Audio Database

AU - α 907i
Commentary

Stereo pre-main amplifier with α -X balanced circuit.

In the α -X balanced circuit, both the + side and the - side of the signal are transmitted and amplified by an independent special amplifier. Since it is separated from the ground, the effect of noise and distortion from the ground is suppressed in principle.
In addition, the input stage of the power section has a differential balance input configuration using a low-noise FET, and the common-mode rejection ratio CMRR (Common Mode Rejection Rato) between the + side and - side of the signal system is large, so that the circuit itself cancels common-mode noise and distortion.
In addition, unlike conventional amplifiers, which drive between the output of the amplifier and the ground, this amplifier is driven from both the + side and the - side. Therefore, noise from the power supply system is not mixed in and IHM (Interface Hum Modulation) due to back electromotive force from the speakers is prevented.

The power supply section uses a unique balanced power source that is independent from the ground and closed loop.
The current is always equal between the + side and the - side, which prevents adverse effects on the signal due to unbalanced power supply and is also resistant to noise from the AC line and power supply fluctuations.
The transformer is equipped with an ultra-large transformer with high-density filler for enhanced vibration and heat resistance.
In addition, a custom electrolytic capacitor for audio equipment with high charge / discharge speed and a high-current capacity fast recovery diode are used.

In addition to the master regulator combined with the power transformer, we have adopted a twin regulator system in which local regulators are placed on the phono equalizer board and preamplifier board.
The 2-stage regulator is resistant to fluctuations in power supply and load, enabling a stable and clean power supply.

A twin monaural construction is adopted in which the power supply section, mainly the power transformer, is placed in the center and the power amplifier section is placed symmetrically on the left and right sides of the power supply section.
In addition, we have adopted boards for the power section boards, which cut the fine vibration of the boards.

A solid and anti-flux chassis designed to eliminate vibration and noise interference is used. Each stage is completely separated and shielded by a separator, and five large insulators (CF5 insulators) with optimum load distribution are used.

The volume employs a high-precision 6-row detent type volume with little sound quality degradation and small left-right interlocking error. It can be narrowed down to around -90dB and the SN ratio on the mounting is improved.

The equalizer section for analog disks uses a discrete phono equalizer.

Equipped with a defeat tone control.

Equipped with a balance input capable of high-purity balance transmission and amplification and a power amplifier direct function.

Equipped with a source direct function that passes accessory circuits of subsonic filter, muting and balance control and connects all input sources directly to the pre-drive stage.

Model Rating
Type Α -X balanced integrated amplifier
Power Amplifier Unit
Rated output (20 Hz to 20 kHz
Both channel drive)
190W + 190W (6 Ω)
160W + 160W (8 Ω)
Total harmonic distortion factor (at effective output) 0.003% or Less (8 Ω)
Cross modulation distortion factor (at effective output) 0.003% or Less (8 Ω)
Damping factor 150 (8 Ω)
Frequency Response (1W) DC ~ 300 khz + 0 -3dB
Input Sensitivity / Impedance Balance, Normal : 1V/3k Ω (1 kHz)
Signal-to-noise ratio (A network) 120 dB or more
TIM (SAWTOOTH) Measurement limit value or less
Slew rate ± 200 v / μ sec (6 Ω)
Rise time 0.5 μ sec
Preamplifier Section
Input Sensitivity / Impedance
(1kHz)
Phono MM : 2.5mV/47k Ω
Phono MC : 300 μ V/100 Ω
CD, Tuner, Line, Prossesor, Tape/DAT/Play1 ・ 2 ・ 3 : 150mV/47k Ω
Phono maximum allowable input
(THD 0.01%)
MM:250mV
MC:25mV
Frequency characteristic Phono MM : 20 Hz to 20 kHz ± 0.2 dB
CD, Line, Tape/DAT/Play1 / 2 / 3 : DC ~ 300 khz + 0 -3dB
Signal-to-noise ratio Phono MM : 90 dB or more
Phono MC : 75 dB or more
Tuner, Line, CD, Tape/DAT/Play1 / 2 / 3 : 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 50Hz:+6dB
10kHz:+4dB
<General>
Rated power consumption 400W
External dimensions Width 448x Height 160x Depth 441 mm
Weight 28.0kg