FET as diode

[seanm]

In the simple mods/tips section it mentions using a FET as a diode. Any recommendations on a FET to use? Would a 2N7000 MOSFET work well?

[petemoore]

Sure @@@

 I liek 2n7000 or Jfet or Si
 Just use G/S of fet
 or B/E on si's and Ge's

[amz-fx]

The Shaka 3 that I developed with Aron uses mosfets for clipping diodes:

http://www.diystompboxes.com/pedals/shaka3.jpg

regards, Jack

[R.G.]

There are three ways a FET can be used as a diode.
(1) JFET gate-channel diode. Short drain and source, and forward bias the Drain/source to the gate terminal. This is an especially low leakage, but high resistance diode.
(2) MOSFET substrate diode. Short source and gate and the source/gate and drain works in the reverse direction of normal conduction. This diode is a fairly normal silicon diode
(3) diode connected MOSFET. Short gate and drain. The MOSFET now acts like a higher forward voltage (2-3V) but very soft clipping diode.

Actually, there is another way. If you connect the gate and source of a JFET, the JFET will regulate current through the JFET at all voltages over Vp. The current it regulates to is equal to the JFET Idss.

[seanm]

The Shaka 3 that I developed with Aron uses mosfets for clipping diodes:

http://www.diystompboxes.com/pedals/shaka3.jpg

regards, Jack

Is the diode attached to the MOSFET necessary, or is it for tone reasons?

[seanm]

(3) diode connected MOSFET. Short gate and drain. The MOSFET now acts like a higher forward voltage (2-3V) but very soft clipping diode.

Is this litterally a diode on a MOSFET like the Shaka 3? I want to soften the distortion, more like a tube amp on 10.

[Paul Marossy]

All BJTs, MOSFETs and JFETs have the capacity to become diodes when connected in such a manner as to make them function like diodes.  :wink:
I built Joe Davisson's Amber Boost several years ago and it used 2N7000s as clipping diodes. It sounded pretty good!