PLENA Universal Pre-Amplifier LBB1920/00

PLENA universal pre-amplifier LBB1920/00

Architects’ and Engineers’ Specifications

The pre-amplifier shall operate on 115Vac or 230Vac with a tolerance of +/-15% to accommodate to a wide range of mains voltage variations, and have its source power supplied by a detachable IEC power cord. A switch on the rear panel shall select between operation on 115Vac or 230Vac. In addition, the unit shall be capable of being directly powered by a 24Vdc source, such as storage batteries. It shall have a power switch on the front panel.

Inputs to the unit shall include at least four actively balanced inputs for either microphone or line signals. All inputs channels have a 5-pin DIN connector with priority contacts as well as a 3-pin XLR connector for use as balanced microphone or line input and a pair of stereo Cinch connectors, internally converted to mono, for use as unbalanced line level input. Selection of active input connectors and sensitivity shall be via internal switches.

In microphone mode all inputs shall have a phantom powering circuit. All inputs channels shall have internally selectable speech filters for improved intelligibility. Each channel shall have a balanced direct output on a 3-pin XLR connector, after the channel controls.

The unit shall have, on its front panel, separate volume controls as well as bass and treble shelving tone controls for each input channel, and a master volume control.

Three priority modes shall be available for the input channels: blocking, serial and mixing. In the blocking mode the input channel that is activated first shall get priority over all other input channels. In the serial mode input channel 1 shall have priority over channels 2, 3 and 4, channel 2 shall have priority over channel 3 and 4, and channel 3 shall have priority over channel 4. Each of the input channels shall be mixed to the master output, irrespective of priority, by separately setting that channel to the mixing mode.

A balanced XLR interconnection input and output shall be provided in combination with an insertion/cascade selector. In insertion mode it shall be possible to connect an external sound processing device, e.g. an equalizer, between these connectors. In the cascade mode it shall be possible to cascade multiple pre-amplifiers to increase the number of input channels. Also, it shall be possible to use the interconnection input as an emergency input with a built-in signal level detector (VOX), by means of an internal switch. If an emergency audio signal is detected, this input shall overrule all other inputs and even bypass the master volume control. The emergency input shall have its own internal volume preset.

In order to get a message through although a local volume control has been set to a low volume level for e.g. background music, override relay contacts shall be provided for overriding local loudspeaker volume controls. Upon closing one of the input channel priority contacts, this relay shall be activated. For the emergency input another VOX activated relay shall be provided to trigger external equipment or for local volume control override. An overload protected 24Vdc output shall be available to supply power to external relays.

In parallel to the balanced XLR master output an additional microphone level output shall be available on a DIN connector, to provide a signal to e.g. a mixing desk or microphone mixer amplifier.

The unit shall have a tape output, using Cinch connectors to facilitate recording.

A monitor selector with headphone connector and LED VU-meter shall allow for monitoring of the master output or one of the input channels.

The unit shall have an operating temperature range of –10 to +55°C and shall be 19”-wide and 2U-high. Brackets for 19”-mounting shall be included. The unit shall comply to EN55103-1 and EN55103-2 for EMC emission and immunity.

The pre-amplifier shall be a Plena model LBB1920/00, manufactured by Bosch Security Systems.