I stumbled upon this while sifting through Aron's archive:
http://www.aronnelson.com/gallery/main.php/v/J0K3RX/BF5_sch.jpg.html (http://www.aronnelson.com/gallery/main.php/v/J0K3RX/BF5_sch.jpg.html)
Looks interesting - but what's with the diodes D1 - D4 between those JFETs' Gates and Sources?
They mimick "grid conduction" of vacuum tubes. Basically, with high-enough grid-to-cathode voltage difference tube's grid begins to conduct and its impedance rapidly decreases. Assuming the circuit is driven from moderately high-impedance source the voltage divider "clamps" the output signal creating clipping distortion at the grid. Essentially the grid behaves like a diode, and that characteristic is replicated in the FET circuit by addition of... ...a diode.
Sometimes you see equivalent junctions of BJTs or FETs used for similar purpose.
Well, the JFET gate is a diode also.
At first glance, this adds nothing.
The diode specified is not a generic, so may be low voltage, so may do a little.
Paul,
At low currents, the specified diode has a Vf of about 0.25v while the jfet junction will be around 0.7v.
regards, Jack
http://www.aronnelson.com/gallery/main.php/v/J0K3RX/SE-1+Schematic.PNG.html (http://www.aronnelson.com/gallery/main.php/v/J0K3RX/SE-1+Schematic.PNG.html)
So here is a gate to drain diode with a MOSFET stage -- is this for a similar reason?
> is this for a similar reason?
No.