iBasso D17 Atheris R2R with 1bit Dual Discrete DAC & Tube AMP

The iBasso D17 Atheris is a portable DAC and headphone amplifier with two of iBasso’s own discrete DACs, a four-channel R2R ladder and a 1-bit PWM design, and a fully balanced amplifier with two Korg Nutube tubes. It delivers up to 1,200mW per channel into 32Ω balanced, with a 24-position stepped attenuator for volume and separate batteries for the DAC and amplifier, setting a new benchmark for portable DAC/amps.

Three DAC modes

• NOS: PCM goes to the R2R DAC and DSD to the 1-bit DAC.
• All to R2R: oversampling mode, everything as PCM.
• All to 1-bit: sigma-delta mode, everything as DSD.

A four-channel balanced R2R DAC

The fully balanced, symmetrical R2R DAC uses 284 carefully selected film resistors with a tolerance of 0.01%, plus iBasso’s own hardware resistor compensation and software compensation algorithms. It reaches −104dB THD+N in R2R mode, more than 10dB better than mainstream R2R devices and on a par with flagship desktop R2R DACs, with a warm, delicate, natural analogue sound.

64 PWM DACs in 1-bit mode

In 1-bit mode, each of the four channel legs (L+, L−, R+, R−) has 16 PWM-DAC units, 64 in all. FPGA-Master 3.0 manages the I/O delay to the nanosecond and compensates for wiring delay, so the signal edges reach the DAC aligned and strictly synchronised: −114dB THD+N, with more detail and density.

FPGA-Master 3.0

iBasso’s FPGA-Master 3.0 works with two Accusilicon ultra-low-phase-noise femtosecond oscillators as a single, pure clock source. It buffers the data, calibrates delay, shapes noise, corrects THD, regenerates the global clock and removes jitter for both the R2R and 1-bit DACs, for very low jitter and distortion.

Dual Nutube amplifier

Two Korg 6P1 Nutubes give a warm, mellow yet dynamic tube character. Their anodes run from a 24V high-voltage supply for better linearity, and TI BUF634A buffers provide steady, strong current, for over 1,200mW + 1,200mW into 32Ω, enough for flagship IEMs and high-impedance headphones. iBasso also uses its own custom film capacitors and vintage Sprague capacitors.

A three-layer composite isolation system reduces microphonics: two circuit boards joined by pin connectors, with damping material, spread and absorb lateral stress, and the tubes sit on the second board on damping material. iBasso measured the microphonic effect below the threshold of hearing, among the best of all its tube products.

Two batteries, two volume controls

The DAC and the headphone amplifier run from separate batteries, so the amplifier gets a stable current and digital interference stays out, even at high gain or under heavy load. Analogue volume comes from iBasso’s 24-position, four-section stepped attenuator, a tenth of the size of a traditional one, with the channels matched within ±0.1dB; a professional DSP adds digital volume for finer steps.

Good to know

• iBasso quotes about −76dB THD+N at the headphone outputs, where the Nutube amplifier adds its tube character, and −103dB to −114dB at the line outputs.
• In the box: leather case, pouch, power cable, audio cables and user manual.
• For iBasso’s stepped-attenuator dongle, see the DC Elite.