Studio Technologies 210 2008 - Manual (Page 15)

Model 210 User Guide Issue 4, October 2008
Studio Technologies, Inc. Page 15
Microphone Preamplifier Gain
Switches SW1-1 through SW1-5 are used
to select the gain of the microphone
preamplifier. The choices are 20, 30, 40,
50, and 60 dB. Only one switch should
be enabled at a time. There’s no problem
changing the gain setting while the unit
is operating. Audio clicks or pops might
occur during gain transitions, but this
shouldn’t be a major issue as long as as-
sociated monitor loudspeakers are tempo-
rarily attenuated or muted.
Selecting the correct amount of gain for an
application might take a little experimenta-
tion. The goal is to bring the mic’s signal
up to line level, nominally –2 dBu for the
Model 210’s main output. Operating at this
signal level will help to ensure the delivery
of “clean” audio to the connected device.
The output of the Model 210’s microphone
preamplifier is used by the main output
and, by way of the compressor circuit, the
talkback outputs. So creating a nice “hot”
signal will help maintain audio quality,
specifically the signal-to-noise ratio, when
driving the often-lengthy cable runs.
Unfortunately, there’s no “perfect” gain
setting that this guide can recommend.
The two issues that impact the setting
are output sensitivity of the connected
microphone and the acoustical output
level of the microphone’s user. With
some headset microphones, such as the
Sennheiser HMD25, selecting an initial
setting of 40 dB is appropriate. Users who
speak loudly might need to have the gain
reduced to 30 dB. Quiet users might need
50 dB of gain.
An LED indicator is provided as an aid
in correctly setting the gain of the micro-
phone preamplifier. Red in color, this LED
is located adjacent to switch assembly 1.
It is visible by observing the bottom of the
Model 210’s enclosure when the security
plate has been removed. Technically, this
red LED lights whenever the compressor
circuitry is controlling the dynamic range
of the signal coming from the microphone
preamplifier. The threshold is set to be
2 dB above the Model 210’s nominal
internal operating level. So a good “rule of
thumb” is to adjust the gain of the micro-
phone preamplifier such that the compres-
sor active LED lights (“flashes”) when the
connected microphone is sending signal
peaks. During normal operation the LED
should not remain fully lit when audio is
present on the mic input.
It’s important to remember that the com-
pressor active LED is used to assist in
setting the gain to the optimal value. It
doesn’t necessarily indicate that the main
output’s signal is being compressed.
Unless specifically configured to perform
otherwise, the output of the compressor
is only used for the talkback output.
It’s expected that the 20 and 60 dB gain
settings will not often be used. But there
are always exceptions and that’s why
Figure 4. Microphone preamplifier gain switch
settings