Bose PM4250 Manual

The Bose PM4250 is a professional power amplifier designed for commercial and installed sound applications. It delivers reliable, high-quality audio amplification with features such as thermal protection, short-circuit protection, and versatile input/output connectivity. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

Features at a Glance

Key components: High-efficiency power amplifier module, front panel controls, rear panel input/output connectors, cooling fan, protection circuitry.

Feature	Description
Power Output	High power output for professional audio applications
Input Connectors	XLR and 1/4" TRS balanced inputs
Output Connectors	Binding posts and Speakon connectors for speaker connections
Protection Circuits	Thermal, short-circuit, and overload protection
Cooling System	Variable-speed fan for efficient thermal management
LED Indicators	Power, signal, clip, and protection status indicators
Gain Controls	Independent level controls for each channel
Bridge Mode	Capability to bridge channels for mono operation
Rack Mountable	Standard 19-inch rack mount design
AC Power Input	Standard IEC power connector

Installation

Unpack and inspect contents. Ensure proper ventilation and secure mounting.

1. Rack mounting: Use appropriate rack ears and screws to secure amplifier in 19-inch rack.
2. Connect audio inputs: Use balanced XLR or 1/4" TRS cables from mixer or source.
3. Connect speakers: Use appropriate gauge speaker wire to binding posts or Speakon connectors.
4. Connect AC power: Use IEC power cable to appropriate power outlet.

WARNING! Ensure proper ventilation to prevent overheating. Use secure mounting hardware.

First-Time Setup

Power on amplifier; verify proper operation.

1. Set gain controls: Start with gain controls at minimum (fully counterclockwise).
2. Connect audio source: Play test signal through connected mixer or source.
3. Adjust levels: Slowly increase gain controls until desired output level is achieved.
4. Verify operation: Check all LED indicators for normal operation (power on, signal present).

CAUTION! Always power off amplifier when making connections. Ensure proper speaker impedance matching.

Specifications

• Power Output: High power rating (consult specific model documentation).
• Frequency Response: 20Hz - 20kHz, ±0.5dB.
• Total Harmonic Distortion: <0.05% at rated power.
• Signal-to-Noise Ratio: >100dB, A-weighted.
• Input Sensitivity: Adjustable via gain controls.
• Input Impedance: Balanced: 20k ohms.
• Cooling: Variable-speed fan with thermal control.
• Power Requirements: 120V/240V AC, 50/60Hz (model dependent).
• Dimensions: Standard 19-inch rack width.
• Weight: Varies by model.

Controls and Settings

Front Panel: POWER switch, CHANNEL 1/2 gain controls, LED indicators (POWER, SIGNAL, CLIP, PROTECT).

Rear Panel: AC power input, input connectors (XLR/TRS), output connectors (binding posts/Speakon), bridge mode switch, ground lift switch.

Operation: Adjust gain controls for desired output level. Monitor CLIP indicators to avoid distortion. Use bridge mode for mono operation when needed. Ground lift switch can help eliminate ground loop hum.

Connecting Devices

Audio Inputs: Balanced XLR or 1/4" TRS from mixer. Speaker Outputs: Binding posts or Speakon to speakers.

1. Turn off all equipment before making connections.
2. Use balanced cables for noise reduction in long cable runs.
3. Ensure proper polarity when connecting multiple speakers.
4. Verify speaker impedance matches amplifier requirements.

Tip: Use appropriate gauge speaker wire for the distance and power level.

Operation

Designed for continuous professional use.

1. Power sequence: Turn on connected sources first, then amplifier. Turn off amplifier first when powering down.
2. Level adjustment: Use gain controls to match input levels from source equipment.
3. Monitoring: Watch CLIP indicators - occasional flashing is normal, constant illumination indicates excessive input level.
4. Bridge mode: Switch to bridge mode for mono operation, connect speaker between CH1 positive and CH2 positive terminals.
5. Thermal management: Ensure adequate ventilation; fan speed will increase with temperature.

WARNING! Do not operate with CLIP indicator constantly illuminated. Avoid operating into impedance lower than specified.

Protection Features

Thermal Protection: Automatically reduces output or shuts down if overheating detected. Short-Circuit Protection: Protects amplifier output stage from shorted speaker connections. Overload Protection: Prevents damage from excessive input signals. DC Protection: Protects speakers from DC offset at amplifier output.

Care & Maintenance

Keep amplifier clean and free of dust. Ensure ventilation openings are unobstructed.

CAUTION! Unplug from power before cleaning. Use dry cloth only; do not use liquids or compressed air directly on components.

Regulatory Information

Complies with applicable safety and EMC standards. Copyright © Bose Corporation. All trademarks are property of Bose Corporation. For technical support, visit www.bose.com or contact Bose Professional support services.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No power	Power cable/outlet	Check power cable connection; verify outlet has power; check circuit breaker.
No audio output	Input connections/settings	Verify input source is active; check gain control settings; inspect input cables.
Distorted audio	Overload/clipping	Reduce input level; check for CLIP indicator illumination; verify speaker impedance.
Protection mode active	Overheating/short circuit	Allow amplifier to cool; check for shorted speaker wires; ensure proper ventilation.
Hum or buzz	Ground loop/cables	Try ground lift switch; use balanced cables; ensure proper grounding of all equipment.

Reset: Power cycle amplifier if protection mode is engaged.

Service: Contact Bose Professional support or authorized service center.