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:
Bottom View:
The primary requirements &
features of this product are:
- Runs for hours on a single 9V
- Small size
- Pro-level fidelity
- 48V phantom as well as 9V "plug-in" type power
- Adjustable gain
- Basic signal level monitoring
Design
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.
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