LFO trigger circuit question

[electricstorm]

I have a question about the circuit below. It is just a snippet of the whole circuit. My question is in regard to the diode in this circuit. Here's the circuit, questions to follow:





First of all, given the voltage range (0.7v - 15v), I assume the diode is to clamp the voltage at the max of 15v. Does this seem like a logical assumption? If not, what is the purpose of the diode?

Would this be a zener or a fast switching diode (such as a 1N914 or 4148)?

I have breadboarded the circuit without the diode and using a 9v trigger voltage and the circuit works just fine. Just stumped on the purpose of the diode. I do not have the actual pedal and therefore cannot read the value from the original diode. The circuit was drawn from a photo and the diode is a glass type. The owner does not want to remove it to see the actual value (can't blame them really).

Those that are more knowledgeable then me, would you shed some light on this please?

Thanks,

Jim

[stecykmi]

not 100% sure, but i think it may be there to help gate function work correctly. the diode should only conduct when the square wave (gate) is on the negative swing, as that is the only time when the anode is at a higher voltage than the cathode. when the diode conducts, the gate of Q1 is at 0V and the transistor is off.

[electricstorm]

not 100% sure, but i think it may be there to help gate function work correctly. the diode should only conduct when the square wave (gate) is on the negative swing, as that is the only time when the anode is at a higher voltage than the cathode. when the diode conducts, the gate of Q1 is at 0V and the transistor is off.

Makes sense. The only thing I was concerned about was using the correct diode. I put the diode symbol there mainly as a place holder for now because I don't know if it is a regular diode, zener, schotky or whatever.

If this is it's function, the 1N4148 should do it then. What do you think?

[stecykmi]

assume its function is what we surmise, then yes! any of the standard small-signal diodes should work fine.

[electricstorm]

Thanks for the confirmation!!