Sony ST-S555ES (1986 - 1988)
An FM-only stereo tuner built in Japan with PLL synthesis and Audio Current Transfer output technology.
Overview
The Sony ST-S555ES is an FM stereo tuner made in Japan from 1986 to 1988. It has a PLL digital frequency synthesizer with quartz lock and covers the Japanese FM band (76 - 90 MHz). It comes with a remote control and stores 8 preset stations. The display shows frequency, stereo/mono status, antenna selection, and more. The output uses an Audio Current Transfer (ACT) system, so you need a dedicated converter cable to connect it to a standard amplifier. The point is to minimize signal interference.
Specifications
| Circuit system | PLL digital frequency synthesizer, quartz lock system Superheterodyne FM tuner |
| Receiving frequency | 76 MHz to 90 MHz (Japanese FM band) |
| Antenna terminal | 75 Ω unbalanced (2 systems) |
| Intermediate frequency | 10.7MHz |
| Usable Sensitivity (50 dB S/N) | Mono: 1.8 μV (IHF) / 16.8 dBf; Stereo: 22.5 μV (IHF) / 37.9 dBf |
| Practical Sensitivity | 0.9 μV (IHF) / 10.3 dBf (new IHF) |
| Signal-to-noise ratio | Mono: 92dB, Stereo: 86dB |
| Harmonic distortion factor (THD) | Mono wide: 0.03%(100Hz,1kHz,10kHz); Mono narrow: 0.05%(100Hz,1kHz,10kHz); Stereo wide: 0.05%(100Hz), 0.04%(1kHz), 0.12%(10kHz); Stereo narrow: 0.07%(100Hz), 0.06%(1kHz), 0.15%(10kHz) |
| Cross modulation distortion factor | Mono wide:0.03%, narrow:0.05%; Stereo wide:0.04%, narrow:0.06% |
| Frequency response | 30 Hz to 15 kHz +0.2, -0.5 dB |
| Stereo separation | 55dB(100Hz), 60dB(1kHz), 45dB(10kHz) |
| Effective selectivity (400 Hz) | Wide:60dB, Narrow:90dB |
| Capture ratio | 1.0dB |
| AM suppression ratio | 65dB |
| Image interference ratio | 120dB |
| IF interference ratio | 120dB |
| Spurious interference ratio | 120dB |
| RF intermodulation interference ratio | 88dB(IHF), 105dB(2.4MHz) |
| Carrier leak suppression ratio | 78dB |
| Muting level | 25dBf |
| Auto-tuning level | 25dBf |
| Output level | 750mV/620 Ω (After Voltage Conversion by Included ACT Cable) |
| Power supply | 100 VAC, 50Hz/60Hz |
| Power consumption | 23W |
| Dimensions (W x H x D) | 430 x 80 x 340 mm |
| Weight | 4.8kg |
Design
The ST-S555ES has a Direct Comparator circuit built around a high-speed PLL IC that runs up to 220 MHz. It raises the comparison frequency to 100 kHz, which reduces beats and noise. The detector is a high-linearity wide-band ratio-detection circuit with dedicated detection driver ICs. The MPX section uses a DC amplifier configuration with a 3-pole linear phase filter. The front end has an FET buffer amplifier and a 5-gang tuning capacitor with an FET balance mixer. The IF stages use four uniphase filters (2 elements/package) and a differential limiter amplifier. Output is by the Audio Current Transfer (ACT) system, with the current-to-voltage conversion done externally in the dedicated cable. There are two antenna inputs (A/B), and input B has a -20dB attenuator. Preset memory holds 8 stations. Non-volatile memory keeps frequency, stereo/mono mode, muting, IF bandwidth, high blend, and antenna selection for each. Tuning modes are Quick Search (Auto), Sweep Tune, and Step Tune (100 kHz). The display shows reception frequency, antenna selection, IF bandwidth, high blend status, stereo/mono mode, muting, and program memory number. A 10-segment LED indicates signal strength. The chassis uses copper-plated, copper-tight cases, and the power cord is oxygen-free copper with polarity display. Specific components include IC103 (TL071), IC203 (TL072), IC204 (TL082 or NE5532), and electrolytic capacitors C221, C271, C143, C154, C155, C218, C219, C201, C202.
Context
Sony developed this FM stereo tuner with original technology to support multi-channel FM and high sound quality. It came out in the mid-1980s and was positioned as a high-performance receiver while digital tuning and audio fidelity were advancing.
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