Portable, 9V powered 2-channel mic preamp and A/D converter with 48V phantom and coax + toslink outputs

This web page documents the development of this product.  This is a shipping commercial product; pricing approx $550, inquire for details.

Board is 4-layer 2.6" x 3.95"
Design timeframe: June 2002 - August 2003, minor functionality enhancements August 2005
Webpage last updated: May 21, 2007

Top View:
(top view)

Bottom View:
(bottom view)

The primary requirements & features of this product are:


This was my first major design and it took five prototype iterations and extensive testing with the Audio Precision to get everything perfect and to fit in a small size chassy.  As you can see, the board is mostly through-hole; all designs since this one are as much SMT as possible.  Through-hole is easier to prototype with, at least for the inexperienced, but drives up manufacturing cost and takes significantly more space than SMT.  Routing is also much harder for dense designs.  This was entirely hand-routed.

As a commercial product I can't get too detailed about the design specifics, suffice to say there is a lot going on here.  Unlike most of my designs, this doesn't have a microcontroller; the battery low indicator and supplying the right combination of inputs to the clock generator based on 4 toggle switches required a bit of cleverness.  Also note the bank of blue capacitors at the bottom edge of the board (top view) - each of these are actually "flying over" 2 diodes and 2 caps to save space.  Its like Manhattan: for more room, go vertical!  This is true of the resistors as well, which are mounted "on edge" to save room.  Note one chip on the back and 8 input protection diodes, put here since there was no way they'd fit on the front, even mounted vertically.