Externally, it is made up of three parts and a volume knob, as shown in the diagram on the left.

The top plate is made of forged carbon with a random pattern, and the rest of the case is made of machined aluminum.

Forged carbon is a carbon material with a pattern that differs from twill and plain weave, and is used in supercars and other vehicles in recent years.
It was adopted to reduce weight and improve appearance.

By placing the volume control at the corner, there are no protruding parts, and the flat sides of the volume knob make it difficult to accidentally operate it.

In addition, the screws are not visible from any angle other than the bottom, so the appearance has also been carefully considered.

The internal structure is a high-density mounting, as the goal was to make it as portable as the Tsuranagi size.

The main circuit board is two stories high, with the sub terminal board located on the third and fourth floors.

The second floor and terminal boards are wired, and the same pure silver wire as the dedicated cable is used.

The method of connecting the main board and terminal board with wires is inherited from Tsuranagi, and the intention of this is to prevent mechanical stress from being applied to the terminals.

This is because if everything is fixed rigidly, stress will be applied to the soldered parts of the terminals, and cracks will form in the solder during use, causing poor contact.

There is a heat sink and shield case on the second floor, and the sides of the shield case are thermally coupled to the aluminum casing with silicone rubber, effectively dissipating heat.

There is a flat area on the second-floor circuit board where there are no components, but it is constructed so that the back of the shield case and the silicon rubber are thermally coupled to that area.

2階の回路基板には部品のない平らな部分があるが、シールドケースの裏側とシリコンゴムが熱的に結合する構造になっている。

The front panel has 3.5mm unbalanced input, 4.4mm balanced input, Rch output, and Lch output from the right.

The back has only a USB Type-C charging port.
When viewed from above, the corners have a sense of volume, and the power is turned on and off by pressing and holding the button.

Only the bottom is covered with Toray's Ultrasuede to prevent scratches.
There is a small hole on the side, which is provided for heat dissipation.

There are small holes on the side, which are provided for heat dissipation. There are 7 power supply systems per channel, making a total of 14 systems for the left and right channels.

The battery voltage is boosted and inverted by the dual power generation circuit, and a linear power supply circuit is used in the latter stage to supply a clean power supply to the amplifier, removing noise.

The dual power supply generation circuit is divided into two parts: one for low voltage and high current, and the other for high voltage and low current.
This is because the electronic volume requires high voltage operation of ±10V or more, so it is set up separately.

If everything were operated at high voltage, power consumption would be very high, reducing the amount of time it could be used and causing the amount of heat generated to become unrealistic, so it was configured in this way.

In addition, the linear power supply circuit uses a super high-performance linear regulator that can even eliminate high-frequency noise, which was also used in Tsuranagi.

Since a total of 14 of these are required, the high cost is unavoidable, but this design is based on prioritizing sound quality.

The reason why there is a separate linear regulator for each block of the amplifier circuit is to prevent interference between circuits and to improve the sense of separation and resolution of the sound.

High-capacity capacitors are placed in various locations to prevent the power supply from fluctuating as it flows from upstream to downstream.

Also, because it was not possible to fit a relay into the amplifier output for protection due to space constraints, it was necessary to protect it using a different method.

The FUGAKU amplifier has a protection circuit that turns off the linear regulator and short-circuits to GND in order to discharge the charge in the large-capacity capacitor.

By shorting the power supply to GND the moment the power is turned off, the amplifier outputs a signal based on the power supply voltage, so if the power supply goes to zero, the output will also go to zero.

The protection circuit operates when the power is turned off normally, when DC leaks from the amplifier, when the power circuit malfunctions, or when the inside becomes extremely hot.

This protective circuit makes it possible to provide protection without using a relay, making it possible to create a palm-sized amplifier.
What's more, the amplifier has no relays in its output, so the output impedance is low, making it possible to drive the earphones more directly.

.This is an amp that has been greatly developed based on the TSURANAGI, with the addition of crossover circuits and a review of the circuits.

The first improvement is that we have added a low-pass filter to the first dan.

In the Tsuranagi, the final stage power amplifier also served as a low-pass filter, but by bringing it to the first stage, we were able to reduce the noise as a whole.

In addition, the fact that there are no longer any power amplifiers with bandwidth limitations also contributes to improved responsiveness when driving earphones.

The capacitors used in this low-pass filter are a special type called an X2Y capacitor, which is a well-matched combination of two capacitors specialized for processing balanced signals.

There is an IC that switches between unbalanced and balanced inputs in front of the low-pass filter, so that all signals are input as balanced signals to the low-pass filter.

This structure is the same as Tsuranagi, but instead of a toggle switch, a very low-resistance, low-distortion semiconductor switch is used, and together with the terminal insertion/removal detection function, it also has a function that automatically selects the input terminal.

The differential line receiver also uses a new circuit that differs from Tsuranagi, and it has been made more powerful by splitting the single IC into two ICs.
As a result, the residual noise here is less than 1/5.

The electronic volume is also an area of improvement, so we've updated it to the MUSES72323 made by New Japan Radio Co.
This improves the sense of airiness and freshness required of high-end equipment.

In addition, the volume steps have been halved from 0.5dB to 0.25dB, making it possible to adjust the volume more finely.

The buffer amp is an OPAMP with FET input, and the electronic volume minimizes the current output and distortion, while the crossover circuit has a large capacity capacitor that drives it firmly.

Power amplifiers have different configurations for dynamic drivers and other types.
In addition, a DC bias circuit has been added to the power amplifier that drives the MEMS driver.

First, the power amplifier that drives the dynamic driver is a circuit that combines a fully differential amplifier and a current feedback amplifier, similar to the TSURANAGI, and drives the signal while converting it to a balanced signal.

What makes it more than just a plus is that we have reviewed the parts used and reduced the output impedance to improve the driving force.

Power amplifiers other than dynamic drivers use voltage feedback amplifiers with completely new circuits.
This is also designed to drive headphones, and has a high performance that is excessive for earphones.

Although it is not shown in the diagram, a DC servo amplifier is also incorporated into the power amplifier other than the MEMS in FUGAKU in order to eliminate the AC coupling capacitor.

We have reviewed the component constants of the DC servo amplifier and further simplified the feedback method to the power amplifier, improving it so that it has low noise with a small number of components.

We have developed a low-noise original circuit based on a linear regulator for the DC bias circuit for MEMS, as shown in the block diagram of the power supply circuit above.

The main circuit board has a two-story structure, and the boards are connected by four terminals.

The main components of the first-floor circuit board are the power supply circuit, charging circuit, and protection circuit, as well as the microcontroller that controls them. The power supply circuit is the main function, so the copper foil is twice as thick as usual to reduce the resistance.

The power supply circuit is equipped with a large-capacity capacitor of 10,000 uF or more, and is mounted as much as possible to achieve a low center of gravity for sound.

Both main boards are double-sided, and the layout is designed so that there is no interference due to noise or other factors through the airspace.

On the back of the first floor, there is a switch that short-circuits the GND of the dual power supply generation circuit, microcomputer, charging circuit, and protection circuit, which are the sources of noise, so that noise does not get into the amplifier circuit.

On the first floor, there are volume and linear regulators, large-capacity capacitors, and comparators for protection circuits, which are all analog circuits.

Similar to Tsuranagi, this system detects the position of the knob using the built-in microcontroller's AD converter and volume, and sends a control signal to the electronic volume.
Sound signals do not pass through the volume control.

High-performance conductive polymer capacitors are used for the large-capacity capacitors.

On the front side of the second floor, only the power amplifier is installed, and a shielded case that also serves as a heat sink is mounted because the amplifier circuit generates relatively large amounts of heat.

On the back of the second floor there is a circuit that ranges from semiconductor switches to crossovers, and the functions are clearly divided between the front and back.

The second-floor circuit board is an 8-layer board, which is used for the first time. It has a structure that allocates four layers for different functions on the front and back, and improves low impedance and noise resistance.

Basically, the audio signal is routed to the inner layer, and the outer layer is used as a GND shield, making the wiring less susceptible to external noise.

As with the Tsuranagi, the power supply and GND are laid out so that they do not have a common impedance, and the GND is consolidated into a single point, connected to the chassis ground with gold-plated screws.

With conventional earphones, matching of left and right sides and adjustment of frequency characteristics have been achieved by selecting the drivers, but this still results in increased costs and limits on the adjustment.

FUGAKU has a trimming function that ensures mass-produced products do not deviate from the target frequency characteristics.

As a result, we have achieved a mismatch of less than ±10% or ±0.83dB between the left and right channels and the target curve.

The power amplifier is configured as an inverting amplifier as shown in the diagram on the right, and is a circuit that allows you to set the attenuation and amplification freely.

The frequency response of earphone drivers varies depending on the type, but since efficiency also differs, it is necessary to adjust the overall level in each band so that they connect smoothly when combined.

The power amplifier is responsible for this level matching, and it has a function that allows the driver's level to be fine-tuned before shipping, and this is the trimming function.

Before the drivers are incorporated into the earphones, we measure the acoustic characteristics of each driver individually to determine what kind of trimming to perform based on the degree of variation.

This is a cable for connecting an amplifier to earphones, but it uses a new type of wire that differs from our SHIROGANE silver wire cable.

The material is the same, but the thickness of the wire per core has been reduced, and even when bundled into a cable with 16 cores, it still retains its practicality and has a sufficient total conductor capacity.

The reason for having 16 cores is because it is necessary to connect the amplifier independently to the 5-way earphones, and because the dynamic driver is a balanced drive, there are 2 cores, 4 cores for the BA and MEMS HOT, and 2 cores for GND.

Even a single core GND is fine, but we use 8 cores rather than 7 because it is more stable in terms of shape, and to separate the GND for BA and MEMS to the earphone jack to prevent a muddy feeling.

By adding up the above, we have 8 cores on one side and 16 cores in total on both sides.

In addition, the internal wiring of the earphones is made of pure silver litz wire, and as there was no wire material that met our standards and was also easy to use as internal wiring, we developed it from scratch for FUGAKU.

We have prepared six colors of insulating sleeves for ease of assembly.

The amplifier side is also wired with a cable between the main board and the terminal board, but this also uses the same 16-core cable and is made of silver wire.

Using a large amount of silver wire was a challenge even in the development of SHIROGANE, as it not only brings out the good points of silver but also its unique quirks, so the high-quality processing of the amplifier's internal components and the 16-core cable's high-quality processing are Ultimate grade, tuned specifically for FUGAKU.

The cable is made of a material that absorbs and shields electromagnetic waves, static electricity generated when it moves, and vibrations near the terminals and at branching points.

We have multiple types of materials, and the final sound is adjusted by deciding which order to process them in and where to process them, and this is the high-quality processing.
These materials are attached to electronic components in portable amplifiers.