Communications Systems | LBB 1920/00 Plena Universal Pre-Amplifier
LBB 1920/00 Plena Universal Pre-Amplifier
www.boschsecurity.com
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Four universal low-noise input channels for
microphone or line
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Separate tone control, speech filter and direct
output per channel
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Selectable blocking, serial and mixing priorities
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Multifunctional inter-connection point
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Priority and emergency relay outputs
The Plena Pre-Amplifier is a versatile, high-
performance unit with four mono-input channels. It
fulfills a wide variety of public address requirements at
a surprisingly low cost.
Functions
All input channels provide the choice of a balanced
3‑pin XLR-connector for microphone or line level
(selectable), a balanced 5‑pin DIN-connector for
microphone or line level with priority contact, or a line
level stereo cinch-connector, converted to mono.
Microphone inputs have a phantom power supply.
Each input channel has its own volume and tone
control, a selectable speech filter to reduce the bass
content of the speech signal for improved
intelligibility, and a balanced, direct output on XLR,
that bypasses the channel controls.
Three priority modes are available for the input
channels. In blocking mode the input channel that is
activated first gets priority over all other input
channels. In serial mode input channel 1 has priority
over channels 2, 3 and 4; channel 2 has priority over
channels 3 and 4; and channel 3 has priority over
channel 4. Each of the input channels can be mixed to
the master output, irrespective of priority, by
separately setting that channel to the mixing mode.
Balanced XLR interconnection input and output are
provided in combination with an insertion/cascade
selector. In insertion mode an external sound
processing device, e.g. an equalizer, can be connected
between these connections. In the cascade mode,
multiple LBB1920/00 pre-amplifiers can be cascaded
to increase the number of input channels to 8, 12, or
even more. Internally the interconnection input can be
switched as an emergency input with a signal level
detector (VOX). If an emergency audio signal is
detected, this channel overrides all others. The
emergency input channel has its own volume preset
and bypasses the master volume control.
For the emergency input another VOX activated relay is
provided to trigger external equipment or for local
volume control override. An overload protected 24
VDC output provides power for driving external relays,
making an external power supply unnecessary.
An additional microphone level output is available on
the DIN connector, parallel to the balanced XLR
master output. This provides an input signal for a
mixing desk or a microphone input channel for a mixer
amplifier, such as the Plena LBB 19xx/10. A tape
output is also available.
