SANSUI AU - α 907i MOS Limited

Commentary

In commemoration of the 40th anniversary of the founding of Sansui, this pre-main amplifier was completed by thoroughly pursuing all elements that make up the amplifier such as circuit, mechanism and material.

The power element that determines the characteristics of the amplifier is a MOS FET that has the same characteristics as the SANSUI specification.
By using a strictly matched parallel push-pull configuration, coupled with an α -X balanced circuit, high-quality and stable drive performance can be obtained even with changes in the impedance and phase of the speakers.

It is equipped with a unique balanced power supply that is independent from the ground line and closed loop, and the current is always equal on the + side and - side to prevent adverse effects caused by power supply imbalance. It is also resistant to noise and power supply fluctuation from the AC line and realizes a clean power supply.
In addition to the master regulator, the equalizer, pre-unit, and main unit are equipped with a local regulator on the PCB to follow the dynamically changing music signal.

It uses an α -X balanced circuit, a transmission and amplification method unique to SANSUI.
The signal circuit including the power stage by the MOS FET and the α -X balance circuit to the power circuit are made to be consistent structure, and by driving from both directions equally on the + side and - side, unnecessary harmonic components are canceled, and a powerful speaker drive with low distortion factor is realized.
In addition, because it is isolated from ground, there is no noise from the power supply system, and there is no IHM (Interface Hum Modulation) caused by back electromotive force from the speakers.

To enable high-purity balanced transmission and amplification, it is equipped with a power amplifier and direct function with balanced input and normal input.
By connecting to a CD player with a balanced output, you can configure a playback system with balanced transmission and amplification from the source to the speakers.

Equipped with a source direct function that passes through the muting, subsonic filter and balance control accessory circuit and connects all input sources directly to the α -X balanced circuit.

The power supply section is equipped with a newly developed ultra-large power transformer filled with high-density filler to prevent vibration and heat generation.
In addition, we have achieved low impedance and high speed in the entire power supply section by adopting a low-distortion, high-speed custom power supply capacitor and fast recovery diode for the newly developed Limited.

The power supply section is placed in the center, and the power amplifier section mounted on a large heat sinker is arranged symmetrically and separately. The twin monaural construction is adopted, and all of signal path, heat radiation, and strength are considered.
In addition, copper plating is applied to the separator that separates each stage to completely eliminate the effects of electromagnetic noise and magnetic distortion due to digital nature.
Each separator is fixed to the bonnet and bottom plate by large screws, and the whole chassis is integrated into a solid structure.

In addition, oxygen-free copper plates are used for mounting parts such as power MOS FET, power transformer, power block capacitor, master volume, etc. in order to completely eliminate vibration and resonance.
In addition, vibration is suppressed by the use of a board with vibration damping measures for the power section and a heat sinker and insulator made of pure copper muku.
Based on multi-mode vibration analysis when a sweep signal is applied to the amplifier to obtain a rated output, we have carefully examined the minimum material and shape to minimize the vibration of each part.

1.1 parts are carefully selected. Resistors are selected to match the characteristics of each circuit. Capacitors are carefully selected after repeated hearings.

It uses a 6-series master volume that can control the level of both the rear of the input selector (2 series) and the front of the power amplifier (4 series) simultaneously.
This increases the volume control range and allows you to narrow down to -90dB.

Model Rating

Type	Reference Integrated Amplifier
Power Amplifier Unit
Rated Output (10 Hz to 20 kHz, Both Channel Drive)	6 Ω : 100W + 100W 8 Ω : 80W + 80W
Total harmonic distortion factor (at effective output)	0.01% or Less (8 Ω)
Cross modulation distortion factor (at effective output)	0.01% or Less (8 Ω)
Damping factor	150 (8 Ω)
Frequency Response (1W)	DC ~ 300 khz + 0 -3dB
Input Sensitivity / Impedance (1 kHz)	Balance / Normal : 1V/3k Ω
Signal-to-noise ratio (A network)	120 dB or more
TIM (SAWTOOTH)	Measurement limit value or less
Slew rate	± 200 v / μ sec (8 Ω)
Rise time	0.5 μ sec
<Pre-part>
Input Sensitivity / Impedance (1 kHz)	Phono MM : 2.5mV/47k Ω Phono MC : 300 μ V/100 Ω CD, Tuner, Line1, 2, Tape1, 2, 3 : 150mV/20k Ω
Phono maximum allowable input (1 kHz)	MM:250mV MC:25mV
RIAA characteristics	Phono (MM) : 20 Hz to 20 kHz ± 0.2 dB
Signal-to-noise ratio	Phono MM : 90 dB or more Phono MC : 75 dB or more CD, Tuner, Line, Tape : 110 dB or more
Tone control	Maximum variation of Bass : ± 5 dB (50 Hz) Maximum variation of Treble : ± 5 dB (15 kHz) Turnover frequency : 75 Hz, 150 Hz
Subsonic filter	16 Hz (-3dB), 6dB/oct.
Loudness (Volume -30dB)	50Hz:+6dB 10kHz:+4dB
Audio Muting	-20dB(1kHz)
<General>
Rated power consumption	260W
External dimensions	Width 472x Height 161.5x Depth 441 mm
Weight	31kg