◇TSURANAGI portable amplifier

 
The TSURANAGI portable amplifier was developed as an evaluation device for the development of BriseAudio's high-end earphone cables and high-end portable line cables (mini-mini cables) in order to create an ideal portable audio environment.
We also use BriseAudio cables for the internal wiring, and have installed electromagnetic wave absorbing shielding material and CNT (carbon nanotube) used in our high-end cables such as MURAKUMO and YATONO on the circuit board to further improve the sound quality.
 
 

 

※The line cable shown in the photo is the YATONO-MINI-LE (for balanced connection).

【Overview】

◆Portable amplifier with analog input and analog output (for both earphones and headphones)
◆Balanced input/output support
◆Balanced output for unbalanced input signals
◆Pentaconn 4.4mm connector
◆Input: Balanced/unbalanced (5-pole 4.4 mm + 3-pole 3.5 mm)
◆Output: Balanced (5pole 4.4mm + 4pole 2.5mm)
◆High quality electronic volume IC MUSES72320
◆High input impedance and high common mode noise rejection by low noise differential line receiver
◆High input impedance & high common mode noise rejection by low noise differential operational amplifier
◆Low distortion current feedback amplifier to drive headphones
◆No input/output coupling capacitors due to double power supply and DC servo
◆Charging from USB Type C
◆Continuous playback time of about 8 hours
◆Translated with www.DeepL.com/Translator (free version)
 
Click here for the latest manual.


【Product Concept】

 
In response to the recent increase in players with balanced LINE OUT and the use of headphones and earphones with balanced drive, Brise Audio has developed a portable amplifier with balanced input and output, which is ideal for the development of mini-mini cables and re-cables.
It also has a 3-pole 3.5mm unbalanced input for connection to conventional players, which is internally converted to a balanced signal with high precision before being output.
The output terminals are equipped with both 5-pole 4.4mm and 4-pole 2.5mm jacks.
With the theme of expressing the source information in its entirety, the design is based on low distortion and low noise.
Low distortion and low noise circuits and components are used in all signal processing circuits, because low performance of any circuit from input to output will result in poor overall performance.
The high input impedance of 1MΩ also minimizes the distortion output by the player upstream.
A differential line receiver converts the balanced signal into an unbalanced signal with high precision once and removes extraneous noise, thus ensuring clean playback even in noisy outdoor environments.
The key composite amplifier in this amplifier performs unbalanced-to-balanced conversion and current amplification simultaneously.
Distortion is further reduced by including a current feedback amplifier in the feedback loop of the fully differential operational amplifier.
A regulator with ultra-low noise and ultra-high PSRR is used for the power supply circuit, and is supplied to each channel independently.
A six-layer circuit board is used to eliminate common impedance and improve signal quality in terms of layout.

 
 
As in the development of our cables, TSURANAGI is designed with the following goals in mind: more sound output, wider bandwidth, no sound distortion, low noise floor, and minimizing the effects of external environments.
TSURANAGI is designed with the guiding principle of minimizing the influence of the external environment and bringing out the best performance of the equipment as much as possible in terms of sound quality and performance.
The TSURANAGI is a reference for our cable development environment, and we aimed to create an amplifier that would not spoil the performance and sound quality of the cable.
Cables are also designed so that they do not become the bottleneck of our equipment, and we aim to further improve the level of our products in-house.

 

  
Other innovations regarding the amplifier include a bandwidth of 2Hz to 200kHz, which ensures flat reproduction in the audible range of 20Hz to 20kHz.
The differential DC servo amplifier detects the differential DC of the balanced output and returns it to the fully differential operational amplifier so that the offset is zero.
This suppresses the output DC offset to +/-50μV and makes it possible to eliminate the coupling capacitor on the input side.
The OPAMP used in the DC servo amplifier is also an ultra-high-performance, low-noise product to prevent deterioration in sound quality.
Even in the unlikely event of a DC offset, the on-board microcontroller detects it and protects the earphones.
All the power supply decoupling capacitors in the signal processing circuits are film capacitors and conductive polymer aluminum capacitors.
For the sake of sound quality, all components have been carefully selected and used without regard to cost.
  
 

 
The power supply circuit has been placed independently in order to ensure thorough separation between Lch and Rch and to provide ample power supply capacity.
The switching regulator and linear regulator, even as stand-alone units, have ample current capability to meet the maximum rating of the amplifier.
In addition, since the regulators are independently supplied, they can keep up with the instantaneous current consumption.
Dual power supplies are generated from the battery power supply using a switching regulator, which is designed to have a switching frequency of 2MHz and a large output capacitor, resulting in very low noise for a switching regulator.
The purpose of generating dual power supplies is to eliminate coupling capacitors on the output side and to achieve low distortion operation due to the high supply voltage.
The op-amps are generally operated at +/-15V, but since the power loss is not negligible when the voltage is boosted to this level, the voltage is set to +/-9.3V to ensure battery life.
An ultra-high performance linear regulator is installed in the second stage of the switching regulator to thoroughly eliminate residual switching noise and achieve low-noise reproduction.
This linear regulator is capable of eliminating noise up to the high frequency band, so even switching noise of 2MHz is reliably eliminated.
Two of the six layers are used for the power supply, and interference is prevented by separating the positive and negative layers and inserting a GND layer in between.
As with the power supply, the GND wiring is also wired in planes to suppress impedance, and the signal GND and power GND are separated to the point where they intersect at a single point, not only between channels but also within channels, to ensure thorough separation.
At the point where they are grounded at a single point, they are grounded to the aluminum chassis, eliminating GND loops and suppressing electromagnetic interference from outside.

 


【Configuration reasons for unbalanced conversion】

 
◆Brise Audio's goal in developing a portable amplifier with ideal sound quality was to express the source information in its entirety.
In order to achieve this goal, low distortion and low noise were given the highest priority in the circuit design, and thorough common mode noise elimination was also focused on to achieve low noise.

◆In order to ensure stable playback at all times without interference from radio waves and other sources, we have adopted a configuration that eliminates common mode noise to the greatest extent possible.
 
◆In order to achieve both low noise and low distortion, an ultra-low distortion audio differential line receiver with a high common mode noise rejection ratio over a wide bandwidth is used for the common mode noise rejection circuit.
◆In order to overcome the problem that the attenuation of the positive side and the negative side of the circuit is different (although the error is small because it is an electronic volume), it is converted to unbalance in the first stage of the electronic volume.
◆In order to make the most of the limited resources of a portable amplifier, the unbalanced circuit in the middle of the amplifier is designed to have low power consumption and a spacious mounting area.
 

【About common mode noise】

Common mode noise is noise that is transmitted in the same phase as the signal. It can be transmitted from the player to the cable, or from the space using the cable, etc. as an antenna.
If the common mode noise rejection capability of the amplifier is insufficient, the noise will leak into the headphones even if the amplifier is balanced. You may feel it when you put the amplifier close to a smart phone or commercial power supply.
With TSURANAGI, you will not hear such noise at all.
The general purpose of a balanced signal is to cancel noise by taking the difference at the receiving end, even if noise is added during transmission (such as on a long cable).
When taking the difference, it is most important that the common mode noise on the positive and negative signals have the same phase and the same amplitude.
As a cable, the two wires that pass through the positive and negative signals are placed adjacent to each other using a twisted pair or similar method to pick up noise in the same phase and amplitude.
Twisted pairs also have the effect of noise cancellation through magnetic field cancellation, so they are often used for unbalanced signals as well.
The amplifier side has the role of taking the difference between balanced signals. At that time, if the positive and negative signals are not differenced with high precision, the cancellation effect will be weakened even if the signals are transmitted in a balanced manner.
When the amplifier actually takes the difference, it inverts (further minuses) the negative signal and adds it to the positive signal. The gain at this time must not be uneven.
The figure below shows a case where TSURANAGI has a balanced configuration in all stages, and the configuration of a product that performs unbalanced conversion.



 
If all stages were balanced, the difference would be in the headphones. The signal passes through various amplifiers and volumes before reaching the headphones.
Therefore, when the signal reaches the headphones, the magnitude of the positive and negative signals is slightly different, so the cancellation effect is weakened.
On the other hand, unbalanced conversion (taking the difference) in the first stage eliminates the degradation of common mode noise rejection caused by gain errors in the amplifier and volume in the second stage.
TSURANAGI uses the MUSES72320 electronic volume, which is an order of magnitude better matched than ordinary variable volumes.
However, in order to thoroughly eliminate common-mode noise, a differential line receiver with integrated high-precision matching resistors is used before the volume, and the difference is taken before signal processing.
As a result, the volume circuit and voltage amplification stage only need to be used for two channels, allowing for a more spacious board layout and reducing power consumption.
The resistors that make up the differential line receiver determine the gain when taking the difference. It is important that the characteristics of this resistor and the internal OPAMP match in positive and negative.
Even with unbalanced inputs, the differential line receiver receives a single-ended signal as a differential signal.
Since it works to cancel the common mode noise riding on the signal line and GND, it is more advantageous to noise than an amplifier with general unbalanced input.
 


 
 
 
 
 

【Why is the output being converted to balanced?】

This is partly to achieve a balanced input/output configuration, but there are several advantages to driving in a balanced manner in the first place.
In order to make headphones sound good, the amplifier needs to supply a lot of current.
The more current an amplifier outputs, the more likely it is to distort. With a balanced amplifier, the even-order distortion that occurs can be cancelled out by the headphones.
As a side note, it is difficult to cancel odd-order distortion, and basically the only way to do so is to use an amplifier (including its configuration) that does not generate odd-order distortion in the first place, even if it outputs current.
In order to suppress odd-order distortion, TSURANAGI has a composite amplifier configuration, in which the distortion of the current feedback amplifier that outputs current is negatively returned, and the fully differential amplifier suppresses it.
This operation also suppresses even-order distortion, so the overall distortion is even smaller.
Another reason is that it can output a large amplitude even with the limited power supply voltage of a portable device.
With a single-ended amplifier, the amplitude is sent to the headphones only on the HOT side, but with BTL, the amplitude is driven by both the HOT and COLD amplifiers (source and sink).
The maximum amplitude that can be sent to the headphones can be doubled even with the same power supply voltage. Since the voltage is doubled, the current is also doubled, which is why BTL amplifiers can deliver four times more power than single-ended.
 
 

【 Product lineup 】
 
▶ TSURANAGI  MPN:PA001-S 
 ※The second lot is now sold out.

The third lot is scheduled to be shipped in small quantities between January and March 2022.
Due to the shortage of semiconductors, there is always a possibility that the delivery date will be changed, in which case we will announce it as soon as possible.
There are also other reasons why we cannot ship all at once, as follows.
 
After the PCB manufacturers and other components arrive, they undergo the following processes.
 
1. All products are assembled at our factory in Japan.
 
2.We will measure all TSURANAGI to see if they have the required characteristics.
 
3.Only those units that pass the test are subjected to special high quality sound construction (shielding, vibration control, etc.).
 
4.Finally, all units are subjected to a listening test before being shipped.
Since the above processes are time-consuming, they are shipped in small quantities.
This is the reason why it is not possible to ship each lot at once.
 
The same production lot will be shipped at different times in different countries, so some regions have already started pre-ordering the third lot, while others have already started shipping the second lot.

  

This is a compatibility chart for mini-mini cables used in combination with TSURANAGI and each player.

 

 4.4mm (player side, line output) to 4.4mm (TSURANAGI)
  ※プレイIf the GND (5 poles) is connected to the 4.4mm output on the player side.

 
 Connect 2 x 4.4mm & 3.5mm (player side, line output) to 4.4mm (TSURANAGI)
※If GND (5 poles) is not connected to the 4.4mm output on the player side.

Hiby
R8, NewR6, R5(Need to be switched on the software side)
Astell&Kern
KANN ALPHA(Need to be switched on the software side)
SONY
NW-WM1Z, NW-WM1A, NW-ZX500series, NW-ZX300series

▶ Connect two 2.5mm & 3.5mm (player side, line output) to 4.4mm (TSURANAGI)

※Unbalanced connection (3.5 mm to 3.5 mm) can be used with any player that has 3.5 mm line output.

Astell&Kern
KANN ALPHA, KANN CUBE, SP1000, SP1000M, SP2000, SE100, SE200, SR15, SR25, SA700
※AK products require line output to be specified on the software side.
※Be sure to insert the 3.5mm plug first; if the 2.5mm plug is inserted first, the balanced line output mode will not be activated.
Hiby
R6

※If you have any questions about products not listed, please feel free to contact us.
  The correspondence table will be updated as needed.
 
 

TSURANAGI specification table


  Unbalanced  Balanced
Input  3pole3.5mm   4.4 mm(4pole+GND)
Output  -- 4.4 mm(4pole+GND) / 4pole 2.5mm 
 Voltage gain (volume max)  10.5 dB 
Maximum input(volume max)   1.5 Vrms (2.1Vpeak)
Frequency response(-3dB)   2 Hz - 200 kHz
Recommended load impedance

 16 ohm or more

Maximum output power(16ohm, THD+N<0.01%)

700 mW + 700 mW

Maximum output power(32ohm, THD+N<0.01%)

1000 mW + 1000 mW

Maximum output power(300ohm, THD+N<0.01%)

100 mW + 100 mW

"THD+N (BW=20kHz, 1Vrms Output,16ohm)"

< 0.005 %
"THD+N (BW=20kHz, 1Vrms Output,300ohm)"

< 0.002 %

"THD+N (BW=20kHz, 3.4Vrms  Output,300ohm)"

< 0.0007 %

Crosstalk(20Hz - 20kHz)

< -100 dB

Battery life

8 h

Weight

360 g

W x H x D, Not including protrusions

80 mm x 30 mm x 120 mm

Charge terminal USB Type-C
Battery capacity 7.4 V 2800 mAh
Charge time < 5 h (Use a 5V2A AC adapter)