8mm Forum: Optical Sound on the GS1200

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Posted by Paul Adsett (Member # 25) on June 01, 2013, 11:55 AM:

Anybody have any expreience with optical sound on the GS1200?
I have a Movietone Newsreel with an optical sound track. A few years ago it played fine. Now the sound level goes up and down over sections of the print. I have cleaned the print to no help. I am wondering if film shrinkage can cause the optical track to move in and out of the exciter lamp beam or the sensor. Can this happen? And how difficult is it to adjust the alignment of the optical sound lens system on the GS?

Posted by Maurizio Di Cintio (Member # 144) on June 01, 2013, 12:37 PM:

Hi, Paul.
Perhaps the problem lies in the plastic black tensioner between the sound assembly and the lower sprocket wheel. If the tension is not consistent, the tensioner may cause a slack in the film which will result in the film being not totally flat against the photocell housing; this on its turn will lower the sound output level.

Also incorrect pressure on the part of the pinch roller arm may affect the problem...

Posted by Hugh Thompson Scott (Member # 2922) on June 01, 2013, 03:28 PM:

A thing that it could be Paul,it happened with me when I sent
my Fumeo for repair and was pointed out by Bill Parsons.I had
been using the 250w lamps instead of the 200w,and was told
by Bill to stick with the 200w regarding transformer safety.On
doing this I noticed a considerable difference in volume on Opt.
snd, I wonder if something similar is happening here.If your lens
hasn't been adjusted on opt. playback, then I can't see that being
a problem,it could be as Maurice suggested, a dreaded plastic
guide wearing.

Posted by Andrew Woodcock (Member # 3260) on June 02, 2013, 02:33 PM:

if this is anything like the ST1200 (which I believe are almost identical),it almost certainly is a tracking issue between the film lens ,lamp and soundtrack. I have adjusted my lens very slightly in the past to find the optimum point for highest gain dB level for the soundtracks. This requires adjusing the two tiny M 2.5 adjusting screws once releasing the retaining screws.Its a very tiny mechanism and operating window though, so unless (as was the case for me) ALL of your optical film soundtracks are sounding poor through slight mistrack then i wouldn't be adjusting the photocell alignment or lamp, I would just concentrate my efforts on finding out what has changed within the film path recently to cause the alignment of the films soundtrack to drift, both physically and therefore Aurally.To this end the previous advice of suspecting a worn guide etc etc seems highly feasable to me.

Posted by Hugh Thompson Scott (Member # 2922) on June 02, 2013, 10:06 PM:

The plastic film guide does wear, as the film cuts into the side,a
repair can be done with epoxy resin or replacement,if you have a
spare. I replaced this part many times on the ST1200.i wouldn't
do any re adjusting just yet, as these lenses & receptors are factory set, and once moved,getting that little light slit re alighned
is a devil of a job.The problem with the guide wearing ,is that it isn't good news for the soundtrack either,being liable for scratching.
In desperation with this part, I once filed out the offendind side
and fitted a little piece of aluminium,held with Araldite that did
the trick for a while,being tougher than the plastic.

Posted by Lee Mannering (Member # 728) on June 03, 2013, 12:48 AM:

Paul I’ve been playing more Optical on my GS recently and usually excellent sound. I would also run a film and have a good look at the track as it passes the reader beam. As the general consensus is saying it may be the guide pulling it to one side.

Posted by Paul Adsett (Member # 25) on June 03, 2013, 04:30 AM:

I'm confused as to which guide you guys are referring to. The white guide that is attached to the sound head is made of ceramic and surely will not wear. The black guide in front of the bottom sprocket is not really a guide but is a sprung film tensioner, and I cannot see this effecting the alignment of the optical track over the photo cell. What am I missing here? I did notice that if I hold down lightly on the lower loop restoring lever that the sound comes in loud and then goes low again when I let go of the lever.

Posted by Lee Mannering (Member # 728) on June 03, 2013, 09:16 AM:

Paul. I had a close look at my own GS and as you know the mag head pressure pads retract when playing Opt films. I’m wondering if the white sound head exit guide has become worn and only showing fault when pressure pads are withdrawn? Might be worth seeing if you have a groove on the white guide forming.

Posted by Paul Adsett (Member # 25) on June 03, 2013, 11:01 AM:

Lee, the problem is in the size of the lower loop. If I manually force the lower loop to be larger (by stopping the projector and opening the gate and pushing film from the top to the bottom loop, closing the gate, and starting back up) then the optical sound is loud and clear. So how does the GS form the size of the bottom loop, and is there a way to adjust it? See my thread on "GS1200 LOWER LOOP".

Posted by Maurizio Di Cintio (Member # 144) on June 03, 2013, 11:02 AM:

Paul I am more and mor epositive the film is not sitting perfectly flat around the drum housing the opt photocell, and in my humble opinion, this might be due to poor pressure on the part of the pinch roller and/or the black film tensioner excising too much pressure thus failing to keep the right tension in that area. Of course the problem does exist even when playing back mag tracks but, as mentioned, the mag heads presser help minimize the problem. But it's a whole different story when those presser are disengaged... Try to apply a gentle pressure on the pinch roller arm and keep it pressed that way, constantly. The film shoud better "embrace" the photocell casing. See if things improve...

Posted by Paul Adsett (Member # 25) on June 03, 2013, 11:05 AM:

I agree Maurizio, it definately seems to be associated with the profile of the film as it goes over the optical sound sensor. I get perfect sound if I force a larger lower loop.
As you suggested I pushed down on the pinch roller and three things happened:
1. The sound became normal

2. The film loop below the gate increased in size

3. The film now 'pulled up" between the sound head and the bottom sprocket , to where it is actually activating the black tensioner arm. Before, it was completely riding free of the tensioner arm.

So how do I increase the load on the sound pressure roller?

Posted by Maurizio Di Cintio (Member # 144) on June 03, 2013, 11:16 AM:

Well. OK, but try leaving the loop's size the same as usual and try forcing the main pinch roller arm, instead, just a little bit: the spot where to apply this pressure is the flat surface on the green pinch roller bearer, right above the roller's hinges.

Ops.. cross-posting...
OK to do what you are asking you must loosen the two tiny allen bolts which fasten the green arm to its spindle: they are placed opposite the exciter lamp or thereabouts; then push the arm 2-3° counterclock wise and tighten the bolts; this should suffice.

Posted by Paul Adsett (Member # 25) on June 03, 2013, 11:19 AM:

As you suggested I pushed down on the pinch roller and three things happened:
1. The sound became normal

2. The film loop below the gate increased in size

3. The film now 'pulled up" between the sound head and the bottom sprocket , to where it is actually activating the black tensioner arm. Before, it was completely riding free of the tensioner arm.

So how do I increase the load on the sound pressure roller?

Posted by Maurizio Di Cintio (Member # 144) on June 03, 2013, 11:20 AM:

See my previous post (I edited it)
Also do not apply too much strength when tightening the blots back or they might crack the plastic of the green arm!!!

Posted by Paul Adsett (Member # 25) on June 03, 2013, 02:04 PM:

Hi Mauritzio,
You hit the nail on the head. It is definately a problem of not enough pressure on the rubber roller. When I push on the green arm at the roller, the loop of film between the roller and the bottom sprocket stabilizes against the black tension arm. When I do not push on the roller, the bottom loop size oscillates up and down, with the sound level also going up and down in phase with the loop size.
I have tried re-adjusting the green arm position anticlockwise, but it did not help.
I went to page 47 and 48 of the service manual and they say to adjust the arm pressure by moving the solenoid position (2). Have you ever done this?

Posted by Lee Mannering (Member # 728) on June 03, 2013, 09:11 PM:

Bit of a stab in the dark but has the locking nuts for the green pressure arm either become loose or have you got the dreaded crack in the plastic?

Posted by Maurizio Di Cintio (Member # 144) on June 04, 2013, 12:45 AM:

Hi, Paul, no I've never done what the manual suggests, but it might be interesting trying: perhaps it's the ultimate solution for this problem, in fact tinkering with thise bolts which kep the green arm in place might be dangerous for the arm itself, if you tighten them too much.

The Italian Elmo specialist suggested a rather simple mod for this arm a few years ago, consisting in a metal sleeve inserted inside the hole the solenoid's spindle is inserted in: of course you have to file this hole in order to make room for the sleeve; then you have to cement it with superglue. Also the remainder of the area around the hole can be reinforced with metal pieces pasted onto it. This will give a much better resiliance. But it's a little time-consuming... Unfortunately this arm seems to be made of the same plastic type used for the film guide channels... Alas!!!

Posted by Paul Adsett (Member # 25) on June 04, 2013, 04:54 AM:

The green arm on my GS1200 already has the metal shaft insert. IMO this situation confirms what I have long suspected, namely that Elmo projectors are sometimes prone to film slippage at the sound capstan, due to insufficient roller diameter or insufficient pressure, or a combination of both. I have heard WOW on some of my magnetic sound films on my GS1200'S which I never hear on any of my Eumig's. Eumig's are totally WOW free. Elmo's can sometimes exhibit detectable WOW with some particular films. Its not every film by any means, but it happens often enough to show that the Elmo is sometimes touchy in regard to the physical properties of the film, how slippery a particular film may be, or how much flexibility it may have.
When you switch to optical sound on the GS1200 the situation apparently gets even more touchy because, as Mauritzio has pointed out, you no longer have the magnetic sound pressure pads clamping the film, resulting in my case to wild swings of the film loop size between the sound capstan and the lower sprocket, which also oscillates the distance of the optical track from the sound sensor.
Since I have only a couple of optical shorts I probably won't persue this issue any further. Magnetic sound is fine almost 100% of the time. I am reluctant to mess around with that solenoid position, who knows what else may get screwed up.

Posted by Maurizio Di Cintio (Member # 144) on June 04, 2013, 08:09 AM:

I agree 100%.
Enjoy your magnetic sound films, Paul.
Best regards

Posted by Lee Mannering (Member # 728) on June 05, 2013, 02:41 AM:

Mind you Paul some of my own optical sound film prints are so thin they are near invisible if you get me. We might just be expecting a bit much from a 35 year old projector on which the tolerance levels of old components are out the window and have even seen a repair or two. It’s nice to have some optical films though and we have been enjoying a bit of a renaissance here over a few Opt films.

Posted by Paul Adsett (Member # 25) on June 05, 2013, 04:20 AM:

Lee, I think one of the great things about super 8 is how well the magnetic sound tracks have held up over decades of use and storage. Back in the 1960's I would have given the opinion that the magnetic tracks would be gone long before the picture. We now know the reverse is true with the early color prints. And the fear of accidental erasure has turned out to be a total non-issue.
I like the concept of S8 optical sound and it is fun to run some once in a while. But it only occurred to me recently that optical sound tracks on color prints also fade out with the picture!
Although S8 optical sound can be suprisingly good, the overwhelming superiority of magnetic sound is obvious to anyone who has done a good stereo re-record on well striped film such as the original Kodak stripe.
The optical sound problem on my Elmo may be resolved soon. I spoke to Leon yesterday and he thinks I should replace the swinging green arm and black roller. I am getting the parts from him in a few days.

Posted by Hugh Thompson Scott (Member # 2922) on June 05, 2013, 08:34 AM:

I had a similar problem Paul on my first GS many years ago. I
narrowed it down to the rubber roller that was not giving enough
pressure, the problem I had was a "gurgling" on sound. I replaced
the pinch rolller with one from an old ST,resulting in clear sound.

Posted by Maurizio Di Cintio (Member # 144) on June 06, 2013, 01:38 AM:

Paul how can I contact Leon? One of my GS tends to have the same problem... And the cracks are obvious.

Posted by Lee Mannering (Member # 728) on June 06, 2013, 01:57 AM:

Leon does seem very knowledgeable over there Paul and yes I’m still getting some astoundingly good recordings out of my Eumig as well so long as the old girl keeps going.

My day to day use GS1200 had cracks in the pressure arm mooring a few years ago so I carried out what is typically known as a botch job filling the crack/split with super glue then loosening the locking bolts and a gentle clamp up to nip tight. I then replaced the part with a dab of super glue on the spindle and re tightened and it’s stopped like that ever since. It was done as a very temporary fix and if it was my best machine I would do a more professional repair which has been spelt out many time on here before, but for now I’ll leave well alone.

Posted by Maurizio Di Cintio (Member # 144) on June 06, 2013, 07:28 PM:

Thank you for your PM, Paul.

Posted by Paul Adsett (Member # 25) on July 02, 2013, 11:38 AM:

Well I installed a new arm (with the metal insert) and it made no improvement in the optical sound situation at all. I have concluded that the optical sound design on the GS leaves a lot to be desired. I think things would have been a lot better if Elmo had left the pressure on the mag heads during optical playback, in order to stabilize the film passing over the optical head.
Anybody know the details of how Eumig tackled the optical sound design on their 800 series machine?

Posted by Maurizio Di Cintio (Member # 144) on July 02, 2013, 01:47 PM:

Hi, Paul! If you apply a gentle pressure with a finger on the arm, opposite the area where the rubber roller is bolted, do you get any improvements? If so try increasing the pressure strength of the new arm.

Also check the lower black tensioner has proper tension.
Good luck

Posted by Lee Mannering (Member # 728) on July 03, 2013, 01:54 AM:

Hello Paul. Some years ago I had a Eumig optical sound model and the sound was warbling all over the show. It took me what seemed forever to adjust it and it’s the only Eumig model I found to be really fussy (on optical obviously) on sound tracks played. My own GS machines I find excellent on optical and a whole different kettle of fish particularly with a much more powerful amplifier inside. It is amazing the sound quality that can be got from that minute optical sound track on 8mm and I fairly often run optical more as a curiosity due to some of the films that made the format. The French also had optical prints out and usually have excellent tracks.

Posted by Paul Adsett (Member # 25) on July 04, 2013, 05:48 PM:

Thanks for that info Lee. Good to hear that the GS1200 is in fact capable of very good optical sound. Clearly, my projector needs some adjustment of the capstan rubber roller pressure, or the small roller pressure to get everything just right for good optical playback.

Posted by Hugh Thompson Scott (Member # 2922) on July 04, 2013, 06:01 PM:

Paul on replay, which is the test I did on mine many years ago,
was to place a little pressure on the sound unit,,which eliminated
any wow or flutter. I then replaced the rubber pressure roller
with the one from a ST1200. i have no skills in electronics or
engineering, I'm a builder for Christ's sakes, but substituting the
flat rubber roller for the "V" shaped roller of the GS solved the
problem of bad sound.
Since then it's been FUMEO for me

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