Sony ST-A5 (1977)
A high-performance FM stereo tuner released in Japan in September 1977, designed to pair with the TA-F5 amplifier.
Overview
The Sony ST-A5 is an FM stereo tuner made in September 1977 for the Japanese market, intended to feed the TA-F5 amplifier in Japan and the TA-F5A elsewhere. It sits below the ST-A6B in Sony’s lineup, offering nearly identical FM performance at a lower price point. The tuner features a 7-gang variable capacitor, a 270mm long dial scale, and a large two-meter system for precise tuning. It lacks variable audio outputs, a multipath indicator, and a 400 Hz test tone generator, distinguishing it from higher-end models.
Specifications
| FM Practical Sensitivity (IHF) | 1.7 μV |
| Signal-to-noise ratio mono | 79dB |
| Signal-to-noise ratio stereo | 74dB |
| Capture ratio Normal | 1.0dB |
| Capture ratio Narrow | 1.2dB |
| Selectivity (IHF) Normal | 35dB |
| Selectivity (IHF) Narrow | 80dB |
| Image interference ratio | 120dB |
| IF interference ratio | 120dB |
| Spurious interference ratio | 120dB |
| Distortion Factor (400 Hz, stereo) Normal | 0.1% |
| Distortion Factor (400 Hz, stereo) Narrow | 0.3% |
| Stereo separation (1kHz) Normal | 50dB |
| Stereo separation (1kHz) Narrow | 40dB |
| Power consumption | 18W |
| External dimensions | Width 410 x Height 145 x Depth 305 mm |
| Weight | 5.9kg |
Design
The ST-A5 uses a double-tune and quad-tune configuration in the tuning circuit with a 7-series varicon and a CG varicon in the FM front-end for high indication accuracy. The mixer circuit employs a dual-gate MOS FET with remote cutoff characteristics to reduce intermodulation and improve interference rejection. A uniphase filter in the IF section enables high selectivity and high distortion factor, with Normal/Narrow bandwidth switching available. The multiplex stereo demodulation uses a PLL IC (HA1196), while the FM IF system uses the LA1230 IC. A reed relay provides muting to eliminate pop noise, and a high-blend circuit reduces noise on weak stereo signals without sacrificing stereo imaging. It includes an F-type connector for 75 Ω coaxial antenna input.
Context
The ST-A5 was positioned below the ST-A6B, which cost ¥10,000 more at ¥49,800, while the flagship ST-A7B reached ¥158,000. The AM/FM ST-A4 was the model directly below the ST-A5 in Sony’s tuner lineup. It was sold with the optional rack handle AH-4A (¥2,500). Internally, it shares significant circuit and component similarity with other models, differing mainly in HF and audio output stages.
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