Sonifex CM-CU21, CM-TBU and CM-TLL provide all the elements of a portable, professional commentator set-up for use in sports grounds.

CM-CU21 Commentator Unit

CM-CU21 Commentator UnitThe CM-CU21offers two fully featured commentator positions and a third ‘guest’ location that can alternatively be used as a line-level input. Each position has an individual output, with two additional outputs that provide a mix of all active commentary channels.

A limit indicator on the main panel shows when the adjustable limiter on the mix outputs is active, and a bright 21-segment LED PPM meter (which can be disabled) shows the main output level. Two talkback output channels, with a built in limiter, are available to each of the two main commentators and they can be linked to provide simultaneous operation.

A wide input gain range and switchable phantom power on each commentary position support of a variety of microphone types, including low-output ribbon, headsets and high-output phantom powered microphones. There are four transformer balanced return audio inputs which, along with the commentator inputs, are routed to the headphone monitor controls. With these headphone controls, any monitor input can be adjusted and sent to either the left, right or both ears.

A GPIO port gives an open-collector driven output indication of any active On-Air or talkback channel and four remote inputs provide an external call/alert to each of the talkback controls.

The unit also has a built in line-up tone generator for easy channel identification and cabling checks. When enabled the test-tone is routed to the required output by pressing the corresponding on air or talkback button. An On-Air lock switch prevents the On-Air buttons from being accidentally deactivated and a T/B Gang switch links the operation of talkbacks A & B.

The CM-CU21 can be powered from a universal mains input between 85-264V AC at 47-63Hz, or from a 12-24V DC input.

CM-TBU Line Powered Telephone Balance Unit

CM-TBU Line Powered Telephone Balance UnitThe CM-TBU line-powered telephone balance unit is compatible with all analogue direct exchange lines and provides a line-powered, 4-wire communications system to interface with the telephone network and the CM-TLL line-powered telephone line listen unit.

The high degree of separation between send and receive signals makes the CM-TBU 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.

This compact unit is powered from the telephone line and provides an interface to a 4-wire circuit with separate level control of send and receive signals.

Optimum rejection of the input signal on the 4-wire output is achieved in a bridge circuit by adjusting three elements (Null, R-Bal and C-Bal) via potentiometers which simulate the complex line impedance. This can be used to compensate for local line variations or to adapt to the telephone systems of other countries, where line characteristics may differ. Optimisation of the sidetone rejection does not involve the use of any test equipment and can be easily carried out while the system is in use.

Although the signal level being sent to the line can be manually adjusted using the Send Level control over a wide range, the level control is followed by a limiter that prevents the telephone line signal level becoming overloaded or distorted. The limiter drives a Linit LED to indicate the onset of limiting.

Although the output stage can drive a presenter’s earpiece in a telephone IFB application, the Receive Level control may not be accessible to the presenter, who is normally situated some distance from the unit. The presenter may then require a local control of the earpiece signal level. The CM-TBU can be used to supply the correct signal level to a suitable battery powered earpiece belt-pack unit.

To enable communication between the 4-wire circuit and the telephone network, once the 4-wire and telephone line cable connections are made to the unit, the Line Connect switch can be pressed to power the unit from the line. This is indicated by the ‘on’ LED, and can either be done after an outgoing call has been dialled on a telephone set connected to the unit, or to answer an incoming call after the ‘ring’ LED is seen to flash. Note that a telephone set is not required for incoming calls unless an audible ring is required. If the sidetone level at the 4-wire output is found to be excessive, the outgoing signal level can be reduced usingthe Send Level control or the balance controls can be adjusted to minimise it.

The unit is supplied with a connector and cable kit that enables connections to be made to both UK Telecom or the universal RJ11 sockets used in most telephone networks around the world.

CM-TLL Line Powered Telephone Line Listen Unit

The CM-TLL provides a low-loss interface to receive audio from a telephone line.

The line-powered unit is compatible with all analogue direct exchange lines and includes an LED indication of incoming calls. It is intended to be used with an earpiece amplifier to receive an audio feed by telephone from a studio.

The line and telephone set are connected to the unit via the RJ11 connectors in order to make an outgoing call. A telephone may not be required if calls are only incoming, because telephone line ringing is indicated by a flashing LED built into the unit. In either case, the Line Connect switch is pressed to make the line connection. The ‘on’ LED indicates that the unit is powered and that audio is routed from the line to the XLR plug.


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