Studio Technologies 220 2004 - Manual (Page 39)

Issue 2, August 2004 Model 220 User Guide
Page 40 Studio Technologies, Inc.
connecting to the Model 220’s direct micro-
phone output should be noted. The first is
that pin 1 on the direct microphone output
is electrically connected to pin 1 on the
Model 220’s microphone input connector,
as well as the Model 220’s signal common/
chassis connection. This is required so that
the Model 220’s phantom power circuit can
function and that proper microphone-cable
shielding can be provided. It’s not expected
that this will cause any problems.
Also, while the circuitry between the mi-
crophone input and direct microphone
output is entirely passive, it will still impact
the microphone signal. The impact is be-
nign but is still worthy of description. The
circuitry associated with the Model 220’s
microphone preamplifier and phantom
power supply is always connected across
(“bridged onto”) the microphone input. This
adds a 2 k ohm essentially resistive load
to the microphone, something that should
have no sonic impact. In some case it may
possibly reduce the microphone signal
level by less than one dB. Two 150 ohm
resistors are electrically connected in series
between the microphone input connector
and the direct microphone output connec-
tor. These resistors provide isolation, al-
lowing the direct microphone output to be
muted while still maintaining microphone
audio on the Model 220’s preamplifier
input. This audio is necessary so that the
talkback functions can continue to oper-
ate. The series resistors will have minimal
impact, simply raising the microphone’s
apparent source impedance as “seen” by
the external preamplifier.