Audio Database

SU-A4
Commentary

An amplifier that pursues the ideal waveform transmission in a preamplifier.

All stages are class A operation and all stages are FET inputs. The MC pre-preamp of the ICL, the phono equalizer of the ICL, and a full DC amplifier (flat amplifier and buffer amplifier) are added. This allows two MC inputs and one MM input to pass through only one coupling capacitor, while the high-level input is DC-amplified to the output terminal without passing through any capacitor.
The flat amplifier and buffer amplifier have a two stage configuration with a SEPP output stage as a dual FET differential amplifier circuit with well-matched input characteristics, cascode, and current mirror load.
The output transistor uses a high-ft SLPT to reduce distortion and provide wide and flat frequency characteristics.

The MC pre-pre-amplifier is composed of 4 para-elements of super-low noise FET, and the phono equalizer is an input stage of differential amplification cascode current mirror load by super-low noise dual FET with well-matched characteristics, thereby realizing ICL.
The equalizer section is equipped with an equalizer subsonic filter to cut out ultra-low frequency noise caused by warping of records, etc.

The SU-A4 is equipped with a DC buffer amplifier in the next stage of the DC flat amplifier to limit the output impedance to 0.2 Ω.
As a result, it is possible to add 2500 additional power amplifiers based on the conventional output impedance standard, and no signal is transmitted even when a power amplifier is connected with a shield cable of 100m.
In addition, since the output impedance is 0.2 Ω, the damping factor is 40 for an 8 Ω load, and the SU-A4 achieves high stability so that it can sound for a short time even when a speaker is directly connected to the SU-A4.

A protection circuit using a current limiter is mounted in anticipation of a short circuit at the output terminal.

As a tone control function, Super Bass / Super Treble is equipped in addition to general bass / treble.
The Super Bass allows you to extend the speaker's frequency response by up to one octave into the lower range with a shelving tone with a steep rise of 12dB/oct. and a boost of up to 12 dB. The turnover frequency can also vary continuously from 50 to 200 Hz to match the speaker.
Super Treble can be used in combination with Treble to correct the mid-range and high-range peaks in the frequency characteristics of the cartridge.
These tone control functions are inserted between the DC flat amplifier and the DC buffer amplifier with a gain of 1 and turned on by a via tone switch. When turned off, the tone control function is in straight DC mode, indicated by an LED on the front panel.

The volume uses CP (conductive plastic) resistor with excellent abrasion resistance (no degradation even at 50 million revolutions). The surface of the resistor is mirror-finished, and combined with the multi-contact sliding brush, the contact resistance is reduced to 1 / 2 of the conventional one.
The SU-A4 uses two CP volumes per channel (before and after the flat amplifier) for a total of four CP volumes to eliminate minute noise after volume reduction, and the CP resistors are accurately calibrated by a computer to provide a decibel indication of volume.

The CP volume is equipped with a loudness tap, and the turnover is switched in two stages.
The 500 hz is for small speakers and the 250 hz is for large speakers.

Equipped with -20dB audio muting.

Equipped with a REC selector.

Two pre-out terminals and on/off switches are used.

Comes with removable pocket door and memory card for controls.

Gold-plated terminals are used for all rear panel terminals.

Equipped with an interlocking AC outlet that can turn the power of the power amplifier on/off.

Equipped with two Phono systems and two tape terminal systems.

Model Rating
Type Stereo DC control amplifier
Input Sensitivity / Impedance Phono1, 2 mm : 2.5mV/47k Ω
Phono1 MC : 100 μ V/47 Ω
Tuner, Aux, Tape : 150mV/47k Ω
Total harmonic distortion rate (20 Hz to 20 kHz) Tuner, Aux, Tape, Phono MM, MC : 0.001% (VR max, 5 Voutput)
0.001% (VR -30dB, 1 Voutput)
Signal-to-noise ratio (IHF-A) Phono MM:90dB
Phono MC : 78 dB (250 μ V input)
Tuner, Aux, Tape : 105 dB
Frequency characteristic Phono MM : 20 Hz to 100 kHz, RIAA ± 0.2 dB
Phono MC/MM : 20 Hz to 20 kHz, RIAA ± 0.15 dB
Tuner, Aux, Tape : DC ~ 20 khz + 0 -0.1 db
DC ~ 400 khz + 0 -3dB
Maximum Allowable Input (1 kHz, RMS) Phono MM:300mV
Phono MC:12mV
Shelving tone Super bass : + 0 to + 12 dB (20 Hz, 12dB/oct)
Bass : + / - 5 dB (50 Hz)
Treble : ± 5 dB (20 kHz)
Super treble : ± 10 dB (50 kHz, 12dB/oct.)
Turnover frequencies Super bass (12dB/oct) : 50 Hz to 20 Hz continuously variable
bass:500Hz
treble:2kHz
super treble:8kHz
Filter EQ Subsonic : 20 Hz, -12dB/oct.
Loudness control
(VR-30dB)
Turnover frequencies 250 Hz : + 8 dB (25 Hz)
Turnover frequencies 500 Hz : + 8 dB (50 Hz)
Output Voltage / Impedance Rec out : 150mV/500 Ω
Pre out : 1V/0.2 Ω
Pre-out maximum output voltage 15V
Power switch interlock AC outlet Maximum power supply : 600W
Pwer 100 VAC, 50Hz/60Hz
Power consumption 65W
External dimensions Width 430x Height 97x Depth 360 mm
Weight 8.8kg