Film-Tech Forum ARCHIVE: Sound issue with a Jax lite

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Posted by Bernie Anderson Jr (Member # 410) on 11-07-2003, 01:47 PM:

Already, I know I'm gonna get a laugh because it's a Jaxlite, but just humor me anyway. I got it for nothing. Here's the deal: I'm using a CP45 with a Kelmar solar cell and Jax lite as an exciter on an RCA 9050. I had it installed for a year now and since that time I've never had a problem with noise or distortion. Until...

Over the last 2 months, especially wiht SR and A prints I've been noticing that I'm getting a really high pitched sound through out all the speakers and it's accentuated when dialog is spoken. Can't descibe it but to say it sits on top of everything. Okay. I though it was the print. I started to notice more and more. And one day...

I played a mono print that I know has a great solid track and I didn't get any kind of gain out of it. The processor was all the way up and so where the amps. As I got through the first reel and half way through the second, the sound kicked in to where I had to turn it down. Then again on another mono print, Same thing almost to the point that I lost sound all together. It's hit and miss. The LED on the front of the CP 45 are bearly lighting as if there is no signal coming in.

Now I haven't done dolby tone since it was installed about a year ago, but I can't imagine that it would just drop off like this that quick.

So this is what I'm thinking. I'm thinking since the CP45 is pretty solid and each one I've come across worked great. And everyone I talk to says that Jaxlite is trouble, I'm guessing that it's probably in the Jaxlite preamp. Maybe it's crapping out. Also, could it be that oil is getting to the wires and breaking them down?

What do you think?

Posted by John Pytlak (Member # 331) on 11-07-2003, 02:08 PM:

Why not check Dolby tone levels again? Optics clean? Why not do an A-chain alignment?

When you just look at it, does the light output seemed to have changed from the original setup? Anything that would change LED current erratically?

Posted by Pete Naples (Member # 761) on 11-07-2003, 02:28 PM:

Yeah I agree with John, perform, or have performed an 'A' chain alignment, the noise you're describing.... Sybillance? Look carefully at the phase and HF response. The biggest problem I have with Jaxlights is the terrible S/N ratio caused by having ot amplify the cell output. I think the Jaxlight pre-pre-amplifier itself is actually fairly quiet, it's the fact that the light hitting the cell is so weak that the S/N ratio is already poor. Avoid having ny lights on in the booth when it's running and also watch out for shutter reflections striking the cell.

One thing springs to mind that I've seen with a CP45. I had one where the ouput level would fly up and down of it's own vocation, I replaced the fader with no effect. Eventualyl I traced the problem to being one of the grounds had come off inside the 9 pin 'D' plug on the backplane, for whatever reason it lost the plot because of that. Quick tickle with the soldering iron and all was well. For the 30 seconds it'll take it'd do no harm to reverse the CP45 pre-amp, just in case it's got a duff input...

Posted by Matt Zeiner (Member # 1914) on 11-07-2003, 03:27 PM:

Any problem with a CP-45 screams grounding. They have had countless issues with the grounding scheme over the years. Glad none of my theatres have them anymore

Posted by Michael Harlow (Member # 1353) on 11-07-2003, 05:28 PM:

JAXLITE [Roll Eyes]

Posted by Mark Gulbrandsen (Member # 72) on 11-08-2003, 08:37 AM:

Well, all JAX Lite does is change your light fomr white to red....nothing else. You still have all the "crap" in there such as the cell and slit lens that in a good system should be thrown away.....anyway....I've ranted on this so many times before.....I wouldn't use one even if it was free....and people actually buy these......

Definately something with a grounding issue and I've seen them oscillate fomr poor grounding. Best thing to do is go reverse scan, or as a conselation prize buy yourself the new preamp for the JAX lite. The new version is balanced and you'll experience alot less of this sort of problem.
Mark

Posted by Matt Zeiner (Member # 1914) on 11-08-2003, 08:41 AM:

The reverse scan units aren't more expensive enough to warrant the installation of jaxlites....Period. The balanced outputs aren't going to help you if you don't have balanced ins anyway.

Posted by Bernie Anderson Jr (Member # 410) on 11-09-2003, 05:23 PM:

Here's my only concern with Reverse Scans. How are they when it comes to reading Density Tracks and Unilateral Area Tracks.

I haven't had a chance to try tone yet. Once I do, I'll let you know what I find.

Thanks

Bernie

Posted by Pete Naples (Member # 761) on 11-09-2003, 05:46 PM:

Actually Bernie, they can be none too clever. Some prints seem to be better than others. I don't think it's the reverse scan that's the problem per se, it's the red light.

The NFT in London has lasers and exciters so they can show older material without problems.

Posted by Gordon McLeod (Member # 33) on 11-09-2003, 05:49 PM:

Red light is red light doesn't matter where it comes from
The only issue would be some of the older red soundtracks but they are unusal
a standard VD track has no issues with red light as one is stil modulating the silver
There may be more noise than older systems mainly beacuse of the extended high frequency response

As to balanced outputs
Almost all processor cell inputs are a balanced input

Posted by Bernie Anderson Jr (Member # 410) on 11-09-2003, 10:42 PM:

People have talked about grounding the cp45. Ground it to what? The conduit pipe? The ground in the outlet? And connect it to anywhere on the chasis of the cp45?

Posted by Steve Guttag (Member # 268) on 11-10-2003, 12:40 AM:

The CP-45 absolutely MUST be grounded to your soundrack ground...for most installations that is the ground pin on the electrical outlet. As such, the electrical box that holds the outlet, if there is no other place, can provide the required ground.

There are many things that just were not thought out real well with the CP-45.

Steve

Posted by Gordon McLeod (Member # 33) on 11-10-2003, 02:26 PM:

Also a jumper from one of the phoneix connecter earth terminals to the chassis is a must and also verify the ground shield of the cell cables is actually connected to the shell of the dsub on the cel input
Also a star washer behind one of the mounting screws is a good idea

Posted by Bernie Anderson Jr (Member # 410) on 11-15-2003, 11:23 PM:

Some updates:

What I did so far was set inputs with Dolby Tone. Remember that for a year everything was fine since the install and it seemed over night things changed.

The input level from the cell was off and I had to up the input to the processor.

I ran some mono and Dolby SR reels. The Dolby sounded alot better but still had the high pitched noise. I ran a mono feature and it ran alot better but once again, I had a loss in volume gain, so I went in and made sure that the Jaxlite preamp was okay. By this I mean that I wingled the wires in the Phoenix connector and tapped on the case to see if I got any static. Nothing. I went to the CP 45 and opened the front panel and once I opened the door I got volume again but went away just as quick. I wingled the preamp board (the far left board with the proj inputs) and the volume came right up to normal. I wingle the rest of them and for the rest of the film for over an hour the mono print ran flawlessly. What do you think?

Now I haven't done any of the other suggestions, (ie. jumper wires and grounding) but I will get to it. But could the problem be a dirty contact on the boards?

Also, remember since this is a screening room; the projector isn't powered up everyday. Lack of use I can assume has something to do with the problem. But I'm still getting the high pitch. Again what do you think?

Thanks

Bernie

Posted by Jack Ondracek (Member # 1466) on 11-15-2003, 11:46 PM:

Bernie, it could be nothing more than a little corrosion on the edge connectors of your cards.

Turn the power off, then pull the cards, one at a time. Burnish the copper-colored edge fingers with a clean pencil eraser (one that you haven't stuck in your ears!). Then, wipe the connectors off with a clean cloth and a little denatured alcohol... the 99% kind. That will probably eliminate any mechanical movement as a source of your troubles. If nothing else, you might have to re-run your dolby tone loop... which will hopefully bring you back to the performance level you had before you noticed your problem.

-----------------------

After you do that:

The "high-pitched sound" issue is interesting... especially over dialog, as you describe. Back in the dark ages, we used to experience that problem when running exciter lamps with AC... or poorly filtered DC. The problem would be most noticeable over dialog... and much less so when the sound track was silent... because the closed silent track shielded the exciter light... and it's AC component from the photocell. Dialog had a distracting 60/120 hz component in the middle of it... which really made you want to find ways to provide better power to the lamp. That may be somewhat similar to what you're experiencing, though I'm not sure how that relates to a high frequency noise. In any case, you should find that it is very noticeable with no film in the projector... as there won't be any soundtrack to filter down the light. If not, there's going to be something in the mechanics of the system... or maybe the ambient light in your booth that's injecting the noise.

In any case, good luck!... Let us know what you find out.

Posted by Josh Jones (Member # 447) on 11-17-2003, 07:27 PM:

you may also want to see if you are experiencing microphonics, that is noise induced by mechanical vibration, usually manifesting itself as a 'ringing' noise. Is the noise audible with no film in the machine and its running? When its not? if there is a difference, you've got microphonics, and the cure would be to tighten down all the parts in the optical assembly, the cell, the lens tube, lamp socket, and make sure none of the optics are loose in their holders, like a lens in the slit tube being loose or something.

Also if the pre-amp is oscilating, try better seperating the input and output leads, as capacitance could theoretically cause it to oscillate.

Josh

Posted by Matt Zeiner (Member # 1914) on 11-17-2003, 09:45 PM:

You probably already did this, but - did you try the projector 2 input? Swap the NR card? Look for cold solder on the main board? Does sound like arcing is going on somewhere, tho... ("The processor was all the way up and so where the amps. As I got through the first reel and half way through the second, the sound kicked in to where I had to turn it down")

Posted by Randy Stankey (Member # 64) on 11-18-2003, 12:46 AM:

To eliminate the question of mechanical vibration (microphonics) and/or AC appearing at the output of the exciter supply run the projector with no film, turn on the sound system and stick a piece of paper or a business card into the path of the light beam and block it.

If the problem goes away when the beam is blocked you know what the problem is. If it doesn't you have eliminated all question on that front.

Posted by Gordon McLeod (Member # 33) on 11-18-2003, 08:06 PM:

Possibly the Rubber isolation gromets are dried out and transmitting vibration into the slit and jax light

Posted by Mark Gulbrandsen (Member # 72) on 11-18-2003, 08:20 PM:

Good Lord guys, this isn't even worth dwelling on..... get rid of the thing and just go back to a regular solor cell and exciter light and your problems will go away!
Mark

Posted by John Eickhof (Member # 323) on 11-18-2003, 09:48 PM:

Actually, I have only had two simular problems to this one with the JAXLITE, (I have at least 3 dozen in use)
Bothwere with a RCA, the lens on the jaxlite had loosened..On one, the customer simply took a liitle
hobby cement and re-glued the lens to the JAXLITE, The other I did myself, the trouble was gone! I have discussed this with Jack Cashin and since his LED array develops a hight temperature they had trouble with the glue failing on the plastic lens.
Give it a try! Good luck!

Posted by Randy Stankey (Member # 64) on 11-18-2003, 09:48 PM:

I had a projector in North Carolina that made a "Ping-Ping-Pingity-Ping!" sound as it was running. No film. Motor running. Sound processor on. Jax-Lite running normally. I could even see these spikes in the scope. I worked on it for HOURS trying to figure it out. I took the whole thing apart and reassembled it at least two times.

Turn out that the drive belt between the motor and the sound head was worn out. The little threads hanging off the edge of the worn belt were hitting against the edges of the drive sheave, making a high pitched "Ping!" sound as each one struck metal.
I replaced and ensured proper alignment of the belt and the problem was solved in minutes what took me hours to figure out.

Yes, I would vote for the complete abolition of Jax-Lites but face it. They are here. Theaters are never going to get rid of the damn things. SOMEbody's got to know the tricks to fixing them!