Op-amp non-inverting amplifier with clamping?
This doesn't directly answer your question, but I have a few suggestions to improve the design which should make it unnecessary for you to use the clamping diode at all.







simulate this circuit &ndash; Schematic created using CircuitLab


Move the 10k/10k resistor-divider to your opamp's non-inverting input to give your input signal a DC bias point of half-supply. The reason for this is with your original arrangement, your AC-coupled signal from your microphone will result in negative voltages applied to the opamp's input - not a great idea when using a single supply.  
Add a capacitor in series with R4 in the gain-adjustment negative feedback part of the circuit.  What this does is ensure that your circuit only has any gain >1 for AC, and only a gain of 1 for DC. Without this feature, the DC bias we applied in step 1 would be amplified along with the signal - quickly saturating the output for any gain much more than 1.  


Now what you have is an output which is normally biased at 2.5V (half of your supply) with the amplified AC signal from your microphone superimposed onto that.
I haven't chosen specific values for the capacitors in this circuit - you may need to make some adjustments depending on the frequency response you're aiming at.