Lectrosonics TH2 Operating Instructions Manual
TH2
DIGITAL TELEPHONE HYBRID
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM
INTRODUCTION
The TH2 Digital Hybrid is part of the LecNetTM family of audio products. The TH2
works with any standard two wire telephone system, to provide a convenient and
inexpensive means of using any sound system for teleconferencing. This product is
microprocessor controlled, with a powerful Digital Signal Processor (DSP) actively
adjusting the line balance to achieve maximum transmit and receive signal separation. In addition, echo suppression based on Lectrosonics patented Adaptive Proportional Gain algorithm (U. S. Patents No. 5402500 and 5414776) minimizes acoustic
echo while maintaining virtually full-duplex operation. The TH2 can be setup manually or with an IBM compatible PC in the PC Remote mode. Manual setup is accomplished by adjusting three trimmer potentiometers and a set of dip switches. Four
push-buttons and a wired remote control port provide a convenient way to control the
operation of the TH2 locally or remotely.
TABLE OF CONTENTS
INTRODUCTION ................................................................................................... 2
FCC PART 68 COMPLIANCE ............................................................................... 3
GENERAL TECHNICAL DESCRIPTION ............................................................. 4
INSTALLATION ...................................................................................................... 5
FRONT PANEL DESCRIPTION ............................................................................ 7
DIP SWITCH OPTIONS ........................................................................................ 7
REAR PANEL DESCRIPTION .............................................................................. 8
OPERATING INSTRUCTIONS ............................................................................. 9
TH2/AM8 SYSTEM SETUP PROCEDURE........................................................ 10
TROUBLESHOOTING......................................................................................... 11
SERIAL CABLE WIRING DIAGRAM ................................................................. 12
AMX CABLE WIRING DIAGRAM ....................................................................... 12
AMX Programming Notes ............................................................................... 12
SERIAL PORT SOFTWARE COMMANDS ........................................................ 13
SPECIFICATIONS ............................................................................................... 16
ACCESSORIES ................................................................................................... 16
SERVICE AND REPAIR ...................................................................................... 17
RETURNING UNITS FOR REPAIR .................................................................... 17
WARRANTY ........................................................................................... Back cover
2
Digital Telephone Hybrid
FCC PART 68 COMPLIANCE
This equipment complies with Part 68 of the FCC rules. On the rear panel of this
equipment is a label that contains, among other information, the FCC registration
number and ringer equivalence number (REN) for this equipment. If requested, this
information must be provided to the telephone company.
This equipment uses the following USOC jacks: RJ11C
The REN is used to determine the quantity of devices which may be connected to the
telephone line. Excessive REN’s on the telephone line may result in the devices not
ringing in response to an incoming call. In most, but not all areas, the sum of the
REN’s should not exceed five (5.0). To be certain of the number of the devices that
may be connected to the line, as determined by the total REN’s, contact the telephone company to determine the maximum REN for the calling area.
If this equipment causes harm to the telephone network, the telephone company will
notify you in advance that temporary discontinuance of service may be required. If
advance notice isn’t practical, the telephone company will notify the customer as
soon as possible. Also, you will be advised of your rights to file a complaint with the
FCC if you believe it is necessary.
The telephone company may make changes in its facilities, equipment, operations, or
procedures that could affect the operation of the equipment. If this happens, the
telephone company will provide advance notice in order for you to make the necessary modifications in order to maintain uninterrupted service.
If trouble is experienced with this equipment, please contact Lectrosonics, Inc. at
(800) 821-1121 for repair and/or warranty information. If the trouble is causing harm
to the telephone network, the telephone company may request you remove the
equipment from the network until the problem is resolved.
The following repairs can be done by the customer: No user serviceable parts
inside.
This equipment cannot be used on telephone company-provided coin service.
Connection to Party Line Service is subject to state tariffs.
Rio Rancho, NM – USA
3
GENERAL TECHNICAL DESCRIPTION
2
The TH2 is built around a powerful DSP which performs all internal calculations using 24 bits, providing an internal
dynamic range of 144dB. The DSP implements both the transmit/receive signal separation, as well as a sophisticated
echo suppression algorithm. The Lectrosonics Adaptive Proportional Gain algorithm (US patent #5,414,776 &
#5,402,500) used for echo suppression dynamically varies the transmit and receive path gain in response to the
signal level present in both paths. This helps prevent retransmission of a received signal caused by acoustic coupling
between near-end system loudspeakers and microphones. Because no abrupt gain changes are made, the perceived effect is a full duplex conversation.
The TH2 is fully interfaced with the AM8 automatic mixer in that it participates in the auto mixing algorithm just like
another microphone. The transmit (or near-end) signal is typically received from the Lectrosonics AM8 Automatic
Mixer via the TH2 Expansion Out jack. When the near-end transmit signal is coming from any other line level source,
it is connected to the TH2 via the Local In/Out port (balanced or unbalanced). The Transmit Level control allows
adjustment of the transmit signal which is passed through a very fast attack limiter prior to being digitized by the 13 bit
A/D converter. The transmit output signal is converted back to an analog signal by the 13 bit D/A converter, buffered,
and output to the phone line coupling transformer.
The far-end signal is received from the phone line coupling transformer, buffered, digitized by the 13 bit A/D converter
and processed in the DSP chip. It is then converted back to an analog signal by the 13 bit D/A converter, and output
either to the Expansion or Local Out port (balanced or unbalanced). The Receive Level control allows adjustment of
the receive signal, while Volume Up/Dn pushbuttons regulate the received volume. LEDs indicate level changes and
show when limits are reached. Volume adjustment range is set with the combination of two dip switches from the front
panel. The Connect push-button connects the TH2 to the phone line, while the Privacy push-button mutes the transmit
path of the TH2, allowing private conversation to take place.
Because of impedance mismatches between the transmit output driver and the transformer and phone line, some of
the transmit signal recirculates through to the receive path. In a normal telephone handset, this recirculated transmit
signal is known as a “sidetone.” In teleconferencing applications, however, this sidetone signal can cause feedback
or loss of intelligibility. For this reason, the DSP is programmed to remove any artifacts of the transmit signal from the
receive signal. The Mix Out connector provides an unbalanced output signal for recording purposes (in the Expansion
or Local mode) consisting of a mix of the transmit and receive signals.
REMOTE CONTROL
INTERFACE
CONNECT SW
PRIVACY SW
VOLUME UP SW
VOLUME DN SW
CONNECT LED
PRIVACY LED
LOCAL IN +
LOCAL IN –
EXPANSION
IN
EXPANSION
OUT
MIX OUT
LOCAL OUT +
LOCAL OUT –
1
MAIN IN
MIX MINUS OUT
2
1
MAIN OUT
2
MIX MINUS IN
AUTO MIX
3
LOG OUT
MIX OUT
LEVEL
LOG
AMP
TRANSMIT
LEVEL
LIMITER A/D
RECEIVE
LEVEL
VOLUME UP
VOLUME DOWN
PRIVACY
PRIVACY LED
CONNECT
CONNECT LED
D/A A/D
68HC705
uC
DIGITAL
SIGNAL
PROCESSOR
TX
SIGTXLIMITRXSIGRXLIMIT
D/A
OUT
LECNET
(RS-232)
IN
ECHO SUPPRESSION 1
ECHO SUPPRESSION
AUTO ANSWER
RX ATTEN
AUTO INITIALIZE
VOLUME LIMIT 1
VOLUME LIMIT 2
PHONE LINE
TELEPHONE
4
Figure 1 - TH2 Block Diagram
INSTALLATION
Digital Telephone Hybrid
WITH THE AM8 AUTOMATIC MIXER
(Figure 2)
Used with the Lectrosonics AM8 automatic mixer, the
interconnections to the TH2 are very simple. Set the
Local Expan switch on the TH2 to the Expan position. Set
the Master/Slave switch on the AM8 to the Master
position. Plug in the supplied 8-pin mini DIN cable as
shown in Figure 2. The TH2 will receive signals from the
AM8 and send signals to the AM8 via this single connecting cable.
PWR
IN
EXPANSION
(CH40)
L
E
20 VAC
O
X
C
P
A
A
L
N
Switch in "EXPAN" position
PWR
IN
EXPANSION
(CH40)
M
A
S
S
L
20 VAC
T
A
E
V
R
E
Switch in "SLAVE" position
PWR
IN
EXPANSION
(CH40)
M
A
S
S
L
20 VAC
T
A
E
V
R
E
Switch in "MASTER" position
Figure 2 - TH2 & AM8 Configuration
IN
OUT
LecNet
(RS232)
TH2 Rear Panel
LECTROSONICS, INC.
IN
OUT
IN
OUT
REMOTE LEVEL
LecNet
CONTROL
(RS232)
LECTROSONICS, INC.
REMOTE LEVEL
LecNet
CONTROL
(RS232)
Local Sound Reinforcement
AM8 Rear Panel
MAIN OUT
+ –
CH8 IN
1 2 3 4
AM8 Rear Panel
MAIN OUT
+ –
CH8 IN
1 2 3 4
DIR
+
–
OUT
DIR
+
–
OUT
INPUT
BALANCED INTERCONNECTION WITH NONLECTROSONICS MIXERS
(Figure 3)
For use with any non- Lectrosonics microphone mixer
and sound system, the Local/Expan switch on the TH2 is
set to the Local position. The cable connections are
made as shown in Figure 3 to maintain a balanced wiring
configuration. Note that the TH2 output signal at the Local
Out jack must be connected to the sound system outside
of the mixer that feeds the TH2. This typically requires the
use of a separate mixer ahead of the sound system
amplifier as illustrated in Figure 3.
An Unbalanced configuration is also possible using these
same jacks. For this configuration, leave the (-) unconnected on the TH2 Local In/Out jack and use the (+)
terminal for signal hot.
PWR
IN
(CH40)
20 VAC
Switch in "LOCAL" position
8-Channel Mixer
Local Sound Reinforcement
Figure 3 - TH2 & Single Bus mixer Configuration with
Rio Rancho, NM – USA
L
E
O
X
C
P
A
A
L
N
EXPANSION
OUT
IN
LecNet
(RS232)
Balanced Outputs
IN OUT
+
LOCAL
+
OUT
OUTPUT
MIX
LEVEL
MIN
IN 1 IN 2
OUT
INPUT
LINE PHONE
TH2 Rear Panel
2:1 Balanced
Mixer
5
LINE PHONE
OPTIONAL UNBALANCED INTERCONNEC-
LINE PHONE
TION WITH NON-LECTROSONICS MIXERS
(Figure 4)
PWR
IN
EXPANSION
(CH40)
20 VAC
IN
OUT
L
E
O
X
C
P
A
A
L
N
LecNet
(RS232)
IN OUT
+
LOCAL
MIX
LEVEL
OUT
+
MIN
A simple method of mixing the incoming phone line signal
with the local microphone mixer output is illustrated in
Figure 4. This is an unbalanced configuration best suited
to short cable runs, such as with components rack
mounted next to each other. This configuration simplifies
the wiring connections and eliminates the need to install
an external mixer ahead of the sound reinforcement
system.
SIMULTANEOUS 2-WIRE/4-WIRE CONVERSION FOR 3-SITE CONFERENCING
BRIDGING
(Figure 5)
The TA1 Line Level Adapter is designed for connecting
an Audio/Video Teleconferencing Hybrid to the Lectrosonics AM8 automatic mixer.
With the AUTO MIX switch in the “ON” position, the video
codec (or other audio source) will participate in the
automatic mixing algorithm applied by the AM8 mixer. An
incoming signal from the far end of the telephone or
ISDN line will attenuate the gain on the local microphones, reducing or eliminating acoustical coupling
between microphones and loudspeakers that could
cause a feedback loop.
Used with the AM8 mixer and TH2 telephone hybrid, 3site bridging is accomplished with the TA1 without the
need for any other mixing or routing devices.
Switch in "LOCAL" position
8-Channel Mixer
Local Sound Reinforcement
OUTPUT
TH2 Rear Panel
INPUT
Figure 4 - TH2 & Single Bus Mixer Configuration with
Unbalanced Outputs
PWR
IN
EXPANSION
(CH40)
OUT
E
L
20 VAC
X
O
P
C
A
A
N
L
Switch in "EXPAN"
position
LECTROSONICS T A 1
EXP OUT
LINE LEVEL ADAPTER
EXP IN
AUTO MIX
ON
OFF
TA1 Front
Panel
PWR
IN
(CH40)
M
A
S
20 VAC
T
E
R
PWR (CH40)
EXPANSION
S
L
A
V
E
IN
LecNet
(RS232)
OUT
IN OUT
+
2
0
INPUT
IN
LecNet
(RS232)
MIX
LOCAL
+
LEVEL
2
4
6
0
TA1 Rear
LEVEL
OUT
MIN
4
6
OUTPUT
TA1 Rear Panel
Panel
LECTROSONICS, INC.
REMOTE LEVEL
CONTROL
MAIN OUT
+ –
TH2 Rear Panel
AM8 Rear Panel
Video
Codec
CH8 IN
1 2 3 4
DIR
+
–
OUT
6
Switch in "MASTER" position
Figure 5 - 3-Site Conferencing Bridging
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