Power Amplifier LBB-1938/20

Bosch – LBB1938/20 – Plena Booster / Power Amplifier


Bosch – LBB1938/20 – Plena Booster / 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

LBB 1938/20 Plena Power Amplifier The amplifier has 70 V and 100 V outputs for constant voltage loudspeaker systems and a low impedance output for 8 Ohm loudspeaker loads.

LBB 1938/20 Plena Power Amplifier 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 battery- back up and on overheating. These supervised functions are indicated on the front panel by 4 LED’s. This high- performance 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 table- top use and rack mounting.


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


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.

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. The power amplifier operates both on mains power and on a 24 V battery power supply for emergency back-up, with automatic switchover. The LBB 1938/20 has a front panel LED that indicates when the unit is battery operated.

Technical Specifications


Mains Voltage 230 VAC, ±10%, 50 / 60 Hz, Max Mains Power Consumption 1000 VA

Max Mains Inrush Current 16 A, Battery voltage 24 VDC, +20% / -10%, Max Battery Current 30 A

Battery Operation -1 dB ref. rated power Performance, Frequency Response 60 Hz – 20 kHz (+1/-3 dB,

@ -10 dB ref. rated output), Distortion <1%@rated output power, 1 kHz S/N (flat at max volume) >90 dB.


Line input (3-pin XLR, 6.3mm phone jack, balanced), Line Input 1, 2 (3-pin XLR, balanced) Sensitivity 1 V

Impedance 20 kOhm, CMRR >25 dB (50 Hz – 20 kHz), Gain 40 dB 100 V Input (Screw, unbalanced)

Sensitivity 100 V, Impedance 330 kOhm, Outputs Line Loop-through Output (3-pin XLR, 6.3mm phone jack, balanced), Line Loop-through Output 1,2 (3-pin XLR, balanced), Nominal Level1 V, Impedance Direct connection to line input, Loudspeaker Outputs (Screw, floating)

Max/rated Output Power 70 / 100 V Output : 720 W / 480 W, 8 ohm Output 62 V (480 W) Output Power @ 24 V

Power consumption

230/115 power W, Max power 986.7W


Operating Temperature -10 to +55ºC, Storage Temperature -40 to +70ºC, Relative Humidity <95%

Acoustic Noise Level of Fan <48 dB SPL @ 1 m, Dimensions 145 x 430 x 370 mm

(19″ wide, 3U high, with feet), Weight approx. 25 kg