Service manual

II.
HEADSETS
AND
MICS
The
RM-120A
provides:
To
assure
proper
level
and
perfor-
mance,
the
dynamic
headset
should
4
--
one
1/4"
phone jack
for
a
stan-
have
the
following
characteristics:
dard
carbon
headset,
AND
mic
Impedance:
150-250
ohms
--
one
4-pin,
male,
XLR
connector
Nominal
Output
Level:
-55
dBv
for
dynamic
headset,
telephone
Headphone
Type:
dynamic
handset,
or
push-to-talk
mic.
Impedance:
300-2000
ohms
NOTE:
If
you
simultaneously
use
a
The
RM-120A's
built-in
headset
amp-
carbon
headset
and
a
dynamic
head-
lifier
can
drive
a
headset
to
le-
set,
the
level
in
the
carbon
head-
vels
greater
than
110
dB
SPL, and
set
drops
audibly.
drives
two
dynamic
headsets
with
only
a 3
dB
reduction
in
level
when
Carbon
headset connections:
connected
with
the
proper
"Y"
cord.
Ring-----Headphone
Tip------Mic
Sleeve---Ground
It's
easy
to
make
an
extension
cord
for
your
dynamic
headset.
For
the
To
assure
proper
level
and
perfor-
cable,
we
recommend
Belden
8416
or
mance,
the
carbon
headset's
mic
the
equivalent
(2-conductor,
25-
impedance
should
be
50
ohms,
and
gauge)
or
Belden
8734
or
the
equi-
earphone
impedance
should
be
300-
valent
(3-conductor,
22-gauge).
2000
ohms.
See
the
diagram
below.
The
cord
length
should
be
15
feet
or
less;
Dynamic headset
connections:
anything
longer
might
lead
to
capa-
Pin
1----Mic
Ground
citive
coupling
between
mic
sig-
Pin
2----Mic
Hot
nal
and
headset
signal,
causing
Pin 3----Headphone
Ground
oscillation
or
a
loss
in
frequency
Pin
4----Headphone
Hot
response.
Caution:
Do
not
connect
mic
ground
and
headphone
ground
together.
Figure
1:
Headset
Extension
Cord
15
OR
LESS
NoTe
Heaosel
eaos
o0
noi
nave
to
De
shiecea
on
BelDen
8734
51A4FLDEDPAIR
BELDEN
8416
PIN
1:
MIC
GROUND
CAUTION:
DO
NOT
CONNECT
PIN
2:
MIC
HOT
MIC
GROUND
&
HEADPHONE
PIN
:
HEADPHONE
GROUND
GROUND
TOGETHER
Pin
4:
HEADPHONE
HOT
2