Marantz EQ 551 Owners Manual

The Marantz EQ 551 is a professional-grade stereo equalizer designed for audio enthusiasts and professionals. This 10-band graphic equalizer features dual-channel operation, slide potentiometers for precise frequency adjustment, spectrum analyzer display, tape monitor loop, bypass switch, and high-quality audio components for superior sound shaping. 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 Guide 8. Spectrum Analyzer 9. Care & Maintenance 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: 10-band graphic equalizer per channel, Spectrum analyzer display, Tape monitor loop, Bypass switch, Slide potentiometers, Input/output jacks.

Feature	Description
Frequency Bands	10 bands per channel (31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz, 16kHz)
Spectrum Analyzer	Real-time frequency response display
Tape Monitor	Allows connection of tape deck for recording/playback
Bypass Switch	Disengages equalizer for direct signal path
Slide Controls	Precision ±12dB adjustment per frequency band
Input/Output	RCA jacks for input, output, and tape loop
Power Supply	AC power input with voltage selector
Signal-to-Noise	>95dB for clean audio performance
THD	<0.01% at 1kHz
Input Sensitivity	150mV for rated output

Installation

Unpack and inspect contents. Place on stable surface near your audio system.

Connect to amplifier: Use RCA cables from EQ output to amplifier input.
Connect source: Use RCA cables from source component to EQ input.
Tape deck connection: Connect tape deck to tape monitor jacks if used.
Plug into AC power using supplied power cord.
Ensure proper ventilation around unit.

WARNING! Ensure all connections are made with power off to prevent damage. Use quality shielded cables.

First-Time Setup

Power on EQ 551; check all connections.

Set all slide controls to center (0dB) position.
Engage bypass switch to verify signal path.
Play test audio through system.
Adjust frequency bands as desired for your listening environment.
Use spectrum analyzer to visualize frequency response.

CAUTION! Make small adjustments to frequency bands; extreme settings may cause distortion.

Specifications

Frequency Response: 20Hz - 20kHz ±0.5dB
Equalizer Bands: 10 bands per channel (ISO centers)
Boost/Cut Range: ±12dB per band
Input Impedance: 47k ohms
Output Impedance: 1k ohm
Total Harmonic Distortion: <0.01% (1kHz)
Signal-to-Noise Ratio: >95dB
Input Sensitivity: 150mV
Power Requirements: 120V/230V AC, 50/60Hz
Dimensions: 440mm (W) × 320mm (D) × 110mm (H)
Weight: 6.5kg

Controls and Settings

Front Panel: Power switch, Bypass button, Spectrum analyzer display, 20 slide controls (10 per channel).

Frequency Bands: 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz, 16kHz

Rear Panel: AC power input, Input jacks, Output jacks, Tape monitor jacks, Voltage selector.

Operation: Adjust slide controls up to boost frequencies, down to cut. Center position is flat response.

Connecting Devices

Standard connection: Source → EQ Input → EQ Output → Amplifier

Turn off all components before connecting.
Connect audio source to EQ input jacks.
Connect EQ output jacks to amplifier input.
For tape monitoring: Connect tape deck to tape jacks.
Ensure all RCA connections are secure.

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

Operation Guide

Basic equalization techniques for various applications.

Music listening: Boost presence frequencies (2kHz-4kHz) for clarity.
Bass enhancement: Gently boost 63Hz-125Hz bands.
Treble adjustment: Use 8kHz-16kHz bands for brightness control.
Room correction: Cut problematic frequencies that cause boominess.
Bypass function: Use to compare equalized vs. direct sound.
Tape monitoring: Engage when recording or playing tapes.

WARNING! Avoid extreme boost settings which may damage speakers or cause distortion.

Spectrum Analyzer

The built-in spectrum analyzer displays real-time frequency response.

Operation: The display shows the current equalization curve being applied. LED columns correspond to each frequency band. Height indicates boost/cut level.

Use the analyzer to visualize your EQ settings and make precise adjustments. The display updates in real-time as you adjust slide controls.

Care & Maintenance

Unplug before cleaning. Use soft, dry cloth for exterior. Clean slide controls with contact cleaner if needed.

CAUTION! Do not use liquids or aerosols directly on controls. Keep away from moisture and extreme temperatures.

Regulatory Information

FCC Part 15: Class B digital device; complies with interference limits for residential use. Copyright © Marantz; all rights reserved. For technical support, contact authorized Marantz service centers. Manufactured to meet international quality and safety standards.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No sound	Incorrect connections/power	Check all cable connections; verify power is on; test bypass mode
Distorted audio	Extreme EQ settings	Reduce boost levels; reset slides to center position
Hum or noise	Ground loop/cable issues	Check cable shielding; ensure proper grounding; use quality interconnects
Spectrum display not working	Power/display issue	Check power connection; allow warm-up time; contact service if persistent
Controls scratchy	Dust/dirt accumulation	Clean with contact cleaner; exercise controls repeatedly

Reset: Set all slide controls to center position for flat response.

Service: Contact authorized Marantz service center for repairs.