Scott Wurcer provides an in-dept analysis of what it takes to build a state of the art mic preamp. An extensive discussion on the noise characteristics of mic capsules is followed by selection criteria for low noise JFET devices and trade-offs in circuit topologies. JFET Spice model modifications to make the models correspond better with the actual device parameters are next, and are used to verify theoretical predictions with simulations, leading to some prototype preamps. (This article will be followed in the next issue with a very high performance, state of the art all JFET class A mic preamp).
Low-noise Microphone Preamplifiers