Marantz 120B Manual

The Marantz 120B is a professional stereo power amplifier designed for high-fidelity audio applications. Featuring robust construction, advanced thermal management, and exceptional sound quality, this amplifier delivers 60 watts per channel into 8 ohms with low distortion. Below are key sections covering specifications, installation, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Connections 6. Connecting Audio Sources 7. Operation Guidelines 8. Maintenance & Care 9. Regulatory Information 10. Troubleshooting

Features at a Glance

Key components: Dual mono construction, toroidal power transformer, gold-plated RCA inputs, binding post speaker outputs, thermal protection circuit.

Feature	Description
Power Output	60W RMS per channel at 8 ohms
Frequency Response	20Hz - 20kHz ±0.5dB
Total Harmonic Distortion	<0.05% at rated power
Input Sensitivity	1V for 60W output
Signal-to-Noise Ratio	>100dB
Damping Factor	>200 at 8 ohms
Input Impedance	47k ohms
Speaker Outputs	5-way binding posts
Power Requirements	120V AC, 60Hz, 300W max
Dimensions	17" W × 4.5" H × 14" D

Installation

Unpack and inspect contents. Place on stable, well-ventilated surface.

Position amplifier: Allow minimum 4 inches clearance on all sides for proper ventilation.
Connect speakers: Use high-quality speaker wire with 5-way binding posts.
Connect audio sources: Use RCA cables from preamplifier or source component.
Connect power cord: Plug into grounded AC outlet.

WARNING! Ensure proper ventilation to prevent overheating. Do not block ventilation slots.

First-Time Setup

Power on amplifier following proper sequence.

Connect all audio components before powering on.
Set volume control on preamplifier to minimum.
Power on amplifier last in the chain.
Gradually increase volume to desired listening level.
Verify proper operation of both channels.

CAUTION! Always power on components in sequence: sources first, preamp, then power amplifier.

Specifications

Power Output: 60W RMS per channel (8 ohms, 20Hz-20kHz)
Dynamic Power: 75W at 8 ohms, 100W at 4 ohms
THD: <0.05% at rated power
IMD: <0.05%
Damping Factor: >200 (8 ohms, 1kHz)
Input Sensitivity: 1.0V
Input Impedance: 47k ohms
Frequency Response: 20Hz-20kHz (+0/-0.5dB)
Signal-to-Noise: >100dB (A-weighted)
Power Consumption: 300W maximum
Dimensions: 17" × 4.5" × 14" (W×H×D)
Weight: 22 lbs (10 kg)

Controls and Connections

Front Panel: Power switch, power indicator LED. Rear Panel: RCA input jacks, speaker binding posts, AC power inlet.

Input Connections: Gold-plated RCA jacks for left and right channels.

Speaker Outputs: 5-way binding posts accepting banana plugs, spade lugs, or bare wire.

Power Switch: Rocker switch with integrated power indicator.

Connecting Audio Sources

Connect preamplifier or source component to amplifier inputs.

Turn off all components before making connections.
Use high-quality shielded RCA interconnects.
Connect left channel to L input, right channel to R input.
Ensure secure connection of all cables.
Connect speaker wires observing proper polarity.

Tip: Use high-quality oxygen-free copper speaker wire for best performance.

Operation Guidelines

Proper operation ensures optimal performance and longevity.

Power Sequence: Always turn on sources first, then preamp, finally power amp.
Volume Control: Use preamplifier volume control; amplifier has no volume control.
Thermal Protection: Amplifier will shut down if overheated; allow cool-down period.
Impedance Matching: Ensure speaker impedance is within specified range (4-16 ohms).
Signal Levels: Avoid input signals exceeding 2V RMS to prevent clipping.

WARNING! Do not operate without proper load connected. Avoid shorting speaker outputs.

Maintenance & Care

Unplug before cleaning. Use soft, dry cloth for exterior surfaces.

CAUTION! Do not use liquid cleaners or aerosols. Keep away from moisture and extreme temperatures.

Regulatory Information

FCC Part 15: Class B digital device compliant. UL listed for safety. CE marked for European compliance. Copyright © 2025 Marantz. All trademarks property of their respective owners. For technical support, visit www.marantz.com or contact 1-800-288-2284.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No sound output	Power/connections	Check power connection; verify input and speaker connections; ensure preamp is on.
Distorted sound	Overload/clipping	Reduce input level; check speaker impedance; verify proper ventilation.
One channel silent	Cable/connection issue	Check RCA cables; verify speaker connections; test with known good source.
Amplifier shuts down	Overheating/short circuit	Allow cool-down; check for shorted speaker wires; ensure proper ventilation.
Hum or noise	Ground loop/cables	Check cable routing; ensure proper grounding; use quality shielded cables.

Service: 1-800-288-2284; www.marantz.com