Author Topic: DAC correction min/max voltages  (Read 3465 times)

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Offline jv4779

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DAC correction min/max voltages
« on: January 09, 2013, 12:20:00 pm »
Since most DAC correction is not a true differential signal, why go to the trouble of setting a zero offset and doing -5/+5 voltage range?  0/+10 volts or some other arbitrary 10 volt peak-to-peak scale would be the exact same result.  I know that -5/+5 is the ILDA standard, but so is differential.


Can I get way with doing correction with a single trimmer pot and just do amplification ?


Jermey

Offline James

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Re: DAC correction min/max voltages
« Reply #1 on: January 09, 2013, 08:11:46 pm »
Think about it like this: with no DAC at all plugged into the projector, you would have (naturally) zero volts on the inputs of the scanners and the color mod inputs of the lasers.

That state should put the scanner mirrors in the center of their rotations and set the lasers to off.

If you tap the DAC (signal) side of the output decoupling caps on a sound card, you will find a DC offset voltage of 1.2 to 2.5 volts (typically). If you give that enough gain to get the voltage swing you need to drive scanners or colors, that offset goes up with the gain.

It is important to note that when a sound card is not playing any wave data, it is ensentially playing a constant stream of digital zeros! So, digital zero MUST correspond to REAL zero volts on the output of each control channel of the correction amp.

James.  :)
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