#1
Out of curiosity, can i replace germanium diodes with silicon diodes? If so, what would the sonic difference be? The circuit in question is a 386 based fuzz. If anyone has indyguitarist's first book, its the one on page 68
#2
You can replace it with a silicon diode of the same value, but I have no idea of the sonic effects it would have.

You can experiment and find out.
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#4
If the diode is being used as a "clipping" diode a germanium will create more distortion/fuzz as the clipping threshold of a germanium is 0.3V while silicon is 0.6V. Takes less signal to clip with germanium.

That's the simple explanation.

You have two diodes side by side going to ground I imagine in that design.
#5
sonic impact depends on the circuit and how they are used, but as kurt said, germanium usually means more clipping if it is a clipping diode. there is a section here about how changing diodes affects that circuit. good place to start if you want to swap out diodes.