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Topic: Distorted dolby tone waveform

Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005

posted 08-11-2009 04:29 PM

As shown in the URL above, I have a nasty output from my Component Engineering basement reader for a Century soundhead. I have checked the power supplies to the reader and the LED and they have very low levels of sawtooth ripple. I have aligned and realigned the LED and reader but end up with this horrible buzzing sound atop the audio signal. The interesting thing is that the buzzing sound increases in amplitude when the audio signal output level increases. All I can conclude is that my reader has failed. Any ideas?

[ 08-11-2009, 05:41 PM: Message edited by: Brad Miller ]

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Tim Reed
Better Projection Pays

Posts: 5246
From: Northampton, PA
Registered: Sep 1999

posted 08-11-2009 05:11 PM

quote: It is important to note that our forum will no longer permit any image links served from off site. This means you may not upload an image to another webserver and display it on the forums. Also not permitted is linking to html pages on other servers containing images whether they comply with the self-upload restrictions or not. (Occasionally the need for a high resolution image is desired. For these types of situations, you need to email them in so they may be served on a seperate page from the Film-Tech servers.) Why so stringent about this? This policy is to preserve all images that are associated with a discussion for future viewing in the archives.

Eric, you should post the picture to Film-Tech proper, so it will remain with the thread for future reference.

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Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005

posted 08-11-2009 05:38 PM

I have tried to post pictures here abiding by every rule and technical detail required and yet I can not post pictures here no matter how hard I try.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 08-11-2009 05:41 PM

Just because you can't figure it out doesn't give you the right to break the site policies. The upload page gives very detailed instructions if you care to read it. If you still can't figure it out by then, you should ask on the forum for assistance.

Next time = banned.

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Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004

posted 08-11-2009 07:11 PM

I have a scanner program in my laptop here that also will do image reduction on either scanned or saved image stored on my HD.

I pull up the image and click on it's properties to see what pixel size it is. Then, through the editing part of the program, I reduce the image down to the maximum (or close-I ususally choose 475 pixels to be safe) required pixel size required by policy rules then cut and paste the description of the image in the required "upload" section to be displayed in my posts.

It does work ... - Monte

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Chris Slycord
Film God

Posts: 2986
From: 퍼항시, 경상푹도, South Korea
Registered: Mar 2007

posted 08-11-2009 07:42 PM

If you shoot me an email w/ the pic attached I'll make it the right size for ya and upload it.

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Eric Robinson
Jedi Master Film Handler

Posts: 538
From: Santa Rosa, CA
Registered: Jan 2005

posted 08-11-2009 11:16 PM

quote: Brad Miller
you should ask on the forum for assistance

Yes, you are right. I'll give it another go round then I'll ask for help if I'm still stuck. This forum is valuable to me so I have no ambitions for being banned.

quote: Chris Slycord
shoot me an email w/ the pic attached I'll make it the right size for ya and upload it

Thanks, I'll email you the pic until I get my technical problem solved.

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Marin Zorica
Jedi Master Film Handler

Posts: 671
From: Biograd na Moru, Croatia
Registered: May 2003

posted 08-12-2009 09:09 AM

Let's get back to problem......probably you have too much gain, or some lose ground inside reader preamp, so:

1: check OP amp, if you can replace it, but before check no 2,

2: check all resistors, because if some resistor (one in feedback) is bad soldered op amp will go to infinity gain = distorzion!

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Chris Slycord
Film God

Posts: 2986
From: 퍼항시, 경상푹도, South Korea
Registered: Mar 2007

posted 08-12-2009 09:53 AM

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Sam D. Chavez
Film God

Posts: 2153
From: Martinez, CA USA
Registered: Aug 2003

posted 08-12-2009 10:04 AM

Any ripple is too much ripple on the LED portion of the supply. Anything more than .1 Volt peak to peak can clearly be heard as hum in the audience. The LED is a direct radiator of anything that feeds it unlike an exciter lamp that lights indirectly by making a filament glow.

The hum would could go up and down with the loudness of the track as you describe because that is the nature of a hum source behind a variable area mask feeding a photovoltaic solar cell.

You should check whether there is hum there with no film and if there is, cover the LED and see if it goes away. If it does, you've found the cause.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99

posted 08-12-2009 11:48 AM

Eric,

If you need a copy of Photoshop just let me know... I can send you one. Makes it a cinch to adjust file size....

Mark

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Demetris Thoupis
Phenomenal Film Handler

Posts: 1240
From: Aradippou, Larnaca, Cyprus
Registered: Apr 2001

posted 08-12-2009 01:07 PM

I am not really aware of the CE readers but one thing to try is to tie the - signal of the dc power supply output to the chasis ground of your rack/projector as well as the ground of the power supply. mmost probably is a ground issue.

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 08-12-2009 09:04 PM

It doesn't realy look distorted, it looks like there is a sine wave added to it. Look at the bottom of the waveform. What does it look like with no film, and with the light blocked? What does it look like (and sound like) with "normal" sound footage?

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 08-12-2009 09:13 PM

So much fuss about film piracy and a member can glibly offer give away photoshop?

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Jarret Chessell
Master Film Handler

Posts: 288
From: London, Ontario, Canada
Registered: Jan 2009

posted 08-12-2009 09:42 PM

Search "GIMP" on the internet. It's an open source photo editor incredibly similar to Photoshop. I recommend it to anyone concerned with piracy. I'm also a big fan of Open Office as an alternative to MS Office (also open source).

BTW, those are some crazy ass wave forms.

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