Marantz 3800 Service Manual

The Marantz 3800 is a high-performance stereo preamplifier featuring advanced audio processing, multiple input/output options, precision tone controls, and professional-grade construction. This service manual provides comprehensive technical information for qualified service technicians, including schematics, alignment procedures, troubleshooting guides, and replacement parts lists for proper maintenance and repair.

Technical Specifications

Detailed electrical and mechanical specifications for the Marantz 3800 preamplifier.

Parameter	Specification
Frequency Response	10Hz - 100kHz ±0.5dB
Total Harmonic Distortion	<0.005% at 1kHz
Signal-to-Noise Ratio	>90dB (IHF-A weighted)
Input Sensitivity	2.5mV (MM), 150mV (line)
Input Impedance	47kΩ (phono), 50kΩ (line)
Output Voltage	1.5V RMS (maximum)
Tone Control Range	±10dB at 100Hz and 10kHz
Power Requirements	120V AC, 60Hz, 15W
Dimensions	17.1" W × 4.7" H × 13.4" D
Weight	18.7 lbs (8.5 kg)

Block Diagram Overview

System architecture showing signal flow and major functional blocks.

1. Input Selector: Routes phono, tuner, aux, tape inputs
2. Phono Equalization: RIAA correction network
3. Tone Control: Bass, midrange, treble adjustment circuits
4. Volume/Balance: Dual concentric potentiometers
5. Output Buffer: Low impedance driver stage
6. Power Supply: Regulated ±15V DC rails

WARNING! Always disconnect AC power before servicing. High voltages present.

Circuit Description

Detailed analysis of each circuit section with component functions.

1. Phono Stage: JFET input with passive RIAA equalization
2. Line Amplifier: Op-amp based with low noise design
3. Tone Control: Baxandall-type active equalization
4. Filter Circuits: Subsonic and rumble filters
5. Power Supply: Transformer, bridge rectifier, regulators

CAUTION! Use proper grounding techniques when testing live circuits.

Alignment Procedures

• DC Offset Adjustment: VR101 for left channel, VR102 for right channel
• Phono Gain: Adjust VR201 for 40dB gain at 1kHz
• Tone Control Center: Set VR301, VR302 for flat response
• Power Supply: Verify ±15V DC at test points TP1, TP2
• RIAA Equalization: Check response at 50Hz, 1kHz, 20kHz
• Filter Circuits: Verify cutoff frequencies
• Input Switching: Test all input selections

Test Points & Voltages

Critical measurement points and expected voltage readings.

Power Supply Section: TP1 (+15V), TP2 (-15V), TP3 (ground)

Phono Stage: TP4 (input), TP5 (output), TP6 (equalization network)

Line Stage: TP7 (input), TP8 (tone control), TP9 (output buffer)

All measurements referenced to chassis ground. Use high-impedance digital multimeter.

Disassembly Instructions

Step-by-step procedure for accessing internal components.

1. Remove rear panel screws (4 places)
2. Lift top cover straight up and away
3. Remove front panel knobs (pull straight off)
4. Unscrew front panel mounting brackets
5. Lift circuit board assembly for component access

Tip: Document wire positions and take photos during disassembly.

Component Replacement

Supported replacement parts and installation procedures.

1. Transistors: 2SC2240, 2SA970 (low noise pairs)
2. Op-amps: NJM4558, replacement with modern equivalents
3. Capacitors: Use same values and voltage ratings
4. Potentiometers: ALPS or equivalent quality
5. Switches: Exact mechanical replacement required
6. Fuse: T1A 250V slow-blow type

WARNING! Observe polarity on electrolytic capacitors.

Troubleshooting Guide

Common issues and diagnostic procedures.

Symptom	Possible Cause	Corrective Action
No output	Power supply failure	Check fuse, regulators, transformer
Distorted sound	DC offset incorrect	Adjust VR101/VR102 for 0V DC output
Hum/buzz	Grounding issues	Check ground connections, shield cables
Intermittent operation	Oxidized contacts	Clean switches and potentiometers
Channel imbalance	Worn potentiometers	Replace volume/balance controls

Reset: Verify all adjustments after repairs.

Parts List

Critical replacement components with manufacturer part numbers.

Component	Part Number	Description
Power Transformer	MAR-3800-TX1	Primary 120V, Secondaries 18V-0-18V
Main Capacitors	MAR-3800-C101	4700μF 35V electrolytic
Input Transistors	2SC2240BL	Low noise NPN pair
Volume Control	MAR-3800-VOL	100kΩ dual concentric
Power Switch	MAR-3800-SW1	DPST rocker switch

Schematics

Complete circuit diagrams for all sections.

• Main amplifier schematic (sheet 1 of 3)
• Power supply schematic (sheet 2 of 3)
• Control circuits schematic (sheet 3 of 3)
• PCB layout and component placement
• Wiring harness diagram
• Front panel control layout

CAUTION! Schematics are proprietary - for service use only.

Safety Precautions

Essential safety procedures for service technicians.

Always use isolation transformer when testing live circuits. Discharge power supply capacitors before working. Use anti-static precautions with MOSFET components. Follow local electrical codes. Service by qualified personnel only.

Service: Authorized Marantz service centers only. Original parts required for warranty service.