<<Hi,
I've been testing out various contact mics with my Sound Devices
recorder & have come up against background noise (of course) on ones
that are unbalanced. Does anyone have any tips for dealing with this -
is there a way to deal with it ? & if not does anyone have suggestions
for either pre-made contact mics that are balanced or for building
some ?>>
I've built many contact pickups over the years from inexpensive piezo
buzzers from Radio Shack. It's a very simple matter of soldering a
1/4" lead onto the piezo element, & it is an unbalanced connection. I
use the instrument DI input on a Sound Devices USBPre to get into the
laptop. Any sort of balancing device will get you into a suitable mic
pre input. A passive transformer, such as the inline Shure or Sescom
units will do, however there is usually an insertion loss with any
transformer, a drop in volume which the mic pre must make up. An
active DI will properly bridge the high impedance unbalanced output
of a piezo element. Before doing any of that, though, I would
recommend trying an XLR connector on one of your pickups, wired hot
(tip) to pin 2, & shield (ground) to pins 1 & 3. You should also try
it with no connection to pin 3 on the XLR, since, with some circuits,
this will give a perfectly fine noise-free unbalanced to balanced
connection, without the several db signal drop caused by tying pin 3
to ground.
Scott Fraser
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