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Thread: Soundcard Dac linearity

  1. #1
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    Default Soundcard Dac linearity

    I have now tried a couple different soundcard correction amps, laserboy and drlava's (EDIT: opening laserboy showed it is the same correction board) I am having a problem with linearity. Playing original source material from ADAT I am getting all the lines and colors to show (thanks drlava for the needed mods); however using the soundcard dac I am getting full output but there seems to be a scaling issues where linearity is nowhere near the same as on ADAT. I am back to the problem of having some lines missing the deep purples and some reds very light in color when using the SC Dac. I have full output wavmax set to 5v and the offsets are near 0 as possible with the pots. Any ideas or is this a known issues with soundcard dacs?

    Thanks
    Last edited by polishedball; 08-29-2010 at 12:12.
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    I should also mention that if i play back the wav files (prior to making them multi channel) in reaper and play them out the lightpipe and use the ADAT as the dac the colors are fine and all lines are present. So I know the rips from tape are good.

    Just looking for a more portable solution than lugging an adat player if needed.
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  3. #3
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    What version of Windows are you running? Have you enabled any "effects" through the sound card's driver utility?

    I've never compared the output of a soundcard DAC to ADAT so I can't say much about this. What I can say is that on a scope the DACs output seems very linear.

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    Quote Originally Posted by ElektroFreak View Post
    What version of Windows are you running? Have you enabled any "effects" through the sound card's driver utility?

    I've never compared the output of a soundcard DAC to ADAT so I can't say much about this. What I can say is that on a scope the DACs output seems very linear.
    this is on a XP build, no I never went into the effects area had read that could be bad. I am using spiderplayer for playback.
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    Quote Originally Posted by polishedball View Post
    this is on a XP build, no I never went into the effects area had read that could be bad. I am using spiderplayer for playback.

    Hmm, I've never tried spiderplayer.. Do you have another multi-channel playback program that you could compare it to? I wonder if maybe the software is tainting things. Does it have an EQ? Also, it would seem to me that if the DAC was the cause it would alter the quality of the scanned image itself along with color response, with wobbly lines etc..

  6. #6
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    Sound card hardware is by design extremely linear (It has to be or you get intermod tones when using it for audio), so it is very unlikely to be the card that is the problem.

    Check that the negative rail is present and correct on the buffer amp, and then break out the scope and have a poke around.

    My bet is either a buffer amp problem or a software issue, if there was a problem with the sound card that was visible with the relatively small dynamic range we use, it would be un usable for audio.

    Regards, Dan.

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    OK upon more investigation, it appears to be an input impedance problem with the red. I use a laserwave 635 and a burner 660 on a flexmod PBS'd. When using the adat it drives both just fine, when using the soundcard it never drives the laserwave correctly and the flexmod is reduced. At full power all is present as long as I tweak the 5V open on meter above 5v slightly

    There was talk of perhaps a buffering circuit or something similar at SELEM, think drlava may have discussed it and there was talk of 300evil a perhaps a builder(?)

    anyone remember or want to confirm if this may be my problem.

    Thanks

    John
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    Quote Originally Posted by polishedball View Post
    There was talk of perhaps a buffering circuit or something similar at SELEM, think drlava may have discussed it and there was talk of 300evil a perhaps a builder(?)

    anyone remember or want to confirm if this may be my problem.

    Thanks

    John
    I'm not sure what your problem could be but If you do get anyone to build buffer circuits let me know. I asked both Dr. Lava and 300evil about it but I'm not sure when they will have the time to build them. I'm looking for 6 of them, one for each of my modulation inputs.

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    Quote Originally Posted by MisterWilling View Post
    I'm not sure what your problem could be but If you do get anyone to build buffer circuits let me know. I asked both Dr. Lava and 300evil about it but I'm not sure when they will have the time to build them. I'm looking for 6 of them, one for each of my modulation inputs.


    Have you a link to the circuit?

    John
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