Film-Tech Forum ARCHIVE: Home made red light optical conversion

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Posted by Cameron Glendinning (Member # 3516) on 09-18-2009, 05:54 AM:

Several months ago, Inspired by Sydney projectionist and local legend Bob Gamlin of Walkie Talkie pictures and the Sydney Film Festival. I decided to give this a go.

It involved a 3w red led, 10 degree lens, heatsink and a power supply from Jaycar electronics (unfortunatly the led is no longer stocked) total cost less than Aust$100 with a battery eliminator that was lying around.

All that I did was remove the existing excier lamp in the victoria 5 and eventually fix the red led in its place.

The results are suprisingly clean and natural sounding, as yet we have still not bothered with a new A chain. The level easly matches the SR*D when we switch from one format to another.

Posted by Demetris Thoupis (Member # 833) on 09-18-2009, 06:46 AM:

I did something approximately the same for several open air venuew where we show some festivals in simple stereo. I used a conventional stereo cell with an off the street Laser pointer and a small modified cylinder to mount the pointer inside. It is suprisingly clear. I used a 9V DC power supply for the laser pointer. It's a cheap solution which is a compromise of course but since these are open air small village venues the client had little money to spend. Hooked the cell on a small tapco mixer (using Mic input) in two separate channels and a small equaliser send to the amp and the speakers does the job fine. 3 years working with no problems each year (just a regular check before te festivals although just typical check). Congrats.
Demetris

Posted by Damien Taylor (Member # 4255) on 09-18-2009, 12:26 PM:

This looks almost exactly like what I did with my 1040, except I don't see nearly as much blu-tack. Like you, mostly built the whole thing at Jaycar. I have almost no electrical knowledge so I barely managed to cobble my bright red mess together.

Posted by Monte L Fullmer (Member # 2797) on 09-18-2009, 01:04 PM:

Obviously, there is enough red light illumination to shoot through the slit lens to get the required brightness for the stock photocell reader to send the same voltage to the preamp section of the processor as if you were still using exciter lamp.....

That was the big downfall with Jaxlights - not bright enough for existing slit lens and photocell pickups .. thus, the preamps had to be cranked wide open and tonnage of noise were induced into the system...

Pretty slick little mod though .. my congratulations to you ! - save some dough on those exciter lamps being spendy as they are..

-Monte

Posted by Scott Christopher (Member # 834) on 09-18-2009, 08:50 PM:

We did it with various kalee projectors without any problems. We used 1watt(all that was available at the time)luxeon star lambertian without the lens/reflector. Excellent results. If we used the jaycar 1watt LED, we'd get noise from the switchmode supply as the gain had to be cranked up.

Posted by Stan Gunn (Member # 554) on 09-22-2009, 10:20 PM:

Hi all i have also done many converts useing the 3 watt leds,when useing the switch mode supplys I have had to fit a electro cap across the supply around 16v150mic stops all nasty noises.
I have have systems running for over 4 years with no probs after the need for the fitting of the cap was found.
Kalee sound lens have a higher slit than most as their pre amps were made without the smpte curve, adjusting the slit realy perks up the sound,but will lower the gain a little.

STAN.

Posted by Damien Taylor (Member # 4255) on 09-23-2009, 02:51 AM:

I'm now getting killer hum and a little bit of soundtrack coming out my speakers. My setup is Wallwart>LED driver>LED-Lux 3W, and the other side is a solar cell stuck straight in a mic input. After the laughter subsides, can anyone suggest some strategies to kill this very loud hum?

Posted by Gavin Lewarne (Member # 5397) on 09-23-2009, 03:54 AM:

is the shielding from the solar cell properly connected at both ends? (chassis of projector to ground terminal of your MIC input)

Is it mains hum or something else?

Posted by Monte L Fullmer (Member # 2797) on 09-23-2009, 04:21 AM:

Wal-warts could be having a bit of ripple issues - not the purest reproduction of smooth DC current..

Posted by Kenneth Wuepper (Member # 1174) on 09-23-2009, 07:37 AM:

Damien,

To determine the source of the hum:
place a card between the light source and the solar cell. A simple business card where the film goes will do the trick.

If the hum stays, it is an input and grounding issue

If the hum goes away, it is a ripple in the power supplied to the LED

Hope this helps to isolate the cause of your distress.

KEN

Posted by Sam D. Chavez (Member # 1841) on 09-23-2009, 03:34 PM:

Good advice Ken.

As to the LED, as I've posted on another thread and more than .1 Volt peak to peak ripple on the LED supply can be clearly heard in the audience.

LEDs are direct radiators of anything you put into them unlike exciter lamps where the light output is an indirect product of heating a wire to incandescence by passing current through it as in a toaster.

Posted by Tuomas Merila (Member # 4578) on 09-25-2009, 06:40 PM:

Hi,

I'm not an expert on electronics and sadly must admit I really don't know very well what I'm doing at most times. However, an earlier experience has shown me that the problem with ripple, that was mentioned, can possibly be easily fixed.

We installed a couple of red leds made by some small company (indeed, I'm almost certain they were hand made individually) that could be directly put into the same slots the original incandescents lamps were seated on the projectors, and thus there was no problem with correct alignment of the led.

First, we tried to use the original exciter lamp power source of the projector to power the LEDs but that did not work out at all for a reason or another, so I resorted to buying a couple of regulated power supplies (15 Euro each) from a local electronics shop, with ability to provide correct voltage and enough current for the LEDs.

Now, on one projector everything was fine - just installed the LED and wired the power source to it - perfect sound quality. The other projector was a different case - a horrible background noise could be heard when film was not loaded. Swapped the power supplies (supposedly identical), and the problem moved to the other machine.

Now, we were supplied, along with the LEDs, with a couple of capacitors that were supposed to be installed if there was a problem with changeover. I assume that meant some noise occurring when one light is switched off and the another one on at the changover but since we omitted that (switching the LEDs on using a manual switch and doing the changeover at the processor only), there was no need to install them at all at first. BUT, as the ripple problem was noticed, we did install the capacitors anyway - and that helpded, everything was perfect on both projectors after that.

While my understanding is quite limited, and I don't know how exactly correct the capacitors used must be, it appears to be fairly easy to mitigate a problem caused by a not-so-good power supply by using them on the power input. So, if you have ripple problems and have some electronics knowledge (more than I have), that could be the way to get rid of them.

--Tuomas

Posted by Bruce Hansen (Member # 281) on 09-25-2009, 07:25 PM:

Don't forget to check that the wall wart can supply enough current, as well bas the correct voltage. Wall warts are usually rather hummy, anyway. Any cap. you put across the LED must be rated to handle the voltage, some head room is always good. I would start with 1000 mfd, and increase it if needed.

Posted by Damien Taylor (Member # 4255) on 09-25-2009, 09:55 PM:

Thanks for all the help guys! I think it is both a grounding issue with the solar cell and the crummy power supply of the LED. I managed to fix the cell grounding with some wires. I'm scrapping the current power supply I am using, and getting a better one. Is there anything I should look out for when buying a good power supply?

Posted by Mark Gulbrandsen (Member # 72) on 09-26-2009, 10:59 AM:

The real bad aspect of this is the fact that you retain the slit lens and solor cell... The two worst items in the whole A Chain!!

Posted by Louis Bornwasser (Member # 3063) on 09-26-2009, 03:15 PM:

Mark: I'd been thinking that during the whole sequence. Louis

Posted by Sam D. Chavez (Member # 1841) on 09-26-2009, 06:15 PM:

Particularly bad on the Cinemeccanica

Posted by Damien Taylor (Member # 4255) on 09-26-2009, 08:47 PM:

It's only a home machine, and I wasn't totally sure I was ready for the finacial outlay of replacing optics. But in the unlikely event I was, who makes kits for the RCA's?

Posted by Mark Gulbrandsen (Member # 72) on 09-26-2009, 10:33 PM:

Damien,

That guy with the beard right above your last post makes the best ones!!

Posted by Monte L Fullmer (Member # 2797) on 09-26-2009, 11:09 PM:

Amen! I have 26 of them BACP units humming away without any hitch...

Posted by Demetris Thoupis (Member # 833) on 09-27-2009, 02:46 AM:

Amen I have sold more than 15 BACP units. Long Live Sam.

Posted by Mark Gulbrandsen (Member # 72) on 09-29-2009, 06:55 AM:

Amen, 26+15... Seems like I've installed at least that many of the BACP DP-70 conversion!

Posted by Charles Greenlee (Member # 3856) on 09-29-2009, 03:49 PM:

We used BACP's at all of the local theare's I've worked at. I was there when they put them in during the cyan track conversion spree. Grant, this wasn't in RCA, but in Strong 1050's and 1060's, and Christie's (i forgot the models). I had no complaints with them.