Marantz 250M Manual

The Marantz 250M is a high-performance stereo power amplifier delivering 125 watts per channel into 8 ohms, featuring dual mono construction, direct-coupled circuitry, thermal protection, and professional-grade components. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

Features at a Glance

Key components: Dual mono construction, massive heat sinks, professional binding posts, LED power meters, protection circuitry.

Feature	Description
Power Output	125 watts per channel into 8 ohms
Frequency Response	10Hz - 100kHz (+0/-1dB)
Total Harmonic Distortion	Less than 0.05% at rated power
Input Sensitivity	1.2V for rated output
Damping Factor	100 at 8 ohms
Signal-to-Noise Ratio	110dB (IHF A-weighted)
Power Requirements	120V AC, 60Hz, 600W maximum
Dimensions	17" W × 7" H × 14" D
Weight	45 lbs
Binding Posts	Professional 5-way terminals

Installation

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

1. Position amplifier: Allow minimum 6 inches clearance on all sides for proper ventilation.
2. Connect speakers: Use heavy-gauge speaker wire to binding posts (red=positive, black=negative).
3. Connect preamplifier: Use high-quality RCA cables from preamp outputs to amplifier inputs.
4. Connect power: Plug into dedicated AC outlet; ensure proper grounding.

WARNING! Amplifier is heavy; lift with care using proper technique. Ensure adequate ventilation to prevent overheating.

First-Time Setup

Power on sequence: Preamp first, then amplifier.

1. Verify connections: Ensure all cables are secure and properly connected.
2. Power up: Turn on preamplifier first, then switch amplifier power to ON.
3. Check indicators: Power LED should illuminate; meters should show minimal activity.
4. Test operation: Play audio source at low volume to verify proper operation.
5. Adjust levels: Set preamplifier volume to minimum before powering on.

CAUTION! Always power on preamplifier before amplifier. Reverse sequence when powering down.

Specifications

• Power Output: 125 watts/channel into 8 ohms (20Hz-20kHz)
• Dynamic Power: 200 watts into 4 ohms, 250 watts into 2 ohms
• Input Impedance: 50k ohms unbalanced
• Input Connections: RCA unbalanced
• Speaker Connections: 5-way binding posts
• Cooling: Forced air with thermal protection
• Protection: DC offset, thermal, short circuit
• Meter Type: LED power display with peak hold
• Finish: Black anodized aluminum front panel

Controls and Settings

Front Panel: POWER switch, LED power meters, protection indicator.

Rear Panel: AC power inlet, fuse holder, input jacks (left/right), speaker terminals (left/right), ground terminal.

Operation: Power switch (ON/OFF), no gain controls (fixed gain amplifier). Meter display: LED indicators show output power from 0.1W to 300W. Protection: Thermal and short-circuit protection automatically engages when needed.

Connecting Devices

Preamplifier: RCA cables from preamp outputs to amplifier inputs. Speakers: Heavy-gauge wire to binding posts.

1. Turn off all equipment before making connections.
2. Connect preamplifier: Use high-quality shielded RCA cables.
3. Connect speakers: Ensure proper polarity (red to red, black to black).
4. Ground connection: Connect ground terminal to system ground if hum occurs.
5. Power connection: Use dedicated outlet; avoid extension cords.

Tip: Use identical speaker wire lengths for both channels to maintain balance.

Operation Guidelines

Designed for continuous high-power operation with proper ventilation.

1. Power sequence: Always turn on preamplifier first, then amplifier.
2. Volume control: Adjust at preamplifier; amplifier has fixed gain.
3. Meter monitoring: LED meters show real-time power output.
4. Thermal management: Ensure adequate airflow around heat sinks.
5. Power down: Turn off amplifier first, then preamplifier.
6. Continuous operation: Suitable for extended use at moderate levels.
7. Peak power: Meters indicate short-term peak power capability.

WARNING! Do not operate with covers removed. Keep away from moisture and extreme temperatures.

Protection Features

Thermal Protection: Automatically reduces output if overheating occurs. Short Circuit Protection: Disables output if speaker shorts are detected. DC Offset Protection: Monitors output for DC voltage.

Care & Maintenance

Unplug before cleaning. Use soft, dry cloth for exterior; compressed air for vents.

CAUTION! Do not use liquids or solvents. Keep ventilation openings clear of dust accumulation.

Regulatory Information

FCC Part 15: Class B digital device; complies with interference limits. UL listed for safety. Copyright © Marantz; all rights reserved. For technical support, contact authorized Marantz service centers. Original specifications subject to change without notice.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No sound output	Protection mode/power	Check protection LED; verify power sequence; check input connections.
Protection LED on	Overheating/short circuit	Allow cooling; check speaker wires for shorts; reduce volume.
Distorted sound	Overload/clipping	Reduce preamplifier volume; check source material.
Hum or noise	Ground loop/cables	Check ground connections; use shielded cables; separate from power cords.
One channel dead	Connection/component	Swap input cables to isolate issue; check speaker connections.

Reset: Power cycle amplifier; allow to cool if thermal protection engaged.

Service: Contact authorized Marantz service center for internal repairs.