Bosch LBB 1938/20 User Manual

Communications Systems | LBB 1938/20 Plena Power Amplifier
LBB 1938/20 Plena Power Amplifier
www.boschsecurity.com
u 480 W power amplifier in a 3U high 19”housing
u EN 54‑16 certified and EN 60849 compliant
u 70 V / 100 V and 8 ohm outputs
u Dual inputs with priority switching
u 100 V input for slave operation on 100 V speaker
line
The LBB 1938/20 is a powerful 480 W power amplifier
in a 3U high 19”case for rack mounting or tabletop
use. LEDs on the front panel show the status of the
amplifier: power, audio output level, and supervised
functions. This high-performance unit fulfills a wide
range of public address requirements at a surprisingly
low cost.
Functions
Dependability
The amplifier is protected against overload and short
circuits. A temperature-controlled fan ensures high
reliability at high output levels and low acoustic noise
at lower output levels. An overheat protection circuit
switches off the power stage and activates an LED on
the front panel, if the internal temperature reaches a
critical limit due to poor ventilation or overload.
The unit operates both on mains power and on a 24 V
battery power supply for emergency back up, with
automatic switchover.
For emergency and evacuation use, the following
functions are monitored: mains presence, battery
present, pilot tone presence, amplifier operation.
Front panel LEDs indicate the status of supervised
functions. The LEDs of pilot tone supervision and
battery status can be switched off for general public
address use. Failsafe (normally energized) relays are
provided for each supervised function. These relays
are always active regardless of the switches on the
rear panel.
Input
The system has two balanced inputs with priority
control, each with a loop-through facility. This makes it
easy to connect remote systems that require priority
control. An additional 100 V line input is provided to
connect the amplifier to a 100 V loudspeaker line, to
provide more power to remote locations.
Gain or level control is located on the rear of the unit
to avoid accidental setting change. A meter with LED-
bar shows the output level.
Output
The amplifier has 70 V and 100 V outputs for constant
voltage loudspeaker systems and a low impedance
output for 8 ohm loudspeaker loads.
The LBB 1938/20 has two separate priority controlled
100 V outputs for zones that only need
announcements made via the priority input, and for
zones that will not get any announcements made via
the priority input.

Bosch LBB 1938/20 Specifications

General

Number of Channels	1
Damping factor (at 1 kHz)	>100
Priority input	Yes
TEL. / 100 V input	Yes
Loop-through output	Yes
Nominal level loop-through output	0 dBu
Headphones output	Yes
Power Supply	100 - 240 V AC, 50/60 Hz
Mains voltage	100 - 240 V AC, 50/60 Hz
S/N (flat, max. gain, rated output)	> 70 dB
Signal-to-Noise Ratio	> 70 dB
Ambient temperature	0 °C to +45 °C
Storage temperature	+70 ºC
Output Impedance	8 ohm

Summary

Product Functions

Dependability Features

Details protection against overload, short circuits, overheat, and battery backup for emergency use.

Input Signal Handling

Describes dual balanced inputs with priority control, loop-through, and 100V slave input.

Output Options

Details 70V/100V constant voltage and 8-ohm low impedance loudspeaker outputs.

Controls, Specifications, and Certifications

Front and Back Panel Controls

Lists front panel indicators and controls, plus back panel connectors and switches.

Certifications and Approvals

Lists safety, immunity, emission, and emergency compliance standards like EN standards.

Included Components

Lists the amplifier, power cord, mounting brackets, and installation manual.

Electrical and Performance Specs

Details voltage, current, power consumption, frequency response, and distortion metrics.

Mechanical, Environmental, and Ordering

Mechanical and Environmental Details

Covers dimensions, weight, mounting, operating temperatures, and humidity.

Product Ordering Information

Provides a summary of the amplifier and its order number for purchase.