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Thread: Analog pallet correction

  1. #1
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    Default Analog pallet correction

    Does anyone have a circuit that can be used to balance and adjust the analog RGB pallet signals in the analog world say if using a soundcard DAC or an ADAT.

    The playback on my pangolin LD2000 looks great, but when playing back from soundcard DAC or ADAT, there are some mixed colors mostly Deep Purple and Brown colors that are barely visible on the screen.

    It seems like there is a linearity problem that needs to be corrected, but not sure what the cause would be as the same drivers are used when on the Pango card.

    Looking for options in case I am not successful at getting more memory into the pango card.
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    Four questions,

    I. You used the Palette setup dialog in Pangolin correct?

    II, Does your projector have any analog controls for offset and gain on the RGBV?

    III. What kind of lasers/drivers are we looking at here?

    IV. Are these tapes you recorded, or others recorded? If recorded for a gas laser system there can be some issues. Some of them are correctable.

    Steve
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    Quote Originally Posted by mixedgas View Post
    Four questions,

    I. You used the Palette setup dialog in Pangolin correct?

    II, Does your projector have any analog controls for offset and gain on the RGBV?

    III. What kind of lasers/drivers are we looking at here?

    IV. Are these tapes you recorded, or others recorded? If recorded for a gas laser system there can be some issues. Some of them are correctable.

    Steve
    I. yes used the pango setup ~ note using the pangolin card output with rips of these tapes (converted using LC-ADAT) looks great. The only problem is when not using pangolin using straight ADAT or soundcard.

    II. No I only have correction on the XY signal with a UGC. This is the circuit I'd like to build,(offset and gain on the RGBV) thinking it may help.

    III. Vaisho Lab Suppy, Flex Mods

    IV. These were purchased tapes, others recorded (will inquire on there originally purchase) it is possible as they are from a planetarium that closed.

    Also

    Switching to TTL only and using a circuit I built (opamp comparator) to take the modulation out and force full TTL shows all the lines but has loss of color pallet.
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  4. #4
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    Conceptual ADAT colorizer, does NOT DO blanking delay adjust.

    Drawn in a hurray.

    see inline attachment

    Provides controls for offset, loss and gain for each channel. Allows addition of a small amount of green to red channel for white balance correction. (aka the Doug Dumalge trick) Allows addition of pseudo log response, clips output to 5.6 volts as needed. USES common parts, needs split power supply +/- 12V, uses TL084 or TL074 opamps.

    Bill Benner has published a similar circuit that adds filters for blanking delay compensation, but is a real witch to adjust as you can only ADD delay as the analog filters are NOT recursive.

    circuit is a inverting summer followed by a inverter/limiter. As drawn, Controls do interact, ie adding gain increases offset, etc.

    The LM7805 gives you a voltage source to add some offset as needed for lasers with weird turn on points.

    If the tapes came out of a LFI or ECCS plantarium rig, there is a good chance the 19" rack had offset and gain controls post adat, so this may fix your problems. OK to delete offset pots and add/delete blending pots as you see fit, after all it is a inverting summer. Might not hurt to blend some red into the blue as well. I would NOT blend green into the blue. Note that I have jumpers on the feedback resistors, so you can do log/linear/both

    Oh and I drew the 1n4001s in the zener legs backwards, all I want them to do is add .6 volts to the 5 V zener drop when it clamps, so it clamps at 5.6V. It wont do that if it wont conduct. Or you can use a 5.6V zener and omit the additional diodes. Note the 1n4001 on the outputs prevent the opamp from outputting more then .7 volts if the output goes negative for some strange reason. Its not that I'm lazy and wont correct the pic, its just I did not save the cad file when I drew this. My bad, mea culpa

    YMMV

    Click image for larger version. 

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    Last edited by mixedgas; 08-09-2010 at 09:56.
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    Quote Originally Posted by mixedgas View Post
    Conceptual ADAT colorizer, does NOT DO blanking delay adjust.

    Drawn in a hurray.

    see inline attachment



    Click image for larger version. 

Name:	ADATCOLOR.png 
Views:	83 
Size:	36.3 KB 
ID:	18606


    WOW! thanks, ordered parts hopefully get it going by the weekend. I'll owe you a drink for sure at SELEM!

    John
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    Quote Originally Posted by mixedgas View Post
    Four questions,



    IV. Are these tapes you recorded, or others recorded? If recorded for a gas laser system there can be some issues. Some of them are correctable.

    Steve
    Yes these were from a gas system using a PCAOM, guessing that explains it abit. Hopefully bumping offset or gain will help. I'll know more this weekend once built. Thanks again.

    John
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    Thanks for the schematic.

    I'm a "get the color right" freak and I wonder what test pattern you guys are using to dial linearity and white balance?
    It doesn't matter how much time I spend dialing RGB gain and offset on my Kvant I never get satisfied with the result if I switch test patterns and always end up with a compromise that kind of works for everything.

    Fred.

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    Quote Originally Posted by infredible View Post
    Thanks for the schematic.

    I'm a "get the color right" freak and I wonder what test pattern you guys are using to dial linearity and white balance?
    It doesn't matter how much time I spend dialing RGB gain and offset on my Kvant I never get satisfied with the result if I switch test patterns and always end up with a compromise that kind of works for everything.

    Fred.
    DZ has some frames around here somewhere. Search his color board or look through his posts. I am fairly certain they are attached here somewhere.
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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    Quote Originally Posted by polishedball View Post
    Get it while you can, my hosting subscription runs out sometime this month and I don't plan on renewing. In the future if anyone needs these files they are welcome to PM me. Maybe I can upload them to the FTP as well.

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