Can an led be used in place of a 9.1V Zener?

[Jumbosize]

I am going to be building a Zvex box of rock from this here page: http://revolutiondeux.blogspot.com/2012/01/zvex-box-of-rock.html (you have to download the schematic from the mediafire link)

The schematic has two 9.1V Zeners in it. I have heard that you can use LED's in place of these, is this true? The only reason I don't want to use zeners is that I like to buy all of my parts from pedalpartsplus and they don't have 9.1v zeners. Alternatively, is there another diode that they supply that would do the trick? Thanks!

[R.G.]

If you mean the two diodes between source and gate of the two MOSFETs (D2 and D3 in that schematic), they don't have to be 9.1V. They are protection devices only, and do not do anything in the normal operation of the pedal.

You can replace them with any zener rated between 9.1V and 18V. 

You can actually use a quick and dirty replacement. The base-emitter diode on most NPN devices breaks down between 6 and 7 volts. You can clip off the collector lead and use the base-emitter as a poor-tolerance zener diode. In this case, you'd use two of them in series to get twice the voltage breakdown.

[JRB]

As far as my knowledge go's you can't. A Light Emitting Diode (LED) works just like a normal diode as in it lets current trough in one direction from the anode to the cathode.

A zener diode also works like a normal diode but it has the added function of letting trough current when the voltage reaches a certain threshold.
In this case that would probably be 9.1V but don't hold me up on that.

[R.G.]

... uh, I didn't answer your question.

Yes, maybe an LED can be used as a "zener". The forward voltage of an LED depends on its color and composition, so they can be used as a clumsy zener in the forward direction as something between 1.2V and 4V, depending on the insides. Obviously, you'd have to stack two or more to get this.

LEDs do have a reverse breakdown "zener" voltage, but they really don't like to be reverse-broken that way. Better to use the broken-over base-emitter junction of an NPN.

And cheaper.