iFi iTube Active Tube Buffer/Preamplifier
Input: 1 pair RCA
Output: 1 pair RCA
Dimensions (H x W x D): 28mm x 68mm x 158mm
Weight: 0.43 lbs
Availability: online and through Authorized Dealers
The iFi iTube active tube buffer/preamplifier is actually more than that. The iTube includes two "active correction circuits" that are meant to improve your listening experience, just like the New Old Stock (NOS) General Electric 5670 tube that's hidden inside the iTube's aluminum shell. I suppose purists have already begun the cold sweats as thoughts of tampering with bit perfection outweighs the promise of greater enjoyment. But let's leave theory behind and see what the iTube delivers, sound wise.
You can think of the iTube as four devices in one; an analog preamplifier with selectable gain, a class A tube buffer, a Digital Antidote Plus® which "provides the appropriate phase correction in the time domain to remove the harsh, 'ringing' digital sound which causes listener fatigue" based on the original Digital Antidote patented by Anthony Taddeo in the 80s, and finally the 3D HolographicSound® for Speakers circuit which "was developed to address the issue of how the human head 'hears' where lower frequencies are less well defined than upper frequencies." You can take each of these features with the exception of the tube buffer in and out of the circuit with the included switches.
On the underside of the iTube's body resides an 8-position dip switch with four available gain/preamp settings; Buffer (0db), Buffer (6db), Preamp (0db), and Preamp (6db). The Buffer settings take the preamp out of the circuit and there are associated diagrams right there as well so you don't need to have a good memory. On one of the iTube's ends sit two toggle switches; a three-position switch for the analog 3D HologrpahicSound circuit and a two-position switch for the Digital Antidote Plus (in/out). Around the other end are the 2 pairs of RCA inputs and outputs and the included wall wart power suppply connects to the iTube's side. There's a also nice detail up top—the dot above the first "i" is actually a circular hole that glows red when the unit is powered on.
Why tube? iFi references a study by Jürgen Ackermann for the Frankfurt University of Music and Performing Arts where 50 participants took part in a blind listening study listening to a tube and a solid state system. The results showed the participants felt the tube system improved their overall level of enjoyment by 187% where the solid state system made 30% of participants feel worse after listening. This study was referenced in the excellent piece by Markus Sauer for Stereophile titled, God is in the Nuances, highly recommended reading. So why tube? It can make you enjoy listening to your music more. The proof of which lies in the listening. BTW that NOS General Electric 5670 tube does get the iTube's chassis warm to the touch and its also soldered into place but according to Vincent Luke from AMR, the tube is run very conservatively and you can expect "...well beyond 100,000 hours!"
The 3D HolographicSound® for Speakers circuit has three settings; Standard for hi-fi speakers (down), off (middle position), and Wide for desktop speakers (up). I asked iFi if they would provide some more information regarding what this feature actually does. From the Chief Designer Thorsten Loesch:
The circuit is all in the analogue domain and is based on work by Alan Dower Blumlein, known as the "inventor of stereo".The Digital Antidote Plus® circuit is based on the original patented Digital Antidote by Anthony Taddeo from the 1980s. According to iFi, "The original patented Digital Antidote circuit takes the analogue input signal and executes various timing and phase correction duties, all in the analogue domain. This drastically reduces phase error introduced by the digital source as well as increasing the amplitude resolution (by nearly one bit)." This Antidote is designed for use with DACs that up/oversample and iFi says if you have a NOS or bitperfect DAC, "then you probably do not need the Digital Antidote Plus®".
What the 3D circuit does is that it corrects for the human perception, where an equal difference in level or time between the two speakers of a stereo set produces less lateral displacement of the phantom sound source at low frequencies than at high frequencies.
Additionally the WIDE setting widens the soundstage for speakers that are placed very narrow (e.g. Desktop monitors left & right of a computer screen).
The iTube can sit in between your DAC and active desktop speakers, between your DAC and preamp/integrated amp/amp, or between any other line-level device and your hi-fi. I mainly used the iTube in my desktop system after the Mytek Stereo192-DSD DAC and AudioQuest Dragonfly and before my ADAM A3X active speakers, and in my main system with the iFi iDAC/iUSBPower combo driving my Pass INT-30A.
The most dramatic difference I experienced with the iTube was with the AudioQuest Dragonfly on my desktop. While switching the iTube in/out takes some time since it involves moving interconnects, I felt I could hear a subtle difference with the iTube in the system even without the 3D or Digital Antidote circuits engaged. The Dragonfly can sound a tad flat and the iTube's tube buffer helped fill this flatness out, where sounds sound like they are more dimensional. But engaging the 3D HologrpahicSound circuit in the up/desktop position increased the size of the perceived sound image in every dimension dramatically. With this larger presentation came an increase in image specificity as well as better defined and controlled bass response. Music sounded bigger and better.
Switching on the Digital Antidote Plus circuit was less dramatic but still seemed to provide a slight softening of upper frequency edges while also filling out the sound of instruments especially those that live in the upper frequencies like violins. Again this was fairly subtle but the sense of a less etched and more full-bodied sound was welcome especially on more aggressive sounding recordings. With the iTube in the system and both options flicked on, the Dragonfly's presentation was more natural, relaxed, and involving.
With the Mytek DAC the only setting that offered a clear improvement was the 3D HologrpahicSound setting which pretty much delivered the same improvements as heard in the Dragonfly—bigger, better sound. The Digital Antidote did not seem to make a notable change one way or another and with both of these options turned off, the tube buffer on its own may have provided a slightly more rich sound but I would be hard pressed to pick out which was which if I wasn't looking. If we compare this to switching between a solid state amplifier and a tube amplifier, like my Pass INT-30A and Leben CS-300XS, the amplifiers offer a much more distinct difference in presentation where I could easily distinguish between the two.
In my main system using the iFi iDAC/iUSBPower combo (see review), the iTube again provided a more natural and relaxed sound. With the 3D HologrpahicSound circuit in the hi-fi (down) position, there was a slight increase in the perceived width of the sound image and again bass response seemed to get some added weight and focus. The sub-bass in Congo Natty's riotous Jungle Revolution became more physically apparent with the 3D HologrpahicSound circuit engaged. Nice. The Digital Antidote had a subtle but positive effect adding a more relaxed and full-bodied sound to trumpets, violins, and other instruments that live in the upper frequencies. Again, I would describe the overall differences as sounding more natural, i.e. all good.
I also took the iTube's analog volume control for a spin, setting my Pass INT-30A's volume to max, and I noticed a slight loss of resolution as compared to running the iTube in 0db buffer mode and using my Pass' preamp. This was a subtle change and the presentation seemed to get just a bit harder sounding as if some dynamic subtlety was lost. Seeing as the Pass retails for $7,150 I should hope its preamp would outperform the $299 iTube.
I also tried the iTube with the Auralic Vega (see review) and here the iTube seemed to soften the leading edges too much, taking away some of the sparkle that makes the Vega so engaging. This held whether the Digital Antidote was engaged or not but this softening seemed to be more pronounced with it engaged. The 3D circuit did widen the perceived sound image when set to the "hi-fi" position but I found that on some recordings it also tended to stick the sound to the speakers. Again this was recording dependent so I could see having this option in and out depending on the recording which would make me appreciate having a remote control. All in all, I preferred the Vega solo without the iTube in the system.
And last but perhaps not least I lassoed my iPhone 5 to the iTube with a length of AudioQuest Victoria cable and here the iTube's triple sonic threat really showed its stuff turning a relatively flat and 1-dimensional sound into acceptably wholesome music. I even spun some, gasp, lossy compressed music and it wasn't at all bad. It was damn near listenable although there was that telltale hollowness and lack of depth to tone colors that are endemic of lossy compressed music files. The iTube certainly worked its magic but it is not a miracle worker.
We All Tube
The perceived benefits of the iFi iTube varied based on the system and DAC it was paired with. The most obvious benefits coming with the Audioquest Dragonfly in my desktop system where the iTube delivered a more natural and engaging sound. With the Mytek DAC there was minimal benefit, the most dramatic difference being the 3D HologrpahicSound providing a larger and more natural sound image. In my main system when paired with its stable mates, the iDAC and iUSBPower, the iTube imparted a more natural and engaging sound whereas with the Auralic Vega I felt the iTube softened the presentation too much. When paired with an iPhone it helped fill out an otherwise threadbare sound and you could say the worse the digital source, the more effective the iTube will be.
With any accessory, even one as imaginative and dexterous as the iTube, your specific system context will help determine how effective or ineffective a given solution will be. The iFi iTube would seem to offer the largest benefit to desktop systems especially those that sound flat, harsh, overtly digital, and spatially challenged due to too narrow speaker placement. Here the tube buffer coupled with the 3D HologrpahicSound circuit and Digital Antidote offer up a triple treat capable of turning your desktop's digits into more natural sounding music.