Bosch LBB-1920 Plena Universal
Mixer Pre-Amplifier

*Four universal low-noise input channels for microphone or line
* Separate tone control, speech filter and direct output per channel
*Selectable blocking, serial and mixing priorities
* Multifunctional inter-connection point
*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.

The master output channel, or one of the input channels, can be selected to be monitored with headphone connector and LED meters

Controls and indicators
Front
• LED power level bar • Power on indication LED (green) • Power button
• Four treble control knobs • Four bass control knobs • Four channel volume control knobs
• Master volume control knob • Headphone channel selection knob
Back
• Mains voltage switch • Insertion/ cascade switch

Technical specifications: Electrical
Mains power supply Voltage 230/115 VAC, ±15%, 50/60 Hz, Inrush current 1.5 A at 230 VAC / 3 A at 115 VAC
Max power consumption 25 VA, Battery power supply Voltage 24 VDC, +15% / -15%
Frequency response 50 Hz to 20 kHz (+1 / -3 dB), Distortion Treble control ±10 dB at 10 kHz, Channel separation >70 dB at 1 kHz

Dimensions (H x W x D) 100 x 430 x 270 mm (19″ wide, 2U high)
Weight Approx. 5 kg, Mounting Standalone, 19” rack, Color Charcoal