Sony ST-S555ESX (1986)
A high-end FM/AM tuner from Sony’s ES series, released in 1986 with advanced RF and audio circuitry for its time.
Overview
The Sony ST-S555ESX is an FM/AM tuner released in 1986 as part of Sony's ES (Elevated Standard) series, a line focused on high-fidelity audio performance. It was priced at ¥74,000 at launch and designed with multiple proprietary technologies to minimize distortion and improve signal clarity. The unit features a 4-station timer-compatible program memory, a 10-station random preset function, memory scanning, and a "cartone" function for station grouping.
Specifications
| Practical sensitivity | 0.9 μV/10.3 dBf |
| Harmonic distortion factor (1 kHz, wide) | mono: 0.005% stereo: 0.008% |
| Effective selectivity | wide: 65dB (400kHz) narrow: 65dB (300kHz) |
| Frequency response (1 kHz, stereo) | 15 Hz to 15 kHz + 0.2–0.5 dB |
| Spurious interference ratio | 120 dB or more |
| Signal-to-noise ratio | mono: 99dB stereo: 92dB |
| Separation (1 kHz) wide | 70dB |
| Power consumption | 21W |
| External dimensions | Width 470 x Height 86 x Depth 345 mm |
| Side Wood Removal | Width 430 mm |
| Weight | 5.6kg |
Design
The ST-S555ESX incorporates the design philosophy of the Sony ES series, featuring an SST circuit (Super Sound Tracing Circuit) to reduce front-end distortion. It separates the control voltage of the varactor diode in the local oscillator and RF tuning section to minimize tracking error. The tuner uses WOIS (Wave Optimized IF System) for high selectivity and sound quality, WODD (Wave Optimized Direct Detector) to enhance detector performance, and WODSD (Wave Optimized Digital Stereo Decoder) in the MPX section. It employs a direct comparator method with a 100 kHz comparison frequency, low-noise, high-slew-rate (20 V/μs typ.) audio op-amps, and low-distortion switching devices. The power transformer’s control and signal windings are independent, and the transformer is mechanically floated using materials with different acoustic impedance. An ES filter improves transformer frequency characteristics, and a unique ES substrate with a top plate hole near the audio stage prevents signal degradation from electrostatic capacitance. The unit has two antenna input terminals.
Context
The ST-S555ESX is part of Sony's ES (Elevated Standard) series and represents one of the first models in Sony’s ES tuner lineup.
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