Bose 901 Series II Equalizer Manual

The Bose 901 Series II Active Equalizer is a critical component designed specifically for use with the Bose 901 Series II Direct/Reflecting® speakers. It provides precise electronic equalization to compensate for the speakers' unique acoustic characteristics, ensuring flat frequency response and optimal sound reproduction. The equalizer connects between your preamplifier and power amplifier, featuring input/output jacks, level controls, and contour adjustments. Below are key sections for overview, installation, operation, specifications, and troubleshooting.

1. Overview & Features 2. Installation & Connections 3. Operation & Controls 4. Technical Specifications 5. Equalization Theory 6. System Setup & Calibration 7. Maintenance & Care 8. Warranty & Support 9. Troubleshooting

Overview & Features

The Bose 901 Series II Equalizer is an active, solid-state unit essential for proper operation of the 901 Series II speaker system. It corrects the speaker's response to achieve a balanced, natural sound.

Feature	Description
Active Equalization	Provides precise frequency contouring for flat acoustic output
Input/Output Jacks	RCA-type connectors for system integration
Level Controls	Separate controls for each channel to balance output
Contour Switch	Adjusts equalization curve for room acoustics (Normal, Reduced)
Bypass Switch	Allows comparison of equalized vs. unequalized sound
Power Requirement	Operates on standard AC power
Design Purpose	Specifically engineered for Bose 901 Series II speakers only

Installation & Connections

Proper installation between your preamplifier and power amplifier is crucial for system performance.

Power Off: Turn off and unplug all system components.
Connect to Preamp: Run cables from your preamplifier's output jacks to the equalizer's INPUT jacks.
Connect to Power Amp: Run cables from the equalizer's OUTPUT jacks to your power amplifier's input jacks.
Power Connection: Plug the equalizer's power cord into a grounded AC outlet.
Speaker Connection: Ensure 901 Series II speakers are properly connected to the power amplifier.

IMPORTANT: The equalizer must be used with the Bose 901 Series II speakers. Do not use with other speakers.

Operation & Controls

Front panel controls allow adjustment of the equalization and system balance.

POWER Switch: Turns the equalizer on and off.
LEVEL Controls (Left/Right): Adjust the output level of each channel. Set for equal loudness from both speakers.
CONTOUR Switch: Selects between NORMAL (typical room) and REDUCED (dampened room) equalization curves.
BYPASS Switch: Engages (IN) or disengages (OUT) the equalization circuit for comparison.
Power Indicator: Illuminates when unit is powered on.

Operation Tip: For initial setup, set CONTOUR to NORMAL and BYPASS to IN. Adjust LEVEL controls while playing familiar music.

Technical Specifications

Type: Active solid-state equalizer.
Frequency Response: 20 Hz - 20 kHz (±0.5 dB with equalization engaged).
Total Harmonic Distortion: Less than 0.1% at rated output.
Input Impedance: 47 kΩ.
Output Impedance: 1 kΩ.
Maximum Input Level: 2 Volts RMS for full output.
Power Requirements: 120V AC, 60Hz, 5 Watts.
Connectors: Gold-plated RCA jacks.
Dimensions: (Approx.) 12" W x 2.5" H x 8" D.
Weight: 4.5 lbs (2 kg).

Equalization Theory

The Bose 901 speaker employs a unique design with eight drivers facing rearward and one forward. This Direct/Reflecting® technology requires significant electronic equalization to achieve a flat, natural sound field. The equalizer boosts certain frequencies and attenuates others to compensate for the speaker's inherent acoustic response, ensuring accurate reproduction of the original source material across the entire audible spectrum.

System Setup & Calibration

For optimal performance, follow these calibration steps:

Place speakers according to the 901 Series II manual (typically on stands, away from walls).
With system powered on and playing music, set the equalizer's BYPASS switch to OUT (equalization off).
Set CONTOUR to NORMAL.
Adjust your preamplifier's balance control to center the sound image.
Switch BYPASS to IN (equalization on). The sound should become fuller and more balanced.
Use the equalizer's LEVEL controls to fine-tune the balance if necessary.
Use the CONTOUR switch to adjust for room acoustics (REDUCED for very live, reflective rooms).

Maintenance & Care

Unplug the unit from AC power before cleaning. Use a soft, dry cloth to wipe the exterior. Do not use liquid or aerosol cleaners. Ensure proper ventilation; do not block vents. Avoid exposure to extreme temperatures, moisture, or direct sunlight.

CAUTION: There are no user-serviceable parts inside. Refer servicing to qualified personnel.

Warranty & Support

Refer to the separate warranty card included with your product for specific terms and conditions. For technical support, service, or product information:

Bose Corporation
Customer Service
Tel: 1-800-999-2673
Website: www.bose.com

This product is protected by patents granted and pending. Bose and the Bose medallion symbol are registered trademarks of Bose Corporation.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No sound from system	Equalizer not powered on Incorrect cable connections BYPASS switch in wrong position	Check power switch & indicator light. Verify INPUT/OUTPUT connections. Set BYPASS to IN.
Sound is distorted	Input level too high Faulty cable	Reduce volume at preamplifier. Check and replace audio cables.
Uneven sound between speakers	Level controls misadjusted Speaker placement	Adjust LEFT/RIGHT LEVEL controls. Verify speaker connections and placement.
Hum or noise	Ground loop Poor cable connection	Ensure all components are plugged into the same AC circuit. Secure all cable connections.
No change when using BYPASS	Internal fault	Contact Bose Customer Service for repair.

Note: If problems persist, contact Bose technical support. Do not attempt to open the equalizer casing.