Audio Database

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Commentary

Stereo preamplifier using W / Super Servo system.

The W super servo system is a system that suppresses cross modulation due to unnecessary ultra-low frequencies and equivalently cancels unnecessary components caused by the impedance between the earth and the ground.
By using the supplied Super Servo code, the + side input of the connection code amplifier detects and suppresses harmful ultra-low frequency components, and the - side servo amplifier cancels harmful components caused by resistance, inductance and contact resistance of the output itself with the main amplifier, thereby preventing interference between channels and degradation of separation.

In order to take advantage of the characteristics of Super Servo, the MC amplifier does not use a step-up transformer, but uses a one stage type equalizer amplifier that can be used with all cartridges from MM type to MC type by increasing the gain of the equalizer amplifier.
In the first stage differential amplifier section, two ultra-low-noise high-Gm FETs are thermally coupled in an aluminum case to improve thermal balance and suppress external thermal noise.
The S/N ratio is improved by connecting the differential part in parallel to lower the impedance. This differential amplifier has a cascode connection to reduce the mirror feedback capacitance to obtain a wider frequency response.
The second stage differential amplifier and the third stage differential amplifier with current mirror ensure large naked gain, and the high gain amplifier with partial feedback by pole setting realizes excellent stability and low distortion factor.
In addition, the final stage uses class A push-pull to transmit the signal to the next stage amplifier with low distortion even under heavy load in the high frequency range.

Direct tone method is used for tone control.
Since it is composed of only passive elements and has a unique circuit system that does not allow harmful capacitors to enter the signal passage path, sound field correction can be performed without deterioration of sound quality.

Since the output amplifier uses the super servo system, there is no need to add an output capacitor. Since the low-frequency time constant is determined only by the servo circuit, the low-frequency shortage at low impedance loads is eliminated.

The power supply section uses independent NF-type constant voltage stabilizing circuits on the left and right sides, and each circuit block is directly connected by copper bus (bus) lines to prevent low impedance of the power supply line and interference between each block.

Non-magnetic materials such as copper, aluminum, and brass are used for shielding materials and parts.
This prevents the magnetic flux generated from the circuit from generating higher harmonics (mainly third harmonics that are harmful to audibility) due to the non-linearity of the magnetic circuit, which adversely affects sound quality.

Equipped with a cartridge selector for compatibility with all cartridges.

In consideration of the effect on sound quality due to the arrangement of each part and the routing of the line, the arrangement analysis of the signal system is carried out in order.
For example, in order to input a signal to a specified circuit at a short distance as possible, direct switching with a remote control switch is adopted to prevent crosstalk and degradation of high-frequency characteristics caused by the routing of signal lines.

All circuit parts have been thoroughly examined and tested, and parts with sufficient characteristics, durability and feeling of use have been adopted.
For example, the input pin jack for handling a weak current is plated with thick pure gold so that the effect of contact resistance does not sound quality.

Model Rating
Type W / Super Servo Type Stereo Preamplifier
Input Sensitivity / Impedance Phono MC : 130 μ V/100 Ω, 330 Ω
Phono High Gain MC : 2.5mV/100 Ω
Phono MM : 2.5mV/47k Ω, 100k Ω
Tuner, AUX, Tape Play : 150mV/47k Ω
Output Level / Impedance Tape Rec : 150mV/2.2k Ω
Output : 1.5 V, maximum 20V/220 Ω
Phono maximum allowable input (THD 0.05%)
MC: 17mV(1kHz)
82mV(10kHz)
MM, High MC : 300mV(1kHz)
1400mV(10kHz)
Total harmonic distortion factor (THD, 20 Hz to 20 kHz
Volume-3dB, Output 3 v)
MC : not more than 0.01%
MM : not more than 0.003%
Tuner, AUX, Tape : 0.003% or less
Intermodulation distortion factor (SMPTE70Hz : 7 khz = 4 : 1) 0.003% or Less (at Rated Output)
Signal-to-noise ratio (IHF-A network input shunt) MC:69dB
MM:86dB
Tuner, AUX, Tape : 100 dB
Tone Control (Volume-20dB) Bass : 70 Hz, ± 8 dB
Treble : 20 kHz, ± 8 dB
Filter characteristic High Cut : 7 kHz, 6dB/oct.
Subsonic Cut : 15Hz/20Hz, 6dB/oct
Muting -20dB
Transient killer operating time Power on:7sec
Power off:100msec
Semiconductor used Transistor : 47
FET : 6
IC : 4
Diode : 37 pcs
Pwer 100 VAC, 50Hz/60Hz
AC outlet Up to 1000W total
Power switch interlock : 2 systems
Power switch not linked : 1 system
Power consumption 20W (Electrical Appliance and Material Control Law)
Maximum external dimensions Width 450x Height 99x Depth 407 mm
Weight 7kg