Fostex HP-A8mk2 – review and test of USB-DAC for headphones with amplifier

Fostex HP-A8mk2

The Japanese company Fostex is widely known as a manufacturer of high-quality studio headphones and other audio equipment, mainly of professional focus – microphones, mixers and studio monitors. However, their products are of no less interest for high-quality home listening. They are significantly different from competitors in the market and are already winning their fans. Read more in our reviews Fostex HP-A8C and Fostex HP-A4BL.

However, time does not stand still, manufacturers of digital-to-analog converters represent new chips, with updated features and more functionality, followed by hardware manufacturers. Following the trend, Fostex introduced the second version of its award-winning DAC – Fostex HP-A8mk2 based on the new AK4490 digital-to-analog conversion chip and other interesting innovations.

Fostex HP-A8mk2 – price. Where is the best place to buy?

The recommended retail price for the Fostex HP A8mk2 in the US is $ 1 197,80. At this cost, you can order it on Amazon. Plus Shipping, so the total cost of Fostex HP-A8mk2 when ordering on Amazon will be about $ 1220,00. I would not recommend ordering anywhere else except on Amazon. Since you are less likely to find cheaper, and if you do not take into account the fact that Amazon is probably the most reliable online store, it still very often provides free shipping.


Packing Fostex HP-A8mk2

A huge and heavy black box with a glass front panel, a bunch of switches and a mass of ports behind – that’s the whole design of the device. Among stationary amplifiers it is difficult to find something unusual, but, it seems to me, Fostex managed to dilute the harsh appearance with pleasant details.


The glass of the front panel is interesting to glare at different angles, and the gold-plated inputs under the headphones immediately attract the eye. The device has an intuitive control, so that it will not be possible to sort out all the twirls of labor: volume, choice of sound source, sound output, power.

OLED-display visually displays all the actions, and the complete control panel allows you to climb into the jungle of settings and in more detail to rebuild the sound, amplification and other parameters.

High quality USB DAC with headphone amplifier Fostex HP-A8mk2
The appearance relative to the first model did not change. The quality of production is also at the same high level.

The first introduction to the Fostex HP-A8mk2 is a pleasant experience. The body is made of cut black thick-walled aluminum, and the front panel is made of glass. The build quality is very high. Controls do not lyuftyat and pleasantly pressed. Soft light OLED-screen, the absence of eye-burning LEDs and excessive congestion buttons, strict design – it all says that the manufacturer from the outset takes care of the consumer.

The presence of two headphone outputs will be useful if you want to share music with someone or compare a pair of headphones. The outputs work simultaneously. With the Output Set button, you can select where the sound goes: to the headphones or to the line output on the rear panel.

The volume control is performed, as it should be, in decibels in 0.5 dB increments. And the volume is regulated both on the headphone output, and on the line.

The Input Set control operates both as a button and as a controller. You can select the desired input, and also enter the menu and adjust the parameters.

Rear view of high quality USB DAC with headphone amplifier Fostex HP-A8mk2

On the rear panel are all kinds of switching connectors, including extremely rare for home appliances Analog In and Digital Out. But first things first.


The manufacturer claims for the device support for all possible digital sound formats from 44.1 to 192 kHz with a resolution of up to 32 bits, as well as a DSD stream from 2.8 to 11.2 MHz. For Apple computers, the DSD frequency is limited to 5.6 MHz, and for playback from the SD card – 2.8 MHz.
USB-input works with its own driver. It has an asynchronous mode of operation, output to ASIO and DSD support. (Asynchronous mode is a standard requirement for all modern DACs, it allows you to control the transmission speed on the receiver side, take data to the buffer and use your own high-quality generator next to the DAC.)
There is also an SD / SDHC card slot with the ability to play WAV, DSF and AIFF files from it, which not only adds functionality to the device, but also makes it work independently.
I would like to note a new remote control – with more comfortable rubber buttons and an increased number of functions.
The menu offers a wide range of settings, of which the most interesting are those that directly affect the sound quality:

  • Up Sampling, possible choice: x1, x2, x4 – multiplication of the sampling rate before applying to the digital-to-analog converter chip
  • Digital Filter, a possible choice consists of five options:
    • Short Dly Shap
    • Short Dly Slow
    • Sharp Roll-Off
    • Slow Roll-Off
    • Super Slow
  • MSCK Sel, possible choice: Dir or XTAL – choice of synchronization method
    • Dir – synchronization of the digital-to-analog converter from the clocks of the signal reconstructed by the S / PDIF-receiver
    • XTAL – use of internal high-quality cloak for DAC synchronization
  • Direct, possible selection: On, Off – when the On mode is turned on, the volume control of the line output is inactive, the volume is always the maximum

In addition to the USB-ASIO driver, the manufacturer offers a cute and minimalistic player that works via an ASIO driver exclusively with Fostex products. The sound at its use is excellent.

USB DAC with headphone amplifier Fostex HP-A8mk2

If you remove the top cover, you can make sure that everything is organized internally quite competently.
Back view high-quality USB DAC with headphone amplifier Fostex HP-A8mk2

The headphone amplifier and the filter coming after the DAC are designed on discrete elements, without the use of operational amplifiers. Stabilizers of power supplies are also made on a discrete basis. The used capacitors in analog and supply circuits are audiophile Nichicon Muse and ELNA. The chip of the digital-to-analog converter is a new chip from AKM, AK4490, it has a signal-to-noise ratio of 123 dB and KG below -112 dB. In addition, AKM added three more new filtering modes.
Fostex HP-A8mk2
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.
Fostex HP-A8mk2
The USB controller is made on a digital processor from Texas Instruments TM320C55. It has a performance of 800 MIPS and a 40-bit arithmetic processor. S / PDIF-receiver and transmitter are made on the chips AK4118. In general, the input digital part of the signal processing is built in the same way as the first version of the HP-A8, but has small differences and the MK2 labeling.

To adjust the volume, the JRC Muses72320 chip is used, its harness uses the Muses8920 opamp to replace the previous OPA604AP. By technical parameters, they are similar, but Muses are positioned as operational amplifiers for audio applications. In addition, the Muses8920, unlike the OPA604, are two-channel, suggesting a more significant change in the circuit than simply replacing the type of op-amp.

Fostex HP-A8mk2
On the linear input, too, there are changes: instead of the previous LME49710NA, one dual-channel OPA1642 is installed, also positioned as an op-amp for sound applications.
Fostex HP-A8mk2
The line output and the ear amplifier have not changed. The line output has its own buffer, independent of the ear amplifier, made on discrete elements, which is a big plus, since it reduces the effect on the sound of the source signal and the capacitances of the connecting cables.
Fostex HP-A8mk2
Output powerful transistors of the ear amplifier 2SA1930 / 2SC5171 are used to build amplifiers up to 20 W, which provides a good power reserve.
Fostex HP-A8mk2

Technical specifications 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 modes of operation:
    • 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 ​​
  • Parameters of the headphone output:
    • Frequency range: 10 Hz – 80 kHz with ± 3 dB
    • Maximum power: 700 mW at 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
  • Line Output Parameters:
    • Frequency range: 10 Hz – 80 kHz with ± 3 dB
    • Harmonic distortion: less than 0.002% at 1 kHz
    • >Optimum load resistance: 10 kΩ
  • Power consumption: 24W
  • Overall dimensions: 213 × 78 × 314 mm
  • Weight: 3.8 kg

To measure the parameters of the DAC, a measuring stand was assembled, providing a galvanic isolation of the measuring card from the 220-volt network in order to eliminate earth loops and to eliminate network noise outside the measured device. A similar bench was used to measure the first version of the HP-A8C, which means that the results can be compared directly. Block diagram of the stand:

Fostex HP-A8mk2
As a galvanic isolation, the Adnaco-S1A board is used, the measuring board is a modified Asus Essence STX with a minimum measured KG = 0.0002% and a noise level of -120 dB. The system is powered by a battery and linear stabilizers, which form the necessary voltages.
Information about USB-ASIO-driver:
Device: Fostex ASIO Driver
Input channels: 0
Output channels: 2
Input latency: 0
Output latency: 270
Min buffer size: 2048
Max buffer size: 2048
Preferred buffer size: 2048
Granularity: 0
ASIOOutputReady – supported
Sample rate:
8000 Hz – not supported
11025 Hz – not supported
16000 Hz – not supported
22050 Hz – not supported
32000 Hz – not supported
44100 Hz – supported
48000 Hz – supported
88200 Hz – supported
96000 Hz – supported
176400 Hz – supported
192000 Hz – supported
352800 Hz – supported
384000 Hz – not supported
Input channels:
Output channels:
Channel: 0 (Fostex USB Audio HP-A8 Out 01) – Int32LSB
Channel: 1 (Fostex USB Audio HP-A8 Out 02) – Int32LSB

Through the driver control panel, you can adjust the buffer size and see the current sampling rate.
Fostex control panel HP-A8mk2
So, a summary table of measurements in RMAA at frequencies from 44.1 to 192 kHz:
Fostex HP-A8mk2 measuring table in RMAA at frequencies from 44.1 to 192 kHz
Similar to the first version, we see excellent measured parameters at all frequencies, practically limited by the characteristics of the DAC chip. This confirms the literacy of the applied technical solutions and the absence of engineering errors. In addition, the measured data were an order of magnitude better than specified by the manufacturer.

The spectrum of nonlinear distortions at a sampling frequency of 192 kHz:
Fostex HP-A8mk2 Spectrum of nonlinear distortions at a sampling frequency of 192 kHz
The only difference from the first version, which draws attention to itself, is a small decrease in the dynamic range due to a greater noise level. If you pay attention to the spectrum, you can see that the noise level is somewhat raised in the range from 1 to 10 kHz. The incipient hump is present in the first version, but in the second it is more extended, which gives an increase in noise. Whether it’s good or bad is hard to judge; The fact is that up to a noise level of less than 110 dB single devices are reached even in a much higher price category, this is not a determining factor for the sound quality of the device.
Fostex HP-A8mk2 Spectrum of nonlinear distortions at a sampling frequency of 192 kHz
Measurements of the headphone amplifier were carried out in the same way, but the signal was taken from the output for the second pair of ears. The output power of the amplifier was 125 mW when using 32-ohm headphones as a load.
Fostex HP-A8mk2 Headphone Amplifier Measurements
As you can see, the parameters are as excellent, 5 times better than the ones claimed, and almost do not depend on the resistance of the headphones. This confirms the high overload capacity of the ear amplifier. Also worth paying attention to the low mutual penetration of channels under load. For amplifiers with a low-power power supply this parameter increases to -70 ..- 80 dB, then everything is all right.

Well and now the most interesting – we will consider modes of operation of filtering Digital Filter, 5 filters with different parameters. By itself, the digital filter (DF) is an integral part of any modern DAC. In general, its function is to shift the DAC conversion products to the high-frequency region, where they will lessen the useful signal and can be filtered by simpler (and therefore less influenced by the audible, audible signal) analog filters. Also, the function DF is an additional suppression of those frequencies in the reproduced signal, which, according to Kotel’nikov’s theorem, go beyond the limits of the workers at a given sampling frequency. In simple terms, DF in the DAC chip serves to ensure the most correct reproduction of a useful signal and filtering everything that is not such a signal.

However, everything is not so simple. The main drawback and reason for the appearance of different types of DF in one chip is the response of the DF itself to the pulse signal. Here is what AKM tells us about it:
Fostex HP-A8mk2 Headphone Amplifier Measurements

The table shows the response curves of the AK4490 chip for a single pulse at various settings in its DF. It is not difficult to see that in some modes the oscillatory process outside the pulse is expressed more clearly than in others. This is the response of DF to a pulsed aperiodic signal. There is nothing to worry about, this is a purely mathematical transformation of a signal with an infinite spectrum that goes beyond the bounds of Kotel’nikov’s theorem and never occurs in real musical material. Moreover, knowing the response, you can reverse the conversion and recreate the type of filter through which the signal passed, that is, the response of the filter is directly related to its characteristics.

Let’s leave for a time the impulse response and pay attention to the measurements of the frequency response of our Fostex at various DF settings:

Fostex HP-A8mk2 Headphone Amplifier Measurements

Fostex HP-A8mk2 Headphone Amplifier Measurements

It is evident that the reduction in emissions after the impact of a mythical pulse with an infinite spectrum occurs due to a decrease in the filter gain at high frequencies – roughly speaking, a decrease in its bandwidth in the high-frequency region. The frequency response of the Dly and Roll-Off filters overlapped, because they spectrally process the signal identically, but the response is differently distributed in the time domain. That is, for a mode with a low delay (Dly), the pulse front is processed practically without distortion, but then a longer response loop follows. In the mode with a large delay (Roll-Off), the response at the output appears before the arrival of the pulse and also symmetrically disappears after. This is because there is a delay line in the DF, whose signal is mathematically processed and only then fed to the output of the digital-to-analog converter. In Dly mode, this delay is sought to minimize, but for the listener this does not play any role. What difference does it make if the signal comes to your ears in 0.67 ms or 0.14 ms (for Dly mode) after the track is started?

Why all this is necessary? The answer for everyone can be different. The author of the article believes that marketers play an important role here, because each new function raises attention to the product. It is not so obvious how real the user really needs. That is, we feed a pulse with an infinite spectrum to the input of the DAC, which can not be mathematically processed by them, and we are heroically fighting the consequences through various installations of the FT. And the fact that high frequencies are cut off – well, sorry, but the momentum is more or less. That’s the whole point of marketing: we are presented with EQ as something completely new and a panacea. Engineers, developers of microcircuits and audio equipment developers are forced to follow this path, there is nothing to reproach them for.

However, there is another side: in some cases, for any particular person, certain music and equipment, it may be subjective to prefer this or that filter. The AKM table tries to shed some light on this issue. For example, if you do not like the sharp sound, you can put the Super Slow mode with a smooth HF downturn, and nothing will annoy you, the instruments will be approximate and more natural. In modes with low Dly delay, theoretically, drum instruments and driving music should sound better. But if you need the maximum quality of reproduction of all frequencies, then the standard mode of Sharp Roll-Off will be unrestricted.

If you are worried about the response to an impulse signal – never a self-respecting recording studio will allow the output of a track with frequencies that go beyond the theoretically acceptable range, and consequently all these response pictures have almost no meaning in real music. In simple words: if you limit the spectrum of the test pulse to the notorious 22.05 kHz, then all the graphics will look almost identical, just slightly different slope of the pulse shelf, which is reflected in the measurements of the frequency response. Since the frequency range of music is limited in exactly the same way, the amplitude of the frequency response of the DF will be much more influenced by the sound than its impulse characteristics outside the operating frequency range.

It is also interesting to compare the performance of AK4399 in Fostex HP-A8C and AK4490 in HP-A8mk2 in Sharp mode at different sampling rates:

Fostex HP-A8mk2 Headphone Amplifier Measurements

44.1 kHz

Fostex HP-A8mk2 Headphone Amplifier Measurements

96 kHz

Fostex HP-A8mk2 Headphone Amplifier Measurements

192 kHz

In the 44.1 kHz mode, both chips show almost the same result, but with an increase in the sampling frequency, the AK4399 has a noticeable decline at low frequencies, while the AK4490 has a noticeable decrease at high frequencies. And if the downturn on the HF AK4490 is most likely programmed to improve the impulse response (the amplitude response above 20 kHz is not so important), then the bust on the AK4399 Bass is likely to be some kind of defect in the chip or its DF. In any case, I would prefer to listen to the AK4490, which, in general, was confirmed during the audition.

A few words about the use of Up Sampling and Digital Out. Apsempling performs two functions. The first – adds “missing” counts. Due to its internal algorithm, it tries to do this as accurately as possible, “arranges” what is lost in the original signal with a low sampling frequency. The second, secondary, function – the up-sampler performs the role of an additional filter, shifting the interference and products of the DAC conversion into a higher frequency, inaudible region. As a rule, all this leads to an improvement of the intelligibility of the sound, the micronuans of recording, echoes, room volume, etc., are better transmitted, but only if the DAC itself digests the high sampling rates well.

It would seem, why does the DAC need a digital output? And then, that it is fed the same thing that is fed to the internal DAC chip! That is, you can send a signal to the S / PDIF or USB input of the Fostex HP-A8mk2, improve the chop by setting XTAL, increase its frequency by 2 or 4 times (or leave it unchanged) and then apply to another DAC – let’s say , Class above, but not having USB. In addition, the S / PDIF output has a sound reproduced from the SD card, that is, this DAC can also be used as a transport. All this expands the possibilities of using the device.

Impressions after listening

At listening headphones of various known manufacturers were used. Since the headphone amplifier in the model has not changed, the results of listening to music on the headphones on the HP-A8mk2 are almost identical to those of the previous HP-A8C.
Fostex TR-90
The volume level produced by the built-in amplifier is more than enough to drive the most “tight” headphones. There were no obvious failures of dynamics and distortions when using low-impedance headphones. Adjusting the volume neat, there is no strong dependence of the timbre on the position of the volume control. And only at very quiet levels there is a noticeable decrease in the detail of high frequencies.

In general, the sound quality of the Fostex HP-A8mk2 is high and more than good for its price, both in the output of sound on the headphones, and on the line output. No twitching of timbres, sound “alive” and open. The positioning of the instruments (scene) is available, and in accordance with its scale corresponds to what is produced by much more expensive devices. Subjective perception of sound in this device does not cause negative feelings or the desire to listen only to a particular style of music.

Replacement AK4399 with AK4490 positively affected the sound: the sound became more accurate and soft, the transmission of the timbres of the instruments and especially the voice improved, although in general the serve remained the same, which can not but rejoice. Significantly improved bass – became more prominent. The sound of the linear output in terms of timbre color and perception is no different from the earpiece.

Enabling the Direct option disables the volume control on the line output. In this case, the improvement in sound quality is more pronounced than in the previous model. More small details appear, echo, the sound becomes freer. Whether this is due to the installation of a new DAC or a change in the volume control scheme, it is difficult to say, it is necessary to listen to both devices, but we did not have such an opportunity.

Using Up Sampling does not give obvious advantages. With it, the sound becomes softer and more accurate, but at the same time, the higher frequencies are more turbid and some of the dynamics in the sound is lost. Perhaps, on certain music (classical, for example) it will be necessary, it is necessary to check personal preferences. It is worth noting that the AK4490 better “digests” the increased sampling rates, the negative moments when using Up Sampling are much less pronounced than in the previous model.

The settings and effects on the Digital Filter sound are described in sufficient detail. The choice of a specific filter and the color of the sound is a matter of personal preferences for everyone.

MSCK Sel, we would recommend always put in the position of XTAL – so much better, especially if the source of the figure is not very high quality. When using a high-quality source of figures, the subjective difference between modes decreases, but does not completely disappear.

Taking into account all of the above, we come to the conclusion that the new Fostex HP-A8mk2 is a reasonable evolution of the initially successful product.The cost of the device is $ 1200, it is a worthy competitor of products that are in the same price category. The ability to use as a DAC, an upsampler and an amplifier for headphones make the Fostex HP-A8mk2 a “three in one” device. Modern DAC, support for all audio formats and natural sounding of the new USB-DAC Fostex deserve close attention of music lovers.

Impressions of owners after long use

Fostex TR-90
The imperishable hits of Michael Jackson have never sounded so natural and lively. As if you are sitting with the singer in one studio and hear every rustle. Similarly, with other artists, tracks and genres. From Daft Punk to Slipknot – this monster can do it.

Do not be surprised only if the usual tracks do not sound as good as you used to hear them. All the jambs and shortcomings of any record immediately pop out.

The amplifier easily pumps high-impedance headphones, and in the settings you can add power, if for someone it seems insufficient.

I will say honestly: such devices are dangerous to take on tests. After such a sound, there is no road back. If even Hi-End players fade in the background of Fostex HP-A8MK2, then imagine how lousy some iPhone sounds. And even with the sound of laptops and personal computers with budget sound cards and chips, it’s not even worth comparing.


  • The simplest management
  • Extensive connectivity and selection of sound sources, including SD cards
  • incredible sound

And as a simple user, I would love to put such an amplifier next to the computer and enjoy your favorite songs daily in maximum quality.

Video review Fostex HP-A8mk2


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