Loading ...
Sorry, an error occurred while loading the content.

Were does that value for Rload=2K2 come from?

Expand Messages
  • tschrama
    Hi all, My name is Thijs Schrama. I ve been a electronic hobbyist for over 3 years now and I ve recently taken up some microphone projects. While optimizing
    Message 1 of 3 , Mar 2, 2004
    • 0 Attachment
      Hi all,

      My name is Thijs Schrama. I've been a electronic hobbyist for over 3
      years now and I've recently taken up some microphone projects. While
      optimizing some of them I got puzzeled by the quoted typical values
      of the load resistor of an electrect microphone capsule. Most of the
      time I see 2K2.

      Were does that value for Rload=2K2 come from?

      I guess it has something to do with the noise contribution of the
      resistor, the transductance of the FET and the headroom of the
      V+supply.

      Furthermore, I am curious about the effect of the V+ at the FET's
      drain. Higher V+ makes more headromm, higher transductance, better
      lineairity but also more noise, but how much?

      I have designed a buffer/preamp for my electrect microphone project
      that incorporates a BJT as a buffer, feeding the output to a split
      load resistor as a bootstrap configuration. This dilivers excelent
      dynamic range and very high sensitivity, ideal for my application,
      but in order to optimize it I need more info about V+ and Rload
      effects?

      Anyone got some indepth theoretical info on this?

      Best regards,

      Thijs Schrama
    • tschrama
      BUMP ...... ;-)
      Message 2 of 3 , Mar 9, 2004
      • 0 Attachment
        BUMP ...... ;-)



        --- In micbuilders@yahoogroups.com, "tschrama" <t_schrama@h...> wrote:
        > Hi all,
        >
        > My name is Thijs Schrama. I've been a electronic hobbyist for over 3
        > years now and I've recently taken up some microphone projects. While
        > optimizing some of them I got puzzeled by the quoted typical values
        > of the load resistor of an electrect microphone capsule. Most of the
        > time I see 2K2.
        >
        > Were does that value for Rload=2K2 come from?
        >
        > I guess it has something to do with the noise contribution of the
        > resistor, the transductance of the FET and the headroom of the
        > V+supply.
        >
        > Furthermore, I am curious about the effect of the V+ at the FET's
        > drain. Higher V+ makes more headromm, higher transductance, better
        > lineairity but also more noise, but how much?
        >
        > I have designed a buffer/preamp for my electrect microphone project
        > that incorporates a BJT as a buffer, feeding the output to a split
        > load resistor as a bootstrap configuration. This dilivers excelent
        > dynamic range and very high sensitivity, ideal for my application,
        > but in order to optimize it I need more info about V+ and Rload
        > effects?
        >
        > Anyone got some indepth theoretical info on this?
        >
        > Best regards,
        >
        > Thijs Schrama
      • Bob Cain
        ... The current through the FET is approximately independant of the voltage across it (someone on the list is right now working out a better approximation
        Message 3 of 3 , Mar 9, 2004
        • 0 Attachment
          tschrama wrote:


          >>
          >>My name is Thijs Schrama. I've been a electronic hobbyist for over 3
          >>years now and I've recently taken up some microphone projects. While
          >>optimizing some of them I got puzzeled by the quoted typical values
          >>of the load resistor of an electrect microphone capsule. Most of the
          >>time I see 2K2.
          >>
          >>Were does that value for Rload=2K2 come from?

          The current through the FET is approximately independant of
          the voltage across it (someone on the list is right now
          working out a better approximation based on various
          voltages.) The 2k load is based on a 2V supply to the
          circuit and will approximately split that so that the signal
          can swing +/- 1V. Since, to a rough approximation, that
          current doesn't change with a higher circuit voltage you can
          just scale the resistor value by the voltage used, figuring
          about 1k Ohm per Volt. This will approximately split the
          supply in half for maximum signal swing.


          Bob


          --

          "Things should be described as simply as possible, but no
          simpler."

          A. Einstein
        Your message has been successfully submitted and would be delivered to recipients shortly.