librecad and brl-cad

guitar pre-amps

http://www.diyguitarmods.com/guitar-preamp.php

Turns out the guitar gives enough level without an amp!  Audacity: line in, select

sysdefault:Line 0

input.

Active filters for home including 6dB/octave dipole compensation and 2nd order hp/lp filters

http://www.linkwitzlab.com/filters.htm

Make 1, 2, 8