Fostex HP-A4

The Fostex HP-A4 is a high-fidelity headphone amplifier that stands out for its ability to handle high-resolution audio formats while maintaining a compact and elegant design. As the successor to the HP-A3 model, this digital-to-analog converter (DAC) delivers remarkable sound quality thanks to its Burr-Brown PCM1792A processor, capable of handling PCM files up to 24-bit/192 kHz and DSD formats up to 5.6 MHz. Its black glass front panel houses a volume knob, source and filter selectors, as well as a series of LEDs indicating the resolution of the processed files. Designed for audiophiles and demanding professionals, the HP-A4 combines advanced features with an affordable price.

Exceptional Sound Quality

At the heart of the HP-A4 is a Burr-Brown PCM1792A digital-to-analog converter, capable of processing signals up to 24-bit/192 kHz. This high-quality component is complemented by an AKM4118 DSP, which converts DSD files (DFF and DSF) so they can be processed by the conversion section. Although it does not perform native DSD processing, this architecture still allows users to fully enjoy high-resolution files.

The headphone amplification section is powered by an OPA3124PA op-amp, delivering an output power of 100 mW at 32 ohms. This configuration enables the HP-A4 to efficiently drive a wide range of headphones, from low-impedance models to more demanding references.

Listening tests reveal that the HP-A4 excels in definition, analysis, and transparency without falling into any kind of sonic exaggeration. The soundstage is precise, positioning each instrument with great accuracy. The frequency range is extended at both ends of the spectrum, reproducing both the finest highs and the deepest lows. Dynamics are also very well preserved, offering a lively and engaging reproduction of musical recordings.

Versatility and Ease of Use

The Fostex HP-A4 stands out for its versatility. It can be powered directly via the USB port, which is ideal for portable use with a laptop, or via an external power adapter for a fixed setup. This dual power option makes it an ideal companion for audiophiles on the go.

Compatibility with a wide range of audio formats is another major advantage of the HP-A4. It supports linear PCM formats up to 24-bit/192 kHz as well as DSD formats up to 5.6 MHz. This ability to play high-resolution files allows users to fully enjoy their music library, regardless of the encoding quality of the files.

The HP-A4 can also serve as a preamplifier in a hi-fi system, thanks to its RCA outputs controlled by the volume potentiometer. This feature makes it a particularly versatile device, capable of integrating into various audio setups.

A Compact and Functional Design

The Fostex HP-A4 features an elegant and minimalist design reminiscent of its larger sibling, the HP-A8C. With its compact dimensions (113 x 34 x 155 mm) and lightweight build of 500 grams, this headphone amplifier is easily portable for mobile use. The black glass front panel gives the HP-A4 a sophisticated look, while the controls are intuitively arranged for easy operation.

The front panel includes a source selector, two filtering options (Roll-off or Cut Off), a sensitivity switch for the headphone output (High/Low -10 dB), an output selector, and a volume knob. A series of LEDs clearly indicates the resolution of the processed files, from standard 16/44 kHz format to DSD 5.6 MHz, allowing users to quickly check the quality of the audio signal being played.

The rear panel offers comprehensive connectivity with an asynchronous USB input, a Toslink optical input, a digital optical output, and two RCA outputs for connection to active speaker systems or an integrated amplifier. A micro SD port is also available for firmware updates, ensuring the device’s longevity.

Technical Specifications

Audio Features

• Professional-quality audio capabilities
• High-precision clock with low phase noise
• Playback of streams in 24-bit / 192 kHz PCM and 11.2 MHz DSD
• High-performance Burr Brown PCM1792A DAC
• Asynchronous USB Audio 2.0 transfer up to 24-bit / 192 kHz
• Selection of filter type and cutoff frequency

Connectivity

• 1 x high-speed USB 2.0 port
• 1 x RCA analog audio output
• 1 x TosLink S/PDIF optical input
• 1 x TosLink S/PDIF optical output
• 1 x 6.5 mm headphone jack connector
• 1 x micro SD slot (SDHC), up to 32 GB

Audio Performance

USB Input

• Sampling rate up to 24-bit / 192 kHz (PCM), 5.6 MHz (DSD)
• High-speed USB interface

Digital Input

• Connector: optical, square
• S/PDIF format (16-bit / 24-bit: 44.1 - 192 kHz)

Headphone Output

• Output level: 100 mW (under 32 Ohms)
• THD: less than 0.04% at 1 kHz, 32 Ohms load, 100 mW
• Frequency response: 20 Hz - 80 kHz +/-3 dB (1 kHz, 32 Ohms load, 100 mW, FS 192 kHz)

Analog Output

• Connector: RCA
• Reference output level: 2 Vrms
• THD: less than 0.01% at 1 kHz
• Frequency response: 20 Hz - 80 kHz +/-3 dB (at FS 192 kHz)

Digital Output

• Connector: optical, square
• S/PDIF format (16-bit / 24-bit: 44.1 - 192 kHz)

General Features

• Micro SD slot for memory card (firmware update)
• Card format: FAT32
• Power supply: via USB bus or AC adapter
• Power consumption: 2.5 W
• Dimensions (w x h x d): 113 x 34 x 155 mm, excluding protruding parts
• Weight: 500 g

Included Accessories

• 4 x adhesive feet
• 1 x USB cable (1.0 m)
• 1 x user manual
• 1 x 12 V AC adapter