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!

 

Won't it just be a simple cascade - the first amp feeds the second?

 

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.