Clear-Com KB-111A Troubleshooting guide

KB-111A
Speaker Station
INSTRUCTION
and
SERVICE MANUAL
III~I~ Clear-Co.
~I' Intercom Systems
945 Camelia St. Berkeley, California 94710 510-527-6666
Clear-Com 810026 8/15/88 REV. C

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DOCUMENTATION ADDENDUM
KB-ll1A MANUAL
• .f REV. A .•
.j
.. ..
November
17, 1987
I .1 r •
MIC TO LINE GAIN LEVEL INCREASE
In effecting a 4dB Mic to Line Increase In gaIn level, the
following changes have been made:
Change:
270K
OHM
R18, 36 390K OHM
27pf
C9 lSpf
180pf
CI0
100pf

CLEAR-COM KB-IIIA SPEAKER STATION
INSTRUCTION & SERVICE MANUAL
TABLE OF CONTENTS
Section
Page II
I Introduction to the KB-IIIA •.•....•..••...•.• 1
II Headsets and Mics •..•...•.........••..•••.••• l
III Installation .•.....••.•••••.•••••••..•••••••• 3
IV
Operating Controls.· •••..••.•.••.••..•••••••. 7
V
Parts Listing ••..•.•..•.•••••.•.•.....•••••.• 8
VI Specifications •...•.•.........••••.•.••.••••• 8
VII Call Signalling Modification.· ••••••....••••• 9
Illustrations
:
Headset Y-Cable .•.•.•••••••.••.•.•.•••• 2 Figure
1
Figure 2:
Headset Extension Cord.·· •••••.•.•••••• 2
Figure
3: KB-IIIA Mounting Dimensions ••..•••.•••• 4
Figure 4:
KB-IIIA Block Diagram •.••.••••••••.•••• 4
Figure 5:
Two-Channel Interconnect Wiring •.•••••• 5
Figure
6:
Portable Unit Connections •.•.•••.•••••• 6
Figure
7:
Alternative Signalling •..•••.•••••••••• 9
Figure 8:
KB-IIIA Schematic ••••.•••••••••••••••. 10
NOTICE:
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In/ormation contained In It.s product •• nua/a. chit inlor.atlon Is .ubJllct CD
change Nithout notice:"

•
I. INTRODUCTION TO THE KB-IIIA REMOTE STATION
The Clear-Com KB-lllA is a Remote
Speaker Station that provides talk/
listen communications on one of two
channels within our closed-circuit
intercom system. It features a
wide frequency response, high out-
put speaker and the ability to
operate with a carbon headset OR a
dynamic headset, handset, or push-
to-talk mic.
The KB-IllA features the Clear-Com
contoured frequency response for
consistently excellent speech in-
telligibility in all surroundings.
The speaker delivers crisp sound
pressure levels, clearly audible in
high- or low-noise environments.
The Remote Station features Automa-
tic Headset Detection; its built-in
mic preamp automatically shuts off
when the headset is disconnected,
eliminating noise pick-up on the
intercom line. The intercom cir-
cuitry incorporates a mic limiter,
which assures constant talk levels
~nd prevents overload.
The KB-lllA's speaker can remain on
at all times, or you can turn it
off so that private conversations
may be carried out with a headset
or telephone handset . The three-
position mic switch allows you to:
1) keep the mic on at all times;
2) activate the mic momentarily;
3) switch off the mic so the KB-
lIlA can function as a "listen-
only" station.
II. HEADSETS AND MICS
To provide you with the ability to
talk on the intercom channel, the
KB-lllA contains:
--one 1/4" phone jack for a stan-
dard carbon headset, AND
--one 4-pin, male, XLR-type connec-
tor (D4M) for a dynamic headset,
telephone-style handset, or push-
to-talk mic
The KB-lllA provides an adjustable
sidetone circuit which allows you
to vary the level of your voice as
you hear it in your headset or
speaker. The circuit also prevents
feedback when using the speaker and
a mic simultaneously. You need
only adjust the sidetone once, even
if other Stations subsequently join
or leave the intercom system.
Designed for custom-mounting, the
KB-lllA is built on a charcoal-
brown, aluminum panel, 5/32" thick,
that can be installed in a cut-out
in any convenient surface, or moun-
ted inside a 6" x 8" Nema electri-
cal enclosure. The Station connects
to the intercom system via a 5-
pin terminal block behind the front
panel.
Clear-Com offers the "P" Box, which
allows you to convert the KB-lllA
to a portable Remote Station. The
P-Box is-a sturdy, sloped-front,
steel enclosure with solid walnut
sides. When installed in a P-Box,
the KB-lllA connects to the inter-
com system with 3-pin, XLR connec-
tors·
~fuen the
KB-lllA is installed in
the P-Box,
it provides talk/listen
capability
on one channel.
Standard two-conductor shielded mic
cable interconnects stations within
the intercom system.
The KB-lllA's built-in headset/
speaker amplifier can drive a stan-
dard headset to levels greater than
110 dB SPL. The Station's mic
preamp automatically shuts off when
the headset is disconnected, there-
by eliminating hum pick-up.
NOTE: If you use a carbon headset
and a dynamic headset simultaneous-

ly . the listen-level in the carbon
headset drops audibly-
The carbon headset connections are:
Ring-- Headphone
Tip-- Mic
Sleeve-- Ground
The D4M connector pins are:
Pin 1: Mic Ground
Pin 2: Mic Hot
Pin 3: Headphone Ground
Pin 4: Headphone Hot
To assure proper
-
level and perfor-
mance, the dynamic headset should
have the following characteristics:
Microphone type: dynamic
Impedance ~ 150-250 ohms
Output level: -55 dB
Headphone type: dynamic
Output impedance: 300-2000 ohms
Clear-Com offers three dynamic
headsets, all with boom-mounted,
noise-cancelling mics. Model CC-
240B is a double-muff and Model CC-
75B is Single-muff; both have boom-
activated mics with on/off swit-
ches. Model PH-7 is a very rugged,
double-muff, high-fidelity headset
with wider frequency response and
greater isolation from ambient
noise. Clear-Com also offers Model
HS-6, a telephone-style handset
with a dynamic mic and push-to-talk
switch; it is interchangeable with
the above headsets. All units have
field-replaceable cords.
The KB-111A drives two dynamic
headsets with only a slight (3 dB)
reduction in level. Clear-Com can
supply you with Model YC-100 "y"
Cable, which allows you to plug two
headsets into the one D4M connector
on the Station's front panel.
Alternately, you may construct your
own Y-cable; we recommend you use
Belden 8416 or the equivalent (2-
conductor, 25 gauge) or Belden 8734
or the eqivalent (3-conductor, 22
gauge). See Figure 1.
You can also build an extension
cord for a dynamic headset, using
the cable specified above. Limit
its length to 15 feet or less;
greater lengths lead to possible
capacity coupling between the mic
signal and the headset Signal,
which causes oscillation or a loss
in frequency response. See Fig. 2.
FIGURE 1: HEADSET "Y" CABLE CONNECTIONS
SHI'EL DEO
A4M
PA IR
PIN 1: MIC GROUND
PIN 2: MtC HOT
PIN J : HEADPHONE
GROUND
PI" 4: HEADPHONE HOT
FIGURE 2: HEADSETEXTENSION CORD
I S' OR LES S
~------~~------~
A4F
>---'T-- ---------- ---I- (~ ! A4M
?
SHI EL DED PA LA
PIN 1: MIC GROUND CAUTION:
:x) NOT CONNEC"
PIN 2.:
MIC HOT
,\l
IC GROUND & ' '' : EADPHo r~E
PIN 3: HEAOPHONE GROUND GROG
NO ~Q G ETHEA
PI" 4: HEADPHONE HOT
A4F
SHLELDED
PAIR
A4M
CAUTION: DO ~OT CONNECT
Mle GROUND & HEAD PHONE
GAO
UN :J TOGETHER AT
AN YPOI NT
2

•
II. KB-IIIA INSTALLATION
The KB-111A connects to the inter-
com system with a five-screw termi-
nal strip, which is located on the
PC Board. Route two-pair (indi-
vidually shielded) cable (i.e. Bel-
den 8723) from a Main Station or
Power Supply output connector to
the location of your Remote Station
(or route two separate, two-conduc-
tor mic cables, one per channel).
Each channel must be fed within its
own shield, although unshielded
cable may be used when run in
condui t.
The KB-lllA can be mounted in a
cut-ou~ in any surface, or it can
mount ins~de a 6" by 8" Black
(electrical) Box (minimum depth,
3"). See figure 3 for dimensions.
After preparing a surface for in-
stallation, bring wiring into the
header on the terminal strip.
While making connections, refer to
the lable adjacent to the terminal
strip; it identifies each pin by
assignment:
Ith
CH.
A
CH .
8
+30
V
~]
Connect the leads according to the
label shown above.
IMPORTANT to prevent ground loops
and buzzes, the common terminal
(pin 5) should NEVER be directly
connected to chassis ground (pin
1). Use conduit or a separate wire
to interconnect two or more KB-111A
Stations to pin 1.
If you
plan to use only one channel
on the
KB-111A, disable the Channel
Select
switch by jumping Channels A
and B
together on the connector
block,
and hook the intercom audio
line to
either terminal 2 or 3.
If you don't disable the Channel
Select switch and are only using
one channel, you must be sure to
keep the Channel Select switch set
to the active channel. If you
switch to the unconnected channel,
the Station will exhibit disturbing
oscillation.
See Figure 5 (page 5) for examples
of KB-111A Two-Channel Wiring.
THE PORTABLE KB-111A
The KB-111A may be mounted inside
the Clear-Com Model "P" Box, there-
by becoming a portable Remote Sta-
tion. The "P" Box is supplied wi th
a handle, rubber feet, and screws
for attaching the handle and the
intercom to the enclosure.
When the KB-111A is mounted in the
P-Box, only one channel can be used
for communication. The wiring in
the P-Box contains a jumper to
defeat the Station's Channel Select
switch.
The portable Station connects to
the intercom system with the 3-pin,
XLR connectors located on the
side of the P-Box. There is one
female connector for input, and
one male connector for extending
the intercom line to other Remote
Stations. Inside the P-Box, the
connectors are wired to a 5-pin
terminal strip, which you plug onto
the header on the KB-111A PC Board.
Refer to Figure 6, Portable Unit
Connections (page 6).
--continued--
3

,
I ~ --- ---
KB-lllA IN MOUNTS
( 8.6"------~1
~
/[\
0
•
5.4
,
,
()
Q
\
A 6"x 8" BACK BOX
-- -- , _.
I(
6 .1"
e e
~
o
6.5"
~ ~ ~~~~
a
e e
I
~
@~
o
5-"
. :::>
-Y-
MINIM UM 3" __ ..::o,j-J
\E-1.25"~
DEPTH 1
FIGURE 3
KB-///A
MOUNTING DIMENSIONS
KB-111A BLOCK DIAGRAM
CARBON
HEADSET
CO' ... NEC TO~
I • ..IC ~
DYNAM,e I ~
HEADSET
C ONNECTOR t
I
M'C GA!N
(TR WI )
"" - - 4 01- --~
I ~
CURRENT
SOURCE
B UFFER
AMP
I
L<
4

•
KB-111A FIXED INSTALLATION WIRING
(TWO-CHANNEL)
CONNECT TO EARTH GROUND IF
NON-GROUNDED ENCLOSURE IS USED 2 2-CONDUCTOR SHIELDED
PAIR
NOTE:
IF WIRES DO NOT FIT IN STATION CONNECTOR BLOCK,
USE SEPARATE TERMINAL STRIP
OR JUNCTION BLOCK TO
CONNECT WIRES TOGETHER
KB111P5. CDR
01

•
To install the KB-lllA in a P-Box:
1) Remove the plastic screw termi-
nal block from the header on the
KB-lllA PC Board; pull straight
up to lift block off.
2) A similar terminal block is
wired to the P-Box's 3-pin con-
nectors; plug that block onto
the KB-IllA's 5-pin header. The
terminal block and the PC Board
are clearly labelled with the
pin numbers to ensure proper
connections- See Figure 5, Por-
table Unit Connection·
3) Because the P-Box accepts one
channel, the KB-IllA' s "Channel
Select" toggle switch is inef-
fective. No matter which posi-
tion this switch is in, the KB-
lIlA operator communicates on
the one channel that's fed into
the P-Box -
4) Attach the KB-lllA to the front
of the P-Box, using the supplied
screws · If desired, attach the
handle and the protective rubber
feet onto the suitable sides-
The enclosure also has cut-outs
on each side for hanging it from
the wall, a console, or where
ever-
Use standard two-conductor mic ca-
ble (i.e-, Belden 8413) with 3-pin
connectors to interconnect the por-
table station within the intercom
system. The pin-out assignment for
each XLR connector is:
Pin 1-- common
Pin 2-- +30 volts DC
Pin 3-- intercom audio
Route cable from the Main Station,
Power Supply, or another Remote
Station to the portable KB-IllA,
and input to the female connector·
Use the male output connector to
"daisy-chain" the intercom line
between the KB-IllA and another
portable Remote Station.
A diode in the DC input of the KB-
lIlA protects the circuitry against
wiring in the interconnect cables.
All Remote Stations bridge the
terminated audio line with approxi-
ma tely 15k ohms.
-Figure 6: Portable Box Connections
o
Removeoriginal
lerminal block. PC
-}.,. B OA RD
-+ ....
~: \ ~
Vl ~
Use pl'n
num bers
on PC Board and
terminal block lor
proper
al ignmenl.
Pl
wg Po Bo x termin al
block onto
he ade rTB 1.
POB ox
o
IN TE RCOM
Ma ch ru bber feet INPUT (F)
10 PoB ox : peel oN ----~r------J,
paper backing a nd I & O
UTPU T
Sl ick feet onto the __ -..-/
(M )
appropnate Side. __
o
6

•
IV. KB-IIIA OPERATING CONTROLS
"A/B Chan. Select"
This toggle switch selects the
channel on which the operator will
communicate. (This switch is de-
feated when the KB-I11A is mounted
in a P-Box.)
"Volume"
This knob adjusts the listen-level
for the speaker/headset.
"Speaker On/Off"
This toggle switch determines the
activity of the speaker.
''Mic On/Off/ (On)"
This three-position toggle switch
determines the activity of the
microphone in your headset, hand-
set, or gooseneck. 1>Then the swi tch
is set to the top "on" position,
the mic remains on. When it's in
the middle position, the mic is
off. The bottom "(on)" position is
a momentary setting.
"Sidetone Adj."
The sidetone control enables the
KB-111A operator to adjust the
level of his/her voice as heard in
the Station's speaker or headset,
allowing up to 35 dB reduction of
acoustical pick-up- You need only
adjust the sidetone once (if at
all), even if other stations subse-
quently join or leave the intercom
system. Adjusting the side tone
does not affect the level of incom-
ing or outgoing signals.
The side tone control is inside a
hole next to the Volume knob. Use
a small blade screwdriver for ad-
justment.
At the factory . Clear-Com sets the
sidetone to be approximately 6 dB
lower than incoming signals. If
you want to change this level, take
these steps:
1) plug in headset
2) turn on mic
3) turn up volume all the way
4) insert screwdriver into hole and
engage the slot on the trimpot
inside
5) begin talking into mic while
slowly turning screwdriver; the
volume of your voice will rise
or drop. When using both the
headset and the speaker, set the
sidetone for maximum null (you
can't hear yourself).
"Call"
The black push-button activates the
visual signal circuit that's stan-
dard on Clear-Com intercoms. It
allows the intercom user to attract
the attention of operators who have
removed their headsets or turned
off their speakers. Call signalling
follows the position of the Channel
Select switch; for instance, if you
are using Channel A, pressing the
Call button activates the signal
circuitry at all stations that are
assigned to Channel A. As long as
you keep the button pressed, the
Call circuit will stay active.
The Call button also activates the
speaker and/or mic at any other
Station (on the same channel) that
is set up for remote control.
The amber Call Lamp illuminates
when any Station, on the same chan-
nel, activates a Call signal.
If you need to receive a Call sig-
nal from the channel you're not
using, refer to the special modifi-
cation diagram on page 9.
7

•
V. KB-lllA FRONT PANEL PARTS LISTING
Schematic Reference
Part"
Description Qty.
210013
Connector, D4M 1
210050
Connector, 1/4" phone jack 1
240015
Knob, 1/2" with 1/8" shaft 1
240020
Button cover, red 1
(510028- switch, snap-action)
250144
Panel, front, KB-l11A 1
280067
Nut, dress cone 2
280071
Nut, 1/4" dress 2
390000
Lamp
cover, amber 1
(390001- bulb, 11387)
500089 Speaker, 3" round 1
510006
Switch, mini toggle 1
510040
Switch, mini toggle 1
510044
Switch, 3-position 1
J2
Jl
P3
Sl
Call, Channel Select
Speaker and Mic On/Off
11
SPI
Speaker On/Off
Channel Select
Mic On/Off IOn
VI. KB-lllA SPECIFICATIONS
AMPLIFIER DESIGN
Solid-state, integrated circuit amplifiers
speaker power amp, and signalling circuitry-
and reverse polarity protection.
MIC PREAMPLIFIER
Freq. Response: 250-lZk Hz, with
mic limiter; contoured
to enhance intelligibility
Mic Input: 200 ohms
Hic Preamp Gain: 31 dB
Hax Input Before Clipping: -20 dB
Hic Limiter Threshold:
-37 dBm
HEADSET/SPEAKER AMPLIFIER
Freq. Response: 100-18k Hz, =2 dB
Load Impedance Range: 8-2000 ohms
(dynamic headset)
Output Level: +20 dBm, 26v p-p
@ 100 ohms
Headset Level: >110 dB SPL
with standard Clear~Com headset
Speaker Level: >98 dB SPL @3 feet
Speaker Type: 3" round, 16 ohms
Power Output: 4 watts peak
Distortion: 0.5% THD @1kHz
Headphone Amp Gain: 40 dB
which include a mic preamp, headset/
Current-limited with short circuit
GENERAL SPECIFICATIONS
Line Level: -20 dB avg-, 0 dB max.
Side tone Adj.: 35dB null to full on
Signal Voltage: IlVDC on audio line
Call Light Sensitivity: 4 volts
Signal-to-Noise: 75 dB
Equivalent Input Noise: -118 dB
Station Bridging Impedance:
>12k ohms (200-1Ok Hz)
Voltage Range: 12-32 volts,
28v nominal
Power Required: 25 ma quiescent,
60 ma talk, 60 ma signalling,
200 ma short circuit
Dimensions (front panel):
8.6" x 6.5" x 3.25" deep
CONNECTORS
Dynamic Headset: Male D4M
Carbon Headset: 1/ 4" phone jack
Line: 5-screw terminal block
(portable unit: 1 Male D3M,
1 Female D3F)
8

•
VII. Special Modification: Signalling Configuration in Multi-channel Systems
In normal circumstances. the KB-
lllA Call Light illuminates when
someone signals on the channel that
the KB-lllA operator has selected
for communication. This is because
the visual signal travels. in the
form of DC voltage. on that chan-
nel's line.
You can alter this configuration by
making the modification described
below.
In our application (Figure 7). a
group of two-channel stations
Remote
Station
Remote
Station
(i.e .• KB-lllA) have selected Chan-
nel B for communication. Yet they
want to be capable of receiving a
Call signal from stations that are
communicating on Channel A.
This is achieved by putting four
diodes (914 type) in series between
the two channels on the intercon-
nect cable. Call signalling is now
possible from Channel A to Channel
B. Since the Call signal follows
the direction of the diodes. this
is one-way signalling; Channel B
cannot send a signal to Channel A.
FIGURE 7:
ALTERNATIVE SIGNALLING
1 1
"-
TWO·CHANNEL
Ch.A
./
MAIN STATION '.
or
j
POWER SUPPLY
Ch .B
.. "-,
./
ByA
B)"
B~f
Remote Remote Remote
DIODES (4)
914
Type
Station
2-Ch.
Station
2-Ch.
Station
2-Ch.
9

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