2 Stage JFET amplifier

Discussion in 'The Projects Forum' started by GammaRay86, Dec 9, 2007.

  1. GammaRay86

    Thread Starter Member

    Dec 9, 2007
    Hey guys,

    I am curious on how to set up a 2 stage JFET amplifier. I've reviewed some analysis on 2 stage BJT amplifiers as well as 2 stage BJT/JFET amplifiers but I cannot find anything on how to use 2 JFETs. I would appreciate any help. Thanks!
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Won't it just be a simple cascade - the first amp feeds the second?
  3. SgtWookie


    Jul 17, 2007
    You must be talking about discrete JFETs.

    JFETs have extremely high input impedance; that makes them great for low-level signals. However, they have low gain - so they are mainly used just to isolate the higher-powered amp sections from the low-level signals. Cascading them would merely make your signal-to-noise ratio worse.

    In JFET-input op amps such as LF353's, TL072's, etc - sure, they have JFET inputs, but the amplifying transistors behind the JFET inputs aren't JFETS. These op amps are so low noise that you can cascade them without hurting your S/N ratio very much.