Sansui AU 777 (1967)
A solid-state pre-main amplifier from Sansui, released in May 1967 with high-fidelity specifications and modular functionality.
Overview
The Sansui AU-777 is a solid-state pre-main amplifier produced by Sansui Electric Co., Ltd., released in May 1967. Designed with the same intent as the AU-111, it combines a fully transistorized preamp and power amplifier section that can be used independently. It was positioned as a high-performance integrated solution, featuring comprehensive input options, protective circuitry, and advanced tone and filter controls for its time.
Specifications
| Year of Production | May 1967 |
| Product Type | Solid-state pre-main amplifier |
| Power Output (RMS) | 25W + 25W ±1 dB (8Ω, both channels driven) |
| Music Power | 70W ±1 dB |
| Total Harmonic Distortion | Not more than 0.5% |
| Intermodulation Distortion | 0.8% (60 Hz : 7 kHz = 4:1) |
| Frequency Response (Power Amp) | 20 Hz – 50 kHz (IHF, 0.5% THD) |
| Frequency Response (Preamplifier) | 20 Hz – 70 kHz +0.5 dB / -1.5 dB |
| Channel Separation | 50 dB |
| Hum and Noise (IHF, closed circuit) | 100 dB |
| Input Sensitivity (Power Amp) | 1 V (at 1 kHz, for rated output) |
| Input Impedance | 300 kΩ |
| Load Impedance | 8 Ω – 16 Ω |
| Damping Factor | 24 (at 8 Ω) |
| Phono Input Sensitivity / Impedance | Phono1: 2 mV / 47 kΩ; Phono2: 2 mV / 100 kΩ |
| Tape Input Sensitivity / Impedance | 1.5 mV / 200 kΩ (19 cm/sec); 1.3 mV / 200 kΩ (9.5 cm/sec); AUX: 140 mV / 100 kΩ |
| Tone Control Range | Bass: ±15 dB at 20 Hz (3 dB steps); Treble: ±15 dB at 20 kHz (3 dB steps) |
| Loudness Control | +8 dB at 50 Hz, +5 dB at 10 kHz (at -30 dB volume) |
| Filters | Low: -21 dB at 20 Hz; High: -22 dB at 20 kHz |
| Power Supply | AC 100V / 117V / 220V / 240V, 50 Hz / 60 Hz |
| Power Consumption | 165 VA (max, at 240 VAC) |
| Dimensions | 435 mm (W) × 155 mm (H) × 334 mm (D) |
| Weight | 12.3 kg |
| Semiconductors | 26 transistors, 8 diodes, 4 thermistors, 1 SCR |
| Original Price | ¥57,000 (May 1967) |
| Optional Accessory | Wooden case (¥4,150) |
Design
The AU-777 uses an all-silicon transistor design, with a C/E split phase inversion circuit in the output stage. All amplifier stages from input to output are based on negative feedback (NF) amplifier circuits. The tone control is a two-stage NF type with a 3 dB-step attenuator. It includes a center channel output with flat (9.5 V) and high-cut (1 V at 200 Hz) options, and a switchable tape equalizer for different tape speeds. A CR feedback system is used for the low and high filters. The unit features a pure electronic PSC protection circuit and a dual protection system combining a power transistor with a quick fuse to prevent damage during output short circuits. The preamp and power amp sections can be used separately, and it includes a headphone jack, muting switch (-20 dB), presence switch (+6 dB at 50 Hz, fo = 125 Hz), and tape monitor function.
Context
The AU-777 was a milestone integrated amplifier that helped establish Sansui's reputation for high-quality audio equipment. It was designed with the same intent as the AU-111, reflecting Sansui’s commitment to high-fidelity performance. The amplifier delivered a warm, musical sound that was competitive with more expensive Western designs of the era.
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