MOSFET forward voltage as a clipping diode?

[Asymmetric]

At the moment I'm choosing my diodes for my OD. I want to use three different ones, but I can't find any info on the forward voltage for the MOSFET when wired as a diode?

[R.G.]

Assuming you're using it with gate tied to drain and preventing the body/substrate diode from being used, it's just a bit larger than the enhancement voltage for the device. For to-92 MOSFETs this is on the order of 2-3V, and is not tightly specified. Count on variations between lots and between manufacturers of the same device type number.

If you set it up to let the body diode do the clipping, you get an ordinary silicon diode forward drop.

[Asymmetric]

Wow, 2-3v. So using MOSFETs as clipping diodes doesn't really clip much? I guess with a forward voltage so high, the opamp will of already maxed out before the MOSFET kicks in? What could I do about that?

[GibsonGM]

Oh, they'll clip, A!     Post a schematic of what you're thinking about doing if you want more specific help, but...

Let's say you use a DUAL opamp (or 2 transistor stages, etc).  1st stage boosts your puny guitar signal to 1V or so.   2nd stage boosts it to 6V.  There you go, now you're clipping.  You're simply clipping a bigger signal... 

Many opamps can get near the power supply rails before they start to, themselves, clip...probably some stuff on here if you search "mosfet clipping"... 

[Asymmetric]

Oh, they'll clip, A!     Post a schematic of what you're thinking about doing if you want more specific help, but...

Let's say you use a DUAL opamp (or 2 transistor stages, etc).  1st stage boosts your puny guitar signal to 1V or so.   2nd stage boosts it to 6V.  There you go, now you're clipping.  You're simply clipping a bigger signal... 

Many opamps can get near the power supply rails before they start to, themselves, clip...probably some stuff on here if you search "mosfet clipping"... 

Thanks a lot GM - I'm thinking about doing it on a few pedals and haven't quite decided which ones yet.

I have a ibanez overdrive II copy pedal that I put LED's inside for clipping, and when I took them out I couldn't hear any difference, so it seemed like it was just the opamp doing all the clipping and the LED diodes weren't even activated due to their high forward voltage? I even tried a laser diode!

[GibsonGM]

Yes, it would depend on how much voltage you're applying, of course.  And where the diodes are...feedback vs. at the output...mess around, that's the best way to learn all this    

An audio probe can tell you a lot about what a particular stage is doing/sounding like, too!  You can listen to what's going in, coming out, and even what's in a feedback loop...