Connect with us

When should you buffer a signal?

Discussion in 'General Electronics Discussion' started by AFex54, May 27, 2015.

Scroll to continue with content
  1. AFex54

    AFex54

    144
    2
    Apr 10, 2015
    I dont know where or when my signals need current buffering,
    I feel buffering randomly could cause a circuit to malfunction,
    but I do know I need it.
    Is someone more knowledgeable could shed some light on this that would be great!
     
  2. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    Hi :)
    In general, signals need buffering when the output impedance of the signal source is too high for the load. This can result in the signal being lost.
    However that might be cryptic advice. You're welcome to be a more specific about your problem, and then you might get a more specific answer.
    Mark
     
  3. AFex54

    AFex54

    144
    2
    Apr 10, 2015
    Hi , Im building a simple CV keyboard for a synthesizer,
    This is the idea but my design is different:
    http://www.musicfromouterspace.com/analogsynth_new/SINGLEBUSSKEYBOARD2007/kbbus.gif

    the string of resistors in the image will be a bare 300mmx2mm copper wire busbar connected to a 9V 2.5A supply,
    when a key (only one key will be pressed at a time) is pressed it will send 9v straight to a 2nd busbar an also to a third but through a potentiometer and diode.

    the potentiometer busbar will connect to this devices potentiometer which you can see in the top right connected the battery and the bare bus bar will connect to bottom right switch:
    http://www.musicfromouterspace.com/analogsynth_new/NOISETOASTER/images/noisetoasterwiring3.gif
     
  4. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    :)
    I see. Where did you suspect a need for the buffer?
     
  5. AFex54

    AFex54

    144
    2
    Apr 10, 2015
    The 'Bus buffer' in the CV Keyboard diagram is making me think I need one
     
  6. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    An op amp buffer as in the circuit you showed is a good idea here. The impedance of your divider network varies quite a bit depending on which key is pressed. The buffer would lower the impedance and make it the same for all keys.

    Bob
     
  7. AFex54

    AFex54

    144
    2
    Apr 10, 2015
    sorry only seeing your reply now,
    Would that not remove the specific impedance of the potentiometer/resistor for each key aswell?
     
  8. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    It is not the impedance that matters, it is the voltage across the divider. The buffer ensures that the input impedance of the next stage does not effect those voltages.

    Bob
     
  9. poor mystic

    poor mystic

    1,066
    31
    Apr 8, 2011
    :)
    Yes, that's the idea. The next stage is a VCO - a voltage controlled oscillator, which is controlled by voltage. Let's call the voltage Vc.
    Ideally, a voltage-controlled circuit samples a voltage without changing it. This is difficult with transistor technology, but easy with op-amps.
    The op-amp puts very little load on the circuit which provides the control voltage Vc, yet provides a low-impedance output which follows Vc exactly.
     
  10. AFex54

    AFex54

    144
    2
    Apr 10, 2015
    now i understand thanks :)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-