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Thread: Opamp for fx loop

  1. #36
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    According to spice, how much current does a TL072 need ?
    Maybe there's too much voltage drop over the 47K

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  2. #37
    "Thermionic Apocalypse" -JT nickb's Avatar
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    If you are using the (texas insts) TL071.301 model it comes up with over 8ma per amp at +/-15V. The datasheet says 2.5mA max. Caveat utilitor!

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    Last edited by nickb; 03-08-2019 at 06:47 PM.
    Experience is something you get, just after you really needed it.

  3. #38
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    Quote Originally Posted by strato56 View Post
    According to spice, how much current does a TL072 need ?
    Maybe there's too much voltage drop over the 47K
    That did it. I'm sure I tried lowering that too!
    Thanks

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  4. #39
    Old Timer J M Fahey's Avatar
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    Capacitors do not affect DC.
    You have a couple schematic errors, Iīll download the image and edit it.

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    Juan Manuel Fahey

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    Old Timer J M Fahey's Avatar
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    Attachment 52833
    Check and post voltages 1 / 2 / 3 / 4 , both with and without load (Op Amp circuit) , open indicated connection and I guess you should add the missing loop jacks in the empty rectangle.

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    Juan Manuel Fahey

  6. #41
    Old Timer J M Fahey's Avatar
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    Click image for larger version. 

Name:	TL072_loop.gif 
Views:	39 
Size:	22.8 KB 
ID:	52837

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    Juan Manuel Fahey

  7. #42
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    Wow, how was it possible to miss that short?

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  8. #43
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    I guess you should add the missing loop jacks in the empty rectangle.
    ^^^That, and make sure you use the same "ground" for send and return.

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  9. #44
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    Ah damn it, that was the wrong schematic. I'm sure I uploaded the one with that corrected :/

    Edit: the inline one doesn't have that short but the attachment does. I tried deleting it but it showed up anyway!

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  10. #45
    Old Timer J M Fahey's Avatar
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    Not that a big deal but it will screw your simulation for sure, try to erase the wire and components conected to it and redraw that area from zero.
    And add the jacks too.

    FWIW I design and build using TL072 all day long since itīs my favorite building brick, and can confirm they "eat" between 3 and 3.5mA per DIP8 package, meaning 2 op amps (which you canīt separate and will sink full supply current even if 1 is unused).

    IF you want to be even "greener", you can use a TL062 which uses around 1/5th of that.
    Not too hot "audiophile" specs but ample for Guitar duty, in fact itīs very popular in Active Bass and Guitar circuits, for long battery life.

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