (if you don't already have them) than it would to hire an experienced tech to do it for you.

Posted by Ken Layton (Member # 133) on 01-14-2003, 11:17 AM:

Kelmar Systems makes the solar cells & mounts for many makes/models of soundheads. Visit their website of www.kelmarsystems.com see the section called "transducers" (linear is mono, bi-lateral is stereo). They also make LED reverse scan kits. It would be helpful to have the model number of your soundhead handy. Component Engineering (www.componentengineering.com) makes an excellent lower cost reverse scan LED kit for the old RCA 1040 and 1050 soundheads that don't require you to carve up the soundhead castings in order to fit it.

Both companies would be glad to provide you with the names of their Australian dealers. Also look in your telephone directory under "Theaterical Equipment & Supplies" for other dealers.

Posted by Paul Trimboli (Member # 1509) on 01-15-2003, 12:16 AM:

I would like to convert it from not only Mono to stereo but to a RED laser light source, but I want to do it as cheap as possible becuase buying something like a JAXLIGHT is going to cost me more then my soundhead and projector is going to cost me! I am hopefully going to get an RCA Photophone soundhead and a Super Simplex head which I am going to rebuild as well as paint to bring them back to perfect working order to put into a cinema. Any help with the laser? Does anyone have any cells they have ripped out of their projector for a reverse scan system they do not need? [Big Grin]

Posted by Leo Enticknap (Member # 534) on 01-15-2003, 01:53 AM:

Scott writes:

quote:
You don't need the LED reverse-scan modification if you just want stereo.

He will if cyan soundtracks are introduced industry-wide. Personally I think this is unlikely now, because we are so close to a possible big scale conversion to [dlp]

that going over to cyan prints no longer makes economic sense.

Posted by Paul Trimboli (Member # 1509) on 01-15-2003, 08:49 PM:

I was talking to a projectionist in Austrlia who said digital cinema has a long way to go, so I do not agree that it will be taking over soon. Is there much point in my worrying for the time being about a red light source? So I just convert it to stereo and leave it at that? Any advantages to red light in normal B & W soundtracks? Is it possible to just buy the stereo cells with a mount to put inside my mono soundhead?

Posted by Steve Kraus (Member # 476) on 01-15-2003, 09:23 PM:

There is a great advantage to reverse scan over a conventional pickup. Currently this is done with red LED's (these are not lasers, BTW). Originally the modern reverse scanners used IR LED's. (Modern because reverse scan was a technique used previously. Specifically it means that the soundtrack is illuminated and an image of it is focused on a slit in front of the pickup element as opposed to focusing a slit onto the track.) The advantages are better frequency response (you can considerably reduce the pre-amp HF gain when going from conventional to reverse scan) and much better channel separation (crosstalk reduced to nil).

Given the costs involved and presuming you have other needs I would just fit it with a stereo solar cell and worry about reverse scan later on. Remember that if you are going all out eventually that leads you to digital sound and your entire analog A chain becomes nothing more than a backup unless you primarily run non digital films.

Posted by Leo Enticknap (Member # 534) on 01-16-2003, 02:37 AM:

In truth I don't think anyone can accurately predict the timescale for the mass-introduction of digital cinema. I just get a sense that the mass-rollout of cyan prints has been quietly abandoned, possibly because of exhibitor resistence or because the labs don't want to invest in upgrading their production lines. If digital cinema is in any way imminent, this could be a possible factor behind that decision.

Posted by Steve Kraus (Member # 476) on 01-16-2003, 06:27 PM:

AFAIK it does not take any investment on the part of the lab, just a different filter pack on the light source of the sound printing head and abandoning the application gear on the processing machine. They would need to run some tests to determine the optimum exposure but that's about it. I'm sure they would gladly do this at the drop of a hat given the order as it will save them money.

Posted by Gordon McLeod (Member # 33) on 01-16-2003, 08:12 PM:

ACL makes an exclent laser scanner for the RCA type scanners
http://www.audio-cine.ch/index-en.html

Posted by John Pytlak (Member # 331) on 01-17-2003, 02:12 PM:

Here is what labs need to do to produce compatible "high magenta" dye+silver prints, and eventually cyan dye tracks without silver:

http://www.kodak.com/US/en/motion/support/sstLabGuide.shtml

http://www.kodak.com/US/en/motion/support/dyetrack.shtml

At this week's ITEA and Inter-Society meeting in Los Angeles, Ioan Allen of Dolby reported that it's likely conversion to cyan dye tracks will happen this autumn (September 2003), after at least 80% of screens meet NATO's recommendation of a July 2003 conversion to red LED readers.

A majority of screens already have red LED readers, with over 80,000 red LED modules having been sold worldwide. Ioan reported that over 5000 red LED modules have been sold by Dolby since September 2002.

Posted by Peter Hall (Member # 695) on 01-19-2003, 05:43 AM:

HI -

Are you looking at going through or replacing the slit lens ? We have a range of laser units that replace the lens with a line generating laser with a special lens and vernier width adjustment. Sleeves are available for most projectors - I think the RCA uses the same lens as the Century ..

Advantages of these are full cyan compatibility plus the same xtalk and hf response of a reverse scan LED reader, plus the lasers last "forever". Have a look at www.fproj.com/cyan for details

Posted by Sam Hunter (Member # 1119) on 01-19-2003, 09:36 AM:

Peter that link is dead for me.

Posted by Mark Gulbrandsen (Member # 72) on 01-19-2003, 09:42 AM:

Peter,
I've used Laser kits before and I agree that the laser's have a longer life, however you still have that damed solor cell hanging there. Can't tell you haow many service trips I've made for those things comming out of alignment, or being chipped by a passing piece of film that is bent over.....I much prefer the reverse scan units over anything else. They're easy to install, and super reliable. Can't remember EVER making a service call on one after it was installed. I have replaced a number of red LED's though, but not a really large number. Most of those led replacements have been in digital sound heads too. Switching the red led's on ond off really saves them big time.
Mark @ CLACO
www.clacoequipment.com

Posted by Paul Trimboli (Member # 1509) on 01-20-2003, 06:39 AM:

I know reverse scan is good, but the cost is too high. If this goes into a cinema it will not be there long as it will be upgraded within a couple of years of service, so providing the sound is good then that is all that matters. The cinema I work at has just installed a reverse scan reader and has had problems, a show was cancled today becuase it died, not sure what the service guy did to fix it, went home [Wink]

! So all I want is stereo and a red light source!

Posted by Steve Kraus (Member # 476) on 01-20-2003, 08:20 AM:

and a red light source!

If your exciter socket and slit lens are good and you have a power supply I'd go the conventional route for now and see what happens. You can always go red later.

Posted by Mark Gulbrandsen (Member # 72) on 01-20-2003, 09:40 AM:

"If this goes into a cinema it will not be there long as it will be upgraded within a couple of years of service"
__________________________________________________________________

Actually, I think it'll be there quite a bit longer than a couple of years! Do you work for Uncle George or something?
Mark @ CLACO
www.clacoequipment.com

[ 01-20-2003, 08:35 PM: Message edited by: Mark Gulbrandsen ]

Posted by Bruce Hansen (Member # 281) on 01-20-2003, 04:19 PM:

I have put a piece of red jell in between the white excitor lamp and the lens. It did not drop the audio level very much, but did turn the light on the film red. I did not have any cyan track film to try through. Has anyone else tried this, and what does everyone think of this as a "fix" on a tight budget?

Posted by Richard Fowler (Member # 893) on 01-20-2003, 05:18 PM:

The red gell may work if the red transmission is 660nm +/- 20nm which is highly doubtful; the infrared output of a conventional exciter bulb would bleach out the gel in a short time so output would be unreliable. Kinoton has an economy retrofit kit for some of their projectors which use a halogen bulb ( very little drift over the life of the bulb ) and a dichoric filter to convert to 660nm red output as an option of using the Dolby DPN 32075 LED that most manufacturers are using or USL large red diode or Laser.
Richard Fowler
Kinoton America Inc.

Posted by Steve Kraus (Member # 476) on 01-20-2003, 08:27 PM:

Huh? I don't understand the point of filters, whether gel or dichroic. They reduce frequencies of light that are not going to be modulated by the cyan-only dye but is that going to increase S/N? I would think you can only do that by increasing red output not by decreasing other colors.

Posted by Mark Gulbrandsen (Member # 72) on 01-20-2003, 08:35 PM:

Steve,
The halogen lamp would be designed for high output in that important 660nm wavelngth region, and the dichroic filter, if designed correctly, would only suffice to trim that a bit further on either side of the operating realm of the lamp and to bring it in to exactly the 660nm +/- 20nm wavelength. The system overall would work more efficiently that way.
Mark @ CLACO
www.clacoequipment.com

Posted by John Pytlak (Member # 331) on 01-20-2003, 09:56 PM:

Any red filter made of dye would be relatively transparent to infrared, and therefore ineffective in reducing the unwanted infrared sensitivity of the reader. They would also be prone to fading. A dichroic filter may be possible, but would likely be more expensive than red LEDs and not have the advantages of a reverse scan red LED reader.

Here are the spectral dye densities of the dyes used in Kodak VISION Color Print Film 2383:

http://www.kodak.com/US/plugins/acrobat/en/motion/products/curves/ti2397d.pdf

You can see that 660nm is right at the peak density of the cyan dye, and that the film dye densities fall off in the infrared.

Posted by Paul Trimboli (Member # 1509) on 01-21-2003, 07:18 AM:

I had thought of just keeping the normal optics, have not got the soundhead so I hope they are in good conditon. I know I can go red latter, just worries me if I can do it cheap though! I had thought of red filters, but thought of the problems as well. What kind of price in Australian $$ would I be looking at for a red light source as well as for a reverse scan reader with red LED?

Posted by Gordon McLeod (Member # 33) on 01-21-2003, 09:48 AM:

Kinoton offers a dichroic filter slide projector styled excitor lamp as an option for there machine

Posted by Peter Hall (Member # 695) on 01-22-2003, 01:32 PM:

Mark -

I agree that if the budget allows it a manufacturers (or third party kit for American machines) is the best option. However where the client is looking at a low cost retrofit kit (esp when they have a penthouse SRD reader and analogue is a back up) we prefer these lasers over the Jax Lite and the ASL laser. We've had bad noise problems on the Jaxlites in Kinotons, and the ASL laser doesn't live up to it's promoise of being operator changeable as the gain and HF change so drastically (or at least they should)

Posted by Peter Hall (Member # 695) on 01-22-2003, 01:33 PM:

Sorry - wrong link

Try http://www.fproj.com/feature.htm

Peter

Posted by Gordon McLeod (Member # 33) on 01-22-2003, 03:11 PM:

peter do they have the same uneven illumination that the Ernamann laser and the Japan one that CPI has exhibit in that with the SMPTE unifomity test film it graphs out like a bell curve. THE ACL is very smooth in my experience

Posted by Steve Kraus (Member # 476) on 01-22-2003, 05:46 PM:

I'm still not clear on this. Is reducing light flux in the regions that will not be modulated by the cyan dye (whether IR or colors other than red) going to increase the signal strength?

If the pickup is a solar cell then I can see how the unmodulated light is going to give...well, make that increase, since it's always there...the DC bias but that should have no effect on a transformer or electronically balanced solar cell preamp input.