Building older version SHO. How important are the diode type?

[chumbox]

Shematic calls for 1n4148 for protection from what I can gather.  Can I put schottkys here and do these effect the tone at all?

Thanks

[Jdansti]

The diodes are there to protect the MOSFET and shouldn't affect the sound.  The question is whether the Schottkys would protect the transistor and not cause unwanted side effects.  Unfortunately, I don't know the answer to this question.

The diode mods I've seen are:
1) a single Zener between the gate and ground.
2) a single Zener between the gate and source.
3) Schottkys used as clippers on the output. These are unrelated to the protection diodes.

[StereoKills]

I use a red LED between gate and source as in the ROG Peppermill.

[earthtonesaudio]

Any method used should employ a current limiting resistor (of 100 ohms or more) between the input capacitor and the diode(s).  This lets the protection circuit live longer in the event of repeated faults.

Bear in mind that the 2-diode scheme will only protect as long as the power supply + diode drop is lower than the safe V_GS for the device.  Also note that the zener-to-ground affects the gate bias voltage slightly (more so when the zener voltage is near or less than the bias voltage).

The best protection (in my opinion) is a 4V to 6V zener between gate and source, with a current limiting resistor between gate and input capacitor.  This works the same regardless of the power supply voltage, and does not affect the gate bias as much as the zener-to-ground.  But again, the limiting resistor is key.