Studio Technologies M233-01151 - Manual (Page 19)

Model 233 User Guide Issue 5, November 2014
Studio Technologies, Inc. Page 19
Unfortunately, there’s no “perfect” gain set-
ting that this guide can recommend. The
two issues that impact the setting are out-
put sensitivity of the connected microphone
and the acoustical output level of the mi-
crophone’s user. With some headset micro-
phones, such as the Sennheiser HMD25,
selecting an initial setting of 40 dB is appro-
priate. 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 microphone
preamplifier. Red in color, this LED is locat-
ed adjacent to switch assembly 1. It is vis-
ible by observing the bottom of the Model
233’s enclosure when the security plate
has been removed. Technically, this red
LED lights whenever the compressor cir-
cuitry is controlling the dynamic range of
the signal coming from the microphone
preamplifier. The threshold is set to be
2 dB above the Model 233’s nominal in-
ternal operating level. So a good “rule of
thumb” is to adjust the gain of the micro-
phone preamplifier so 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 typical
audio signals are present on the mic input.
It’s important to remember that the com-
pressor active LED is used to assist in set-
ting the mic preamplifier gain to the optimal
value. It doesn’t necessarily indicate that
the main output’s signal is being com-
pressed. Unless specifically configured
to perform otherwise, the output of the
compressor is only used for the talkback
output functions.
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 they were
included. It’s possible that with a very “hot”
microphone, such as a phantom-powered
condenser, 20 dB of gain could be correct.
It’s also possible that a microphone with a
very low level output, such as a ribbon-type,
would need 60 dB of gain. But in general,
the 30, 40, and 50 dB gain settings will
serve most applications.
Note that if no gain switch is set to its ac-
tive (on) position the preamplifier will oper-
ate at unity (0 dB) gain. This is provided for
compatibility when line-level signals need
to be connected to the microphone input.
But with a microphone connected as the
input source one should never use the 0 dB
setting. The issue is that with no gain added
to the microphone input signal, the relative
noise floor on the main and talkback out-
puts will be much too high.
Phantom Power On/Off
The Model 233 can provide nominal 48
volt phantom power to a connected micro-
phone. Switch SW1-8 controls whether or
not phantom power is active. By phantom
power’s very nature it could be left applied
to the microphone input at all times. But
generally people prefer to turn it off unless
required for a specific microphone.
Figure 5. Phantom power switch settings