A pre-main amplifier from Sansui's Classic Models lineup, featuring comprehensive tone controls and robust protection circuitry
Overview
The Sansui AU-5500 is a pre-main amplifier produced by Sansui Electric Co., Ltd. It belongs to the brand's "Classic Models" lineup and was priced at ¥68,800 around 1975. Designed for high-fidelity audio systems, it combines a sophisticated phono stage with flexible signal routing and strong performance specifications.
Specifications
| Power Output | 30W + 30W (8 Ω, 20 Hz – 20 kHz) |
| Maximum Power Output | 38W + 38W (8 Ω, 1 kHz, single channel) |
| Music Power | 130W (4 Ω, 1 kHz) |
| Total Harmonic Distortion | Pre Amp: ≤0.1%, Main Amp: ≤0.1%, Overall: ≤0.15% |
| Intermodulation Distortion | Pre Amp: ≤0.1%, Main Amp: ≤0.1%, Overall: ≤0.2% (SMPTE) |
| Power Band Width (IHF) | 5 Hz – 30 kHz |
| Frequency Response (1W) | 10 Hz – 35 kHz ±0.5/-1 dB |
| RIAA Deviation | ±0.5 dB (30 Hz – 15 kHz) |
| Damping Factor | 30 (8 Ω) |
| Input Sensitivity / Impedance | Phono: 2.5mV/50kΩ, Tuner/AUX/Tape: 100mV/50kΩ, Main Amp: 800mV/50kΩ |
| Phono Maximum Input | 200mV (THD <0.2%) |
| Output Voltage (1 kHz) | Tape Rec (Pin/Din): 100mV/30mV, Pre Amp: 800mV |
| Channel Separation (1 kHz) | Phono: ≥50 dB, Tuner/AUX/Tape: ≥55 dB, Main Amp: ≥60 dB |
| Hum and Noise (IHF) | Phono: ≥70 dB, Tuner/AUX: ≥85 dB, Main Amp: ≥100 dB |
| Tone Control Range | Bass: ±13 dB (50 Hz), Midrange: ±5 dB (1 kHz), Treble: ±13 dB (15 kHz) |
| Loudness Compensation | +10 dB at 50 Hz, +8 dB at 10 kHz (Volume -30dB) |
| Low Filter | 70 Hz = -3dB (6dB/oct) |
| High Filter | 7 kHz = -3dB (6dB/oct) |
| Muting | -20 dB |
| Rated Power Consumption | 70W |
| Dimensions | 434 mm (W) × 130 mm (H) × 315 mm (D) |
| Weight | 10.4 kg |
Design
The AU-5500 uses a differential amplifier circuit with a matched pair transistor at the first stage of the power amplifier for stable amplification. The drive stage employs a 3-stage Darlington connection, while the final output uses heteropolar power transistors with uniform characteristics. A high-gain monolithic IC handles equalization in the phono stage, which uses an NF-type circuit with a selected low-noise transistor at the input. Grounding avoids the chassis at the equalizer amplifier input. The unit features a triple tone control system with adjustable midrange and complete defeat functionality. A large, regulated power transformer supplies power, with stabilized voltage delivered to the equalizer and tone amplifiers. It includes a dual tape monitor system allowing bidirectional copying when two units are used. Additional features include a loudness switch, audio muting switch (-20dB), stereo/monaural selector, speaker A/B/A+B switching, pre-main disconnect, DIN outputs, grounding terminal, and a spare AC outlet. A protective circuit combines electronic detection, relay, and short-circuit fuse, with temperature and voltage monitoring for power transistors and pop-noise suppression at power-on. The design also includes both low and high filters to reduce unwanted noise across the frequency spectrum.
Context
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