FiiO K5 Pro ESS

Headphone amplifiers are part of everyday life without us being directly aware of it. These days we find them in every smartphone. Older generations will also remember their home hi-fi systems where they could also find headphone sockets. This raises the question of why such an additional device might be required, what you could use it for, and what added value it offers compared to integrated solutions.

In practice

Founded in 2007, the Chinese company FiiO focuses on developing high-quality, contemporary portable audio solutions. Their portfolio includes portable digital audio players (DAP), in-ear headphones and headphone amplifiers.

We tested the FiiO K5 Pro ESS model, which is promoted as a “desktop headphone amplifier” and comes in an attractively designed box. In addition to the device itself, the package includes an external power supply unit, a USB cable, a quick start guide and a warranty card.

This transistor amplifier impressed us with its appealing exterior. At the same time, its simple design made it pleasant to use. The operating elements and the rear connections, which are partly attached to the rear panel and not to the circuit board, sit firmly. Nothing wobbled, which gave us hope for the longevity of the device.

The electronic innards are housed in a CNC-milled, sandblasted aluminium casing in matt black with rounded outer edges. It weighs 418 grams and, with dimensions of 12 x 13 x 5.5 cm, is primarily intended to sit on a desk. However, with this weight and size, it also meets all the requirements for mobile use – provided there is a power socket.

On the tidy front panel, the input selection can be made via a miniature switch (USB, line, coaxial), the three-stage pre-amplification (0 dB, -6 dB, -10 dB) can be selected, and the volume can be set in steps of 0.5 dB with the large controller. The latter also serves as an on/off switch. A 6.35 mm headphone output finishes off the front.

The rear offers (digital) coaxial and optical S/PDIF inputs, USB and line inputs and outputs in RCA format. There is also a connection for the external power supply. In this price range, however, you won’t find multiple headphone outputs or symmetrical connections.

Operation

The FiiO K5 Pro ESS is switched on by turning the volume control clockwise. This control also serves as a visual indicator of the selected sampling frequency. This useful feature is already used in other FiiO devices such as the FiiO M17 and it enhances the device’s appearance. A blue LED outlines the control when digital signals are received at 44.1 or 48 kHz. Frequencies above 48 kHz are visualised with a yellow light, while DSD signals light up green. If no signal is detected at the USB input, it lights up red.

Advanced value: preamplifier

The FiiO K5 Pro ESS is not only a headphone amplifier but also a D/A converter that, when connected to a computer, outputs audio signals via the headphone or line output. Another scenario might be connecting to an amplifier to listen to connected devices like a CD player in high quality. A digital audio player (DAP) can also benefit from connection to the FiiO K5 Pro ESS: If the output signal of such a player does not provide enough power for a particular pair of headphones, this can be compensated for via a dedicated headphone amplifier. This enables optimal adaptation to different headphone models. Furthermore, the line output offers the possibility of a direct connection with active loudspeakers or power amplifiers. Thus, the FiiO K5 Pro ESS can serve as a central unit in combination with a computer, analogue and digital players, loudspeakers, and as a dedicated headphone amplifier with power adjustment.

Technology and D/A converter

The unit’s frequency response is claimed to be 20 Hz to 80 kHz. The high output power of a whopping 1,650 mW into 16 ohms and 1,500 mW into 32 ohms also seems powerful and should support a wide range of headphones. The manufacturer itself recommends a headphone impedance of between 16 and 300 ohms.

An up to date chipset from ESS (ES9038Q2M) is at the heart of the K5 Pro, with a maximum resolution of 768 kHz, 32 bits and DSD 512. The optical and coaxial digital inputs work with a resolution of 24 bits and up to 192 kHz sampling frequency. The full resolution of 768 kHz and 32 bits in linear PCM format and DSD 512 is played out via the USB interface using the XMOS XUF208 chip.

However, high resolution does not guarantee good sound. For this, FiiO uses additional technology that is usually reserved for higher-priced devices: internally, the amplifier path and the signal processing are supplied with power independently of each other via a filtered power supply. This is said to result in a less disturbed music signal and a better overall sound.

Sound

The wireless MTX monitor with integrated headphone amplifier was used as an external player with direct comparisons with the FiiO K5 Pro ESS. A Cambridge Audio CXN V2, a CD player (NAD 512), a smartphone (Samsung Galaxy S7) and an iBasso DX 240 Reference DAP were used as feed players. The headphone section department was handled by models from Stax, Focal Spirit Pro, Sony MDR-V600, iBasso SR2 and the Sennheiser HD 25 II. Last but not least, a Lavry DA11 served for the transducer evaluation.

In our first test, minute increases in volume were applied immediately after switching on to check whether the stereo imaging remained stable at low and increasing volumes or changed in the panorama. Test passed! The next test was to check the control path of the volume potentiometer. Here, too, there were no volume jumps.

All headphone models received enough support to reach ear-splitting volumes and beyond. In view of the available level reserves, it can be assumed that even high-impedance devices can be adequately supplied.

Sound-wise, the FiiO K5 Pro ESS reproduced fine dynamic gradations and impressed us with differentiated and clear reproduction of instruments in the stereo image, along with depth gradation. Due to the high power reserves, even particularly quiet classical passages were audible at a pleasant listening level without perceiving additional noise, assuming you’re listening to a high-quality recording. This is a pleasant side effect not only when just listening to music but also when editing music in a studio environment.

The FiiO K5 Pro ESS reproduces deep bass without effort. The mid-range is fanned out in a differentiated way, even with dense information content, and it can reproduce overlapping frequencies for instruments. Due to its extended frequency spectrum, the device also reproduces high-frequency signals with fine resolution. Compared to an integrated headphone amplifier, the FiiO K5 Pro ESS offered not only the added value of high power reserves but also a thoroughly improved sound image, which was about on a par with the headphone amplifier of the Funk MTX.