Marantz Model 240 (1972-1977)

Name: Marantz MODEL 240
Brand: Marantz

At 11.8kg, it arrives like a promise kept—solid-state muscle wrapped in minimalist chassis, ready to drive speakers with unflinching control.

Overview

Specifications

Manufacturer	Marantz
Model	Model 240
Type	Stereo Power Amplifier
Year of Production	1972-1977
Power Output (8Ω)	125W per channel (250W total)
Power Output (4Ω)	150W per channel (300W total)
Power Output (16Ω)	64W per channel (128W total)
Total Harmonic Distortion	0.1% or less (20 Hz – 20 kHz, rated output)
Cross Modulation Distortion	0.1% or less (rated output, any two frequencies 20 Hz – 20 kHz)
Frequency Response	2 Hz ~ 100 kHz + 0 -1.5 dB
Power Bandwidth (IHF)	5 Hz to 45000 Hz
Input Sensitivity	1.5V for full output
Input Impedance	100kΩ
Damping Factor	100 or more (at 8Ω)
Total Noise	Better than 106 dB below rated power (into 8Ω)
Power Consumption	480W
Dimensions (W×H×D)	362 × 156 × 241 mm
Weight	11.8 kg

Key Features

Differential Amplification with Pure Complementary Symmetry

The Model 240 employs a fully balanced, differential amplification topology with pure complementary symmetry—an advanced design for its time. This means the signal path uses matched transistor pairs in both the differential input stage and the push-pull output stage, minimizing distortion and ensuring symmetrical drive to the speaker load. According to the design documentation, transistors are selected as "perfect pairs" during manufacturing, a process that enhances channel matching and long-term stability.

All-Stage Direct-Coupled OCL Circuit

Unlike amplifiers that use coupling capacitors between stages, the Model 240 features an all-stage direct-coupled OCL (Output Capacitor-Less) circuit. This eliminates phase shifts and signal degradation associated with capacitors, extending low-frequency response and improving transient accuracy. The result is a seamless, coherent sound that maintains integrity from input to output—particularly evident in complex orchestral passages or deep bass transients.

Dual 20,000μF Power Supply Capacitors

Power delivery is handled by two massive 60V 20,000μF smoothing capacitors, providing a stable reservoir of energy for dynamic peaks. This dual-capacitor setup supports the amplifier’s high current demands, especially when driving low-impedance loads like 4Ω speakers. The robust power supply contributes to the amplifier’s 100+ damping factor at 8Ω, allowing tight control over speaker cone movement and cleaner bass.

Separate Circuit Boards for Signal Isolation

To prevent crosstalk and interference, the Model 240 uses discrete circuit boards for each functional block—input, driver, and output stages. This modular construction isolates sensitive low-level signals from high-current output sections. Combined with a generously sized ground plane, the layout minimizes ground loops and electromagnetic interference, a hallmark of Marantz’s engineering discipline during this period.

No Front-Panel Power Switch

One of the most discussed quirks among owners is the absence of a front-panel power switch. The amplifier is designed to be powered on via an external source—either a preamp with switched outputs or a standalone power controller. While unconventional, this design choice reduces front-panel clutter and eliminates a potential failure point. However, it also means users must integrate the Model 240 into a system with coordinated power sequencing to avoid turn-on thumps.

Collectibility & Value

The Model 240 has seen rising interest in recent years, with collectors noting that units are increasingly listed and selling for over $1,000 (Facebook group reports). Its reputation for high build quality and musical performance contributes to its appeal, but so does its vulnerability—owners and repair technicians frequently describe the amplifier as "notorious for blowing up if the transistors do not meet certain specs." This sensitivity to component tolerances makes original, unmodified units desirable, but also means many have undergone restoration. Service manuals are available (Retronik.fr), and there are active discussions about restoration kits and replacement transistors on forums like diyAudio. While no official market valuation data exists in the fact sheet, anecdotal evidence suggests well-maintained or professionally restored examples command premium prices.

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