Closer Examination

Perhaps it was knowing this is a flagship product that has quite a few tricks up its sleeve that made me think the iFi Pro iDSD Signature was larger than it actually is! Indeed, at 21 x 22 x 6 cm and weighing under 2 kg, the Pro iDSD Signature easily occupies room on a desk while leaving plenty of space of other things. The more typical landscape-style form factor also makes it amenable to be stacked up with the iFi Pro iCAN Signature or another such flat-top amplifier / preamp / external clock or anything else that might be in your audio chain. The chassis uses high grade aluminium that is machined and then shaped to be not just a flat box, with subtle curves and cutouts to add to the aesthetics while maintaining functionality. The silver color scheme is also never going to look old and guarantees the Pro iDSD Signature will not be outclassed in the looks department either. Your eyes will also be immediately drawn to the convex window up top that comes marked to confirm the use of GE NOS tubes inside and the window will provide a sneak peek when they are on. The cutouts around help with ventilation and cooling but will also glow red as we will see later on.


The front is what you will be interacting with most and we see iFi has adopted a thick, brushed aluminium cover plate. It doesn't fully match the metal design on the chassis itself but I presume most people will be distracted by all the shiny gold elements instead. There is quite a lot going on here, beginning with that power button at the bottom left corner which is easy to use courtesy the gentle curve to the cover plate. The iFi logo is visible via literal holes cut into the aluminium at the top left corner and there are RGB LEDs underneath to light up the logo in a few different colors to indicate the operating status of the Pro iDSD Signature. Next up is a large input wheel to select among the various inputs and you can press it to toggle through the display brightness or hold to invert the polarity of the device—hence the optional plug that comes with the iPower Elite too. There's a smaller wheel, again with a gold accent around it, for digital filter selection including DSD remastering and even WPS for easy WiFi pairing with a router. Underneath is a switch allowing you to choose between the three output modes here in the form of Solid State, Tube, and Tube+ to where the Pro iDSD Signature now really begins to show its potential.

The center is occupied by a large circular OLED display to maintain the theme with branding in the form of "Signature" and the Hi-Res Audio sticker that I could have personally done without. Moving further along we see the three headphone outputs in the form of a 1/4" (6.35 mm) single-ended TRS connector, a 4.4 mm balanced TRRS output, and a special 3.5 mm TRRS IfI S-Balanced connector that gives you the benefits of a balanced wiring despite single-ended amplification. The goal with the Pro iDSD Signature should be to try and use balanced outputs whenever possible to take advantage of the true balanced nature of the electronic circuitry inside. A gain switch is placed here to be symmetric with the output mode selector and here we get options of 0 / +9 / +18 dB as mentioned on the cover. It's not the easiest thing in the world to go from either extreme to the middle point rather than the other extreme end, so use less force than you would initially think. Keeping up with the symmetry theme is another large circular wheel for volume control using an analog Alps 6-track motorized servo system—go ahead and try it with the remote control to see what that results in. Speaking of which, that black circle at the bottom right corner is where the remote control IR sensor is located.


Now we get to the back where there are somehow even more things on offer! iFi does a decent job marking them to where you know, for example, the 3-pin dual XLR connectors on the left are balanced outputs you can send out to a compatible amplifier, should you wish to only use the Pro iDSD Signature as a DAC as many would do. There are also RCA outputs on offer for a single-ended connection and the provided interconnects will be handy here, although you will not be using the DAC to its full capabilities that way. Whether or not that makes a tangible difference to your ears is a whole other matter! Then comes the part where the Pro in Pro iDSD Signature feels truly warranted with iFI providing an output mode selector where the plastic tool from the accessory box comes in handy. HiFi mode is what the vast majority of end users reading this review will want to be on and perhaps the default HiFi (Fixed) is the way to go wherein you get a ~4.6 V balanced signal output level compared to the ~11.2 V with the Pro (Fixed) option that can ruin your audio chain if not trigger any OVP protection available. It goes without saying that only use the Pro modes if you have compatible hardware, and the variable options allow for a configurable output voltage using the volume control wheel on the front.

The iFi Pro iDSD Signature is also a network streamer and here we get an RJ45 Ethernet port for a wired connection directly from a router or NAS. There's also a WiFi antenna where the provided external antenna screws into for increased reception, but note that you are limited to 2.4 GHz wireless n here and the Ethernet port is also capped at 100 Mbps, neither of which are going to be bottlenecks for music streaming. The other inputs include a USB 3.2 Gen 1 (USB 3.0) Type-B input from a PC, a coax / optical digital input, a microSD (SDHC) where only FAT32 formatted cards up to 128 GB size are supported—a miss in my books compared to the competition that allows far higher storage capacities, an AES / EBU 3-pin XLR-style input if you have a prosumer or higher level digital audio workstation (DAW) or CD player for content creators and distributors, and a BNC input that is multi-functional in offering SPDIF input or AES3id with an external clock for those who prefer one over the internal clock system, which is why there's a clock sync mode and clock sync output too. Rounding off the overview here is the DC input from the iPower Elite and a DC loop through for compatible devices such as the Pro iCAN Signature.


The underside is much simpler by comparison given all there is to see is a pre-installed large silicone rubber pad that helps lift the Pro iDSD Signature off your desk to prevent scratches to the metal chassis in addition to minimizing any slip during use. It comes iFi branded and has a cutout with the same GE markings at the same spot underneath the one on the top itself—small things like this were not vital and yet add up in terms of attention to detail or even as Easter eggs. After all testing was finished, I decided to try and open up the unit to get a closer look inside. I was not expecting to see four super-long screws that pan the width of the unit going from the back to the front! There are seven other socket-head shorter screws too which aren't all necessary to remove yet leave no doubt as to the part where you can't easily disassemble the unit. This means you might as well forget about any tube rolling and even swapping out the tubes, should they go bad, will be more likely involving an RMA ticket with iFi.


As it turns out, there's not much to gain from that limited disassembly either given the soldering done on the other side. You could potentially pull out the knob covers and see if the entire PCB assembly can be pulled through the back but given the nature of this highly expensive product I did not want to take any chances. My photos above only help confirm the use of a stacked PCB layout with plenty of heatsinks and thermal interface materials as well as the two GE NOS 5670 tubes that iFi mentions are hand selected for pairing and longevity. Luckily, iFi provides some more information that goes over the other primary components used here, including the aforementioned Alps volume controller as well as high quality capacitors from the likes of Murata, Panasonic, ELNA, and Kemet. The DAC section uses four Burr-Brown chips in a custom interleaved configuration allowing for eight pairs (four per channel) of differential signals. There is iFi's Crysopeia FPGA for digital filter duties as well as an internal low-jitter Global Master Timing derived master clock from the AMR DP-777. The clock also drives the so-called X-Core 200 that handles most decoding with the FPGA engine handling the PCM to DSD remastering up to DSD1024. iFi also boasts about a galvanically isolated set of inputs, including the USB input to where anything added to the USB bus upstream or downstream doesn't affect the power provided to the port that is handled separately—no digital processing noise is involved thus. While the Pro iDSD Signature isn't boasting a powerful amplifier section, it effectively uses a line/headphone stage that is shared with the Pro iCAN line. This is fully balanced and 100% discrete, direct-coupled (without coupling capacitors) and tube/solid-state user-selectable with a design that is not just op-amp based discrete but uses pure Class A topology to help differentiate it from most other DAC/amp combo units. The user manual provides more detail about the design of the Pro iDSD Signature, and you can refer to the specifications there as well as on the front page to see the rated measurements for the various connections in the form of output impedance, dynamic range, and more.