The D18 Crotalus is made for listening on the go, yet it aims at a drive power typical of desktop devices. Connected to a phone, computer, player or digital transport it can be the centre of a personal HiFi system, and it fits into both portable and desktop setups.

The story of the device rests on three main pillars: the R2R Ultra DAC, the high-current amplifier and the dual power supply, from battery and from an external source. The following sections present these separately, and the detailed figures are found in the specifications block.

The R2R Ultra derives from the development of the iBasso flagship DAC. The 20-bit R2R and 4-bit string DAC structure is based on a discrete resistor ladder, and the eight-channel, fully differential architecture is a solution designed to reduce zero-crossing distortion.

The converter uses 344 high-precision metal film resistors, 76 of which form a hardware compensation network. The equivalent accuracy stated by the manufacturer is 1.4 parts in 100,000. The accuracy of the R2R ladder determines the linearity of the conversion, so this network is one of the key elements of the discrete solution.

The operation of the R2R Ultra is governed by the FPGA-Master 3.0 with an upgraded algorithm. The device offers a NOS mode and four proprietary oversampling filters, so the sound can be adapted to listening preferences. The NOS mode works without digital oversampling.

Precise timing is ensured by two Accusilicon femtosecond oscillators. The filters can be selected from the display of the device and from the control app, and the impulse response charts illustrate the time-domain behaviour of the different filters.

The amplifier stage consists of two TI dual operational amplifiers and four BUF634A current buffers. The 4.4 mm balanced and the 3.5 mm single-ended headphone outputs give flexible connection to in-ear monitors as well as full-size headphones. The 4.4 mm output is capable of up to 2 × 1750 mW into 32 Ω.

The output can be matched to the sensitivity of the headphones in three gain stages (low, mid, high). The power is a significant advantage, but the impedance alone does not decide how well a headphone can be driven: the sensitivity and the nature of the headphone also matter. The output impedance is 0.7 Ω (4.4 mm) and 0.4 Ω (3.5 mm).

The D18 comes with a custom low impedance lithium-polymer battery. The 8.4 V pack allows a voltage swing of up to 16.8 V, and therefore, compared with a single 3.7 V cell, provides more stable sustained output, stronger transient performance and better power efficiency, while also reducing the ripple resulting from DC-DC conversion.

A 12 V DC external power supply can also be connected to the amplifier section, a solution protected by a Chinese national invention patent. With it the power of the 4.4 mm output rises from 2 × 1530 mW on battery to 2 × 1750 mW into 32 Ω, preserving the control of dynamic passages. The charging time of the battery is about 2.5 hours and the playtime about 9 hours.

The D18 offers three digital inputs: USB-C, coaxial and optical. It can be connected to a phone, computer, music player or digital transport, so it can serve as the audio hub of a personal HiFi system and of quality gaming and movie playback. The 3.5 mm and 4.4 mm line outputs make it simple to connect an external headphone amplifier.

Format support differs by input: USB-C (DATA) accepts PCM up to 768 kHz and DSD512, the coaxial input PCM up to 768 kHz and DoP256, and the optical input PCM up to 192 kHz and DoP64. The level of the line output can be set with the DAC gain stage, so it can be matched to the input sensitivity of the external amplifier.

The 1.3-inch OLED display and the multifunction switch clearly show the operating status and allow quick adjustment, so the digital filters and the gain stage can also be changed on the device. The iBasso Android app and the online control panel make the setting of the EQ, filters and gain accessible as well, with several EQ presets and a dedicated Gaming EQ.

For gaming the Gaming EQ serves to optimise sound effects, and the microphone input of the 3.5 mm connector allows intelligible voice communication. According to the manufacturer a future firmware update will add 7.1-channel virtual surround sound to the device. The online control panel can be reached at ibasso.com/uac.

The housing of the D18 is made of CNC-machined aluminium alloy, and the finely anodised finish is corrosion resistant and clean in appearance. The tempered glass panel shows the circuitry of the R2R Ultra while providing protection, and the back carries a dual-layered, etched stainless steel panel.

The pattern of the stainless steel back panel contrasts with the brushed metal finish and gives a characterful look that emphasises technical details. The device measures 140.4 × 75.3 × 18.8 mm and weighs 271 g, and the design is geared to portable use.