Lectrosonics TH1 User manual

TH1
ACTIVE TELEPHONE HYBRID MODULE
OPERATING INSTRUCTIONS
and trouble-shooting guide
LECTROSONICS, INC.
Rio Rancho, NM

2

INTRODUCTION
The TH1 Active Telephone Hybrid provides a convenient way to use a Modular Audio Processing sound system for
teleconferencing purposes. The TH1 works with any standard two wire telephone system. A powerful Digital Signal
Processor (DSP) actively adjusts the line balance to achieve maximum transmit and receive signal separation. In
addition, echo suppression based on Lectrosonics unique Adaptive Proportional Gain algorithm minimizes acoustic
echo while maintaining near full-duplex operation.
TABLE OF CONTENTS
INTRODUCTION .......................................... 3
FCC PART 68 COMPLIANCE ................................. 4
GENERAL TECHNICAL DESCRIPTION .......................... 5
INSTALLATION ........................................... 6
FRONT PANEL DESCRIPTION ................................ 7
REAR PANEL DESCRIPTION ................................. 8
OPERATING INSTRUCTIONS ................................. 9
TROUBLESHOOTING ....................................... 10
SPECIFICATIONS ......................................... 10
SERVICE AND REPAIR ..................................... 11
RETURNING UNITS FOR REPAIR ............................. 11
WARRANTY ........................................ Back cover
3

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 it’s 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
[phone] 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.
4

GENERAL TECHNICAL DESCRIPTION
The TH1 is built around a powerful DSP microprocessor. The DSP performs all internal calculations using 24 bits,
giving an internal dynamic range of 144dB. All A/D and D/A converters are 16-bit, sigma-delta types with 64 times
oversampling. The DSP implements both the transmit/receive signal separation, as well as a sophisticated echo
suppression algorithm. Please refer to the block diagram of the TH1 for the following discussion.
Remote Control Interface
CONNECT SW
PRIVACY SW
VOLUME UP SW
VOLUME DN SW
CONNECT LED
PRIVACY LED
ECHO SUPPRESSION
ECHO SUPPRESSION
SETUP/OPERATE
TRANSMIT IN +
TRANSMIT IN -

MIX OUT

RECEIVE OUT +
RECEIVE OUT -
MODULAR
AUDIO
PROCESSO
R
INTERFACE
LIMITER A/D
D/A
SIGNAL
DIGITAL
PROCESSOR
A/D
D/A
VREF
MAIN BUS
VARIABLE THRESHOLD
FIXED THRESHOLD
NOM
PRIORITY
CONNECT
PRIVACY
VOLUME DOWN
VOLUME UP
DIGITAL
uCONTROLLER
TRANSMIT
LEVEL
MIX OUT
LEVEL
RECEIVE
LEVEL
TX TX RX RX
SIG LIMIT SIG LIMIT
AUTO ANSWER
AUTO INITIALIZE
VOLUME LIMIT
VOLUME LIMIT
LOG
DETECTOR
The Transmit (or near-end) signal is typically input from the Auxiliary output of the AC1 Controller module. The
Transmit Level control allows adjustment of the transmit signal level for best operation. The transmit signal is passed
through a very fast attack limiter prior to being digitized by the A/D converter. The transmit output signal is converted
back to an analog signal by the D/A converter, buffered, and output to the phone line coupling transformer. Because
of impedance mismatches between the transmit output driver, 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
(or far-end) signal.
Echo suppression is also programmed into the DSP. The Lectrosonics Adaptive Proportional Gain algorithm 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.
5

INSTALLATION
Before installing the module, see the Operating Instructions section for guidance as to how to select the various
jumperable options on the TH1.
The TH1 is installed from the rear of the Modular Audio Processor mainframe. Care should be taken when aligning
the circuit board with the card guides. Once the module is aligned, slide the card forward in the mainframe until the
female edge connector on the module seats firmly onto the male pins of the main bus board.
Four #4 machine screws are provided with the TH1 module. The two screws with captive washers are used to
secure the rear panel to the top and bottom rails of the mainframe. After this is accomplished, fit the front panel (also
supplied) over the front of the module and secure it, using the two flat-head #4 machine screws, to the front panel of
the Modular Audio Processor mainframe. Once these four screws are in place, the installation is complete.
6

FRONT PANEL DESCRIPTION
RECEIVE LEVEL UP/DOWN - Adjusts the receive audio level. Operates in
parallel to the remote Volume Up/Down buttons. The range of adjustment is set by
the Volume Limit dipswitch settings. Note that the Connect LED will flash each
time a change in volume (up or down) is made. This flashing will stop when the
volume limits are reached.
PRIVACY - Mutes the transmitted audio to allow private conversations to take
place. The phone connection is maintained.
CONNECT - Connects or disconnects the TH1 from the phone line. The Connect
button is used to pick up an incoming call or to switch back and forth from the TH1
to a handset.
TX LEVEL - Adjusts the transmit volume level. The TX SIG LED indicates the
presence of transmit signal, and the TX LIM LED indicates overload in the transmit
channel.
RX LEVEL - Adjusts the receive volume level. The RX SIG LED indicates the
presence of receive signal, and the RX LIM LED indicates overload in the receive
channel.
DIPSWITCH OPTIONS - Figure 3 shows
ECHO SUPPRESSION
the dipswitch setting options for the TH1.
7 7 7 7
6 6 6 6
Echo Suppression - Selects the amount
of echo suppression used. Auto is the
normal setting. Auto uses the least echo
suppression possible to achieve
acceptable performance. Use the other
settings as necessary if too much of the
received signal is acoustically coupled
back out the to the transmit signal.
Auto Answer - Selects whether the TH1
will automatically connect if it receives a
phone call.
Setup/Operate - Selects the operational
mode of the TH1. The Setup mode is
usually used when the
system is initially installed. Thereafter,
AUTO 12dB 18dB 24dB
AUTO ANSWER
55
ON OFF
SETUP/OPERATE
4 4
SETUP OPERATE
AUTO INITIALIZE
33
ON OFF
VOLUME LIMIT
2
1
NO LIMIT +6/-12dB +6/-6dB +3/-6dB
1
2
1
2
1
2
Figure 3 - TH1 Dipswitch settings
the switch should always be left in the Operate mode.
Auto Initialize - Selects whether the TH1 will re-initialize every time it connects. If
Auto Initialization is on, the far-end listener will hear a short noise burst as the TH1
resets it adaptive filter coefficients. If Auto Initialization is off, the adaptive filter
coefficients stored from the system setup are used. The best performance will be
obtained with Auto Initialization turned on.
Volume Limit - Selects the limitation placed on the volume adjustment range.
PRIVACY
ACTIVE HYBRID
CONNECT
RECEIVE
LEVEL
UP
DOWN
LIM
SIG
LIM
SIG
TH1
TX
LEVEL
ECHO SUP
ECHO SUP
AUTO ANS
SETUP OP
AUTO INIT
VOL LIMIT
VOL LIMIT
RX
LEVEL
7654321
Figure 2 - TH1 Front Panel
This limitation only affects the front panel Receive Level pushbuttons, or the Receive Level pushbuttons of the remote
control (if used).
7

REAR PANEL DESCRIPTION
REMOTE CONTROL - Allows the Connect, Privacy, Volume Up/Down, and indicator LEDs to
be operated from a remote location. Figure 5 shows the connection diagram to the 9 pin
D-Sub Remote Control connector.
MIX OUT LEVEL - Controls the audio level of the Mix Output. This output may be used for
recording of the conference, etc.
IN(+), IN(-) - Accepts a balanced or unbalanced transmit input signal. Typically driven from the
balanced Aux Output on the AC1 Controller Module.
OUT(+), OUT(-) - Outputs the received audio signal. This output is not normally used when the
TH1 drives the MAP system Main or Aux bus.
MIX OUT - Provides an unbalanced signal consisting of a mix of the transmit and receive
signals.
LINE - Accepts a standard two wire telephone line on an RJ-11 style connector.
PHONE - Accepts a standard RJ-11 style connector to enable a telephone to be used in
conjunction with the TH1.


VOLUME DOWN
VOLUME UP
PRIVACY
CONNECT
PRIVACY LED
CONNECT LED
Figure 5 - TH1 Remote Control Connections
LINE
PHONE
IN+
IN-
GND
OUT +
OUT -
GND
MIX OUT
ACTIVE HYBRID
TH1
MIX OUT
LEVEL
REMOTE
CONTROL
Figure 4 - TH1
Rear Panel
8

OPERATING INSTRUCTIONS
The following instructions assume that the TH1 will feed the Main bus of a MAP system, and that the Aux Output of
the AC1 Controller module will feed the Transmit Input of the TH1. This is the standard setup for the TH1 when used
with a sound system configured around the MAP system.
1) Refer to Figure 6 for the
Reference Variable
positions of the configurable
jumpers. Note that if the TH1
J11J11
DC Bypass Jumper
J7
Threshold
In/Out
J10
Priority
J8
Threshold
Send
is being used in the standard
setup, no changes from the
factory configuration will be
Auto
Disconnect
Position
RUN RUN
Manual
Disconnect
Position
OUT IN OUT IN OUT
OUT
IN
IN
necessary.
2) Connect the telephone line to
the LINE input RJ-11 jack. If a
local telephone is to be used in
conjunction with the TH1,
F
R
O
N
connect it to the PHONE input
T
RJ-11 jack. Note that to
originate calls, a local phone
must be connected to the
system.
3) Connect the Aux Output of the
AC1 to the IN(+), IN(-), and
ground terminals of the TH1.
Pin 2 of the Aux Output should
connect to the IN(+) terminal, Pin 3 to the IN(-) terminal, and Pin 1 to GND.
4) Set the both TX LEVEL control and the RX LEVEL control to the mid position (9 o’clock). Set the Aux Output
level control on the AC1 to the mid position.
5) Set the dipswitch options as desired. Factory settings are:
Echo Suppression Auto
Auto Answer On
Setup/Operate Operate
Auto Init On
Volume Limit No Limit
6) If a local phone is connected, originate a call to a remote site. If no local phone is present, someone at a remote
site must call you. If you are the originating site, press the CONNECT button to connect the TH1 to the phone
line after the call has been established. If the remote site originates the call, and Auto Answer is On, the TH1
will establish the connection automatically.
7) Adjust the receive (near-end) volume level using the RX LEVEL control. Then adjust the transmitted level using
the Aux Output level control on the AC1.
8) When all volume levels are acceptable, disconnect the call by pressing the CONNECT button again.
9) Set the Setup/Operate dipswitch to the Operate position. If any limitation on the remote volume control range is
desired, set the Volume Limit dipswitches accordingly.
10) The TH1 revisions 1.2 and higher now include firmware support for the J11 DC Bypass jumper. This jumper can
be used to bypass the automatic disconnect circuitry on the TH1. This feature is intended to be used in
installations where the TH1 is connected to an outside phone line through a PBX system which does not supply
DC battery. By changing the position of the DC Bypass jumper, and by selecting the dipswitch option AUTO
ANSWER to OFF, the TH1 will be transfered to fully manual operation. The factory default position is Auto
Disconnect.
U11
U7
J1
J2
U6
C1
J3
RL1 T1
U2
U1 U3
U9
U8
U23
J10
J7
U25
J9
J8
U13
U12
U22
U10
U26
U24
TP1
D25
RL2
J6
D26
D27
D28
R43
R56
SW4
LINE
PHONE
J9
NOM Send
CONNECT
TX
LEVEL
RX
LEVEL
J11
RUN
Figure 6 - TH1 Configurable Jumpers
9

TROUBLESHOOTING
SYMPTOM POSSIBLE CAUSE
No receive sound from TH1 1) RX Level control not turned up
2) Connect LED not lit
3) Phone line from wall jack to TH1 not connected
4) The Send to Bus dipswitch is in the Off position
(switch to On)
No transmit sound from TH1
to remote site
1) TX Level control not turned up
2) Aux Output level control on AC1 not turned up
3) Aux Output not connected to IN(+) and IN(-).
Feedback or hollow sound 1) Not enough Echo Suppression (increase Echo
Suppression)
2) Large variations in phone line impedance (set Auto
Initialize On)
SPECIFICATIONS
Power Requirements: 200mA at ±15V
Connectors: Audio: Depluggable terminal blocks
Telephone/Line: RJ-11 Modular
Remote Control: DB-9
Output Audio: 100 Ohms, actively balanced
Input Audio: Actively balanced, RF filtered
Input Impedance: 10kΩ, balanced
5kΩ, unbalanced
Telephone Hybrid: Standard hybrid transformer with DSP line return
cancellation
Auto Answer: Selectable - answers after first complete ring
Remote Volume Control: Range: +6dB to -24dB and Off in 1dB steps.
Range Limit: Selectable - No limit,
+3dB/-6dB, +6dB/-6dB, +6dB/-12dB
Echo Suppression: Selectable: Auto, 12dB, 18dB, 24dB
Call Frequency Response: ±1dB 200Hz to 3.5kHz
Caller THD (250Hz to 3.3KHz): Less than 0.1% (0dBu out)
Send THD (250Hz to 3.3KHz): Less than 0.1% (0dBu out)
Maximum Output Level: +26dBu
10