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 LEDbar 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.
2 | LBB 1938/20 Plena Power Amplifier
Controls and indicators
Front
• Meter (LED's for -20, -6, 0 dB and Power ON)
• Battery operation indicator
• Overheat indicator
• Air inlet for forced air cooling
Back
• Level control input 1
• Level control input 2
• Power button
• Mains switch
Interconnections
Back
• Priority line input 1 (XLR/balanced)
• Line loop-through 1 (XLR/balanced)
• Program line input 2 (XLR/balanced)
• Line loop-through 2 (XLR/balanced)
• Priority controlled loudspeaker output terminals
• 24 VDC power supply terminal
• Three loudspeaker direct output terminals
• Two 100 V slave input terminals
• Input 2 enable control terminal
• Input 1 priority control terminal
• Earth connection screw
• Mains socket
Certifications and approvals
Battery power supply
Voltage 24 VDC +15% / -15%
Current max 30 A
Performance
Output power (rms/maximum) 480 W / 720 W
Power reduction on backup
power
Frequency response 50 Hz to 20 kHz (+1/‑3 dB @ ‑10 dB
Distortion <1% @ rated output power, 1 kHz
S/N (flat at max volume) >90 dB
Line inputs 2 x
Connector 3-pin XLR, balanced
Sensitivity 1 V
Impedance 20 kohm
CMRR >25 dB (50 Hz to 20 kHz)
Gain 40 dB
100 V input
-1 dB
ref. rated output)
Safety acc. to EN 60065
Immunity acc. to EN 50130‑4
Emission acc. to EN 55103‑1
Emergency acc. to EN 54‑16 / EN 60849
Region Certification
Europe CE
CPD
Poland CNBOP
Parts included
Quantity Component
1 LBB 1938/20 Plena Power Amplifier
1 Power cord
1 Set of 19" mounting brackets
1 Installation and User Instructions
Technical specifications
Electrical
Mains power supply
Voltage 230 VAC, ±10%, 50/60 Hz
Inrush current 19 A
Max power consumption 2200 VA
Connector Screw, unbalanced
Sensitivity 100 V
Impedance 330 kohm
Line loop-through output 2 x
Connector 3-pin XLR
Nominal level 1 V
Impedance Direct connection to line input
Loudspeaker outputs 3 x
Connector Screw, floating
Direct output 100 V, 70 V, 8 ohm
Priority only (from input 1) 100V or 70 V internally selectable
Music (non-priority) only 100V or 70 V internally selectable
Power consumption
Mains operation
Max power 990 W
-3dB 715 W
-6dB 510 W
Pilot tone* 110 W
Idle 25 W
24 VDC operation
Max power 32 A (770 W)
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