Audio Database

SU-V7
Commentary

Based on the new class A amplifier technology developed in the SU-V10, this integrated amplifier further reduces distortion by installing linear feedback that realizes the distortion theoretical value = 0.

The linear feedback circuit is a circuit that returns to the ideal of NFB theory and assumes that the naked amplification degree of the amplifier is ∞. By forming an independent feedback circuit that enables the naked amplification degree of the amplifier to be ∞ in the NFB loop by making the best of the multiple feedback circuit technology, the theoretical value of distortion = 0, pure gain without the influence of elements or power supply, and speaker drive without the influence of back electromotive force or wire.
In the SU-V7, the bandwidth of the independent feedback circuit is limited, and the feedback amount is gradually reduced as the frequency increases. With this configuration, a gain increase of about 20 dB is obtained at 100 kHz. Even in the ultra-high frequency range, the NFB is 10 times more stable than the conventional one, and the distortion is greatly reduced. In the DC region, gain increase up to infinity is obtained, and the input conversion is 2 μ V / ℃, which is excellent stability against DC drift.

The synchronous bias circuit developed by Technics Co., Ltd., which is the foundation of New Class A, eliminates switching distortion caused by pause by supplying a constant bias current in synchronization with the pause cycle to output transistors that normally go into complete pause alternately in order to obtain high efficiency in class B and class AB, and keeping the output stage in the active state at all times.
In addition, since the signal path and bias current path are independent, the output stage always keeps an appropriate operating point. Together with the function of a high-speed diode with dual characteristics, crossover distortion is eliminated, and high efficiency and A-class nigori sound quality is achieved.

By integrating the output stage and power supply unit, it uses an insulated power block that completely eliminates the adverse effects of electromagnetic fields, and suppresses the generation of electromagnetic waves from the root.
In addition, magnetic materials with a high shielding effect are used for the chassis and cover to suppress external induction.

It uses a newly developed servo power supply that drives all stages including the output stage at a constant voltage.
This circuit consists of two thyristors (SCRs) on the secondary side of the power transformer and a reference voltage / output voltage comparison circuit for time-controlling the energization angle. This reduces the influence of voltage fluctuations on the primary side and when the output stage consumes large power and large current, and supplies a constant voltage to all stages including the output stage.
This circuit realizes a constant impedance of 1 / 10 that of conventional power supply, and has excellent regulation equal to 10 times the power supply part of conventional power supply.
In addition, because the secondary side of the power transformer controls the conduction angle of the SCR, switching noise does not affect other equipment unlike the control method on the primary side.

The equalizer section is equipped with a high gain phono equalizer of MC basic design.
The first stage employs a low-noise dual-FET differential amplifier. Both MM and MC are ICL equalizers that eliminate capacitors. This realizes a simple circuit configuration with only one coupling capacitor between the phono input and the speaker terminal when the operation mode is set to straight DC.
In addition, a high-gain IC (100 dB or more) is adopted in the next stage of the phono equalizer. Combined with the adoption of low-noise FET, gain switching between MM and MC is realized, and the MC cartridge can be used directly.
In addition, the other high-gain inputs at the straight DC position are amplified directly to the speaker terminal by the high-gain DC amplifier, enabling faithful waveform transmission.

The tone control uses the NF loop of the main amplifier to achieve a high SN ratio and low distortion.

It is equipped with a pure electronic protection circuit. If a DC component occurs at the speaker terminal, the speaker is disconnected by relay.
This circuit also protects the amplifier against shorting of the speaker terminals or an abnormally low impedance load.

The power transformer is a resin-sealed power transformer with low vibration and low leakage flux.

Equipped with a rush current prevention circuit to save peak current for a few seconds after power is turned on.

It is equipped with a subsonic filter that can cut out unwanted low-frequency signals due to warping or eccentricity of records.

A stand-alone rec/input selector is used to enable FM air check and tape-to-tape dubbing while listening to records.

Equipped with two speaker outputs.

Model Rating
Type Integrated DC amplifier
<Overall characteristics of Tuner, Aux → SP out>
Effective output (20 Hz to 20 kHz) 80W + 80W (4 Ω, 0.007%)
80W + 80W (8 Ω, 0.003%)
Total harmonic distortion factor 0.003% (Rated Output -3dB, 20 hz to 20 khz)
Power Bandwidth (THD 0.02%) 5 Hz to 100 kHz
Frequency Response (Straight DC) 20 Hz ~ 20 kHz + 0 -0.2 dB
0.5 Hz ~ 170 kHz + 0 -3dB
TIM Unmeasurable
SN ratio (IHF-A, straight DC) 100dB
Residual Noise (straight DC) 550 μ V
Damping factor (8 Ω) 60
Load impedance Main or remote : 4 Ω ~ 16 Ω
Main and remote : 8 Ω ~ 16 Ω
<Other characteristics>
Input Sensitivity / Impedance Phono MM : 2.5mV/47k Ω
Phono MC : 170 μ V/220 Ω
Tuner, Aux, Tape : 150mV/27k Ω
Phono maximum allowable input
(1 kHz, RMS, THD 0.01%)
MM:150mV
MC:10mV
Pre-part total harmonic distortion factor Phono MM → Rec out (5 V) : 0.005%
Phono SN ratio MM:86dB
MC (250 μ V input) : 68 dB
Phono frequency characteristics 20 Hz to 20 kHz
RIAA ± 0.5 dB
Tone control Bass : ± 10 dB (50 Hz)
Treble : ± 10 dB (20 kHz)
Filter High : 7 kHz, -6dB/oct.
Subsonic : 20 Hz, -12dB/oct.
Loudness control + 9 dB (50 Hz, Volume -30dB)
Pre-part output voltage Rec out:150mV
<General>
Pwer 100 VAC, 50Hz/60Hz
Power consumption 140W
External dimensions Width 430x Height 120x Depth 362 mm
Weight 9.5kg