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Thread: Trying to build a homemade servo amp. Is the AGC needed?

  1. #1
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    Default Trying to build a homemade servo amp. Is the AGC needed?

    hello. i am new to this great forum. props to all the posters and contributers.

    I am planing to build a servo amp for some cti 6230's i got off ebay. I am modeling the circuit from the cambridge 658XX amp. does any body know if the AGC circuit is needed for decent linearity? it seems that the differential input from the PD sensors would do fairly good alone. if i omit the AGC i can save on one opamp, the precision voltage ref and several passive parts. thanks for any input

    -woody

  2. #2
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    Hi,

    Using CT6810 I found the basic schema without AGC for optical feedback part OK for lasershow purposes. Since You're likely designing a PCB from scratch I'd suggest including the AGC part in the design, then jumpering it to reduce parts cost. This way You could add it in future.
    Piotr.K

  3. #3
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    thanks fore the input. i have most of the boards drawn up in eaglecad with the agc included. Now i am trying to decide if i want to use 2 X lm12, 2 X lm3886, or a hybrid op-amp and push-pull transistor combo.

    -woody

  4. #4
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    Since a bunch of them are sleeping in my drawer I'd go for OPA549 pair, but these are not cheap. What I like in them is smart current limiting option, also unity gain is solid-rock stable.
    Piotr.K

  5. #5
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    Oh wow, hey Piotr.K! How have you been? Welcome to PL!

  6. #6
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    Hi there!
    Oh well, been stuck around alt.lasers but apparently mainstream discussion moved towards PL and so I moved as well. Nice to see You all laser folks gathered together !
    Piotr.K

  7. #7
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    Yep, this is the place to be! I don't think I've looked at alt.lasers in almost 2 years... There a bunch of great folks here thats for sure!

  8. #8
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    Default AGC

    Hi Piotr.K

    Iīm working in a home made servo amp for ct66210, I Start with reverse engineering of a chinnese driver clone of CT, I remove the agc control and drive the IR led with 9 v to 10v, work lineal, and I canīt to see any change.
    I see on diagram that AGC control return noise that diferential op amp removed from wires sensors.
    Are you test or have any info about AGC control.
    I decided remove AGC control.
    best regards
    Angel
    quote=logsquared;47529]hello. i am new to this great forum. props to all the posters and contributers.

    I am planing to build a servo amp for some cti 6230's i got off ebay. I am modeling the circuit from the cambridge 658XX amp. does any body know if the AGC circuit is needed for decent linearity? it seems that the differential input from the PD sensors would do fairly good alone. if i omit the AGC i can save on one opamp, the precision voltage ref and several passive parts. thanks for any input

    -woody[/quote]
    Attached Thumbnails Attached Thumbnails agc.JPG  


  9. #9
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    I took Piotr.K advice and designed it in to the circuit. In testing i have used only a resistor to set the diode current to about 15ma. I started with 30ma but at 30 ma the posistion detectors saturated. I am totally impressed with the 6230 motors. I can get 30K no problem. although, I do have small mirrors. I have some noise issues i have to iron out with my amps ( there is a 5KW radio transmitter in my back yard) then i may try some larger mirrors. one good thing about building my own amp is the size. I was able get the size fairly small. Plus the end mount pots will make placement and tuning easier when installed.
    Attached Thumbnails Attached Thumbnails DSCN0004.JPG  

    DSCN0005.JPG  


  10. #10
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    Default AGC


    Looks nice! Good job

    I check the current and I use 19mA IR emiter.
    moving size small and big and this work fine.

    Are you using current monitor and coil temp calculator?

    Angel



    Quote Originally Posted by logsquared View Post
    I took Piotr.K advice and designed it in to the circuit. In testing i have used only a resistor to set the diode current to about 15ma. I started with 30ma but at 30 ma the posistion detectors saturated. I am totally impressed with the 6230 motors. I can get 30K no problem. although, I do have small mirrors. I have some noise issues i have to iron out with my amps ( there is a 5KW radio transmitter in my back yard) then i may try some larger mirrors. one good thing about building my own amp is the size. I was able get the size fairly small. Plus the end mount pots will make placement and tuning easier when installed.

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