Sony ST-S555ES (1986 - 1988)
An FM-only stereo tuner built in Japan with advanced PLL synthesis and Audio Current Transfer output technology.
Overview
The Sony ST-S555ES is an FM stereo tuner manufactured in Japan from 1986 to 1988. Designed for high-fidelity reception, it features a PLL digital frequency synthesizer with quartz lock and supports the Japanese FM band (76–90 MHz). It includes a remote control, 8 preset memory stations, and an integrated display showing frequency, stereo/mono status, antenna selection, and more. The unit uses an Audio Current Transfer (ACT) system, requiring a dedicated converter cable to interface with standard amplifiers, minimizing 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 features a Direct Comparator circuit using a high-speed PLL IC operating up to 220 MHz, increasing comparison frequency to 100 kHz to reduce beats and noise. It employs a high-linearity wide-band ratio-detection circuit with dedicated detection driver ICs and a DC amplifier configuration in the MPX section with a 3-pole linear phase filter. The front end includes an FET buffer amplifier and a 5-gang tuning capacitor with an FET balance mixer. IF stages use four uniphase filters (2 elements/package) and a differential limiter amplifier. The tuner outputs via the Audio Current Transfer (ACT) system, with current-to-voltage conversion performed externally using a dedicated cable. It includes two antenna inputs (A/B), with a -20dB attenuator on input B. Preset memory stores 8 stations, retaining frequency, stereo/mono mode, muting, IF bandwidth, high blend, and antenna selection via non-volatile memory. Tuning modes include Quick Search (Auto), Sweep Tune, and Step Tune (100 kHz). The integrated 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 unit includes an oxygen-free copper power cord 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
This FM stereo tuner was developed with original technology to support multi-channel FM and high sound quality. Introduced in the mid-1980s, it was positioned as a high-performance receiver during a period of advancing digital tuning and audio fidelity.
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