The Japanese company Fostex presents the second version of its premium DAC – Fostex HP-A8mk2 based on the new AK4490 digital-to-analog conversion chip and other interesting innovations. The appearance has not changed compared to the first model. The workmanship is also at the same high level.
The first acquaintance with the Fostex HP-A8mk2 evokes a pleasant impression. The body is made of faceted thick-walled black aluminum, and the front panel is made of glass. The build quality is very high. The controls have no play and feel nice to press. The soft light of the OLED screen, the absence of eye-burning LEDs and excessive overload of buttons, the strict design – everything suggests that the manufacturer cares about the consumer from the very beginning.
Having two headphone outputs will be useful if you want to share music with someone or compare a pair of headphones. The outputs operate simultaneously. Using the Output Set button you can select where the sound will go: to the headphones or to the line output on the rear panel.
The volume is adjusted, as expected, in decibels in 0.5 dB steps. Moreover, the volume is adjustable both on the headphone output and on the linear one. The Input Set control functions as both a button and a knob. You can select the desired input, as well as enter the menu and configure parameters. On the rear panel there are all kinds of switching connectors, including Analog In and Digital Out, which are extremely rare for household appliances. But first things first.
The manufacturer claims that the device supports all possible digital audio formats from 44.1 to 192 kHz with a resolution of up to 32 bits, as well as DSD streams with a frequency from 2.8 to 11.2 MHz. For Apple computers, the DSD frequency is limited to 5.6 MHz, and for playback from an SD card – 2.8 MHz. The USB input works with its own driver. It has an asynchronous operating mode, ASIO output and DSD support. (Asynchronous mode is a standard requirement for all modern DACs. It makes it possible to control the transfer rate on the receiver side, receive data in a buffer and use its own high-quality generator next to the DAC.) There is also a slot for an SD / SDHC card with the ability to play files from it WAV, DSF and AIFF, which not only adds functionality to the device, but also makes it work independently.
The headphone amplifier and post-DAC filter are designed using discrete elements, without the use of operational amplifiers. Power supply stabilizers are also discrete. The capacitors used in the analog and power supply circuits are audiophile Nichicon Muse and ELNA. The digital-to-analog converter chip is a new chip from AKM, AK4490, it has a signal-to-noise ratio of 123 dB and a KG below −112 dB. In addition, AKM has added three more new audio filtering modes. For frequencies that are multiples of 44.1 and 48 kHz, separate quartz oscillators are used, which eliminates the need to recalculate non-multiple frequencies.
The USB controller is based on a Texas Instruments TM320C55 digital processor. It has 800 MIPS performance and a 40-bit arithmetic processor. The S/PDIF receiver and transmitter are made on AK4118 chips. In general, the input digital part of the signal processing is built similarly to the first version of the HP-A8, but has slight differences and is labeled MK2.
To adjust the volume, a JRC Muses72320 microcircuit is used; it is powered by Muses8920 operational amplifiers instead of the previous OPA604AP. They are similar in technical parameters, but Muses are positioned as operational amplifiers specifically for audio applications. In addition, the Muses8920, unlike the OPA604, is dual-channel, which suggests a more significant design change than just changing the type of op-amp.
There are also changes at the line input: instead of the previous LME49710NA, one two-channel OPA1642 is installed, also positioned as an op-amp for audio applications. The line output and ear amplifier have not undergone any changes. The linear output has its own buffer, independent of the ear amplifier, made of discrete elements, which is a big plus, as it reduces the influence of the signal source impedance and the capacitance of the connecting cables on the sound. The output power transistors of the ear amplifier 2SA1930/2SC5171 are used to build amplifiers with a power of up to 20 W, which provides a good power reserve.
Characteristics of Fostex HP-A8mk2
Inputs: USB port, 2 optical S/PDIF, XLR-3 AES/EBU, SD slot, RCA analog stereo
Outputs: 2 × Jack 6.3 mm for stereo headphones, RCA analog stereo, optical S/PDIF
Supported operating modes: 16/24/32 bit 44.1/48/88.2/96/176.4/192 kHz, DSD 2.8/5.6/11.2 MHz, USB High Speed
Headphone output parameters:
Frequency response: 10 Hz – 80 kHz at ±3 dB
Maximum power: 700 mW into 32 ohm load
Harmonic distortion: less than 0.002% at 1 kHz, 32 ohm load and 100 mW power
Allowable headphone impedance: 16 —600 Ohm
Linear output parameters:
Frequency range: 10 Hz – 80 kHz at ±3 dB
Harmonic distortion: less than 0.002% at 1 kHz
Optimal load resistance: 10 kOhm Power consumption
: 24 W from 220 V mains
Dimensions: 213×78× 314 mm
Weight: 3.8 kg
