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Thread: Sound Card DAC Tutorial

  1. #1
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    Default Sound Card DAC Tutorial

    UPDATE: Tutuorial has been updated with a complete wiring diagram and detailed tuning instructions from DrLava himself!

    EDIT: drlava is presently sold out of full correction amp kits, but you can still buy bare boards from him. If you want a full kit, assembled or unassembled, you can get them from 300EVIL here: http://www.photonlexicon.com/forums/...696#post139696 These kits are a tad more expensive, but they include a very good 12V dc-dc converter (results in a larger scanned image) and a built in DB-25 connector. I highly recommend them. Wiring the 300EVIL amp is actually a bit easier than the drlava amp kits since the DB-25 output connector is already installed. All you need to do when using these is wire the connections between the soundcard and the amp.

    I've tried to include everything necessary for construction of a soundcard DAC here in this tutorial. Many thanks to Drlava for his help and input. Hopefully someone finds this useful! Also, special thanks to Dean Hammonds for the original correction amp design.

    This system is typically used with LFI Player show software as the free option, but there is other software available for sound card DACs at cost to the user. These are available online for download:

    LFI laser player: https://sourceforge.net/projects/lfiplayer3d/

    This tutorial assumes you already are familiar with soldering electronic components and very basic electronic theory and are comfortable building DIY kits. It also assumes you are aware of how to set up and install drivers for a computer USB sound card.

    The most commonly used sound card for this setup is this cmedia sound card from DX. (the correction amp can be purchased here or here) The only other tutorial that talks about a sound card DAC on this forum uses the previous revision of this card. The most recent revision has slightly different connections, since it is an 8 channel card as opposed to 6 channels for the previous revision. Due to issues with buggy Vista drivers, I don't recommend using this sound card with any OS other than Windows XP 32bit or Linux. Any other sound card can be used as long as you feel comfortable finding the proper channel output capacitors to connect to on whatever card you might use.

    For the DAC setup, we'll only be using the first 6 channels. You'll end up with the correction amp outputs connected to your laser modulation (up to three for RGB) and your galvo amps (to control X,Y movement).

    The connections must be made on the positive side of each output capacitor so that we get a DC signal (you can see exactly where to connect in the closeup photo below).

    In the following image, on the sound card, the connection points are as follows:

    Blue wire = L Front channel
    White wire = R Front
    Yellow wire = L Rear
    Red wire = R Rear
    Black wire = Center
    Orange Wire = Subwoofer




    On the correction amp board there is a row of input pins. The first two pins are labeled 5V and Ground, and the last pin is also labeled Ground. Both these ground connections must be connected to ground for the correction amp to work. The middle G is a redundant ground pin on the correction amp, so it needs no connection. On the USB sound card board are some solder points right behind the USB connector that can be used to supply power to the correction amp.
    The power connections to the correction amp are as follows:

    Red wire = 5V (pad furthest to the left)
    White and Black wires = Gnd. (both pads furthest to the right)

    The connections can be seen in this image:



    The defaults in most software are as follows:

    Soundcard channels | Scanner function | Soundcard Pin in Picture Below (looking from left to right.. you can also see my channel labels written on the card)

    Left | X galvo | 1
    Right | Y galvo | 2
    Left Rear | Red Laser Modulation | 3
    Right Rear | Green Modulation | 4
    Center | Blue Modulation | 5
    Subwoofer | Intensity | 6



    Here's a complete wiring diagram:


    You have to go into the settings for the sound card (which you access through the little white and blue icon in the system tray in the case of this specific card) and set it to 6ch. By default it is set to stereo 2ch, which will not work. 2ch does not allow for your modulation channels, and using the DAC in 2ch mode will make it impossible to tune.

    __________________________________________________ _____________
    NEW!!

    Here's tuning instructions direct from drlava himself:

    Tuning the sound card DAC correction amp:

    Tuning the amp is simpler than it looks. There are 6 channels, but only two adjustments per channel, and each channel is adjusted the same way. Tuning only needs to be done once after construction of the audio card DAC.

    First, a note of caution: Never plug in or unplug the USB sound card while your projector is on and connected to the DAC. Doing so will cause the sound card DAC to produce out-of-spec voltages that may cause dangerous beams to shoot out of your projector.

    Tuning the sound card DAC. Needed: multimeter, small flathead screwdriver, max.wav, wires.

    1) plug in the sound card DAC, open the control panel for the sound card and set it to 6 channel mode.
    2) Set the wav and output volume to max, mute all others, and confirm no 'effects' are on, and each speaker gain is set to 0dB.
    3) In the windows 'Sounds and Audio devices' control panel, 3rd tab, verify your sound card DAC is the default device.
    4) while no audio is playing, connect your multimeter in volts mode between the output G and output channel 1. Adjust the channel 1 Offset pot with your screwdriver until the meter reads 0 volts.
    5) repeat step 4 for all 6 channels.
    6) play max.wav in windows media player, repeat on, volume all the way up. Measure the voltage between output G and output channel 1 and adjust the channel 1 Gain pot till your multimeter reads either +5V or -5V (adjust to whichever it is closest to)
    7) repeat adjustment in step 6 for all 6 channels while max.wav is playing
    8) stop windows media player, and exit. Go back to windows 'Sounds and Audio Devices' control panel, 3rd tab. Set the default playback device back to your normal audio card.

    That is all the hardware adjustment that needs to be done. Later I can write about setting up Laseroids with EzAudDac and the sound card DAC.
    Happy lasing!

    If you have trouble playing max.wav, download and install the AC3 decoder here. (thanks to MISTERWILLING for pointing this out) The AC3 decoder is not free, but should work long enough to accomplish the tuning. If it's not sufficient, You could probably also use klcodec pack.

    There have been reported issues with the supplied cmedia sound card drivers. If you experience issues with jumbled output from the DAC, make sure you are using this driver: CMEDIA AUDIO DRIVER

    __________________________________________________ _____________

    The soundcard DAC comes with a +-9V DC-DC converter. This will limit the scan angle that is possible with the DAC. I highly recommend replacing the DC-DC converter with one that supplies +-12-15VDC such as this: 580-NKA0512SC This is a drop in replacement for the correction amp board which will vastly improve the scan angle.

    Here's the complete setup:


    Here's a diagram of how the PC, DAC, and scanner get connected:

    To maintain the ILDA standard in your system, you'll need to install a DB-25 connector on the DAC to connect the DAC to the scanner. Here's the pinout for ILDA DB-25 connectors:


    Here's some video of the completed DAC in action:





    Anyone with questions can PM me or email me at faze4djs@yahoo.com.
    Last edited by ElektroFreak; 10-13-2010 at 06:41.

  2. #2
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    Maybe a little tip for improvement:

    If you wire an SPNO relay in the interlock loop (between A and B) which is driven by the amp's power supply, the interlock will only be active if the DAC is plugged in. Unplugging the DAC will break the interlock and shut off the laser.

    The relay need not be heavy current, maybe even an optocoupler is enough to do the job.

  3. #3
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    Nicely consolidated info- thanks! (I know what you mean about the other threads)
    I thought I might paste in a sample of the EzAudDac.ini file, the file that goes in the same directory as your EzAudDac.dll. It provides an easy way to tweak custom configurations.

    *********************************************

    [Sound Card Selection]
    UseCardNumber=2

    LowLatencyBuffering=no
    ;not all programs work smoothly with minimal buffering, try yes if you have a hyperthreading
    ; or dual core computer and like to try to speed up timing.
    ; yes works with zoof games, LDS, HE-Laserscan
    ; no works best with LazyMame, LFI player

    SampleRate=48000
    ;choose a standard samplerate that your card can handle 44100, 48000, 96000 etc.


    RepeatFrameWhenOut=no
    ;'yes' or 'no'
    ;Repeats the last frame displayed if the program doesn't feed another frame in time
    ; if 'no', then the DAC output goes to 0 until a new frame is fed.


    BlankDelay=5
    ;enter the number of points that the laser blanking should be delayed.
    ;enter 0 for galvo based blanking, 3-7 for solid state or AOM blanking.

    [Channel Invert]
    ;enter 'yes' to invert the channel output, 'no' otherwise.
    X=no
    Y=no
    R=yes
    G=yes
    B=yes
    I=yes

    [Channel Selection]
    ;Enter the desired output chanel number (1-8 only) of the signals:
    X=1
    Y=2
    R=3
    G=4
    B=5
    I=6
    AL=7
    AR=8


  4. #4
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    I built my own correction amp in the meantime, but I'm still a little wondered about the blanking.

    There is both an 'Intensity/Blanking' signal and an intensity signal for each separate laser. Which one does the actual blanking and which ones should I wire to my laser drivers?

    BTW, the laser intensity outputs are specced by ILDA as being 5V differential outputs. On channels 3-6, the gain should therefore be set to read +/- 2,5V, not +/-5V, to operate within ILDA specifications. See:

    http://www.laserfx.com/Backstage.Las.../ISP-DB25.html

    Your mileage may vary with different laser driver circuits, though. Another option is to correct the gain for +/-5V and lower the volume control for the channels with 6dB.

  5. #5
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    Quote Originally Posted by ElektroFreak View Post
    The soundcard DAC is single ended rather than differential, so in that regard it isn't ILDA compliant. I'm not sure that those specifications apply to this DAC.
    It's true that the sound card coupled with that particular correction amplifier board isn't ILDA-compliant, but I want to clarify that this is no limitation of the sound card. It's easy to make ILDA-compliant, differential outputs the same way that most commercial DACs including Riya, EasyLase and Pangolin FB3 XE do. Those commercial DACs don't use underlying DAC chips with differential outputs either!

    Quote Originally Posted by ElektroFreak View Post
    Would you be willing to post the schematic you posted in another thread here as well? That way people can see the circuitry involved..
    Of course, I should have realised to post it here too: http://www.photonlexicon.com/forums/...&postcount=349
    Last edited by weartronics; 11-10-2009 at 17:06.

  6. #6
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    Quote Originally Posted by ElektroFreak View Post
    The soundcard DAC is single ended rather than differential, so in that regard it isn't ILDA compliant. I'm not sure that those specifications apply to this DAC. Also, I've never seen a laser that can be modulated by a negative voltage. Most if not all direct modulation lasers use either 0-5V TTL or 0-5V analog. The soundcaed DAC supplies exactly that. I might be misunderstanding what you're saying, though.
    Remember that the laser's modulation ground need not be the same as the ILDA ground and cable shield. With a differential output, both of your lines have a high impedance (floating) with respect to ground and the projector chassis, you just connect the negative signal to your laser's modulation GND, and the positive signal to the modulation input.

    On the soundcard DAC, all of the negative outputs are essentially hard-wired to ground (since they're not there!), this will make the connection a little more sensitive to noise over longer distances and half your laser output and scan angle. Making the outputs differential is an easy fix, though.

    Remember, ILDA was designed as a low-impedance system (100 ohms), but we're driving it as a high impedance connection with the correction amp.

  7. #7
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    Default Voltage jumps while tuning - should I be concerned?

    I put together a soundcard amplifer using DrLava's bare PCB board... (DrLava is a hero btw). It works like a champ with once concern. While I'm tuning the channel 1 offset, the voltage jumps around like mad. Say it's reading 0.1 and I start turning the offset screw, it will jump to -10.05 and then when I stop, it goes back to the right voltage. I can get it adjusted OK, but it seems weird to be getting these fluctuations while tuning. My concern is somehow during normal usages, it might send an out-of-spec voltage to the scan amp and cause damage.

    Thoughts?

    Thanks,
    Mike

  8. #8
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    Hi Bowfly thanks it sounds like you have a bad solder joint below that pot or in the area, touch them up with a little flux and solder and it should be stable.

  9. #9
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    Default Voltage fluctuation fixed!

    Sure enough, one joint on the pot hardly had any solder. Quick touch up and the offset adjustment is steady. Swaaweeet!

    Thanks!!!!
    Mike

  10. #10
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    Great post.
    Thanks from all of us sound card users.

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