Bosch LBB 1925/10 Plena System Pre-Amplifier

The Plena system pre-amplifier is a versatile, high- performance unit with call and mono BGM (background music). It fulfills a wide variety of public address requirements at a surprisingly low cost. It can provide dual channel operation for simultaneous calls and BGM for up to six different zones, using two Plena amplifiers.

Function

The call channel provides two inputs for the Plena call stations, LBB 1941/00 (all-call) or LBB 1946/00 (six- zone), with loop-through capability, and universal, balanced input. One is a 3-pin XLR connector for microphone or line level (selectable), and the other is a 5-pin DIN-connector with all‐call priority contact, which may also be used to start one of the available chime attention signals.

The microphone input has a selectable speech filter for improved intelligibility, a volume control, and bass and treble tone controls with shelving characteristics optimized for speech. The call channel is available on the balanced XLR master output.

The BGM channel provides three inputs on stereo cinch-connectors, converted to mono, with front panel selection, volume control and bass and treble tone controls with shelving characteristics optimized for music. The BGM channel has a direct output on balanced XLR for dual channel operation. It can also feed the master output, with the lowest priority, for single channel operation. Zone selector switches on the front panel control the BGM routing. An overload protected 24 VDC output provides power for driving external relays, often making an external power supply unnecessary.

An emergency/telephone input with signal level detector (VOX) and volume preset has the highest priority to all zones. Two trigger inputs (contact closure) activate alarm or time signals to pre-selected zones. Many different chime tones are available. A PC audio input with RS-232 control provides software controlled zone configuration, or automatic messaging in combination with the LBB 1965/00 Plena Message Manager. There are six levels of priority available for BGM, microphone, call stations, trigger inputs and emergency input. A set of relays directs the amplifier output(s) to different loudspeaker groups (zone switching).

LBB 1925/10 Plena System Pre-Amplifier

Each zone has a tri-state control on the front panel that can turn it off, switch it to the call channel, or to the BGM channel. The all‐call microphone input and emergency activation override the call station selection on the call channel. Each zone has separate priority overrides with preset volume levels. This assures an appropriate message volume, independent of any local volume settings, such as for BGM. Both three‐wire and four‐wire override schemes are supported. An override also activates a voltage-free contact (call-active) available for external control and monitoring. The master output channel, or one of the input channels, can be monitored through the headphone connector and/or the LED VU‐meter.

Controls and indicators Front

• LED power meter
• Power on LED
• Call active LED
• Three knobs for mic/line volume, treble, and bass levels
• Three knobs for BGM volume, treble, and bass levels
• BGM source selection knob
• Six zone-selections keys
• Six zone status LEDs
• On/off switch

Back

• EMG input volume control
• Main voltage switch

Interconnection Front

• Headphone Jack

Back

• One (DIN or XLR) Mic/line input
• Two (DIN/DIN) call station inputs
• PC audio (cinch) input
• Priority input
• Master (XLR) output
• BGM (XLR) output
• Emergency signal input
• Two trigger inputs
• RS-232 (DE-9)
• Three (cinch) CD, tape, aux inputs
• Six 100 V speaker outputs
• 24 VDC output
• 24 VDC input
• Three control inputs
• Ground screw
• IEC mains socket

Technical specifications

Electrical Mains power supply

• Voltage : 230/115VAC, ±15%, 50/60 Hz
• Current inrush : 230/115 VAC, 1.5/3 A
• Max power consumption : 25 VA

Battery power supply

• Voltage : 24 VDC, +10% / -15%
• Current max : 1A

Performance

• Frequency response ; 50 Hz to 20 kHz (+1 / -3 dB)
• Distortion : <0.5%
• Bass control : ±10 dB @ 100 Hz
• Treble control : ±10 dB @ 10 kHz
• Channel separation : >70 dB @ 1 kHz
• Priority mute : >40 dB
• Dynamic range : 100 dB
• Mic/line input : 1x
• Connectors : 5‐pin DIN, 3‐pin XLR, balanced, with phantom power
• Sensitivity : 1 mV (mic), 200 mV (line)
• Impedance : >1 kohm (mic); >5 kohm (line)
• S/N (flat at max volume) : >63 dB (mic); >70 dB (line)
• S/N (flat at min volme/muted) : >75 dB
• CMRR : >40 dB (50 Hz – 20 kHz)
• Headroom : >25 dB
• Speech filter : -3 dB @ 315 Hz, high-pass, 6 dB/oct
• Phantom power supply : 16 V via 1.2 kohm, (mic mode only)
• Line input : 3x
• Connector : Cinch, stereo converted to mono, unbalanced
• Sensitivity : 200 mV
• Impedance : 22 kohm
• S/N (flat at max volume) : >70 dB
• S/N (flat at min volume/ muted) : >75 dB
• Headroom : >25 dB
• Master output : 1x
• Connector : 3-pin XLR, balanced
• Nominal level : 1V
• Impedance : <100 ohm
• Tape output : 1x
• Connector : Cinch, 2 x mono
• Nominal level : 350 mV
• Impedance : <1 kohm
• Headphone output : 1x
• Connector : 6.3 mm jack stereo, signal mono
• Nominal level : 3V
• Impedance : <100 ohm
• Zone relays : 5A
• Contacts voltage : 250 V
• Contacts current : 8A
• Interconnection input / emergency : 1x
• Connector ; 3-pin XLR, balanced
• Sensitivity : 200 mV (interconnection), 100 mV to 1 V adjustable (emergency)
• Impedance : >10 kohm
• VOX threshold : 45 mV (emergency)
• Interconnection output : 1x
• Connector : 3-pin XLR, balanced
• Nominal level : 200 mV
• Impedance : <100 ohm
• Relay contacts ; 30 V, 1 A
• DC supply output voltage : 24 V, 250 mA max

Mechanical

• Dimensions (H x W x D) : 100 x 430 x 270 mm (19" wide, 2U high)
• Weight : Approx. 5 kg
• Mounting : Standalone, 19" rack
• Colour : Charcoal

Environmental

• Operating temperature : -10 oC to +55 oC (14 oF to +131 oF)
• Storage temperature : -40 oC to +70 oC (-40 oF to +158 oF)
• Relative humidity : <95%

Ordering information

LBB 1925/10 Plena System Pre-Amplifier 6-zone, 2-channel distribution system unit with call and BGM (background music) Order number LBB1925/10