Marantz Model 1150mkII (1977)

Eighty watts per channel in fifteen kilograms of Japanese restraint - the Model 1150, refined, not reinvented.

Overview

The Marantz Model 1150mkII is an improved version of the Model 1150. It was introduced around 1977 at a list price of ¥129,000. It is a pre-main amplifier, or integrated amplifier in Western terms. It keeps its predecessor's basic character and refines the preamp and power supply sections. The Japanese sources that document this unit agree on that point: this is the Model 1150's basic power, polished.

Rated output is 80W + 80W into 8 ohms from 20 Hz to 20 kHz with both channels driven. That put it in the serious-listener class of the late 1970s. Frequency response is spec'd at 20 Hz to 20 kHz ± 1.0 dB, with total harmonic distortion at 0.1% or less across the same band. Power bandwidth runs from 7 Hz to 45 kHz, so the amplifier isn't straining at its rated output the way lesser designs do. Damping factor is 45 or more into 8 ohms. That's not the stratospheric figure of later monster amps, but it's plenty for most domestic speakers of the period.

What's striking about the 1150mkII's measured behavior is how carefully Marantz separated the preamp from the power amp in its specifications. The preamplifier section claims 0.05% THD and 0.05% intermodulation distortion — figures meaningfully better than the power stage's 0.1% and 0.15% — which suggests the company understood that the line stage was where signal integrity was won or lost. Phono input sensitivity is 1.8mV into 47kΩ, with line inputs at 180mV into 60kΩ. Dynamic range on phono is rated at 106dB, with input equivalent noise at 1.0μV — numbers that speak to a quiet, well-regulated front end.

Key Features

56,000µF Power Supply Capacitance

The big change over the original Model 1150 is the power supply. Marantz fitted a 56,000µF large-capacity filter condenser. The documentation admits that electrically, 26,000µF would have been sufficient. The larger capacitance is there for sound quality, not just ripple rejection. The power supply capacitors use an internal series type with low ± capacitance deviation, which the company claims reduces high-frequency distortion. Power consumption is 250W for an 80W-per-channel amplifier. This is the component that gives the 1150mkII its authority on dynamic peaks.

Inverted Darlington Output Stage with Pure Complementary OCL

The power amplifier section uses a push-pull drive, all-stage direct-coupled pure complementary OCL circuit, with Marantz's characteristic inverted Darlington method at the output stage. The architecture is textbook high-end for the era: direct coupling throughout, no coupling capacitors in the signal path of the power stage, and complementary symmetry for symmetrical push-pull operation. The inverted Darlington configuration was Marantz's house approach to output stage linearity, and it serves the 1150mkII's measured distortion figures well. A 100% DC feedback loop stabilizes the circuit.

Three-Stage Direct-Coupled NF Equalizer

On the phono side, the equalizer stage is a 3-stage direct-coupled NF circuit with differential amplification at the input. It is built around a pair of differential input transistors, a constant current source, a high-gain amplifier stage, and a stabilized ±power supply. Marantz designed it to handle a wide range of cartridges, which made sense in 1977, when the phono input was still the primary source for most listeners. The preamplifier section also uses lorry cage type coupling capacitors, chosen to improve phase characteristics and, in the company's telling, enable finer expressive detail. The spec sheet lays out the gain structure clearly: 58dB from phono to pre-out, 40dB from phono to record out, and 18dB from line to pre-out.

Three-Band Tone Control with Turnover Switching

The tone control section adjusts bass, mid, and treble independently. Three bands were becoming common on serious integrated amplifiers by the late 1970s. Bass offers ±10 dB at 100Hz or 250Hz depending on the turnover switch position. Treble offers ±10 dB at 10kHz or 4kHz. The mid band provides ±6 dB at 700Hz. The turnover switches set the range of influence, and a tone switch bypasses the entire circuit. The tone amplifier section uses four transistors per channel in a two-stage Darlington connection.

Active Filters with Front-Panel Push Buttons

Three front-panel push buttons engage the active filter circuit, which removes motor noise and scratch noise from program material. The High filter operates at 9kHz, the Low filter at 30Hz, and a Subsonic filter at 10Hz, each at 12dB/octave. Pressing any of the three buttons connects the corresponding filter element into the amplifier's feedback circuit. For worn vinyl or warped pressings these were useful. The subsonic filter in particular could keep low-frequency garbage from warped records out of your woofers.

PEP Protection Circuit and Gold-Plated Speaker Relay

Marantz equipped the 1150mkII with its PEP (pure electronic protection device) circuit, which guards the power transistors against excessive current and voltage from sudden load shorts. A temperature compensation circuit maintains normal operation under severe thermal conditions, and the control circuit elements use Darlington connections throughout. The speaker protection relay has gold-plated contacts sealed in a dust cover. It also works as a delay circuit, disconnecting the speakers for approximately four seconds after power-on to suppress the pop noise that would otherwise hit your woofers.

Dubbing Jacks and Tape Flexibility

For a 1977 integrated amplifier, the 1150mkII is generous to tape recordists. The front panel carries dubbing jacks. Plugging into the dubbing-in jack automatically disconnects the Tape 2 input, while the dubbing-out and Tape 2 out jacks are wired in parallel. Sources appearing at the rear panel output jacks also feed the dubbing-out jack, so you can record simultaneously on three recorders or perform mutual dubbing between Tape 1 and the front-panel source. A monitor switch lets you check any source at any time.

Optional Cabinets and Rack Adapter

The 1150mkII was sold as a bare chassis, with two wood cabinet options and a rack mount adapter available separately. The Mahogany Cabinet WC-3N was priced at ¥11,000, while the Walnut Cabinet WC-3 ran ¥5,900. The Rack Mount Adapter RA-2 also listed at ¥5,900. A 1150mkII with its original WC-3 or WC-3N cabinet is worth more to collectors.

Historical Context

The Model 1150mkII appeared in approximately 1977 as a refinement of the Model 1150, which had established the basic architecture: 80W + 80W into 8 ohms, 20 Hz to 20 kHz ± 1.0 dB frequency response, and a 15kg chassis. The mkII's improvements were concentrated in the preamplifier and power supply sections, where Marantz clearly felt the original could be improved without altering its fundamental character.

In Marantz's late-1970s integrated amplifier lineup, the 1150mkII sat above the Model 1120 (60W + 60W into 8 ohms, 12.2kg) and below the Model 1250 (130W + 130W into 8 ohms, 18.5kg, 450W power consumption). Its damping factor of 45 or more exceeds the Model 1120's 30 or more, which suggests the power supply refinement paid off in amplifier control. The 1150mkII's intermodulation distortion of 0.15% or less matches the original Model 1150's figure. The improvements were in the preamp and power supply, not in the output stage design.

At ¥129,000, the 1150mkII was a serious investment for the Japanese domestic market. The configuration, centered on phono and line inputs, reflects a 1970s setup where the record player and tuner were the primary sources and tape decks were the recording tools.

Documentation from the period is thin. No major English-language audio publication appears to have reviewed the 1150mkII, and most specifications trace back to Japanese vintage audio databases that share overlapping data. The enthusiast site ヴィンテージオーディオ図鑑 describes the 1150mkII as a model that inherits the basic power of the Model 1150 while refining the preamp and power supply sections, and notes that its phono stage pairs well with a 31.5cm coaxial speaker unit for coherent voice and instrument reproduction. The 15kg chassis houses the 80W-class output with a power supply whose physical presence is immediately apparent when you lift the lid.

The 1150mkII's documentation is thinner than for many comparable Marantz models. No production end year is confirmed, no service manual is documented in the available sources, and no independent period reviews from English-language publications have surfaced. Units do appear on auction sites. One Yahoo! Auctions listing noted "音質不良" (poor sound quality), and forty-five-year-old electrolytic capacitors are well past their designed lifespan. An eBay listing graded a unit as "Condition Rank: B - signs of use such as scuffs and dirt, but in good condition for normal use." As with any amplifier of this vintage, budget for a recap before trusting it with your best speakers.

The 1150mkII represents Marantz at a particular moment — the company had the engineering confidence to refine rather than redesign, and the market appetite for a well-executed integrated amplifier at a premium price. It's not the most famous Marantz of the era, but for listeners who want 80 clean watts with a phono stage that was clearly designed by people who listened to records, it deserves a place on the shortlist.

Similar items on eBay

No exact Marantz Model-1150mkII listings are live right now — these searches show current Marantz and similar vintage audio gear on eBay:

As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.

Related Models

• Marantz 1200 (1972–1975; some sources say 1974–1976)
• Marantz Model-1030
• Marantz Model-1040
• Marantz Model-1122
• Marantz Model-1152
• Eico 3150 (1967)
• Fisher CUSTOM-ELECTRA-I (K-14/K-15) (1957)
• Fisher CUSTOM-ELECTRA IV (E33/E44) (1960)
• Akai AM-2400 (1978)
• Akai AM-2600 (1977)