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Op amp dirty signal.

Discussion in 'Electronic Basics' started by Chris, Dec 5, 2004.

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  1. Lord Garth

    Lord Garth Guest

  2. Ban

    Ban Guest

  3. peterken

    peterken Guest


    It often helps to "decouple" outputs from their loads using small resistors,
    especially if the loads have a capacitive component.
    Often opamps begin oscillating caused by this component.
    The small resistors used will cause a small voltage drop which will be
    compensated by the opamp itself, so operation remains identical.

    for IC1(A) (less needed here, but might help)
    - small resistor (say 100e) from pin 1 to feedback junction
    - small resistor (say 100e) from feedback junction to pin 2
    (cut direct connection of course)
    - small cap directly from pin1 to pin2
    for IC1(D) (needed if load (out1) has a capacitive characteristic)
    - small resistor (say 100e) from pin 14 to feedback junction
    - small cap directly from pin14 to pin 13
    for IC1(B) (needed if load (out2) has a capacitive characteristic)
    - small resistor (say 100e) from pin 7 to feedback junction
    - small resistor (say 100e) from feedback junction to pin 6
    (cut direct connection of course)
    - small cap directly from pin7 to pin6
    for IC1(C) (needed if load (out3) has a capacitive characteristic)
    - small resistor (say 100e) from pin 8 to feedback junction
    - small resistor from feedback junction to pin 9 (cut direct connection of
    course)
    - small cap directly from pin 8 to pin 9

    principle:
    (see drawing in notepad using fixed font)

    |\
    -----|+\
    | \-+-/\/\-+--
    | / | |
    +-|-/ === |
    | |/ === |
    | | |
    |______+_/\/\-+
     
  4. Chris

    Chris Guest

    Input looked the same ,. well turns out it's an bad wall socket,
    realised this when i checked my probe on the scope and got a little jolt
    moved it all off to another socket and a nice signlan added a small cap
    filttered it right down :)
     
  5. Guest

    Gee, your schematic looks just fine with the fixed font in this entry
    window. Don't ya just love how people 'fix' things?
    GG
     
  6. Chris

    Chris Guest

    small cap, ceramic? about how small?


    Thanks
     
  7. peterken

    peterken Guest

    depends on the highest frequency you want passing through the circuit of
    course since it's a filtering circuit
    I'd begin with say 1nF and go up by decade while looking at the signal on
    your scope until the output satisfies your needs
     
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