The Microphone Amplifier - BRUEL & KJAER 1022 Instructions And Applications
Beat frequency oscillator
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The Microphone Amplifier.
The block diagram
of
the
Microphone Amplifier
is
shown
in Fig.
4.2, and
the
amplifier consists of
two independent
amplifier sections
which may
either
be
connected
in
cascade
or have
a
filter
system
interposed between them.
The
power
supply contains
the necessary rectifiers
and
filters for the opera-
tion
of
the
amplifiers and can supply
the
external
B
&
K
Condenser
Micro-
phone
or
Preamplifier in use.
Micr:
lnp.
Ampl.
lnp.
"Input Potentiometer"
Weighting
Networks
"Range Multiplier"
161012
Fig. 4.2
.
Block diagram
of
the
Microplwne Amplifier.
The first two
stages of
the input
amplifier consist of
resistance-capacitance
coupled
triodes
,
while the third
stage
is built
as a
cathode-follower.
A
great
amount of negative feed-back is introduced to
stabilize
the amplifier and
to
ensure
a low
source
impedance
of approxima tely
12
.
Q ,
at the FILTER
INPUT terminal.
The
output
amplifier
consists of
three
stages and shows an
input impedance
of
1.46
M...Q.
The
output circuit of
th
e ou
tput
amplifier is connected
both to the
output terminal 1111arked RECORDER
and
to the rectifier and meter
circuit.
The RECORDER
t
erminal
is provided for
connection
to level recorder, head-
phones,
oscillograph, etc. Additionally
it
can
be
connected
to the
compressor
input of the Beat Frequency Oscillator Type 1022. The output impedance
at
the terminal is
50 Q
.
The input
and
output
amplifier sections can, as
mentioned, be
cascaded,
this
being
accomplished
by means of a
switch on
the front panel. By this means
a
high
gain
ampHfier with
a
linear frequency
characteristic
in the range
from 2
c/
s--40·
kc/
s
is obtained. The
switch also enables
a
series
of built-in
weighting networks, which
conform
to IEC proposed
standards,
to be
inserted between the amplifier
sections,
or in turn the amplifier
sections
to
be isolated from
each
other
and connec ted
to terminals provided for
external
filters.
44
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