Bose 901 Series 1 Equalizer Manual

The Bose 901 Series 1 Active Equalizer is a critical component designed specifically for use with the revolutionary Bose 901 Direct/Reflecting® speaker system. It provides the precise electronic equalization required to achieve the system's intended acoustic performance, compensating for the unique characteristics of the nine full-range drivers in each speaker enclosure. This manual covers setup, operation, controls, specifications, and maintenance for optimal sound reproduction.

1. Introduction & Overview 2. Key Features & Components 3. Installation & Connections 4. Controls & Operation 5. Technical Specifications 6. Equalization Theory & Application 7. System Setup & Calibration 8. Care & Maintenance 9. Troubleshooting 10. Warranty & Support

Introduction & Overview

The Bose 901 Series 1 speaker system relies on electronic equalization to deliver its acclaimed spacious, lifelike sound. This dedicated equalizer is not a tone control but a sophisticated active filter network that corrects the speaker's frequency response. It must be connected between your preamplifier (or receiver tape monitor loop) and power amplifier to function correctly.

IMPORTANT: The Bose 901 Series 1 speakers must be used with this specific equalizer. Operating the speakers without it will result in improper sound and may risk damaging the speakers or amplifier.

Key Features & Components

Front Panel: POWER switch, LEVEL control, 9-band equalizer sliders. Rear Panel: INPUT FROM PREAMP jacks, OUTPUT TO AMP jacks, AC power cord.

Feature/Component	Description
POWER Switch	Turns the equalizer's active circuitry on/off. System power should be off when toggling.
LEVEL Control	Master gain control to match system output level with other sources.
9-Band Equalizer	Fixed, proprietary EQ curve sliders (typically not user-adjustable for standard operation).
INPUT FROM PREAMP	RCA jacks receiving line-level signal from preamp tape output or receiver tape monitor output.
OUTPUT TO AMP	RCA jacks sending equalized signal to the main power amplifier inputs.
AC Power Cord	Powers the equalizer's internal active circuitry.

Installation & Connections

Proper connection via the tape monitor loop is essential.

Turn off all components. Unplug amplifiers and receivers from AC power.
Connect Equalizer to Preamplifier/Receiver: Use high-quality RCA cables. Plug one pair from your preamp's or receiver's TAPE OUT (or REC OUT) jacks to the equalizer's INPUT FROM PREAMP jacks.
Connect Equalizer to Power Amplifier: Plug a second pair of RCA cables from the equalizer's OUTPUT TO AMP jacks to your power amplifier's MAIN INPUT jacks. If using an integrated amplifier/receiver, connect these to the TAPE MONITOR IN (or PLAY) jacks.
Connect Speakers: Ensure Bose 901 Series 1 speakers are connected to the amplifier's speaker outputs, observing correct polarity (+/-).
Power Up: Plug in AC power. Turn on the equalizer first, then your preamplifier/receiver, then the power amplifier last.

WARNING! Incorrect connection can cause feedback, distortion, or damage. Never connect the equalizer output to a phono input.

Controls & Operation

Normal Listening:

Set the equalizer's LEVEL control to the 12 o'clock (mid) position initially.
On your receiver or preamplifier, engage the TAPE MONITOR switch (or select the Tape Monitor input). This routes the signal through the equalizer.
Play a source and adjust overall volume from your main preamp/receiver volume control.
Fine-tune the equalizer's LEVEL control so that the volume of the 901 system matches that of your other sources (e.g., tuner, phono) when switching between them.

Bypassing the Equalizer: Disengage the TAPE MONITOR switch on your preamp/receiver. This will send signal directly to the amplifier, bypassing the equalizer. Do not play the 901 speakers in this mode.

Technical Specifications

Type: Active, solid-state electronic equalizer.
Frequency Response: Designed to complement the Bose 901 Series 1 speaker response.
Input Impedance: 47k ohms (nominal).
Output Impedance: 1k ohm (nominal).
Maximum Input Level: 2.5V RMS for 0.1% THD.
Gain Range: Adjustable via LEVEL control.
Power Requirements: 120V AC, 60Hz (US model).
Dimensions & Weight: Refer to unit label. Compact chassis for rack or shelf mounting.

Equalization Theory & Application

The Bose 901 design uses eight drivers facing rearward and one forward, relying on reflected sound. This unique configuration requires substantial equalization to achieve a flat overall power response in a typical listening room. The Series 1 equalizer provides a fixed curve that boosts both low and high frequencies significantly while attenuating midrange frequencies. This compensates for the natural roll-off of the full-range drivers and the acoustic effects of the Direct/Reflecting® design.

Note: The equalizer sliders are pre-set at the factory. For standard operation, they should not be altered. Adjusting them will defeat the intended acoustic calibration of the 901 system.

System Setup & Calibration

For optimal performance:

Speaker Placement: Position 901 speakers on sturdy stands or shelves. They should be placed against the long wall of the room, well away from corners, with the serial numbered side facing the listening area. Angling them slightly inward can improve imaging.
Room Interaction: The system is highly dependent on room acoustics. Experiment with placement to minimize bass boominess and maximize spaciousness.
Level Matching: Use the equalizer's LEVEL control to match the loudness of the 901 system to other sources in your setup. Use a familiar piece of music and switch between a flat source (like a CD player direct) and the tape monitor (901) loop to compare.

Care & Maintenance

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 ventilation: Do not block vents or place the equalizer on top of heat-producing components like power amplifiers.

CAUTION! Never open the chassis. There are no user-serviceable parts inside. Refer servicing to qualified Bose personnel.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No Sound from Speakers	Equalizer off or bypassed; incorrect connections.	Ensure equalizer POWER is ON. Engage TAPE MONITOR on preamp/receiver. Verify all RCA cables are secure and connected to correct jacks.
Distorted Sound	Input level too high; amplifier clipping.	Reduce the output level from your source or preamp. Ensure the equalizer's LEVEL control is not set excessively high.
Hum or Buzz	Ground loop; poor cable connections.	Ensure all components are plugged into the same AC circuit. Check RCA cables for damage. Try lifting the ground on the equalizer (if safe and codes permit).
Sound is Thin or Lacks Bass	Tape monitor not engaged; EQ sliders altered.	Confirm TAPE MONITOR switch is engaged. Verify all EQ sliders are in their original, factory-preset positions.
Intermittent Sound	Faulty cables or internal connection.	Swap RCA cables to test. Gently wiggle connections to check for loose jacks.

Warranty & Support

Refer to the original warranty card included with your Bose 901 system for specific terms and duration. The equalizer is typically covered under the same warranty as the speakers.

For technical support, service inquiries, or to locate an authorized service center:

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

This manual covers the Bose 901 Series 1 Active Equalizer. Specifications and features are subject to change without notice. Bose and Direct/Reflecting are registered trademarks of Bose Corporation.