Fostex HP-A4BL

An entry-level headphone amplifier for audiophiles

Audio files are no longer limited to MP3 players and poor audio convertors found in sound cards. What’s more, .flac, .wav and Apple Lossless can, if desired, easily overcome the technical limitations of the traditional audio CD.


Elsewhere in the streaming sector, there are more and more providers who are specialising in high-res audio formats. A quality convertor that brings sounds from the computer into the living room or through headphones helps ensure listening is digitally adjusted for maximum enjoyment. Things are all the more practical if the device, such as the HP-A4BL from Japanese manufacturer Fostex, combines both applications. That’s exactly what you’ll find here – a headphone amplifier and digital-to-analog convertor in a single device.

Processing & Connectivity

The metal housing of the HP-A4BL impresses with its robust nature and high-quality finish. The side panels are made of black brushed metal, while rubber feet provide a very sturdy base. The volume control is smooth with a clean aesthetic, although the dial buttons could do with a little more snap. However, they look more than solid enough. Seven LEDs can be found above the buttons, with these lights responsible for displaying sample rates of source material and providing information about file resolutions.

The bandwidth ranges from 44.1 to 192 kHz, proving more than adequate for most recordings. In addition, the DAC is capable of playing back DSD files that are sampled at a much higher sample rate from a computer or via a digital input. On the rear of the device, this Fostex amplifier offers a line output, a USB port, a micro SD slot and a digital input and output for connecting digital amplifiers and CD players. Sadly, the Micro SD slot cannot be used for file playback, only for uploading firmware updates. This was necessary during our test, since an update is needed in order for operation with MacOS Sierra. With all other Apple operating systems, no update is necessary. Windows users have to install a specific driver in order to use the HP-A4BL. The Fostex amplifier is connected via USB 2.0, although it cannot be operated in stand-alone mode via USB as with the HP-A4.



The volume controls handle both headphone output and line output, ensuring that the DAC can be used with additional amplifier hardware or active speakers. The digital output cannot be levelled. Four buttons on the front panel are designated for choosing between optical input and USB, as well as the headphone and line output, gain and filter.

The filter switch performs varying tasks depending on the source material. If classic audio files are played between .mp3 and .flac formats, you can choose between a flat and a steep low-pass filter. The differences are very subtle. In position one, the DAC sounds more open and slightly wider, while position two makes the sound more tight. Transients sound a little bit more present, with the sound image more integrated overall. For large ensembles or band music, position one proved to the more suitable choice in our test as the depth and width of the stage was used to advantage. Electronic music or soloist compositions were more effective with level two selected. The gain button on the right increases the output of the headphones by a further 10 dB. Most applications benefit less from this switch as the output level of the HP-A4BL is already quite high. In addition to the jack output for the headphones, this Fostex amplifier also has a balanced XLR headphone output.


The sound of this product is certainly convincing. The bass is tight, without ever pushing too much into the foreground. Highs are pleasantly airy and seem to be slightly accentuated, which can sometimes enhance cheaper headphones with a low treble. The mids are unobtrusive and neutral sounding, with convincing transparency. The master even complex passages of audio with pleasant layers of depth and detail. The sound is wide and open, rather than focused.

As far as music styles are concerned, the HP-A4BL feels at home in all genres and masters every one to full satisfaction.
The HP-A4Bl is a good DAC/headphone amplifier for its price segment. Fostex certainly lives up to its name. Of course, it does not come close to the HPA8, although this admittedly occupies a whole other price range. However if you’re looking for a high-quality device for enhancing your audiophile credentials, the HP-A4BL is a solid choice.

Nils Neuneier-Quak
6 years ago by Nils Neuneier-Quak
  • Rating: 4.25
  • Sound
  • Handling
  • Price/Quality
  • Function

The Fostex HP-A4BL is a high-quality DAC and headphone amplifier for audiophile requirements. It’s also one that feels equally at home with all music styles and genres.

Technical specifications

  • Weight without cable630 g

What's in the box

  • 4 rubber feet
  • USB cable
  • Instruction manual
  • Power supply

Special features

  • DSD support up to 11.2 MHz
  • BurrBrown chip
  • Linear PCM with up to 24 Bit / 192 kHz
  • Asynchronous USB2.0 connection
  • Optical S/PDIF connection
  • Headphone jack with 6,3mm stereo jack and 4-pin XLR (balanced)
  • Two-stage switchable amplification
  • Selectable digital filters
  • Recommended load: 16 Ohm to 600 Ohm
  • Frequency response: 20 Hz - 80kHz (+/- 3dB @ 32 Ohm / 100mW)
  • Dimensions: 150mm x 34mm x 157mm (BHT)
  • Weight: 630g (plus power supply)

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