Bose 901 Equalizer User Manual

The Bose 901 Active Equalizer is a critical component designed specifically for use with the Bose 901 Direct/Reflecting® speaker system. It provides precise electronic equalization to correct the speaker's frequency response, ensuring optimal acoustic performance. The equalizer connects between your preamplifier and power amplifier, featuring input/output jacks, level controls, and defeat switches. Below are key sections covering features, installation, setup, operation, specifications, and troubleshooting.

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

Features at a Glance

Key components: Equalizer unit with level controls, input/output jacks, defeat switch, and power indicator.

Feature	Description
Input Jacks	For connection from preamplifier tape output or source
Output Jacks	For connection to power amplifier input
Level Controls	Adjusts equalization intensity for proper balance
Defeat Switch	Bypasses equalizer for direct signal comparison
Power Indicator	LED shows unit is powered on
AC Power Input	For connection to standard wall outlet

Installation

Unpack and inspect contents. Place near your amplifier/preamplifier.

Connect to audio system: Use RCA cables to connect from preamp tape output to equalizer input.
Connect to amplifier: Run cables from equalizer output to power amplifier input.
Connect speakers: Ensure Bose 901 speakers are properly connected to amplifier outputs.
Plug equalizer into AC power.

WARNING! Always turn off all components before making connections to prevent damage.

First-Time Setup

Power on all components; follow setup procedure.

Set initial levels: Turn level controls to midpoint (12 o'clock position).
Play test music: Use familiar music with wide frequency range.
Engage equalizer: Ensure defeat switch is OFF (equalizer active).
Adjust levels: Fine-tune level controls while listening for balanced sound.

CAUTION! Do not operate at extremely high volume during initial setup.

Specifications

Type: Active electronic equalizer
Frequency Response: Tailored for Bose 901 speaker correction
Input Impedance: 10k ohms
Output Impedance: 1k ohms
Signal-to-Noise Ratio: >90dB
Total Harmonic Distortion: <0.05%
Power Requirements: 120V AC, 60Hz, 5W
Dimensions: Standard component width (approx. 17")

Controls and Settings

Front Panel: Level controls (typically two for different frequency ranges), defeat switch, power indicator.

Operation: Level controls adjust equalization curve intensity. Defeat switch bypasses equalization for A/B comparison with direct signal.

Optimal Settings: Start with controls at midpoint. Adjust while listening to achieve natural, balanced sound across all frequencies.

Connecting to Your System

Standard connection: Preamplifier → Equalizer → Power Amplifier → Bose 901 Speakers.

Turn off all system components.
Connect preamp TAPE OUT to equalizer INPUT using RCA cables.
Connect equalizer OUTPUT to power amp INPUT using RCA cables.
Ensure all connections are secure and cables are undamaged.

Tip: Use high-quality shielded cables for best performance.

Operation and Adjustment

The equalizer must remain in the system whenever Bose 901 speakers are used.

Normal operation: Keep defeat switch OFF (equalizer active).
Level adjustment: Make small adjustments while listening to various music types.
A/B comparison: Use defeat switch to compare equalized vs. unequalized sound.
System matching: Adjust levels to match your room acoustics and listening position.

WARNING! Never operate Bose 901 speakers without the equalizer connected and active.

Care & Maintenance

Unplug before cleaning. Use dry, soft cloth only; avoid liquids.

Keep unit in well-ventilated area away from heat sources and moisture.

CAUTION! Do not open unit; no user-serviceable parts inside.

Regulatory Information

FCC Part 15: Class B digital device; complies with interference limits. Copyright © Bose Corporation. All rights reserved. Bose and 901 are registered trademarks of Bose Corporation. For support, visit www.bose.com or contact Bose customer service.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No sound	Incorrect connections/power	Check all cable connections; ensure power is on; verify defeat switch position.
Distorted sound	Levels too high	Reduce level controls; check amplifier volume.
Hum or noise	Ground loop/cable issues	Ensure proper grounding; check cable quality and routing.
Unequalized sound	Defeat switch engaged	Switch defeat to OFF position for normal operation.
Incorrect frequency balance	Level control settings	Readjust level controls; refer to setup guidelines.

Service: Contact authorized Bose service center. Do not attempt internal repairs.