A-102 Open Loop Amplifier.

[lasermaster1977]

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.




ua791.pdf







Edit: Dec 14, 2021
I found in one my old TV interviews open-loop scanner examples of the resonant frequency ringing in the General Scanning G-115 scanner I used. I clipped a few frames from the video to show as examples.

I'm fairly certain (after 41 years) the first two images show a 45Hz square wave (1st harmonic signal) with 90 degree XY phase shift, the second just slightly phase-shifted from the first.



The third image shows a 90Hz square wave (2nd harmonic) with a 90 degree XY phase shift.


I still intend to get these old scanners hooked up to a pair of u791 opamp drivers shown earlier in this post and take some videos to post here that shows the "magic" of the ringing at or near the scanner's open-loop resonant frequency.

[glorocks]

Thanks for looking-
Can anyone else help?

[lasermaster1977]

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:



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:





My DIY A-102 schematic shown here:



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!)