How do you test a condenser preamp circuit?

[Arbolito]

Hey everyone, I ordered pcb and components to build this project Simple, ultra high performance condenser microphone circuit - Share Project - PCBWay

Before connecting this circuit to my capsule and destroying it, I was wondering if there's a way to test the circuit to make sure I soldered everything properly, and that its working as intended. As far as I know it should deliver 80 volts to the capsule.

 

[Khron]

You probably won't want to apply 80v to a large-diaphragm capsule. 60v should be quite safe still (more or less "standard"), but above that, you're on your own, and it's up to you to decide whether the extra 1-2dB of sensitivity is worth the much-increased sensitivity to plosives.

That being said, you'll want to measure that voltage BEFORE the series resistor(s). Although given how the circuit is made up, that's gonna be difficult to measure reliably, unless you temporarily bypass R9 with a piece of wire. Keep in mind, your voltmeter has an input impedance of 1-10Meg; connecting that to ground *after* a 100Meg resistor means you end up measuring 1/10th or 1/100th of the voltage you might expect.

And there's nothing stopping you from not using C19 at all, and connecting the capsule between the bias voltage and the opamp input directly (unless you have good reason to want/need to connect one side of the capsule to the 6v opamp-supply-midpoint).

Other than that, download & start up REW, output of your audio interface to the opamp input, output of the circuit into a mic input, phantom power on. Check that all DC voltages are roughly as they should be, and... Not much else to it.