The Marantz PM-5 is one of the more intriguing integrated amplifiers of the late 1970s, offering something relatively unusual for its time: switchable pure Class A and Class AB operation. With 20 watts per channel in Class A and 80 watts per channel in Class AB, the PM-5 was designed to combine the refinement of Class A with the practical power of conventional high-power amplification.
.jpg "Marantz PM-5 (1979) | Class A/Class AB Integrated Amplifier")
Marantz PM-5 Main Specifications
Type: Stereo pre-main amplifier
Year: 1979
Power output: 20 W + 20 W, 8 Ω, pure Class A
Power output: 80 W + 80 W, 8 Ω, Class AB
Total harmonic distortion: ≤ 0.015%, 20 Hz–20 kHz
Wide-band response: 5 Hz–100 kHz, +0/−2 dB
Damping factor: ≥100 at 8 Ω
Signal-to-noise ratio: 86 dB MM / 68 dB MC / 108 dB line
Dimensions (W/H/D): 416 × 146 × 332 mm
Weight: 13 kg
Power consumption: 200 W
The PM-5's Class A and Class AB Technology. The central attraction of the PM-5 is its dual-mode power amplifier. At the flick of a switch, the amplifier can operate as a 20 W-per-channel pure Class A amplifier or deliver four times the power—80 W per channel—in Class AB. Marantz did not simply treat Class AB as the "power" setting and leave it at that. Considerable attention was paid to making its performance approach the quality expected from the Class A mode. High-speed transistors were used in the power stage, with a high cutoff frequency of approximately 90 MHz. The objective was to reduce the switching-related distortion normally associated with Class AB operation. The output stage uses a complete push-pull DC amplifier configuration throughout the signal path. This was intended to minimize transient intermodulation distortion and improve the amplifier's basic linearity without relying excessively on negative feedback. The result is a rather characteristic late-1970s engineering philosophy: instead of simply chasing a large power rating, Marantz concentrated on making the amplifier behave cleanly under dynamic conditions. Heat-Pipe Cooling: An Unusual Engineering Solution. The cooling system is one of the PM-5's most interesting mechanical features. Rather than mounting the power transistors directly onto a conventional heatsink arrangement, Marantz employed a newly developed heat-pipe system. Heat generated by the power devices is transferred away from the circuit to a separate radiator. This allowed the transistors to be positioned more conveniently from a circuit-design perspective, while also simplifying the physical layout and potentially reducing unwanted thermal and electrical interactions. The power supply was equally serious. The PM-5 uses a large-capacity audio-grade capacitor arrangement together with a compact, high-power transformer filled with resin intended to improve heat resistance and mechanical stability. A Surprisingly Capable Phono Section. Vinyl playback received considerable attention in the PM-5. The phono amplifier uses multiple transistors in a low-distortion, high-S/N design and includes separate MM and MC capabilities. The MC input is particularly interesting, offering a sensitivity of just 200 μV through a 75 Ω input impedance. Marantz also incorporated a straight DC signal path from the phono amplifier toward the power stage, reducing unnecessary signal-path stages between the cartridge input and amplification section. A dedicated MC head amplifier is included, together with a subsonic filter. Interestingly, the subsonic function is applied specifically within the equalizer section rather than being implemented as a broader system-wide function. Tone Controls and Everyday Usability. The PM-5 was not designed to be a purist amplifier with every convenience removed. Its tone controls provide ±8 dB of adjustment at both 100 Hz and 10 kHz. The amplifier also incorporates a loudness control for compensating low- and high-frequency response at reduced listening levels. A precision volume control was used to maintain a flat response around the central position, while the balance control permits independent adjustment of the left and right channels. The front panel is completed by a large central peak-power meter. Unlike a conventional bar display, the PM-5 uses point-style LED indications to show output power in both Class A and Class AB operation. It is a particularly distinctive visual feature and gives the amplifier a much more instrument-like appearance. Marantz also made the PM-5 practical for a serious 1970s audio system. The amplifier includes a dubbing circuit that allows recordings to be transferred between tape decks. A speaker selector provides comparison between two speaker systems and can also be used for simultaneous playback. Marantz PM-5 Versions and Identification. Early PM-5 examples are particularly interesting to collectors. The earliest units carried the Marantz ESOTEC designation on the upper-right portion of the front panel. There are differences between markets: the ESOTEC marking is found in gold on U.S. examples, while European-market units generally use a black version. Later PM-5 units dropped the ESOTEC marking and simply carried the PM-5 designation on the front panel. This makes the front-panel treatment a useful first point of reference when identifying an individual example. Original sale price in Germany: 1.900 DM | Wooden cabinet WC-76 walnut 120DM | Wooden cabinet WC-76N mahogany 190DM
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.jpg "Marantz PM-5 (1979) | Class A/Class AB Integrated Amplifier")
.jpg "Marantz PM-5 (1979) | Class A/Class AB Integrated Amplifier")
.jpg "Marantz PM-5 (1979) | Class A/Class AB Integrated Amplifier")
.jpg "Marantz PM-5 (1979) | Class A/Class AB Integrated Amplifier")
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