Audio Database

Image of A-717

This pre-main amplifier was developed as the culmination of a fundamental review of the circuit, construction and physical properties, which are the origins of the amplifier, in order to respond to digital sources.

The design philosophy of this amplifier is roughly divided into three points.
First, each signal block is appropriately arranged in order to make the signal path the shortest distance. Second, thorough anti-vibration and anti-resonance measures are taken. Third, the drive performance of the speaker is improved at low load.
We are solving various problems by investing various technologies in these areas.

First, a structure called direct construction is adopted in order to make the signal path the shortest distance.
By separating each circuit block and shielding the I/O block, adverse effects such as internal signal degradation and interference between signals can be prevented.
The input block allows remote mechanical control of the Input & Recording Selector and the main volume to minimize signal routing. The input signal selected by the Input Selector does not flow to the front panel when the Source Direct Switch is turned ON, so you can enjoy even more pure sound.
The power amplifier block is laid out along the signal flow and guides the output of the power stage directly to the speaker selector. Again, the distance from the power supply is the shortest.
In the speaker selector block, the speaker terminals are directly attached to the circuit board on which the relay is attached so that the shortest speaker terminal A is given priority and the terminal A is placed on the lower side.

In order to completely eliminate vibration and resonance, a resonance free construction method is adopted. Four types of honeycomb shapes are adopted, and vibration and resonance are totally reduced by combining the transformer part and volume system.
Honeycomb made by punching is used for bottom plates and bonnet cases. For extruded aluminum honeycomb heat sinks to effectively suppress vibration and resonance of power transistors. Honeycomb made by resin molding is used for large honeycomb insulators to suppress external vibration.
The transformer case is made of cast iron with high shielding effect, high rigidity, high internal loss, excellent vibration damping characteristics, and almost no resonance frequency. Pitch material with high thermal conductivity is filled between the case and the transformer body, and a heat radiation fan is installed to prevent the internal resistance of the transformer winding from increasing due to temperature rise.
In addition, it uses a newly developed large-capacity sealed capacitor that is less susceptible to electromagnetic induction.

Since sound quality is adversely affected by a structure in which a load is applied to the axis of the volume or vibration is generated, we have adopted a method of balancing the weight in both directions centering on the bearing of the rotary knob of the volume to prevent mechanical stress from being applied to the volume body. In addition, in order to minimize the effect of the vibration of the amplifier, the shield cover supporting the volume base is floated from the body part with special paper to absorb the resonance of 2 to 4 kHz which is harmful to sound quality.

Non-switching circuit type III is adopted.
This circuit is an upgraded version of Type II, in which switching distortion does not occur in principle, and has succeeded in suppressing thermal distortion by instantaneously stabilizing the idle current that drifts when the power switch is turned on, when a large signal is input, or when the outside temperature changes.
In addition, detection and correction of input / output signal difference of the power stage is improved to reduce non-linear distortion. Furthermore, voltage amplification stage and power amplification stage are clearly separated. Since the power amplification stage concentrates on the speaker drive, there is no influence on the voltage amplification stage even at large output, and speaker drive performance at low load is improved.

It uses a newly developed sealed capacitor in which the cathode of the aluminum electrolytic capacitor and the aluminum case are connected more securely. By strongly shielding the capacitor element, noise from the capacitor itself is eliminated, and high S/N is achieved.

The Phono equalizer can be turned off when you do not listen to a record to prevent unwanted noise.
In addition, the recording selector also has an OFF function, and the sound purity is enhanced by a simple circuit configuration.
The equalizer uses a unique NF-CR type circuit to stabilize the operation in the mid - and high-frequency range, and uses low-noise Hi-gm FET to improve S/N.

Copper plated parts are used for the rear panel and bottom plate to prevent electro-striction and vibration.

The power cord is a thick oxygen-free copper power cord with polarity indication. This cord is made of insulating material with low dielectric constant to reduce the capacitance of the power cord, thus reducing the influence of external noise.
In addition, the polarity of transformer windings is controlled to minimize noise coming through the cord.

Uses parts that emphasize sound quality such as fuse for audio.

Machined pure aluminum is used for rotary knobs and other parts.

Model Rating
Type Stereo pre-main amplifier
Effective power
(both channels driven, 20 Hz to 20 kHz)
100W + 100W (0.003%, 8 Ω)
120W + 120W (0.003%, 6 Ω)
150W + 150W (0.005%, 4 Ω)
Damping factor (1 kHz, 8 Ω) 200
Input Sensitivity / Impedance Phono MC : 0.2mV/100 Ω
Phono MM : 2.5mV/50k Ω
CD, Tuner, Line, Tape : 150mV/50k Ω
Phono maximum allowable input
(0.008% harmonic distortion rate, 1 kHz)
Phono MC:19mV
Phono MM:200mV
Output Level / Impedance Tape Rec, ADPT Out : 150mV/2.2k Ω
Frequency characteristic Phono MC : 20 Hz to 20 kHz ± 0.3 dB
Phono MM : 20 Hz to 20 kHz ± 0.2 dB
CD, Tuner, Line, Tape : 1 hz to 150 khz + 0 to 3 db
Tone Control (-40dB) Bass : ± 8 dB (100 Hz)
Treble : ± 8 dB (10 kHz)
Subsonic filter 5Hz(12dB/oct)
Loudness contour (-40dB) 100Hz/10kHz(5dB/3dB)
(IHFA network, short circuit)
Phono MC:71dB(0.25mV)
Phono MM:89dB(2.5mV)
CD, Tuner, Line, DAT/Tape1, Tape2 : 108 dB
Speaker load impedance 4 Ω ~ 16 Ω
Power supply voltage 100 VAC, 50Hz/60Hz
AC outlet Power switch interlock : 2 systems (200W)
Power switch not linked : 1 system (100W)
Power consumption (Electrical Appliance and Material Control Law) 270W
External dimensions Width 420x Height 162x Depth 435 mm
Weight 19.6kg