Spirit532/studio_mic

I needed a good quality microphone, but all of the options available were either a bit pricy or just not really good in performance, so I decided to build my own.

The microphone build uses a clone RK12/CK12 capsule($40-50 on Aliexpress/Ebay/etc, search for "edge terminated capsule"), a U87 donor body($15-30, also Aliexpress, search term "U87 mic"), and a custom preamp board($20-30, this project).

The board is very simple, yet high performance - it uses a dual FET input opamp in a single package to both convert the capsule's impedance and provide a differential signal, while the bias is provided by a slightly cursed hex schmitt trigger inverter charge pump.

With the setup pictured below, the results are, to the non-audiophool ear, perfect. There is practically no self-noise due to the simplicity of the circuit and performance of the chosen opamp, plenty of dynamic range, and no signal distortion/"colortaion". You get exactly what the capsule sees on the XLR connector.

You can use pretty much any FET input opamp, however you must pay close attention to the quiescent current. This circuit uses a fairly high impedance power path, and the phantom power standard can't provide much current in the first place. Total power consumption of the two opamps should be no more than ~7-8mA(3.5-4mA per).

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