Bose MA 3 Amplifier Manual

The Bose MA 3 is a professional-grade power amplifier designed for high-fidelity audio applications, offering robust power output, advanced thermal management, and reliable performance. It features balanced XLR and unbalanced RCA inputs, Speakon and binding post outputs, protection circuits (thermal, short-circuit, DC offset), gain controls, and status indicators. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Settings 6. Connecting Devices 7. Operation Modes 8. Protection Features 9. Care & Maintenance 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: High-efficiency power supply, toroidal transformer, advanced cooling system, protection circuitry, input/output connectors, status LEDs.

Feature	Description
Input Connectors	Balanced XLR and unbalanced RCA inputs
Output Connectors	Speakon NL4 and binding post speaker outputs
Gain Controls	Independent level adjustment per channel
Status Indicators	Power, Signal, Clip, and Protect LEDs
Protection Circuits	Thermal, short-circuit, DC offset, and overload protection
Cooling System	Variable-speed fan with temperature sensing
Power Switch	Front-panel rocker switch with standby indicator
Bridge Mode	Switch for mono bridged operation
Ground Lift	Switch to eliminate ground loop hum
Rack Mount	Standard 19-inch rack mountable with included ears

Installation

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

Rack mounting: Attach rack ears using provided screws; secure in rack with adequate space for airflow.
Connect audio inputs: Use balanced XLR cables from mixer/preamp to amplifier inputs.
Connect speakers: Use appropriate gauge speaker cable to Speakon or binding post outputs.
Connect power: Plug into grounded AC outlet matching voltage rating.

WARNING! Amplifier is heavy; use two people for rack mounting. Ensure proper ventilation to prevent overheating.

First-Time Setup

Power on amplifier; verify status indicators.

Set gain controls: Turn to minimum (fully counterclockwise) before powering on.
Power sequence: Turn on connected sources first, then amplifier; reverse for shutdown.
Adjust gain: Gradually increase gain while playing audio to achieve desired level without clipping.
Verify operation: Check that Signal and Power LEDs illuminate normally; no Protect LED.

CAUTION! Always use proper power sequencing to avoid speaker damage from turn-on/off thumps.

Specifications

Power Output: 300W per channel at 8Ω, 500W per channel at 4Ω (stereo).
Frequency Response: 20Hz - 20kHz, ±0.1dB.
Total Harmonic Distortion: <0.05% at rated power.
Signal-to-Noise Ratio: >105dB, A-weighted.
Input Sensitivity: 1V for rated output (adjustable via gain).
Input Impedance: 20kΩ balanced, 10kΩ unbalanced.
Damping Factor: >200 at 8Ω.
Cooling: Variable-speed fan, rear exhaust.
Power Requirements: 120V/230V AC, 50/60Hz, auto-switching.
Dimensions: 19" x 5.25" x 15" (rack width x height x depth).
Weight: 35 lbs (15.9 kg).

Controls and Settings

Front Panel: Power switch, Gain controls per channel, Bridge mode switch, Status LEDs (Power, Signal, Clip, Protect). Rear Panel: Input connectors, Output connectors, Ground lift switch, AC inlet, Circuit breaker.

LED Indicators: Power (green) - AC power present; Signal (green) - input signal detected; Clip (yellow) - clipping detected; Protect (red) - protection circuit active.

Gain Control: Adjusts input sensitivity from minimum to +26dB. Bridge Mode: Combines both channels for mono operation (check manual for proper wiring). Ground Lift: Breaks ground connection between input and chassis to eliminate hum.

Connecting Devices

Inputs: XLR balanced (pins: 1-ground, 2-hot, 3-cold) or RCA unbalanced. Outputs: Speakon (pin 1+: ch A+, 1-: ch A-; pin 2+: ch B+, 2-: ch B-) or binding posts (+/- per channel).

Turn off all equipment before making connections.
Use shielded cables for inputs; keep away from power cables.
For bridged mode: Connect speaker between CH A+ and CH B+; set bridge switch.
Ensure proper polarity: Maintain consistent +/- connections to speakers.

Tip: Use appropriate speaker wire gauge for cable length and impedance to minimize power loss.

Operation Modes

Supports stereo, parallel, and bridged mono operation.

Stereo: Normal two-channel operation; inputs to respective channels.
Parallel: Input to CH A; internal jumper routes to CH B for identical output.
Bridged Mono: Combines both channels for higher power; use bridge switch and proper speaker connection.
Protection Monitoring: LEDs indicate normal operation, clipping, or fault conditions.
Cooling Fan: Automatically adjusts speed based on heat sink temperature.

WARNING! Do not operate in bridged mode into loads below 8Ω. Verify speaker impedance matches amplifier capability.

Protection Features

Thermal Protection: Automatically reduces output or shuts down if overheating. Short-Circuit Protection: Limits current if output is shorted. DC Offset Protection: Shuts down if DC detected at output. Overload Protection: Limits output during sustained clipping.

Care & Maintenance

Unplug before cleaning. Use dry cloth to remove dust; vacuum vents periodically. Ensure ventilation paths are unobstructed.

CAUTION! Do not use liquids or compressed air inside unit. Service by qualified personnel only.

Regulatory Information

FCC Part 15: Class A digital device; may cause interference in residential areas. CE compliant. Copyright © Bose Corporation. All trademarks are property of Bose Corporation. For support, visit www.bose.com or contact Bose Professional support.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No power (LED off)	Power cable/breaker	Check AC connection; reset circuit breaker on rear panel.
Protect LED lit	Overheat/short/DC fault	Allow cooling; check speaker wires for shorts; disconnect and power cycle.
No sound output	Gain/connections/mute	Increase gain; verify input signal and cable connections; check source mute.
Distorted sound	Clipping/overload	Reduce gain; check input level; ensure proper load impedance.
Hum or buzz	Ground loop/cables	Engage ground lift switch; use balanced cables; reroute away from power cables.
Fan noise excessive	Dust/overheating	Clean vents; ensure adequate ventilation; check ambient temperature.

Reset: Power cycle amplifier after correcting fault condition.

Service: Contact Bose Professional support or authorized service center.