Sonifex CM-TBU Line Power Telephone Balance Unit

The CM-TBU line-powered telephone balance unit is compatible with all analogue direct exchange lines and provides a 4-wire communications system to interface with the telephone network. The high degree of separation between send and receive signals makes it suitable for use in telephone IFB (interrupted foldback) applications and the high drive capacity at the 4-wire output enables a presenter’s earpiece to be connected directly to the unit without an external amplifier.

Key Features

• Isolated, full-duplex 4-wire interface to direct non-digital telephone exchange lines
• Line powered, requiring no battery or external power
• Simple optimization of sidetone rejection with any country’s telephone system
• LEDs indicating ‘Ring’, ‘Line Hold’ and ‘Limit’ conditions
• Input level control with line-sensing limiter and limit indicator
• High drive output with level control for direct feed to presenter’s earpiece, etc
• Loop-through RJ11 line sockets provide universal connection to line and telephone set
• Connection to the telephone set is maintained while the unit is in use
• Small, rugged extruded aluminium case with XLR3 male & female 4-wire connectors

Technical Specifications

4-Wire Input
Input Impedance
10kohms, transformer coupled
Input Connector
3 pin XLR female connector
Input Level Range
-12dBU to +4dBU before limiting when connected to an average line
4-Wire Output
Output Impedance
150ohms, transformer coupled
Output Connector
3 pin XLR male connector
Output Level Range
-6dBU to +6dBU, for average line level
Sidetone Rejection
30dB to 40dB average, depending on line characteristics
2-Wire
Off Hook Voltage
6V minimum
2 Wire Connectors
RJ11 socket - line
RJ11 socket handset
Front Panel Operational Controls
Line Connect
Push button with indicator
Send Level
Small rotary control
Receive Level
Large rotary control
Null Balance
Recessed preset potentiometer
R Balance
Recessed preset potentiometer
C Balance
Recessed preset potentiometer
Ring LED
Indicates incoming ringing
Limit LED
Indicates limiter active
On LED
Indicates connection to the telephone line
Physical
Dimensions
77mm (W) x 83mm (D) x 42mm (H)
3.0” (W) x 3.3” (D) x 1.7” (H)
Weight
Nett: 0.25kg Gross: 0.75kg
Nett: 0.60lbs Gross: 1.7lbs