SANSUI AU-D707X (1983)
A high-end integrated amplifier from Sansui’s 07 series, released in 1983 with advanced balanced circuitry and MC cartridge support.
Overview
The Sansui GX 707 refers to a hi-fi system that likely included the SANSUI AU-D707X, a high-performance integrated DC amplifier released in 1983. While no standalone component named "GX 707" was documented, the AU-D707X amplifier—presumed to be its core—was engineered with extensive refinements for audiophile-grade signal purity. It features an X-balanced amplifier design with fully balanced input, output, power supply, and feedback circuitry. Built as an evolution of the AU-D707F Extra, it includes ground floating circuits and a dual bridge power supply to minimize interference and distortion.
Specifications
| Exact product name | SANSUI AU-D707X |
| Manufacturer | Sansui |
| Product type | Integrated DC amplifier / Integrated amplifier |
| Production years | Released in 1983 |
| Original price | ¥ 129,000 |
| Effective output (both channel drive) | 150W + 150W (8 Ω, 1 kHz) |
| Effective output (both channel drive) | 200W + 200W (4 Ω, 1 kHz) |
| Effective output (both channel drive) | 170W + 170W (6 Ω, 1 kHz) |
| Effective power | 110W + 110W (8 Ω, 10 Hz to 20 kHz, THD 0.003%) |
| Total harmonic distortion factor (10 Hz to 20 kHz at effective output) | 0.003% or Less (8 Ω) |
| Intermodulation Distortion Factor (60 Hz : 7 kHz = 4 : 1, SMPTE) | 0.003% or Less (8 Ω) |
| Output Bandwidth (IHF, both channel operation, THD 0.02%) | 5 Hz ~ 80 kHz (8 Ω) |
| Damping factor (new IHF, 20 Hz to 20 kHz) | 100 |
| Frequency Response (1W) | DC ~ 300 kHz +0 -3dB |
| TIM Strain (Sawtooth method) | Below the measurement limit |
| Envelope distortion | Below the measurement limit |
| Slew rate | ± 200 V / μ sec |
| Rise time | 0.5 μ sec |
| Input Sensitivity / Input Impedance (1 kHz) | Phono MM : 2.5mV/47k Ω |
| Input Sensitivity / Input Impedance (1 kHz) | Phono High MC : 2.5mV/100 Ω |
| Input Sensitivity / Input Impedance (1 kHz) | Phono MC Low : 100 μV/5.3 Ω (Uses MC transformer) |
| Input Sensitivity / Input Impedance (1 kHz) | Phono MC High : 300 μV/40 Ω (Uses MC transformer) |
| Input Sensitivity / Input Impedance (1 kHz) | CD, Tuner, Tape1, 2 : 150mV/47k Ω |
| Phono maximum allowable input (1 kHz, THD 0.01%) | MM: 300mV |
| Phono maximum allowable input (1 kHz, THD 0.01%) | MC High : 25 mV (Transformer Type) |
| Output Level / Impedance | Tape rec : 150mV/600 Ω |
| RIAA Deviation (MM, Rec out) | 20 Hz to 300 kHz ± 0.2 dB |
| Signal-to-noise ratio (A network, short circuit) | Phono MM: 90 dB or more |
| Signal-to-noise ratio (A network, short circuit) | Phono MC : 80 dB or more (70 μV) |
| Signal-to-noise ratio (A network, short circuit) | CD, Tuner, Tape : 110 dB or more |
| Phono input equivalent noise (A network, short circuit) | Phono1, 2 mm : -142dBV |
| Phono input equivalent noise (A network, short circuit) | Phono1, 2 mc : -160dBV |
| Channel Separation (1 kHz) | Phono1, 2 mm : 60 dB or more |
| Channel Separation (1 kHz) | Phono1, 2 mc : 50 dB or more |
| Channel Separation (1 kHz) | Tuner, Aux, Tape play : 80 dB or more |
| Tone control | Bass : ± 10 dB (50 Hz) Treble : ± 10 dB (10 kHz) |
| Tone selector | Bass : 150 Hz, 300 Hz Treble : 3 kHz, 6 kHz |
| Filter | Low : 16 Hz (-3dB, 6dB/oct.) High : 20 kHz (-3dB, 6dB/oct.) |
| Loudness (Volume -30dB) | + 8 dB at 50 Hz, + 6 dB at 10 kHz |
| Audio Muting | -20dB |
| Rated power consumption (Electrical Appliance and Material Control Law) | 320W |
| External dimensions | Width 466 x Height 161 x Depth 431 mm |
| Weight | 17.5kg |
Design
The amplifier uses an X-balanced design with balanced input, output, power supply, twin diamond balanced differential circuit, and balanced feedback. It builds on the AU-D707F Extra with ground floating circuits to isolate input, output, and power supply grounds. The power supply features a large toroidal transformer and pure focus capacitors in a dual bridge configuration with independent windings to reduce IHM distortion. Four independent power supplies serve the pre, pre-drive, and power sections (L/R) to prevent interference. A linear step MC transformer supports MC cartridges with two-stage impedance switching (Low/High). The RIAA equalizer is discrete, non-IC, and accurate to ±0.2 dB from 20 Hz to 300 kHz. The power amplifier uses a diamond differential pre-drive stage and Super FF (NFB + feed-forward) in the power stage, regulated by a linear servo. High-quality components include copper foil Styrofoam capacitors, non-resonant RM resistors, and non-magnetic (NM) elements. The chassis is copper-plated to eliminate magnetic distortion, with gold-plated speaker terminals, a polarity-display AC cord, twin relay speaker switching for two systems, dual source recording selectors, and two-circuit tape monitoring/copying. Mirror-finish side wood panels are available in black and silver.
Product Family
The AU-D707X is part of Sansui's "07" series, which includes models like the AU-D707F Extra and AU-D707X.
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