Film-Tech Forum ARCHIVE: Static on RCA 1040 Soundhead?

This is topic Static on RCA 1040 Soundhead? 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=009587

Posted by Bill Duelly (Member # 3612) on 11-03-2008, 08:23 AM:

I have an odd problem with my RCA 1040 soundhead (or I at least think it is from that). I have a static on the output (only when film runs through the projector) and it's frequency/intensity seems to differ depending upon the film that's run. I do not think the reader (JAX Light & Dolby PU) is reading hairline scratches in the soundtrack as when I put the alignment slightly out of focus, it is still there in equal intensity/volume. I changed the bearings and pressure roller within the past few months and to be honest I did not notice it, but now I do again. Can the JAX unit be so sensitive that it is somehow picking up static from the film itself? Any grounding hints? In terms of tightness of the film over the flywheel, I usually run it with a looseness of one or two sprocket holes away from 'tight'. I'm sure there is something obvious I am missing...

Posted by Gordon McLeod (Member # 33) on 11-03-2008, 10:10 AM:

Because the output level of the cell with theJax Lights is very low you have to add that extra preamp
As such any source of extranious noise is prone to being picked up
Bearing noise is one as is the motor
check your grounding
I ended up using transformers to decouple the cell to preamp and preamp to processor in one location
Also if it is a Smart Mod2 2b 2c 3 4 5 or SR130 SR135 or SR300 processor the processors preamp is really not properly balanced and there used to be a tech note on Smarts web site about Jax Lites with them

Posted by Sam D. Chavez (Member # 1841) on 11-03-2008, 10:31 AM:

The noise is most likely a minute amount of static on the film producing a tiny current that runs through the sound drum to ground.

Check to see if there is a grounding strap between the main sound head chassis and the sub chassis the exciter lamp sits on. These sound heads were built with a braided copper strap connecting the sound head and the sub plate that often gets discarded over time. This has come up a number of times in the past so is not mere speculation.

Posted by Bill Duelly (Member # 3612) on 11-03-2008, 11:12 AM:

Gordon & Sam, thank you for your input! I was always under the impression that the sound head and exciter asssembly needed to be isolated as there are those hard (Rubber?) mounts that held the two together. I'll put a jumper between the two tonight and see if that corrects it. Also, Gordon, what transformers did you use between the solar cell & Jaxlight pre-amp?

Posted by Sam D. Chavez (Member # 1841) on 11-03-2008, 03:06 PM:

The rubber mounts are for vibration isolation, not electrical isolation. Try this first, it costs nothing.

Posted by Gordon McLeod (Member # 33) on 11-04-2008, 12:48 AM:

I used ones from Hammond
Also I often with solar cells made a copper shoud over the top to the cell that came over the lip and was grounded to give a better point for static to fly off to rather than the cell face
This used to be a big issue on the Bauer U2 and other machines with a lot of plastic the film ran latterly against

Posted by Steve Guttag (Member # 268) on 11-04-2008, 07:00 AM:

Also, the mounts are not supposed to be hard! I believe Wolk still carries the necessary rubber shock mounts.

BTW...there is some truth to the electrical isolation theory. As I recall, the Simplex SH has separate connection points for Chassis ground and the rest. One could bond the chassis to building steel and bond the soundhead components to the sound system ground.

In any event, electricity will find its path to ground through least resistance...even if that means going through the drum, cell...or what not.

Steve

Posted by Bill Duelly (Member # 3612) on 11-04-2008, 09:15 AM:

Well I tried the grounding suggestion of Sam's and I still have the static. Just for laughs I reversed the bearings and that did not seem to make any difference so I think I am looking at the static as electrical from film contact vs. picking up something mechanical (I also disconnected all other fans, etc as well to see if they might have been playing havoc and there was no difference).

Tonight, I'll try to move the solar cell further from the drum and see if that proximity is the culprit (right now the distance is about the thickness of 2-3 pieces of film)

Posted by Jonathan Bodge (Member # 4072) on 11-04-2008, 04:24 PM:

I had the same problem and of course depending on humidity or the moon phase it would come and go. I grounded everything. These types of problems with mix and match cinema equipment and changes in technology over the years was and is frustrating. But, pretty soon, it (film) will all be gone!

Posted by Tim Reed (Member # 137) on 11-04-2008, 05:27 PM:

Does the noise go away if you block the scanning beam with a business card? If so, the noise is probably on the film.

Posted by Bill Duelly (Member # 3612) on 11-04-2008, 05:31 PM:

Tim, I pulled the exciter light source out and the crackle
was still there.

Posted by Marin Zorica (Member # 1716) on 11-04-2008, 06:10 PM:

That is point that problem is in static discharging between cell and film. Maybe grounding of machine did loosed or grounding of projector head or sound rack and processor itself??

Another thing that you could try is to ground sound rack and projector, to get all potential at zero, actually you should have all grounding connected to one place (star point) of room.

This could be pain in ass, i remember one booth, same problem...but just did acour like that, everything was ok until one day started....I did check all grounding 10000 times, everything was okay....AND if you play movie in morning there wasn't problem probably because of humidity in air, because in summer night can be hot there!

First thing to save show and only thing that helped was wire between sound rack and projector....and than all pops were gone, I did than ground projector from mains panel (but is all ready grounded like that) but pops again, that I grounded sound rack to main (already grounded like that and ok) but pops again....only thing that helped was wire from rack to projector...than I did put wire in parallel with wires from cell to processor.

As i said it can be numerous of reason...this way only 2 month setup and happy it happened only 3-4 days before ending of season....so next year is to recheck all....but I did that....

Posted by Tim Reed (Member # 137) on 11-04-2008, 09:58 PM:

Okay, Bill. That's a good one. If it does it with film running but not without film, then it must be static discharge. Try running with the lateral guide roller open and see if that affects it.

If, however, the noise turns out to be there regardless of whether there's film in the machine or not, it could be a bad ground or possibly a skinned wire.

If you're running carbon arc, it could be noise generated by motor brushes.

I'd start up some film and verify that the noise is there, then do the lateral guide thing I mentioned earlier. If that doesn't help, remove the solar cell assembly screws and slowly pull the cell back away from the film plane and see if it goes away. I'd go as far as to totally remove it from the proximity of the sound drum and let it hang by the wires. If the noise is still present, the trouble lies elsewhere. Maybe interference picked up at the preamp?

As others have said, it really sounds like it's picking up static off that guide roller. Since the cell face is pointy and closer to the sprocket holes and the end of the film than the sound drum is, it's proving an easier discharge path for a charge accumulating on the emulsion side. Regardless, there is some point in the chain that you should be able to isolate it.

Posted by Bill Duelly (Member # 3612) on 11-05-2008, 09:49 AM:

Taking Marin's advice, I went through the grounding path again and found that the A/C ground was not connected in the junction (need to talk to that electrician!) I mounted that and made a new connection to the projector. I think the level of the static is a little less but certainly still there.

Referencing Tim's note:
If it does it with film running, but not without film, then it must be static discharge. Try running with the lateral guide roller open and see if that affects it.

If, however, the noise turns out to be there regardless of whether there's film in the machine or not, it could be a bad ground or possibly a skinned wire.
(It is only there when film runs throught the projector)

If you're running carbon arc, it could be noise generated by motor brushes.
(Xenon- makes no difference if off or on)

I'd start up some film and verify that the noise is there, then do the lateral guide thing I mentioned earlier.
(Still there)

If that doesn't help, remove the solar cell assembly screws and slowly pull the cell back away from the film plane and see if it goes away. I'd go as far as to totally remove it from the proximity of the sound drum and let it hang by the wires. If the noise is still present, the trouble lies elsewhere. Maybe interference picked up at the preamp?

(Tried this with the PU cell but there still is static. If I had another pre-amp, I could try that, but I don't. Now that I think of it, I am hard pressed to recall if I had this with the incadessant which I changed out 6-8 months ago)

Regardless, there is some point in the chain that you should be able to isolate it.

(Thanks to all for their continued input! [thumbsup]

All suggestions are valid and welcome. I just have to keep experimenting to find the right combination. [Roll Eyes]

)

Posted by Marin Zorica (Member # 1716) on 11-05-2008, 10:13 AM:

Try also check for main grounding that goes from main of booth to other main panel......

Well in mine case we do have changeover, one machine did have same static issue, other not...

So try to experiment a bit, try ground machine on different places and also try to ground sound rack on different places and processor itself....this is very tricky, because you said everything was okay until now?

Posted by Sam D. Chavez (Member # 1841) on 11-05-2008, 10:39 AM:

I believe I am right and the static is travelling from the film through the drum and somehow through the chassis of the Jaxlight or the line amp. Static is very strange and the last guy who truly understood it was Tesla.

Is the line amp chassis attached to the projector?

Posted by Al Biers (Member # 1961) on 11-05-2008, 10:57 AM:

Better idea, dump the JAX and purchase one of Sam's BACP, problem solved, they work.

Posted by Louis Bornwasser (Member # 3063) on 11-06-2008, 06:04 PM:

I really can't think of anything neutral or good to say about a Jax-light. Louis

Posted by Bill Duelly (Member # 3612) on 11-06-2008, 10:13 PM:

The Pre-amp is not mounted to the chasis. It is approx 4-5 feet away from the projector to keep it away from potential hum issues.

Pardon my ignorance, but what is a BACP?

Posted by Sam D. Chavez (Member # 1841) on 11-06-2008, 11:19 PM:

He is referring to a reverse scan reader. These are made by Kelmar, Component Engineering and BACP, which is my company. As it happens BACP does not make a reader for RCA 1040, only a 9030/9050.

All reverse scan reader are superior to a Jaxlight as they include all new electronics and imaging lens. They cost a bit more than a Jaxlight, but you get what you pay for.

Posted by Louis Bornwasser (Member # 3063) on 11-08-2008, 06:26 AM:

Sam, would have thought they were the same??? 9030/1040 Louis

Posted by Tony Bandiera Jr (Member # 2365) on 11-08-2008, 12:48 PM:

quote: Louis Bornwasser
I really can't think of anything neutral or good to say about a Jax-light. Louis

Then your experiences with them are opposite of mine. I had installed a few dozen of them in various locations, and until recently had one in my own projector, in the course of several years of use had only one pre-amp module go bad, and U*S replaced it no questions asked.

Remember what it was designed as, which is a low-cost alternative to the (then) much more expensive reverse-scan readers. In that respect, with a decent slit-lens assembly it performed well.

Now of course, reverse-scan readers have come down in cost and gone up in performance.

And the BACP is by far the best in terms of quality, reliability and value. [thumbsup]

Oh, and Sam, why won't the BACP fit in the RCA 1040?

Posted by Sam D. Chavez (Member # 1841) on 11-08-2008, 03:51 PM:

Trust me, it won't fit. The 1040 exciter cabinet is shorter than the 9030 and the back of the reader hits the metal louvers plus a little.

I've actually had one person saw out the back of the cast iron sound head to make it fit, but I would send business to a competitor rather than do this kind of butcher work. This is not the world's best sound head, flutter and wow wise, so I never made a version for this one or for the Motiograph although this is the first system I ran.

Posted by Tony Bandiera Jr (Member # 2365) on 11-08-2008, 11:57 PM:

Thanks Sam, that makes sense. I haven't had any hands-on with a 1040 for too many years, and forgot about the housing size issue. I was of the mindset that the slit lens barrel was the same size...thus should not be a problem.

I too would refuse such a hack solution.....too bad the previous owner of my XL head didn't feel the same way, they hacked it to allow pic and track, and now I can't mount a door. [Mad]