The
polarization voltage
of
the
condenser microphone cartridge
is
sup-
plied,
in
the
2619,
through
a long
time-constant
charging circuit.
After
switching
on,
or
changing cartridges, several seconds should be allowed for
the
cartridge
to
charge up.
3.3 ACCELEROMETERS
The
Type
2619
preamplifier can be used with
any
of
the
B&K
accelero-
meters, with
the
adaptor
JJ
2615
for
miniature cables.
The
voltage sensitivity
of
the
accelerometers, complete with cable,
is
given
in
the
calibration
chart
supplied with each accelerometer. If a cable,
different
from
the
one
used
in
the
calibration,
is
employed, it
must
be
remembered
that
the
voltage sensitivity
of
the
new accelerometer/cable
combination
will be
different.
The
new sensitivity,
Sv
'is given
by
Sv' = S (C, + C,)
v (C , + C\ )
Where
Sv
is
the
calibrated sensitivity, with cable capacitance C
e
connected,
C
t
is
the
a
ccelerometer
capacitance
only, C
e
'
is
the
new cable capacitance.
3.4 OUTPUT
The
output
impedance
is
low (
rv
25
S1
)
but
the
maximum peak
current
limits
the
high
frequency
response when capacitive loads are used (as shown
in
Fig.2.31. and
this
should be remembered when long extension cables are
used
between
the
preamplifier and analysing
equipment
.
B&K
extension
cables
Type
AO
0027
and
AO
0028
/
29,
have capacitances of
100
pF
/m
and
57
pF/m
respectively.
14
To Next Page
Loading...
Need help?
General
