A Studio Condenser Microphone For A Constrained Budget

As the Internet has turned so many of us into content creators, we’ve seen the quality of webcams and microphones steadily increase to the point at which even a fairly modestly-equipped YouTuber now captures their wisdom at a quality far exceeding that you might have found in some broadcast studios not so long ago. Still, decent quality costs money, and for that reason [Spirit532] has built his own high quality condenser microphone for less expenditure.

The capsule and body are off-the-shelf items — what he’s produced is the bias voltage supply and preamplifier. In both cases these are the interesting parts of a condenser microphone, so their circuit bears a second look.

The condenser microphone takes a diaphragm and turns it into one side of a capacitor. If you apply a charge to this capacitor, the voltage over it changes minutely with the capacitance as the diaphragm vibrates. Thus to have a usable audio signal level a high-voltage bias supply is required to provide the charge, and a very high impedance preamplifier circuitĀ  to catch the signal without draining the capacitor.

His bias supply is a charge pump using a string of diodes and capacitors fed by a chain of CMOS inverters, with an RC filter and resistor chain to provide that super-high impedance. The preamplifier meanwhile is a unity gain high-impedance op-amp with an inverting stage to provide a balanced connection. For good measure the circuit also includes a phantom power supply.

This is an interesting project for anyone with an interest in audio. if you’re further interested in condenser microphones, how about also looking at electret microphones?

Taking A Capacitor Microphone To The Next Level

There was a time when a microphone for most people was a cheap plastic affair that probably came for free with their sound card, but in the age of pandemic video streaming no desktop is complete without a chunky model that looks for all the world as though it escaped from a studio. Few people make their own microphones, so the work of [DJJules] in building very high quality condenser microphones is a particularly fascinating read.

A condenser microphone is a capacitor in which one plate is formed by a conductive diaphragm. A bias voltage is supplied to the diaphragm via a resistor, and since the charge on the plate remains constant as its capacitance changes with the sound vibrations, the voltage on the capacitor changes accordingly. This is picked up by a high impedance buffer and from there fed to a normal microphone input. This Instructable uses a commercial condenser microphone capsule, and takes the reader through generating the bias voltage for it before describing the op-amp buffer circuit.

The most interesting part comes at the end, as we’re shown how the sensitivity pattern of a dual-microphone array can be tuned to be omnidirectional, cardoid, or figure-of-eight. This is probably the norm among audio engineers, but we rarely see this sort of insight in our community. We may never build a microphone of our own, but it’s fascinating to see this one from the ground up in the video below the break.

If you’re confused about the difference between a condenser microphone and the more common electret condenser microphone, we have published a guide to that topic. Continue reading “Taking A Capacitor Microphone To The Next Level”