Bosch // Plena Power Amplifier

Description

LBB 1938/20 Plena Power Amplifier 480 W power amplifier in a compact housing 70 V / 100 V and 8 ohm outputs
Dual inputs with priority switching 100 V input for slave operation on 100 V speaker line Temperature controlled forced front to back ventilation, directly stackable. Mains, battery back-up and pilot tone supervision

The LBB 1938/20 is a very powerful 480 W power amplifier with supervision on the functioning of
amplifier, on power supply of both mains and batteryback up and on overheating. These supervised functions
are indicated on the front panel by 4 LED's. This highperformance mono amplifier is capable of fulfilling a
wide variety of public address requirements. The LBB 1938/20 comes in a 19", 3U high housing for tabletop
use and rack mounting.

Functions

The amplifier is protected against overload and short circuits. A temperature-controlled fan ensures high
reliability at high output power and low acoustic noise at lower power output. Additionally, the power amplifier
has an overheat protection circuit that switches off the power stage if the internal temperature reaches a critical
limit due to poor ventilation or overload. On the LBB 1938/20 this is shown by the front panel overheat
indicator.

The LBB 1938/20 has two balanced inputs with priority control, each with a loop-through facility. This allows for
easy and automatic switching between e.g. a local music source and a priority announcement from a remote
system. An additional 100 V line input is provided to connect the power amplifier to a 100 V loudspeaker line,
for additional output power e.g. on remote locations.

Supervision is implemented for functioning of the amplifier. Three relays are provided on the rear panel for
each supervised function. The relays are normally energized (fail safe) and have three contacts each
(normally open, common, normally closed).
If supervision is not necessary, it is possible to switch off the indicators on the front panel by switches next to
the relay outputs (to prevent the fault indicators from lighting up continuously). The relays are always
functioning regardless of the settings of these switches. The pilot tone supervision monitors the presence of a
20kHz pilot tone. The pilot tone level input is 100mV -20dBV for input, and thus -20dB ref max power. Pilot
tone supervision is done after the power stage at the loudspeaker line connections, thus monitoring the
correct functioning of the amplifier.

Sensitivity or level control is located on the rear of the unit to avoid accidental setting change. A VU-meter with
LED-bar shows the output level.

▶ 480 W power amplifier in a 3U high 19”housing

▶ 70 V / 100 V and 8 ohm outputs

▶ Dual inputs with priority switching

▶ 100 V input for slave operation on 100 V speaker line

▶ Temperature controlled forced front to back ventilation, directly stackable

▶ Mains, battery back-up, and pilot tone supervision

▶ EN 54‑16 and EN 60849 complian

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