8mm Forum: Optical Sound Question

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Topic: Optical Sound Question

Brian Hendel
Jedi Master Film Handler

Posts: 902
From: New York, New York
Registered: Jun 2003

posted April 04, 2006 07:01 PM

I recently bought my first Optical Sound print (ISLAND OF DR. MOREAU) to try out on my GS 1200. I must be doing something wrong because the sound is playing so low and hissy. Is all optical sound this bad? I can't get the sound to come out of the usual outputs I use (the ones near the power connection) and I feel I must be doing something wrong. Is there a secret to good optical sound? Any advice would be appreciated!

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Mark Todd
Film God

Posts: 3846
From: UK
Registered: Aug 2003

posted April 05, 2006 04:01 AM

Hi Brian, sometimes it can be a bad optical sound original, or you may have bad marks through the sound track.
The Gs is not the best optical sound machine, the st1200`s are better but GS`s are OK.
The optical reader or lens etc may be a little out of line that can somtimes make the sound bad with these.
Does it all appear to click over properly when you set it to optical as it were.
I`m sure its sortable, maybe soemone here stateside has an odd decent optical reel they can send to test it out.
Best Mark.

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Jean-Marc Toussaint
Film God

Posts: 2392
From: France
Registered: Oct 2004

posted April 05, 2006 04:23 AM

Brian: Mark is right, the print could be at fault.

But, before getting too technical, have you tried this:
1/ Clean and lube the print
2/ Clean and lube filmgate and path
3/ Clean soundhead area and optical lens assay (don't try to realign the lens)
4/ Check pressure pad (it might be a little too tight, but careful, if it's too loose, the sound will gargle).

--------------------
The Grindcave Cinema Website

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Kevin Faulkner
Film God

Posts: 4071
From: Essex UK
Registered: Jun 2003

posted April 05, 2006 10:52 AM

Mark is right up to a point. The ST1200's have better optical over the GS's.
On the GS the sound from the optical track is fairly low which results in the volumme controls having to be turned up much more. This in turn adds some noise to the optical sound.
I have removed a resistor on my GS and changed the value of another in the amplifier and now get optical tracks which do peak into the red on the meters. This now gives me the sound I used to enjoy from my old ST1200.
As Jean-Marc said above, it's important to make sure the optical lens and pickup cell is clean.

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Paul Adsett
Film God

Posts: 5003
From: USA
Registered: Jun 2003

posted April 05, 2006 11:26 AM

Hi Kev,
Just out of curiosity, what is the difference in the ST1200 and GS1200 optical sound system? Do they use the same optical relay lens assembly and optical cell, and are they mounted in the same way? One impression I have is that the optical sound sytem on the GS1200 is almost an after thought. The relay lens is on a fixed mount just bolted in place, and there is no provision for fine tuning the alignment to the optical sound track (with azimuth and elevation adjusting screws).

--------------------
The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj

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Dimitrios Kremalis
Expert Film Handler

Posts: 129
From: Athens - Greece
Registered: Oct 2004

posted April 05, 2006 11:28 AM

Kevin, can you please shed some more light regarding the mod for improving the optical sound reproduction on GS machines?
Which resistor needs to be changed, and whichone has to be removed?

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Kevin Faulkner
Film God

Posts: 4071
From: Essex UK
Registered: Jun 2003

posted April 05, 2006 11:48 AM

I was waiting for that question. I will look at the circuit and post the details.

Paul, The parts for the Optical sound are the same on both the ST and the GS. Althogh its looks like it is just bolted in place the lens does have adjustments. One tiny screw on the lens holder can undone and the the lens can be moved about, in out etc and a screw on the bracket allows further adjustment. The adjustments are very critical due to the small size of the optical track and not a job for someone with shakey hands.

On the GS when Optical is selected Elmo decided to attenuate the optical signal on its path through one of the IC amps. They say this is because of the variation in output level of various tracks. I think they actually went over the top with this on the GS. Its not done on the ST and that works much better.

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Kevin Faulkner
Film God

Posts: 4071
From: Essex UK
Registered: Jun 2003

posted April 05, 2006 03:34 PM

Ok before I get any more emails about my optical sound mod on the GS....... [Smile]

The two resistors in question are R190 10K and R177 15K.

These are both on the bottom board of the two amp boards. You have to remove the cover which goes over all the front Vol & Tone controls and its then the bottom of the two boards. In the centre at the extreme bottom edge is where R190 lives. This is 10Kohms (brown, black, orange, gold) and is simply removed or at least cut. As these resistors stan on their ends it's a simple job to just cut one of the resistors wire legs and then leave it in place. R177 is more difficult to get to. Its again on the bottom board and is right behind the Mic 1 jack socket. This is currently a 15Kohm resistor (brown, green, orange, Gold) and really needs to be unsoldered and replaced with a 100Kohm resistor. To do this the whole amplifier section really needs to be removed. I do know that you can just cut this resistors leg as before and then leave it with out replacing it. Give this a try first but just keep an eye on the level meter when using optical films. If the majority of films playback and peak in the red area a lot of the time then you may have to think about putting a 100K resistor in that position.

I will not be held responsible for any cock ups. You do these mods at you own risk.

Dont forget that the full GS1200 manual is in the manual section so its worth referring to this for taking the machine to pieces.

This does make a big differnce to the optical sound levels. I will take some pics of the amp so that I can point people to the exact position of these 2 resistors but that wont be till the weekend.

Now what other mods can I tell you about..... [Wink]

Kev.

--------------------
GS1200 Xenon with Elmo 1.0...great combo along with a 16-CL Xenon for that super bright white light.

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Osi Osgood
Film God

Posts: 10204
From: Mountian Home, ID.
Registered: Jul 2005

posted April 08, 2006 10:08 AM

Personally, I adjusted the screw that holds the exicter lamp in, (on my Elmo) and the sound was suddenly booming. As Kevin faulkner stated, with such a small optical track, even the slightest adjustment can affect sound levels immensely.

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"All these moments will be lost in time, just like ... tears, in the rain. "

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John Whittle
Jedi Master Film Handler

Posts: 791
From: Northridge, CA USA
Registered: Jun 2003

posted April 09, 2006 10:11 AM

Another thing to remember is that there are real differences in optical sound quality between prints and laboratories. Normal 35mm and 16mm color positive prints have special processing on the sound track to capture silver along with the dye. This provides higher density and effectively blocks IR from the pick up. Most sound pick ups are very sensitive in the IR region.

Super 8 optical sound prints were often produced four up on special 35mm film stock (perf 5R1667) and thus applicating the sound track developer was very difficult since any splash would should has dark yellow stains in the picture area. Many labs elected not to applicate sound on Super8.

Also the dyes used in the print stock had a major effect on IR blocking and thus sound output. The cyan dye used in the Agfa-Gevaert print stock had a much higher IR block than did the Eastman stock and that couple with cyan dye fading on Eastman stock made them a poor choice for optical sound Super8 prints.

John

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