The talkback unit 1FB246 provides six channels of full-duplex 4-wire communication for small studios or broadcast vehicles. The unit provides four  IFB (Interrupted Fold Back) inputs. The unit offers great variability where IFB operation is required. All line inputs and line outputs are balanced and transformer isolated. Gain is adjustable on all inputs. It is possible to monitor all input lines (and / or mix them into a reproducing amplifier).

The command buttons are illuminated. They operate either in PTT Push-to-Talk (momentary) mode  or in HOLD (latching) mode. It is possible to use a gooseneck microphone and a built in speaker (or an external speaker) or a headset. The 1FB246 unit’s control elements are on its front panel, the unit it is easily configurable to fit  different demands of the user. Almost all of the settings can be done through navi-keys and the LCD display. The unit fits into a 1RU 19”rack space. It is powered by 230V~/50 Hz.

Operation and control of 1FB246:

Talkback unit 1FB246 provides six identical channels. XLR connectors of 4-wire input and output are placed on the back panel of the unit. Following diagram shows a single channel simplified schematic.  Switches configured via navi-keys and LCD display are marked by hollow arrows. Incoming Call from REV TB IN-n (REVERSE TALKBACK INPUT) is fed into a RTB / IFB lever switch.  This switch enables the user to monitor either the REV TB line or the IFB line routed to this channel. Volume contribution is controlled through the MON potentiometer.

One of these presets (IFB lines or reverse talkback RTB or silence) can be sent to TB OUT–n when the unit is idle. When a command comes from 1FB246 unit, idle modulation is either dimmed or interrupted (according to the pre-settings) and TALK signal from a microphone is fed to output.

The outgoing command buttons are illuminated. A longer depression of the button activates PTT (Push to Talk) mode; while pushing the button the operator can talk, LED in the button turns on. Releasing the button ends the command, LED turns off.

 A short depression of the button activates the HOLD mode, a command route is selected, LED turns on. The operator can talk with free hands. Next depression of the button cancels the connection, LED turns off.

A green “CALL” LED announces an incoming call. Internal jumper sets the “CALL” LED to indicate either a REV TB IN-n input or pre-set of the RTB / IFB switch.Default setting is RTB.

Each of the channels is individually configurable. The configuration is automatically stored in the nonvolatile memory.

Common functions for all channels:

The GROUP TALK button issues commands to all outputs.

The MIC/HS switch selects between a gooseneck microphone + loudspeaker or a headset (5‑pole XLR connector). Selecting the headset switches off internal speaker. Inserting jack into the PHONES socket switches off  the internal speaker. Inserting jack into back panel  socket switches off internal speaker as well.

The TALK potentiometer adjusts output signal level. Two LEDs indicate the 0 dBu and +8 dBu levels.

The volume control of the monitored signal mix is on the right side of the front panel. Above this knob there is an illuminated button for the loudspeaker cut function. The button lights red when the loudspeaker is off. The reproducing amplifier is dimmed if there is an outgoing command. The level of the dimming is adjusted through the LS DIM potentiometer.

User manual 1FB246 - 

Block diagram 1FB246 -