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Author Topic: Low cost homebrew red LED light source for cyan tracks Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-14-2003 01:45 PM                     Here’s a low cost way for those of us with home theaters (and a beer budget) to upgrade to a red LED light source for reading those “dreaded” cyan sound tracks. I adapted a $10 (approx) Lumiled Luxeon Star LED to replace the tungsten exciter lamp in one of my SH-1000 soundheads. See Lumileds : Lumileds homepage The Luxeon Star red LED array comes mounted to an aluminum backplate about the size of a US twenty-five cent piece. It produces a maximum of 55 lumens, which is 10 times the light of a so-called “super bright” LED. It can be operated at 200 mA without a heat sink and up to 300 mA with additional heat sinking. 100,000 hours is the predicted lifetime. Here’s how to adapt one for use in your soundhead: (1) Take an old exciter lamp and remove the glass envelope, keeping the base and center wire. Put the lamp in a heavy clear plastic freezer bag and carefully break the glass using a pair of pliers. Carefully remove all the broken glass – might be a good idea to use safety glasses when doing this job. (2) Clean the center wire and metal lamp base with fine grit sandpaper to prepare for soldering. (3) Place some tubing over the center conductor to keep it from accidentally shorting to the base. (4) Using two pieces of reasonably stiff solid wire, solder the ground terminals of the Luxeon star to the lamp base. (5) Solder the center conductor (using some flexible light gauge stranded wire) to the two positive terminals of the Luxeon star. NOTE: the center of the LED array should be positioned approximately in the location where the filament of a standard tungsten exciter lamp would be. See photos: Front view: Side view: Back view: (6) Be sure the positive of your exciter supply is connected to the center pin of the lamp base. (7) Next install a suitable dropping resistor in the positive lead feeding the removable lamp assembly. I opted for a 68 ohm, 5 watt resistor, which gives a current of 170 mA from my 13.5 V supply. I also placed a 1000 MFD capacitor across the exciter terminals to reduce the turn on “pop”. There’s plenty of room inside the soundhead for these parts. See photo below of series resistor and capacitor: These LED’s are REALLY bright. Don’t stare at it. Performance is superb! Using an eye loupe, the slit appears to be VERY evenly illuminated. I didn’t even have to increase the gain of the preamp. (Although I had to touch up the focus and buzz track adjustment slightly) All this was done using standard silver soundtracks and a Kelmar mono pick up. I need to get another red Luxeon star to test my other soundhead that has a stereo solar cell. No reason to doubt that performance will be just as good. Also, does someone have a small amount of film with a cyan track to test this contraption? Sorry about the poor available light photo of the LED in operation. Thoughts? Ideas? Additional experiments?  |  IP: Logged Jim Spohn Film Handler Posts: 95 From: Bakersfield, CA, USA Registered: Jan 2003 posted 08-14-2003 02:13 PM                     Jeff...Nice work. Very cool idea. Thanks for sharing. Jim Spohn  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 08-14-2003 02:46 PM                     The big problem I am seeing is the potential for the light to not be evenly spread across the slit. Do you have a uniformity loop? I would be interested in knowing the results.  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-14-2003 02:56 PM                     Brad, No I don't have any test film. I'm just a tinkerer using what I have. Best info I can give you is that I examined the slit of light projected on a piece of white paper affixed on the sound drum. I looked at it with a 5X eye loupe and it looked uniform to me.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 08-14-2003 03:12 PM                    The other question would be whether vibration is going to vary the alignment enough to create microphonics. But overall it seems like a great idea. Someone ought to go into production on this.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 08-14-2003 03:26 PM                        Possible issues: 1. Light output (effect on S/N) 2. Uniformity of illumination across soundtrack 3. Microphonics (variation of light with vibration) 4. Life expectancy (how hard do you need to drive the LED?) 5. Wavelength (near 660nm? any unwanted wavelenghts?) 6. Cooling (should you use the recommended heatsink?)  |  IP: Logged Jeff Stricker Master Film Handler Posts: 481 From: Calumet, Mi USA Registered: Nov 1999 posted 08-14-2003 04:09 PM                     I've beat on the soundhead and don't notice any microphonism, but that's not to say there's not any (my ear in the speaker is the "test equipment"). Certainly could stiffen up the support wires if need be. John, I believe heat sink isn't necessary as I'm running below 200 mA. The Spec sheet I have says heat sinking only necessary from 200 - 300 mA. I decided not to add any additional mass (additional heat sink) to the structure for microphonism reasons. I'm getting plenty of output at this current level (170 mA) and don't see the need to run it at a higher current. BTW, putting finger on heat sink shows it is only slightly warm.  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 08-14-2003 04:46 PM                        The wavelength of the Luxeon Star is 630nm... a bit higher frequency than the 660nm standard, but close enough "for jazz" as they say. I'm going to try one myself!  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-14-2003 08:50 PM                     Everyone here overlooked the fact that you still have the two pieces in there that cause the MOST degradation to the sound to start with. That is the slit lens, and the solor cell. Thats why I could never ever install a JAX Light and still sleep at night. You're not really doing your customer ANY favor at all by installing one. Now if ya can come up with a 10 buck way to get rid of those......... Mark  |  IP: Logged Phil Radosevich Film Handler Posts: 22 From: Centerville, IA, USA Registered: Jun 2000 posted 08-16-2003 06:29 AM                     Two comments. What color do you use as the web site lists a cyan color. To reduce vibration why not add a third ground wire or use music wire  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 08-16-2003 06:46 AM                        None of the listed potential problems seems to be too difficult to overcome. Which shows us that we could have had a simple LED based conversion lamp with a solid frame for maybe $20-30. Yes, I know the real improvement is the reverse scan, but as a solution for converting to red LED readers it is a great prototypical concept. We want to play in digital anyway, and only have the analog readers as fallback. After all, our main concern here is the environment, right?  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 08-16-2003 09:26 AM                     Did you use the LXHL-MD1D Luxeon star? I want to try this as well. Someone correct me if I am wrong, but doesn't a reverse scan reader still have a slit lens, and solar cells? Yes, the lens is better designed, and the whole thing works in reverse, but there is still a lens, and those are solar cells on the other end of the lens, I believe.  |  IP: Logged Paul Trimboli Master Film Handler Posts: 274 From: Perth Western Australia Registered: Dec 2002 posted 08-16-2003 09:32 AM                     That is true about reverse scan, but what Marc is saying is that a bad splice for example can come past and rip the cells out of aligment. That is their main advantage, the ones I have used had no real aligments, all soldered into place. Well in a Cinemecannica one anyway! I am very excited about this cheap development in cyan track reading!  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 08-16-2003 10:48 AM                    Yes, conventional cells are subject to damage from errant splices but I believe Mark is referring to the huge improvement in separation and HF response with reverse scan. But let us be careful here as we are mixing apples and oranges here when we start equating the change to red LED with the improvement that is brought about by reverse scan. Then you fall into the trap promoted by the dye track people who would like everyone to believe that dye tracks lead to better sound. Reverse scan leads to better sound. I don't know the price of a JAXlight vs. a full reverse scan upgrade but I agree with Mark in general that, assuming a JAXlight is not inexpensive, one would be better off investing in reverse scan and get the big jump in quality. BUT, conversely, if someone is content with the quality of conventional scan--let's say they run almost always in digital and analog is just a rare backup; or a home user, maybe even mono--well then a ten dollar conversion makes a lot of sense and you don't feel like you're wasting money that ought to have been spent towards reverse scan. If and when you do reverse scan later on you've only wasted ten bucks. Even Mark could probably sleep soundly with that. Bruce: No, a reverse scan system does not have a slit lens per se. The image of the soundtrack is projected ON TO (and focused on) a mechanical slit with the pickup behind it. Because the image is being enlarged a slit of a given width is the optical equivalent of a much finer slit on a conventional slit lens system but without weird diffraction effects. You also don't have the weird crosstalk effects from light bouncing off the cell, off the back of the film and back to the cell. Separation--at least visually on a scope looking at X-Y--becomes virtually 100%.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 08-16-2003 11:11 AM                     A conventional forward scan is in effect looking at a shadown of the soundtrack on the cell face so in fact you will not get as good of HiFreq response or seperation because of the scatter effect. The only alternate is the use of a laser slit (ernamann and ACL and Peter Hall et all) as it projectes at a constant width through the film to the cell Also the gain with red light needs to be higher so an exposed cell is more prone to amplifie extranious noise  |  IP: Logged

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