Part I of this article appeared in Linear Audio Vol 1 in Spring 2011 and readers have been asking for Part II ever since. This is a very comprehensive treatment of all factors involved in designing condenser mic preamps. Scott discusses mic capsules, how to select jFETs, the issues of battery versus phantom power. Each discussion is accompanied by illustrative circuit diagrams that in themselves are gems. Balanced or unbalanced outputs, bipolar output versions and biasing are thoroughly addressed. Combinations of discrete and opamps in mic preamps are also shown and the merits discussed, as is capacitive feedback as well as techniques to get the most out of the battery lifetime. Finally, an example implementation is shown which was used to record live performances, and the resulting recording is available at the Linear Audio website and illustrates the incredible realism that can be obtained when addressing all important design factors.
DIY Low-noise Microphone Preamplifiers, Part II