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Re: Contact Microphones

Subject: Re: Contact Microphones
From: "Scott Fraser" scottbfraser
Date: Wed Feb 18, 2015 7:59 am ((PST))
< I just use what's known in the music business as a DI (for converting hig=
h
impedance guitar outputs to match with mic preamps). They're just a
transformer in a steel box with 2 1/4" TR (I/O)and one XLR output. The
downside of DI's is that they're usually built for rough stage/road use,
are bulletproof and probably heavier than you want. I use a dual one that
weighs over a Kg. Not nice, but I don't hike far and it works very well.
That does make that preamp I linked to look rather attractive if you want
something light. >

Direct Inject boxes, or DIs, come in two flavors: as described above, with =
an impedance converting transformer, or alternatively, containing an active=
 opamp circuit to convert an unbalanced high impedance source to low impeda=
nce balanced. The active DIs have the advantage of lower cost, lower weight=
, & lower insertion loss, but require phantom or battery power. Transformer=
s have the advantage of superior RF rejection, require no power, but are he=
avy, expensive & there is some loss of gain. DIs are all over the map quali=
ty-wise, & you definitely get what you pay for. The low cost models will de=
finitely degrade audio. Count on $150 & up for a pristine quality unit. In =
the studio world the Countryman type85  active DI is pretty much the gold s=
tandard. I use Countrymans with home made piezo contact pickups & they prov=
ide a very good rendition of the very bad frequency response of piezo eleme=
nts.

SF




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