Marantz ST-50BL (circa 1989–1993)
The ST-50BL is a digital synthesizer FM/AM tuner from Marantz's late-1980s Japanese lineup. It is the black-fronted variant of the ST-50, which was also offered in a gold finish for ¥3,000 more. Introduced around 1989 at ¥35,000, it sold through roughly 1993. It's a Japan-market component, as its FM tuning range of 76-90 MHz (the Japanese FM band) and its 100V AC power requirement show.
Marantz took the design seriously. The Japanese sources describe it as "thoroughly pursuing" the difficult balance between reception performance and sound quality. The front end uses a dual-gate MOS FET in a four-stage configuration to minimize distortion and beat interference. The IF section uses a ceramic filter chosen for good group-delay characteristics. Marantz skipped the quadrature detection built into the LA1266 IC and used a separate ultra-wideband ratio detection circuit instead, for lower harmonic distortion and wider frequency response. A quartz PLL synthesizer handles tuning. You can preset up to 20 stations, and each preset remembers the AM/FM band, IF bandwidth (wide/narrow), mono/stereo mode, and antenna selection.
The rear panel has two F-type antenna terminals with relay switching, so you can connect two antennas pointing in different directions and switch between them. On the front, the IF BAND switch (WIDE/NARROW) handles weak-signal and strong-signal situations.
The body is light enough to hold in one hand, and the circuit board takes up only the rear half of the chassis. Then Marantz bolted on heavy die-cast metal side weights, about 3kg for the pair, which give it a substantial feel on a shelf. A repair blog examining one unit described the front panel as simple and unadorned, with a display showing the FM frequency.
Specifications from the Japanese catalog data:
- FM tuning range: 76–90 MHz; AM: 531–1602 kHz
- FM sensitivity: 19.2dBf/2.5µV mono; 39.2dBf/25µV stereo
- FM THD (1kHz): 0.08% mono, 0.1% stereo (wide)
- FM S/N: 85dB mono, 76dB stereo
- Selectivity: 40dB wide, 75dB narrow
- Stereo separation (1kHz, wide): 50dB
- Output: 940mV/1.5kΩ (100% modulation, FM)
- Power consumption: 10W
- Dimensions: 420 × 104 × 353 mm; weight: 3.8kg
Inside are an LA1266 AM/FM tuner IC, an LA3450 PLL MPX stereo demodulator, and an LC7218 PLL synthesizer IC. The FM front end is a Mitsumi-made package. One documented repair involved a unit that received no FM or AM at all. The culprits were a shorted capacitor (C314), a failed 2SA1309A transistor (replacing it restored AM reception), and a faulty LA1266 IC, which the technician replaced with one salvaged from a Kenwood KT-5020 board. The same repair blog recommends the gold ST-50 variant if you're buying one, noting that its appearance benefits from the heavy side weights.
Documentation on the ST-50BL is thin outside Japanese sources, and little is recorded about its market reception or long-term reliability across multiple units.
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