Film-Tech Forum ARCHIVE: Jax Lite cracking sound.

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Posted by Bernie Anderson Jr (Member # 410) on 01-25-2010, 09:42 PM:

I probably know the answer to this question, but I just want to bounce it off you guys to see if I'm right.

Booth:
(2) RCA 9050 sound heads with Super Simplex and ORC 1000 lamps.
CP45 with Jax Lite and kneisley exciter supply.

Right machine is fine. Sound is good (for a jaxlite), decodes fine, no hum, pops or cracking noise.

Left machine... has a popping/snapping noise, seems to be mostly in the left speaker (bleeding over into center), right channel has it, but faint. Very little buzz, not noticable in playback. Noise is only there when film is playing. If machine is on (lamp, motor, etc.) but has NO FILM in it, there is no popping/snapping sound. Only when film is present.

I think it's static build up from the running of the film in the projector (especially since its winter and dry) and its discarging on the cell and is being picked up in the cell. I just don't know how to isolate it. The wiring is set up as normal except the sheild is not hooked up at either end (projector or processor). When it is, I do get a buzz in the sound. If I try, grounding the cell to the casting, nothing seems to happen. The manual says that you can tap off of one of the LED power leads to the casting but only if there is a buzz or hum. That is not the problem. I did swap the projector inputs and its present on both Projector 1 and 2 inputs, so its definitely from the cell wiring back to the projector.

Any suggestions?

Thanks

Bernie

Posted by Monte L Fullmer (Member # 2797) on 01-25-2010, 09:51 PM:

Sounds like left machine needs an "A" chain alignment .. optics picking up a bit of the edge of the DTS timecode track if the noise is left/center.

Posted by Gordon McLeod (Member # 33) on 01-25-2010, 10:01 PM:

It is static probably the sounddrum bearings
I usually add a piece of copper wire hammered flat on the top surface above cell and ground to the soundhead

Posted by Louis Bornwasser (Member # 3063) on 01-25-2010, 10:01 PM:

On a 1050, the sub frame is insulated on rubber standoffs. Be sure grounding cable connects the sub frame to the case of the soundhead. A good place to start. Louis

Posted by Darryl Spicer (Member # 711) on 01-25-2010, 10:50 PM:

You may have tried this but run the the reel on the good projector and make sure the soundtrack is not scratched. Change any belts that are being used. DTS soundtrack being read will make a high pitched blurrr sound or at least that is the sound I heard when this happens. Make sure all solar cell wiring connections are tight.

Posted by Bernie Anderson Jr (Member # 410) on 01-25-2010, 10:56 PM:

Its not the DTS track (print I ran was pre DTS LLP 1993 stock). I know what that sounds like. This is more electrical interference instead of optical.

Gordon: do you have a picture of how you mount the wire? I get the concept, the static is discharged through the wire instead of the cell. How close to the tip of the cell should the wire be? What gauge wire? I'm assuming this has more to do with static and not grounding, right?

Louis: I tried that, didn't do a thing.

I can say this, the snapping noise seamed consistent as if its sometimes more of a pulse, although it can be random at times.

Posted by Gordon McLeod (Member # 33) on 01-26-2010, 01:37 AM:

I take a piece of 12awg solid and hammer it flat then laminate it to the top of the cell so that the lip of the copper is just slightly forward of the cell so it is just slightly closer to the film than the cell face

Posted by Gavin Lewarne (Member # 5397) on 01-26-2010, 04:24 AM:

we had this exact issue on our pair of westars with jaxlites and a cp45.

This to checl:

The preamp on the offending machine, is it an XLA-650 A or B?

We had 2 B units (difference being they supposedly have balanced outputs) and one machine developed crackles. I eliminated everything except the preamp, so i swapped it for a A varient i had spare (unbalanced version). Then changed the jumper in the CP45 to Proj 2 Unbalanced, did A-Chain and cracking gone for good. I have swapped out the other B preamp for an A now as well, and i have to say our sound is excellent now compared to what it was before.

Posted by Bernie Anderson Jr (Member # 410) on 01-26-2010, 03:48 PM:

Gordon: how did you laminate the wire to the cell?

Thanks

Bernie

Posted by Mark Gulbrandsen (Member # 72) on 01-26-2010, 06:41 PM:

I'd get rid of the Jax Lights... Don't try running BACP scanners off that Kneisley supply either... [uhoh]

Posted by Bernie Anderson Jr (Member # 410) on 01-26-2010, 06:48 PM:

getting rid of the jax lite really isnt an option. Too much money to replace for 2 projectors.

Posted by Gordon McLeod (Member # 33) on 01-26-2010, 11:41 PM:

I used some epoxy to glue the shield down
LAP associates used to make nice split cells that had a shroud and even vernier adjustment

Posted by Bernie Anderson Jr (Member # 410) on 02-06-2010, 11:29 PM:

Okay, so get this one. I did everything that everyone suggested. I even ran a leg off the power supply to the chassis of the soundhead. The popping/clicking sound has subsided, but it shows up every now and them. BUT, tonight I ran a hour reel of a film and I was getting this pulsating wooshing sound. When the projector is running with out film, its not present. I spun the sound drum by hand to where it was turning by itself, the sound was recreated. Now what is that about? Seems like I'm picking up the bearings on the drum in the sound. Why? Is it static electricty being cause by friction in the bearing and now that's being discharged? Its strange its only the left machine. Right machine, same set up, is fine.

Posted by Sam D. Chavez (Member # 1841) on 02-07-2010, 12:20 AM:

Are you sure the solar cell or its bracket is not touching the sound drum? Try temporarily unscrewing the bracket baseplate from soundhead. See if the sound goes away.

You could also have a solar cell with an internal short on one of the 3 wires.

Posted by Gordon McLeod (Member # 33) on 02-07-2010, 03:11 AM:

some bearings have caused issues as well

Posted by Bernie Anderson Jr (Member # 410) on 02-09-2010, 10:59 PM:

So here's an update. Its the weirdest thing. Checked all connections, checked to see if cell was hitting the drum. Then I found on the gear side that the cell wire was hitting the casting of the sound drum and when I pulled out the pre amp the cell wire rubbed against the balance drum and it made the sound even worst. So evidently the cell wire is picking up all different kinds of noises and introducing it into the pickup.

So the question is, what is the best way to sheild the wire from the cell?

Is there a better place to put the preamp instead of the soundhead casting? Should the power for the preamp come off of the exciter lamp or should it be a separate power supply? Strange little thing, these Jax lites. What's the best wiring for wiring the pick up? Can it be two independent wires for left and right input of the cell?

Posted by Sam D. Chavez (Member # 1841) on 02-10-2010, 12:28 AM:

Is the cell wiring shielded or just 3 wires running loose to the Jaxlight?

It should be 3 wire plus shield starting as close to the cell itself as practical. The shield needs to be connected at the preamp end. The wiring should be secured so it does not move physically as this will induce noise when the signal is so low as it is with a Jaxlight.

The light output from the Jaxlight is much lower than what you had with the old exciter lamp so it's more sensitive to noise.

Posted by Bernie Anderson Jr (Member # 410) on 02-10-2010, 06:40 AM:

Its just the 3 colored wires coming out of the cell. There is no shield nor is there rubber insulation. That would explain things a bit. Any suggestions on the best way to shield those wires?
Thanks

Bernie

Posted by Steve Guttag (Member # 268) on 02-10-2010, 08:33 AM:

Almost any sheath will do. Including heat shrink tube but don't apply the heat...let the tube remain at full size to space the wires off. Note you could even use the stripped off jacket from another cable...it really doesn't matter.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 02-10-2010, 10:11 AM:

Thanks Steve, I'll give that a try. So I still have 2 questions then: Should the preamp be at the projector end or processor end? What kind of wire is best to connect the cell? I have a feeling that all of this will clear up my popping sound. I'm still getting a pop (similar to when a splice goes through) when any electric contact happen, example, when the C/O opens, when the curtain/masking opens and closes. You hear a pop. I'm assuming this would case that too.

Thanks

Bernie

Posted by Louis Bornwasser (Member # 3063) on 02-10-2010, 02:21 PM:

I know you have a $$$$ issue, but the sure cure for a Jax Lite making noise is anything else and the Jax Lite in the trash barrel. You not only won't be sorry, but you will have to do it eventually anyway. Louis

Posted by Steve Guttag (Member # 268) on 02-10-2010, 02:45 PM:

I definitely with Louis on this one...part of your problem is the JaxLight.

We will need to know more about your sound system to help with the other electrical pops. Those that use unbalanced or ground referenced inputs tend to be more prone to them. Also, the quality of the ground on the sound system and just what else is on that ground will affect it.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 02-10-2010, 03:52 PM:

Hi Steve,

The system is 2 projector setup with RCA 9050 Sound heads. The cell goes to the jaxlite preamp. The preamp is powered by a tap off the exciter lamp which is powered by a kniesley exciter supply. Then a leg of the exciter lamp goes to the projector casting, like the jaxlite manual says. From there the sound cables go though a seperate conduit to the back of the soundrack about 10 feet away. The conduit is about a foot below the high voltage trough. The shield is connect at the preamp but not at the cell input on the back of the processor. The processor is then a CP45. The CP 45 outputs to a consumer Yamaha 6 channel input amplifier (I use this so I can also run DVD and Cable TV through it). The rest of the setup has Simplex Supers and the lamps are ORC 1000. I'm using Eprad Co-operators for automation. (I know, it's a grave yard but it works) Unfortunately, since its a house, I'm using the same ground, so I'm sure there is something going on there. Everything is grounded back to the breaker box. It doesn't matter if I ground the processor or not. I get no hum in the sound, unless I connect the cell's shield to the processor, then it hums like a bitch.

I was curious and thought because the left machine (the one that is problematic with the jaxlite) came on line after the right machine, I thought maybe it had something to do with that. It didn't. I removed the left machine's input wire. The pops went away for about a min or two as I was testing the equipment. The pop came back even when only one machine was hooked up. The pop is more predominate on the closing opening of the curtain and masking, C/O's, Automation impulses (any relay pulse, cues, starts, etc.) I do not get a pop, though on the soundchange over relay (latching relay), any light switches in the booth or even the 110v framing light switch. (frankly those are the only things that aren't grounded, they're all two wire). Obviously, it has something to do with the ground.

Posted by Sam D. Chavez (Member # 1841) on 02-10-2010, 06:16 PM:

How long are the cell wires going to the jaxlight preamp? Any more than a few inches and you should put them on a terminal strip and make a transition to a shieled cable.

As to where the best place for the Jaxlight, the closer to the cell the better. There were a couple of different models of the preamp, unbalanced out and later, balanced out. I don't disagree with Steve or Louis about the need to upgrade, just trying to make it better.

From the sound of it, you have more than one problem with pops.

Best way to troubleshoot them is, disconnect the cell wires from the Jaxlight input and see what pops remain. If still there, disconnect the output from the Jaxlight.

Also, do the pops show up in any other formats, non sync, etc?

That's enough for me today. You have your homework assignment

Posted by Steve Guttag (Member # 268) on 02-10-2010, 06:59 PM:

First off...the CP45 should be grounded...period...get a good bond on its chassis.

The shield of the cell wire should then be connected there...if you get a hum...move on down to the JaxLight preamp...it is on the same reference as the CP45? If not, bond it...preferably not with the shield but with a dedicated wire of 18awg or larger...however, while troubleshooting, the shield will do.

Lets start with that.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 02-10-2010, 07:16 PM:

Steve,

What exactly do you mean by "same reference"?

Sam,

No pops anywhere else. I removed the cell inputs and with it in any of the optical formats I get no pops what so ever. So its definitely being picked up in the cell wires. The cell wires are short and were extended about 4 inches to reach the preamp

Thanks
Bernie

Posted by Gordon McLeod (Member # 33) on 02-11-2010, 12:36 AM:

You might try braiding the short cell leads

Posted by Steve Guttag (Member # 268) on 02-11-2010, 05:22 AM:

Same reference = same ground potential. Using an 18awg wire will do that for you...tying the shield at both ends will do it too but compromise the electrostatic shielding and due to its smaller gauge, may not bring the potential close enough (have a bit of a ground loop of its own). You don't want ANY current flow on the shield...just the noise to have somewhere to drain.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 02-11-2010, 01:26 PM:

I think I'm gonna just start over and rewire this machine using everyone's suggestion, because its all wrong based off your answers. I started on this machine years ago and just within the last year got it running.

Steve, you're just saying attach the shield (or 18 awg wire) to the processor (body of the connector) and if it continues to hum connect it to the shield connection at the jax lite preamp, but either way, it must be connected to the processor. Basically, there no where for crap interference to go except into the cells input and that's what's causing the popping.

The cell wires are not braided and are hanging loose to the preamp. And then I used crappy Radio Shack w\2 conductor with shield wire too.

Is it okay to use (2) 2 conductor and shielded wire as long as the shields are connected? It doesn't need to be all in a 4 conductor single cable, right?

Posted by Steve Guttag (Member # 268) on 02-11-2010, 02:57 PM:

Yes, more or less. A shield must drain to ground...that is how they shield. In a perfect world they can connect at both ends of the cable if both ground potentials are the same. It is safer by only terminating at one end. At the cell end, you don't have a good ground reference and you do at the processor end, typically. To minimize ground loops, it is best to bond the devices to the same ground...the bigger the wire gauge, the better the bond and the closer the potential. What you don't want to do is then bond that to the projector case. You want the JAXLight preamp to be an extension of the sound processor..as well as the cell itself.

While you are doing this...seriously ...price out the cost of a basement reader system...and save up...they just are not that expensive.

Steve

Posted by Bernie Anderson Jr (Member # 410) on 02-11-2010, 03:05 PM:

Makes sense...

Does that go for the exciter supply too? Right now, the supply is not only lighting the LED, but is powering the preamp. The preamp has one leg grounded to the chassis of the soundhead. Should the preamp be powered by another source? or does that not interferre because it DC at that point?

Posted by Bernie Anderson Jr (Member # 410) on 02-17-2010, 05:52 PM:

So just to give you an update. I installed the wiring per your suggestions (treating the cell as an extention of the processor). I eliminated the pop on the curtain open/close, but I still have a pop on any automation function or Changeover open/close. I even hear a little tiny pop on sound format changes too.

How much does the quality of wire matter? I'm using the crap from Radio Shack but am planning on changing it out to a Belden wire.

Posted by Demetris Thoupis (Member # 833) on 02-18-2010, 02:53 AM:

I think you should try bringing an electrician to check for proper grounding between rack & power and also between projector & power. From there on, make sure you connect a wire between the power ground at the chasi of both the projector and the soundhead. Loose ground between the two can give you a lot of static pops. Also I would suggest changing the power supplies for both LED and pre-amp to DC (separate power supplies for each) and tie the - leg to the chassi ground on both situations. Actually is redoing the installation or rather power distribution all over again. AC power is a killing factor.
Demetris

Posted by Sean McKinnon (Member # 612) on 02-18-2010, 12:31 PM:

you should see if it is possible to isolate the pre-amp on a completely seperate A/C circuit from anything else.

Posted by Bernie Anderson Jr (Member # 410) on 02-18-2010, 01:07 PM:

The preamp actually taps off the DC exciter supply. So it goes to the LED and the preamp. Now, I hooked up the standard exciter lamp yesterday and just jumpered the terminals to make it work. First, I can't believe how much I had to drop down the input compared to the Jaxlite when I ran Dolby Tone. Also, the line was so quiet, it was night and day.

I opened up that particular preamp and discovered that it has been altered. I'm assuming that's half the problem. I'm working on getting another preamp.

I do have a scanner and LED from a Component Engineering ASR 40. I'm missing the mount for the LED and a collar for the scanner to fit into the RCA. Also I would need a power supply. I'm not sure if its cheaper to buy a complete used Reverse Scan or find the extra parts needed to make it work.

But I want to thank everyone for their suggestions. Although, its not perfect, buts 150% better.