Audio Database

AU - α 907 Limited
Commentary

This is a limited third generation pre-main amplifier made by kneading everything without deflection to any circuit, mechanism or parts.

It is equipped with the HYPER α -X balance circuit of the wide range DC amplifier configuration of all stages, which is a high-dimensional integration of SANSUI's original α -X balance amplifier technology.
In order to minimize dynamic noise in the circuit, a Uilson current mirror high CMRR type constant current circuit is incorporated in the first stage of the power amplifier and pre-amplifier to realize a theoretical CMRR improvement effect of 140 dB.
We have also selected an old-model MOS FET (2SK405/2SJ115) as an amplifier.

For the power amplifier part, Premain is the first to use Teflon substrate, which was used in C-2302 VINTAGE, the highest model at the time of SANSUI, and proved effective in improving sound quality.
The dielectric constant and dissipation factor of Teflon are extremely small, eliminating adverse effects on signals passing through the circuit, such as electromagnetic wave hopping.
By utilizing the ability to absorb vibrations caused by internal loss, we prevent interference with sound quality caused by vibrations in the circuit.

The power supply section uses a closed loop configuration that is independent from the ground so that a large current can be supplied stably.
Each stage such as power stage and voltage amplification stage is completely separated to prevent mutual interference.
In order to achieve low leakage flux, the power transformer has a four layered shield case with high-density fillers inside, resulting in a larger size with a total weight of 13 kg. Both the primary and secondary drawers use OFC leads that emphasize sound quality.
We have also developed a custom-made, oval-shaped electrolytic capacitor.

Based on the concept of realizing a housing design that takes into account the nature of vibration rather than suppressing vibration blindly with a heavy chassis, it uses reinforced twin monaural construction that takes the optimum weight balance of the set into consideration.
The natural vibration interference between the power supply system and signal system is canceled by the layout effect.

As a countermeasure against various vibrations caused by electrical and mechanical operations and changes in tone color caused by the physical properties of materials, we have established our own isolation theory using Teflon and pure copper materials.
Based on this concept, the generation and transmission of vibration is totally interrupted and controlled from the viewpoint that all parts and parts of the amplifier are linked together, not separately.

In order to effectively absorb unwanted internal and external vibrations, we cut pure copper materials with excellent damping characteristics and apply gold plating to the insulators.
In addition, a Teflon sheet is sandwiched between the pure copper base plate and a felt is attached to the installation part to further improve stability and vibration control.
In addition, a 6-mm-thick aluminum bonnet coated with paint containing copper powder is fixed with Teflon material and gold-plated screws to enhance the rigidity of the housing.

Sound quality parts are examined through repeated viewing to prevent unnecessary coloring, and all possibilities to prevent distortion, noise and loss, such as the use of high-purity 6N copper band for power supply, are examined.

The speakers are connected using an OFC alloy 24-carat hardened gold plated terminal made by WBT of Germany that boasts an exquisite cutting accuracy of 2/100mm or less.
It supports bi-wiring connections as well as banana plugs and very thick speaker cables.

It is equipped with functions such as power amplifier, direct, source power direct, phono equalizer (MC, MM) and REC selector, and has 10 gold-plated input terminals.

Model Rating
Type Integrated amplifier
Power Amplifier Unit
Effective output (10 Hz to 20 kHz
Simultaneous operation on both channels)
6 Ω : 100W + 100W
8 Ω : 80W + 80W
Total harmonic distortion factor (at effective output) 0.01% or Less (8 Ω)
Frequency Response (1W) DC ~ 300 kHz, + 0 -3dB
Cross modulation distortion factor 0.01% or Less (8 Ω)
Damping factor 150 (8 Ω)
Input Sensitivity / Impedance 1V/5k Ω (1 kHz)
Signal-to-noise ratio (A network) 120 dB or more
Dynamic Power 6 Ω : 100W
4 Ω : 130W
2 Ω : 170W
TIM (SAWTOOTH) Measurement limit value or less
Slew rate 200 V / μ sec
Rise time 0.5 μ sec
<Pre-part>
Input Sensitivity / Impedance
(1kHz)
Phono MM : 2.5mV/47k Ω
Phono MC : 300 μ V/100 Ω
CD, Tuner, Line, Tape/DAT1 ・ 2 : 150mV/20k Ω
Phono maximum allowable input MM(THD 0.01%):250mV
MC(THD 0.1%):25mV
Frequency Response (1W) Phono MM : 20 Hz to 20 kHz, ± 0.2 dB
CD, Tuner, Line, Tape/DAT-1 / 2 : DC ~ 300 Hz, + 0 -3dB
Signal-to-noise ratio (A network) Phono MM : 90 dB or more
Phono MC : 75 dB or more
CD, Tuner, Line, Tape/DAT-1 / 2 : 110 dB or more
Subsonic filter 16 Hz (-3dB), 6dB/oct.
Loudness 50Hz:+4dB
10kHz:+3dB
<General>
Rated power consumption 280W
External dimensions Width 466x Height 166x Depth 453 mm
Weight 34.0kg