Sansui AU 5900
A mid-range integrated amplifier from Sansui’s AU-series, featuring a pure complementary direct-coupled power stage and comprehensive tone controls with selectable phono input impedance.
Overview
The Sansui AU-5900 is a solid-state integrated amplifier developed as part of Sansui's AU-xxx0 series, positioned between the AU-6900 and AU-7900 models. It shares design concepts with the higher-end AU-7900 and was built around a pure complementary direct-coupled power amplifier stage. The unit supports separation of preamp and main amplifier sections via a rear-panel switch and includes a full suite of audio controls including loudness, low/high filters, muting, and a stereo/mono selector.
Specifications
| Rated power output (both channels driven, 8Ω, 20Hz–20kHz) | 45W + 45W |
| Rated power output (both channels driven, 4Ω, 20Hz–20kHz) | 55W + 55W |
| Maximum power output (4Ω, 1kHz) | 80W + 80W |
| Total harmonic distortion (at rated output) | 0.1% or less |
| Total harmonic distortion (at 1/2 rated output) | 0.08% or less |
| Intermodulation distortion (SMPTE) | 0.1% or less |
| Power bandwidth (IHF, 8Ω) | 5 Hz – 40 kHz |
| Frequency response (at 1W) | 10 Hz – 50 kHz +0, -1.5 dB |
| Damping factor (8Ω) | 80 |
| Channel separation, Phono (1 kHz) | 50 dB or more |
| Channel separation, Aux/Tuner/Tape (1 kHz) | 55 dB or more |
| Channel separation, Power amp in (1 kHz) | 60 dB or more |
| Signal-to-noise ratio (IHF), Phono | 75 dB or more |
| Signal-to-noise ratio (IHF), Aux/Tuner/Tape | 90 dB or more |
| Signal-to-noise ratio (IHF), Power amp in | 100 dB or more |
| RIAA equalization deviation | 30 Hz to 15 kHz ± 0.3 dB |
| Phono maximum allowable input (1 kHz, THD 0.1%) | 250 mV |
| Input sensitivity/impedance, Phono1 | 2.5 mV / 30kΩ, 50kΩ, 100kΩ (selectable) |
| Input sensitivity/impedance, Phono2 | 2.5 mV / 50kΩ |
| Input sensitivity/impedance, Aux/Tuner/Tape (pin) | 130 mV / 50kΩ |
| Input sensitivity/impedance, Tape (DIN) | 130 mV |
| Input sensitivity/impedance, Power amp in | 700 mV / 50kΩ |
| Record output, Tape Rec (pin) | 130 mV |
| Record output, Tape Rec (DIN) | 30 mV |
| Tone control range, Bass (50 Hz) | ± 13 dB |
| Tone control range, Midrange (1.5 kHz) | ± 5 dB |
| Tone control range, Treble (15 kHz) | ± 13 dB |
| Loudness contour (volume at -30dB) | +10 dB at 50 Hz, +8 dB at 10 kHz |
| Low filter cutoff | -3 dB at 70 Hz (6 dB/octave) |
| High filter cutoff | -3 dB at 7 kHz (6 dB/octave) |
| Muting attenuation | 0 dB, -20 dB |
| Power consumption, rated | 106W |
| Power consumption, maximum | 300W |
| Dimensions (W x H x D) | 430 x 132 x 312 mm |
| Weight | 11.5 kg |
| Original price | ¥53,000 (approx. 1976) |
Design
The AU-5900 uses a pure complementary direct-coupled power amplifier circuit with a ±51V dual power supply. The driver stage features a Darlington 3-stage configuration with active load and first-stage dual transistors, while the input stage is a differential amplifier with good DC balance. The phono equalizer employs an NF-type circuit with four low-noise transistors and precision CR components, and Phono1 offers 3-step impedance selection (30kΩ, 50kΩ, 100kΩ). The preamp and power amp sections can be separated via a rear switch. The chassis-less design uses a one-point grounding system with an independently mounted transformer to reduce noise, and internal components are mounted directly to a single board to minimize wiring. Protection circuits include DC output detection (relay), temperature monitoring, and ASO current limiting. A stabilized power supply serves all stages except the driver and output stages, and the unit includes a spare AC outlet.
Product Family
The AU-5900 is part of Sansui’s AU-xxx0 series and is closely related to the AU-6900 and AU-7900, sharing service manual documentation and core design principles.
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