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Thread: A-102 Open Loop Amplifier.

  1. #11
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    Sep 2014
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    Colorado USA
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    Quote Originally Posted by glorocks View Post
    Does anyone out there have a photo of the old GS A-102 amp card?
    I need to see the parts layout- going to build a couple
    Thanks,
    Jay
    Yes, I do, and will post shortly.

    (Oops, sorry. I thought I did but only have their A-600 driver board.)

    If interested, here is my version of an open-loop drive amp that I used on the GS-115 galvos back in 1977-1979 using the single uA791 op-amp driver. This could easily be modified to be a non-inverting version and/or differential balanced input version. I used 7812 abd 7912 1amp voltage regulators. The nice thing about the 791 op-amp driver was that its output was current limiting to 1 amp, bipolar and therefore protected the galvo load. I used 4 pairs of these drivers on my 1st RYGB projector. Never had a failure.

    If you need to drive heavier current loads like for the GS-300 series or similar you can use the 791 as the pre-driver to an differential output using two 3055 transistor drivers in a push-pull arrangement and using + and - 24vdc supply rails on the 3055's.


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    ua791.pdf

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    Attached Thumbnails Attached Thumbnails 791 Scan Amp-2.jpg  

    Last edited by lasermaster1977; 07-21-2021 at 14:27.
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  2. #12
    Join Date
    Nov 2013
    Location
    St George UT
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    120

    Default A-102 amp photo

    Thanks for looking-
    Can anyone else help?

  3. #13
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    Sep 2014
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    Colorado USA
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    Quote Originally Posted by glorocks View Post
    Thanks for looking-
    Can anyone else help?
    I built a DIY A-102 drive amp based on GS's schematic in their GS-100 series open-loop galvos, shown here that uses back EMF feedback to improve step response:

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    Unless you are just wanting an exact duplicate of their original A-102 drive amp, layout isn't that critical. My version is shown here, front and back:

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    My DIY A-102 schematic shown here:

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    The trade-off for improved, more critically damped step response is reduction in maximum rotor deflection angle (about half). Overall it is an impressive improvement given this downside.

    (dang, should have looked at the first pages of this thread...sorry for the duplications...doah!)
    Last edited by lasermaster1977; 07-21-2021 at 18:55.
    ________________________________
    Everything depends on everything else

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