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Thread: A-102 Open Loop Amplifier.

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    Default A-102 Open Loop Amplifier.

    Posting for attachment. Note to you young-ins, this only works for galvos with Torsion Bars, Ie GSI open loop scanners such as G330 or G124.
    This derives it's Back EMF feedback from the difference voltage between the purely resistive network and the inductive load from the Galvo. Aka a Bridge Circuit.
    The value of "C3" is critical in the design of the bridge. Terminals CDJ go to the external DC offset potentiometer. A value of 1OK Ohms is just fine for that part.

    Steve
    Attached Thumbnails Attached Thumbnails GS-A102.gif  

    Last edited by mixedgas; 01-06-2021 at 08:36.
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    Open Loop Sample Back EMF amplifier, fleshed out on a sample design handed out by GSI to "select" customers who got the large brochure, not the data sheet.
    ~
    Known informally as the " RoC = L" Back EMF amplifier , from the title line in the schematic. R and C are two components in the circuit, L is the inductance of the Galvo coil. Please note again, this only works with galvo scanners and actuators with Torsion Bars..
    ~
    Posted for another fellow who has a pile of G124s. As it is set up for G115 in this version, he'll have to alter R or C a bit.
    ~
    GSI would never suggest parts values for R and C, leaving that as "An Exercise for the Reader".
    ~
    A TL082 would drop right in if you do not have the Raytheon or Maxim part.
    ~
    I do believe this edition came from either Laserist or PhotonBeam.
    ~
    Steve
    Attached Thumbnails Attached Thumbnails open loop back emf amp.jpg  

    Last edited by mixedgas; 01-06-2021 at 08:32.
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    Default

    Quote Originally Posted by mixedgas View Post
    Open Loop Sample Back EMF amplifier, fleshed out on a sample design handed out by GSI to "select" customers who got the large brochure, not the data sheet.
    ~
    Known informally as the " RoC = L" Back EMF amplifier , from the title line in the schematic. R and C are two components in the circuit, L is the inductance of the Galvo coil. Please note again, this only works with galvo scanners and actuators with Torsion Bars..
    ~
    Posted for another fellow who has a pile of G124s. As it is set up for G115 in this version, he'll have to alter R or C a bit.
    ~
    GSI would never suggest parts values for R and C, leaving that as "An Exercise for the Reader".
    ~
    A TL082 would drop right in if you do not have the Raytheon or Maxim part.
    ~
    I do believe this edition came from either Laserist or PhotonBeam.
    ~
    Steve
    That is my drawing from the early '80s based on GS brochure info and I believe I've posted it before. Photonbeam could have as well as I probably gave him a copy. I still have this original.
    I can attest that this really peps up the step response for the G-series with decent damping characteristics. The key is to not drive the galvos beyond half their maximum angle of scan in order to get the full benefit from the Back EMF feedback.

    I still have at least 4 DIY circuit boards I made back then for my G-115 scanner pairs. Here is a photo of one axis driver I used in one of my disco projectors. A TLO84 would be an excellent alternative to the 4136 in my drawing.

    Click image for larger version. 

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    Last edited by lasermaster1977; 01-09-2021 at 11:34.
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    Thank you for owing up to your copyright!

    It had been posted here before, so I snagged it. Right now that is helping a long time retired laserist have fun with eight 124s he just received.

    I used to have the GSI brochure/ book but I cant find it in the piling system.

    So I hope you don't mind if I reposted it.

    Thanks,

    Steve
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    Quote Originally Posted by mixedgas View Post
    Thank you for owing up to your copyright!

    It had been posted here before, so I snagged it. Right now that is helping a long time retired laserist have fun with eight 124s he just received.

    I used to have the GSI brochure/ book but I cant find it in the piling system.

    So I hope you don't mind if I reposted it.

    Thanks,

    Steve
    I'm glad to hear that it is helping your friend and hopefully others will find benefit from it, too. I'll see if I can find my GSI source...and I did. Here it the 2 1/2 page Series G Scanner brochure with the general schematic mine is based upon:

    Click image for larger version. 

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    Last edited by lasermaster1977; 01-09-2021 at 18:48.
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    I'm curious how these amps would work on some Stocker Yale R4-077's. I have an old XYP-1000 missing a scan head and was thinking of putting my R4-077's to use as a replacement.
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    Quote Originally Posted by absolom7691 View Post
    I'm curious how these amps would work on some Stocker Yale R4-077's. I have an old XYP-1000 missing a scan head and was thinking of putting my R4-077's to use as a replacement.
    I know nothing about your Stocker Yale's and can only suggest you compare the GS G-Series specs in the scanned brochure pages I attached. If their coil characteristics are similar then it might work for you. (today, I'd use a modified push-pull driver output section but the one shown in my schematic works like a champ).
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    Not exactly but workable.

    Click image for larger version. 

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    Quote Originally Posted by absolom7691 View Post
    Not exactly but workable.

    Click image for larger version. 

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    Thanks. So, your galvo coils are 15ohm each and wired in parallel would be close to 8 ohm. Your galvo coil's inductance is 5 times larger, however. You would have to play with the RC values to tweak it, but workable.
    Last edited by lasermaster1977; 01-10-2021 at 17:35.
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    Default Need photo of old GS A-102 amp card

    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

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