Marantz PM-50 (1989)
The Marantz PM-50 is a stereo pre-main (integrated) amplifier from the late 1980s. It sold in Japan at ¥45,000 and in the UK at £230. It was the smaller sibling to the PM-80. Gramophone noted that the two models clearly shared both their styling and a number of specific features of layout and circuit topology. A Hi-Fi Review observed that Marantz had long followed a policy of continuous development rather than annual model changes for their own sake.
The design brief was evidently about getting the fundamentals right. The power supply uses a pair of 15,000 µF capacitors for stable current delivery. The power supply circuitry is kept separate, and its layout is arranged to keep noise out of the signal path. The phono stage uses a low-noise FET and an audio IC. It handles both MM and MC cartridges - the MC input accepts 250 µV into 100 Ω. A source direct switch routes the selector straight to the master volume and bypasses unnecessary circuitry. The volume pot uses Marantz's proprietary resistance taper, for a natural feel through the rotation. Tape monitoring is provided for two decks, and you can dub from deck 1 to deck 2.
Rated output is 80W + 80W into 8 Ω (20 Hz-20 kHz, both channels driven). Dynamic power reaches 240W into 2 Ω, and Hi-Fi Review remarked that the PM-50 should be very load-tolerant as a result. Distortion is rated at 0.008% (THD, 20 Hz-10 kHz, 8 Ω). The CD direct frequency response extends from 10 Hz to 100 kHz (+0/-3 dB). Signal-to-noise is 105 dB on high-level inputs. Some sources list the 8 Ω output at 70W rather than 80W. The 80W figure comes from the most detailed specification source.
One known weak point, reported by repair technicians on forums, is a hybrid preamplifier stage. It can overheat with age and damage the output transistors - a failure mode shared with the PM-80. Replacing the offending IC has been quoted at around €70 in parts. The PM-50 turns up occasionally on the secondhand market, often described as a vintage unit in good working order.
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