iFi Audio Pro iDSD D/A processor/headphone amplifier

On the first page of the owner’s manual for iFi Audio’s Pro iDSD tubed/solid-state multibit DAC and headphone amplifier, the British company unabashedly describes it as “a ‘state of the art’ reference digital to analog converter” and “a wireless hi-res network player or the central DAC in an expensive high-end home system.” As if in an afterthought, it continues: “The on-board balanced headphone section means high-end headphones can also be directly connected to it.” The manual doesn’t describe the headphone “section” as “state of the art,” so I’m deducing that the Pro iDSD is really more a fancy-pants DAC than a high-tone headphone amp. Which is probably okay, because one of iFi’s other Pro models, the Pro iCAN line stage and headphone amp, which I reviewed in June 2018, was possibly intended to accompany the iDSD.

I’m a slow learner. Only now am I beginning to recognize how relevant, value-oriented, and forward-thinking iFi Audio’s digital products actually are. IFi makes seven DACs, starting with their portable Nano iDSD LE DAC–headphone amp ($139). In the middle of their product line is the popular xDSD, a portable, high-resolution Bluetooth USB DAC ($399). They also make a range of digital “enhancement” products, including the Nano iGalvanic3.0 signal regenerator, which I sometimes use in my reference system. Now iFi has introduced this new monster DAC, the Pro iDSD ($2499), which uses four Burr-Brown converter chips in what iFi calls an “interleaved” array.

I promised myself that I wouldn’t get snarky or sarcastic about the Pro iDSD’s swarm of high-tech features—my mantra is Accept and adapt. Please stay with me as I patiently list them all:

The Pro iDSD is built around four of Burr-Brown’s hybrid MultiBit/DSD DAC chips and a Crysopeia FPGA Digital Engine that allows PCM up to 32-bit/768kHz, DSD up to 49.152MHz, and DXD and double-speed DXD. The Pro iDSD’s digital inputs are: USB (required for DSD, DXD, and sample rates above 192kHz), AES3 (XLR, single link), S/PDIF (coaxial/optical combo), and multifunction BNC (S/PDIF in or sync input). All inputs, including USB, are galvanically isolated. The USB input is self-powered and does not draw power from the USB bus. In addition to its own internal clock, the Pro iDSD can accept an external word-clock signal.

The playback options include: Airplay network audio playback from iPhone and iPad, and Mac computers; DLNA network audio playback from smartphones, tablets, and computers running Windows or Linux; playback from a hard-disk drive (HDD), USB memory, or SDHC memory card; playback from Network Attached Storage (NAS); streaming playback from Napster, Qobuz, QQ Music, Spotify, Tidal, and others; and MQA.

The little Pro iDSD measures 8.7″ W by 2.5″ H by 8.4″ D and weighs 4.4 lb. On its rear panel are balanced (XLR) and single-ended (RCA) analog output jacks, as well as a four-position screwdriver-slot rotary switch that offers a choice between fixed and variable outputs, and between output levels appropriate for professional- and domestic-audio settings. The XLR jacks output 11.2V when set to Pro mode and 4.6V when set to HiFi mode, while the RCA jacks offer 5.6V in Pro and 2.3V in HiFi. In variable mode, those numbers describe the maximum output available when the Pro iDSD’s front-panel volume knob is turned fully clockwise.

Supplied with the Pro iDSD is the 15V version of iFi’s iPower wall-wart. According to the manual: “All incoming DC is converted to a high-frequency waveform and then rectified and filtered by a choke input capacitor filter. . . .” Also according to the manual: “The digital section is powered by a bank of ELNA Dynacap DZ&153;(tm) super capacitors of 6.6 Farad (6,600,000µF) value in total . . . [that have] around 400x lower internal impedance (in comparison to similar products of regular grade). . . .”

The illuminated iFi logo at the top left of the front panel indicates power-on in four different states: green for warming up, white for solid-state mode, orange for tube mode, red for protection mode. At bottom left is the power/standby button. To its right is a large knob for choosing among the inputs: WiFi, Ethernet, Hard Disk, Micro SDHC, USB, Coaxial/Optical, XLR Digital, and BNC Digital. With this knob you can also adjust the signal polarity, and shut off or dim the brightness of the circular OLED display at the center of the front panel.

To the right of the input selector is a little knob that selects among three forms of digital processing:

1) Direct—Bit-Perfect: Neither PCM nor DSD signals are processed in any way (non-oversampling for PCM, direct-to-analog conversion for DSD files).

2) PCM Upsampling: PCM is upconverted to 16x PCM (705.6/768kHz) using one of the following filters:

a) Bit-Perfect: no digital filtering applied; 44.1–192kHz always used for 352.8–768kHz.

b) Bit-Perfect+: no digital filtering applied, sinc rolloff corrected.

c) Gibbs Transient Optimized: 44.1–96kHz.

d) Apodizing: 44.1–384kHz.

e) Transient Aligned: 44.1–384kHz.

3) DSD–Remastering: Incoming audio (except DSD512) is converted to either DSD512 or DSD1024, as selected, using the filter selected. Inputs other than USB are limited to maximum sample rates of 192kHz PCM and DSD64 via DoP. A fixed third-order analog filter operates at 80kHz with correction for DSD’s 6dB attentuation.

Below that little knob is a tiny three-way switch with a series of charming symbols representing the Pro iDSD’s three options of output circuit:

1) Solid-State: pure class-A J-FET topology

2) Tube: a totally separate, pure class-A circuit based on two GE5670 tubes

3) Tube+: reduces the tube circuit’s negative feedback to a minimum

I roll my eyes at any audio product with as long a list of features as this. But all of the Pro iDSD’s features seem useful and worth including in a serious digital converter that aspires to professional quality and long-term relevance.

To the right of the display is an equilateral triangle of headphone outputs: at top, a 6.3mm socket; at bottom left, a single-ended 3.5mm socket; and at bottom right, a balanced 2.5mm socket. Between the last two is another tiny, three-position switch for selecting the headphone gain: 0, 9, or 18dB.

The big knob at the right is the analog volume control, which can be set as fixed or variable with the screwdriver-slot rotary switch on the back. To the right of that is the infrared sensor for the remote control.

Inside iFi’s elegant packaging was a box containing the tiny remote handset, a USB cable, a 0.5m RCA interconnect, and a Bluetooth antenna. In a second box I found the LN-1540 iPower power supply (15V at 1.5A), which requires an IEC line cord and plugs into the Pro iDSD with its attached, 1m-long cord.

Whew! I just spent a thousand words just telling you about the Pro iDSD’s features and accessories. Now let’s see if all those fancy dee-luxe things made my systems sound better or worse than do my reference DACs: the HoloAudio Spring “Kitsuné Tuned Edition” Level 3, the Mytek Brooklyn and Manhattan II, and Schiit Audio’s Yggdrasil Analog 2.

As I did with iFi’s Pro iCAN, I compared all three of the Pro iDSD’s output modes, but consistently preferred the Tube+ mode; to my ears, a dollop of second-harmonic sauce stimulates my sensory neurons in a manner that lets my brain fill in the lost data necessary for me to enjoy richer instrumental textures and a more complete tonal-harmonic spectrum. To my mind, second-harmonic “distortion” (I call it “doubling”) lubricates the neurotransmission of complex sensory data, enhancing voice articulation and soundstage mapping.