Headphone amps are found in many devices, so what can a standalone one offer those with cash to splash?
UK‑based iFi currently offer around 50 products aimed at the hi‑fi market, but some may appeal to the professional audience too. I was recently sent their flagship Pro iCAN Signature headphone amp/preamp to review, and this latest model is a high‑power, high‑quality, balanced‑headphone amp that doubles up as a preamp and simple monitor controller. Compared with their original iCAN, it features audiophile‑grade components throughout, an upgraded power supply, selected valves, an infrared remote control and a Pentaconn 4.4mm balanced headphone socket (more on that below). iFi have clearly put a lot of effort into the design, and the asking price reflects that!
Overview
The Pro iCAN Signature looks roughly half‑rack width but it’s taller than 1U, measuring 213 x 193 x 63mm and weighing 1.9kg. The substantial top panel features arced cooling slots and a glass bubble view port revealing the valves. Instead of conventional feet, a thick “quad‑damped isolation base mount” is glued to the base with two elastomer layers (silicone and ethylene/vinyl acetate) for damping and vibration isolation, and two metal layers (aluminium and a ferrous alloy) for electromagnetic screening.
Rear‑panel connectivity comprises four selectable stereo inputs: three unbalanced on RCA phono sockets, and the fourth balanced on female XLRs. Both balanced and unbalanced preamp outputs are provided on male XLRs and RCA phonos. Power comes from an external high‑quality line‑lump SMPS unit generating 15V DC at 4A, and accepting any mains voltage from 100‑240 V AC via a standard C14 IEC inlet. A captive output lead delivers the DC power through a standard (non‑locking) coaxial plug. Unusually, alongside the coaxial power input socket there’s a second loop‑through power output, intended to supply optional accessories such as iFi’s electrostatic headphone energising module. Something akin to an HDMI socket just below passes audio to that module, too.
The preamp has an array of selectable inputs and outputs on its rear.
On the front panel, a trio of XLR sockets for headphone connections is flanked symmetrically by four silver knobs. The larger outer pair select the input source (left) and listening volume (right), while the smaller inner knobs configure bass compensation EQ (XBass) and a stereo‑width enhancement facility (3D), which I’ll return to shortly. Two miniature toggle switches select the signal path mode and adjust the overall gain, and there are two more headphone socket options alongside. The on/off power‑standby button is cunningly concealed in the bottom left‑hand corner (the iFi logo top‑left lights when active), and the infrared remote control receiver window occupies the opposite corner.
Internally, the iCAN employs discrete surface‑mount analogue circuitry, configured with a fully differential (ie. balanced) signal path throughout. Consequently, the high‑quality ALPS volume control is a six‑ganged affair, with four tracks used for the balanced left/right audio signal paths, and the remaining two for control‑system positional information (the knob is motorised and can be moved using the remote control).
You’ll have spotted my mention of valves earlier: the pair of selected and matched military‑spec GE5670 dual‑triode valves can be selected for the front‑end of the signal path as an alternative to a solid‑state J‑FET topology. The second stage of preamp circuitry (which handles the EQ and 3D processing) uses bipolar transistors, while a MOSFET Class‑A output stage powers the headphone outlets. Apparently, this amplifier is biased to operate mostly as Class‑A, but slides into Class‑AB for low impedance phones at very high levels. All three amplifier stages are DC‑coupled, avoiding coupling capacitors in the signal path.
Modern equipment rarely uses fully differential signal paths, not least because it’s an expensive approach needing twice as much audio circuitry and careful gain matching throughout. But it offers several potential technical advantages, including lower distortion, reduced crosstalk, greater headroom, and higher output power. On that last point the Pro iCAN’s specifications state it delivers a maximum output voltage (in balanced mode) of over 20V RMS (around +28dBu), with a maximum peak current of 1.4A. That equates to an astonishing 14W of peak output power into 16Ω (balanced) headphones! Perhaps not surprisingly, then, the unit’s idling power consumption is toasty by modern energy‑saving standards, at 22W, pulling up to 50W when running flat out.
Headphone Connectivity
By my reckoning, the Pro iCAN has seven headphone connectors. Four are intended for connecting ‘balanced’ headphones in various ways, but they’re all a bit unusual in one way or another. Starting with the smallest, conventional headphones or in‑ears with a TRS mini‑jack can be plugged into a 3.5mm socket below the small XBass knob. This is marked SE for ‘single‑ended’, meaning a single amp per channel, rather than ‘balanced’. This output also features the company’s ‘S‑balanced’ and ‘iEMatch’ technologies. The latter is essentially a fixed attenuator in the signal path, since IEMs are usually pretty sensitive and iFi don’t want to melt the user’s ears with excessive power!
‘S‑balanced’ is a contraction of ‘single‑ended compatible balanced’, and essentially it’s a TRRS socket with the rearmost ring and sleeve both wired to ground — so that it works correctly with both standard three‑wire TRS and four‑wire PRO3.5 plugs. iFi claim this also reduces distortion by 50%, but that’s based on ‘balanced’ operation using two (bridged) amplifiers for each earpiece, whereas this S‑balanced configuration employs only one, and hence halves the noise and distortion! This is not wrong, but it’s not the whole story. If it were, there’d be no point in providing all those balanced output connections...
Moving along the bottom of the panel, a slightly larger headphone socket below the 3D knob is marked ‘BAL’. This a Pentaconn TRRRS connector (see box), a neat format that’s popular for ‘balanced’ headphones and more convenient than a bulky four‑pin XLR. But there’s also an XLR4 ‘balanced’ headphone output in the centre of the panel. Although these XLR4 and Pentaconn connection are common for balanced headphones, some models and adaptor cables use dual three‑pin XLRs, one for each channel, and, naturally, the Pro iCAN accommodates those, through two combi XLRs either side of the XLR4.
The use of combi XLRs is quite clever, as they also provide quarter‑inch TRS connections for standard (three‑wire) headphones without using more panel real‑estate. But all is not quite as it might seem. Whereas the left XLR3 socket carries L+/L‑ balanced signals and the right XLR3 carries the R+/R‑ balanced signals, these are of no use to a standard three‑wire stereo headphone, which needs L/R/return — so iFi have arranged for the right combi TRS socket to carry the expected L+/R+/return unbalanced signals. The left socket could carry the same, but that would potentially double the load on the positive side’s output amplifiers. Instead, iFi have use the left TRS socket to carry the inverted polarity signals, giving L‑/R‑/return. Thus two conventional quarter‑inch TRS headphones can be connected simultaneously, each driven by their own separate amp, so headphones with different impedances won’t affect one another’s volume. The headphones plugged into the left socket will have inverted absolute polarity, but can anyone detect that over headphones? I certainly can’t! Moreover, a suitably wired adaptor cable would allow a balanced headphone connection via dual TRS plugs as an alternative to the dual XLRs, if necessary.
Before leaving the topic of headphones, I should flag up a potential issue regarding using the Pro iCAN as a monitor controller. The preamp’s line outputs aren’t muted when headphones are connected, and can’t be muted manually — this could affect the practicality of using the Pro iCAN as a monitor controller in some applications.
Other Functions
I mentioned the XBass and 3D functions earlier, and both are performed entirely in the analogue domain using passive circuitry. They’re also fully bypassed when not in use. The XBass rotary switch has four settings (Off, 10Hz, 20Hz and 40Hz) and controls a passive bass‑boost equaliser intended to compensate for any (real or perceived) bass deficiency in headphones or loudspeakers. My Audio Precision frequency response tests indicated that this provides around 12dB of boost below the stated frequencies. As the chart shows, the equaliser affect reaches up to about three octaves above the selected frequency.
EQ responses for the XBass facility.
iFi’s 3D Holographic Matrix system is fundamentally a frequency‑dependent stereo widening matrix, with three settings. The knob is marked with dual values for headphones and speakers, starting with Off which fully bypasses all matrix circuitry. The processing options are 30/+, 60/30+, and 90/60+, the first number referring to headphone auditioning and the second to loudspeaker usage. In simplistic terms, some signal from each channel is fed into the other in opposite polarity, and the level of this crosstalk is reduced above about 300Hz. The effect is a widening of the perceived stereo image — just as increasing the Sides signal in a Mid‑Sides rig does. (In contrast to many crossfeed systems, there’s no delay involved.)
The amount of crosstalk introduced with different 3D settings. The top four traces are from the first channel, and the lower four illustrate the frequency‑selective crosstalk levels into the opposite channel.
Sufficient crosstalk is introduced for headphone users at the 30/+ setting to simulate the typical image width of loudspeakers spaced with a 30‑degree angle (shown in red on another Audio Precision plot). For speaker applications this first setting is similar to EMI’s Stereosonic correction system from the 1950s, which was intended to compensate for the spatial distortions arising from certain recording scenarios, as well as during reproduction via conventional stereo speakers.
The second setting simulates 60‑degree speakers over headphones (shown in green on the plot), and adds 30 degrees of additional image width for loudspeaker listening. The final setting (blue) pushes the width even further, simulating speakers at 90 degrees for the headphone listener, and adding around 60 degrees for speaker listeners.
In the Audio Precision chart, the top four lines illustrate the level and frequency response of one channel, with the lower four lines the corresponding (opposite polarity) crosstalk into the opposite channel. No crosstalk would give normal stereo, with higher crosstalk levels giving increased stereo width. In all cases, the stereo width is enhanced more for low frequencies than high ones, adding considerably to the sense of spaciousness in recorded material.
Turning to the two toggle switches, the left one determines the front‑end circuit topology. Its first position selects the solid‑state J‑FET signal path. The second routes the signals to the GE5670 valves, in a conventional triode arrangement with negative feedback to minimise distortion. The third reduces the amount of negative feedback (NFB) to a minimum, which increases harmonic distortion and transient dynamics in a way that can sound very attractive on some material.
These two plots show the levels of third harmonic (upper) and second harmonic (lower) distortion for the different circuit topologies. The valve stage with full NFB is best for second harmonic, but the solid‑state stage is better for third harmonic. Though consistently poor in the specs, the valve stage with minimal NFB can sound more exciting!
When changing the signal path options, the output is muted for about six seconds as the circuits stabilise. If the valves are unused for an extended period they’re automatically de‑powered to preserve their working life and, consequently, when selected a 20‑second warm‑up period is required (during which time the J‑FET path remains active). The iFi logo illuminates in different colours to reflect the current status, with flashing orange indicating the initial valve warm‑up period, white for normal J‑FET operation, steady orange for valve operation, and red if the unit enters a protective state.
The last toggle switch sets the overall gain (0, 9 or 18 dB), to suit the sensitivity of the user’s headphones. The appropriate choice allows the volume control to work in the 10 to 2 o’clock region for normal listening levels. When used as a preamp, the Pro iCAN delivers unity gain from balanced input to balanced output with the volume control at maximum, at the 0dB setting, and either 9 or 18 dB of gain with the alternative gain switch settings. Roughly 6.5dB of attenuation is introduced with the volume knob at 12 o’clock.
The manual claims the balanced outputs are capable of 20V RMS, which is about +28dBu. I don’t doubt it, but couldn’t test it because my Audio Precision system maxes out at +26.5dBu. Nevertheless, a +26dBu balanced input using the solid‑state signal path gave a THD figure of 0.03%, while a +4dBu output level measured a little under 0.002%. Switching to the first valve mode delivered around 0.003 at the +4dBu reference level, rising to 0.015% in the second valve mode, and the THD figure increased rapidly with higher signal levels, as you might expect.
Not surprisingly, the solid‑state mode delivered the lowest level of third‑harmonic distortion, and the minimal‑NFB valve mode the worst (by an order of magnitude), as shown in the AP plot. However, for second‑harmonic distortion, the first valve mode proved the best, and the minimal NFB valve mode the worst.
iFi claim a signal‑to‑noise ratio for the Pro iCAN of 147dB (A‑weighted). That sounds a lot, but it’s relative to the maximum output level (the best figure I obtained was 140dBA at +26dBu). I measured 113dBA referred to +4dBu (in solid‑state mode). A measurement which really couldn’t be bettered is the frequency response. This measured flat to within 0.1dB between 10Hz and the 80kHz limit of my AP system — iFi claim 0.5Hz to 500kHz (‑3dB limits), and I can easily believe it.
A measurement which really couldn’t be bettered is the frequency response. This measured flat to within 0.1dB between 10Hz and the 80kHz limit of my AP system.
Conclusion
iFi’s Pro iCAN Signature is undoubtedly a very high‑quality and powerful headphone amplifier, with scarily high volumes available even for the least sensitive and difficult‑to‑drive headphones. The XBass and 3D Holographic Matrix functions bring nicely judged and useful tweaking options to suit personal preferences, too.
My only four‑wire headphones are Sennhesier HD600s, which I was able to audition using both XLR4 and Pentaconn cables. The results were stunningly good, with plentiful volume, brilliant dynamics, solid control of the low‑end, razor‑sharp transients, and effortless headroom. Testing the XBass options, all were audible, and I often found myself leaving it on the 10Hz setting, to give a little better weight and definition at the very low end. The 3D Holographic Matrix also works nicely, helping to move the perceived sound outside the head, and many will find this results in less listening fatigue over extended auditioning. Needless to say, the iCAN also sounds impressive with standard three‑wire headphones (tested with AKG K702s, Sony MDR 7509 and Sennhesier HD25iis), and in‑ears (Sennheiser ie800 and Shure SE215).
For professional settings, a locking DC power connector would be nice, but other than that I have no complaints at all. This is a seriously capable headphone amp for seriously high‑quality listening. It supports every common headphone connection format, and copes perfectly regardless of sensitivity or impedance. It has some helpful and interesting features too. If you’re in the market for a truly excellent headphone amp, it’s well worth a look — especially if you favour ‘balanced’ headphones.
Pentaconn
Left to right: the 3.5mm TRS, 4.4mm Pentaconn TRRRS, and 6.35mm A‑type TRS standard headphone plugs.
The 4.4mm Pentaconn connector (sometimes known as the Nippon DICS) was introduced in 2015 by Sony, and has subsequently been adopted by Sennheiser, TEAC, iFi and others. The compact 4.4mm plug is sized midway between a 3.5mm mini‑jack and the quarter‑inch (6.35mm) A‑type plug. It has the same diameter as a TT or Bantam studio patch plug, but with the pointy triangular tip shape of an A‑type quarter‑inch plug. Uniquely (at least amongst audio‑industry connectors), the Pentaconn has five contacts in a TRRRS format. In other words, a tip, three rings, and a sleeve, which together permit the conveyance of a stereo balanced audio signal with a common shield. The wiring convention is, in order from the tip, L+, L‑, R+, R‑, Gnd. Consequently, in addition to balanced headphone applications, the Pentaconn is increasingly being found on semi‑pro equipment for line‑level stereo balanced audio inputs and outputs, too.
Balancing Act?
I grimace at the term ‘balanced headphones’ because they aren’t ‘balanced’ any more than passive loudspeakers are! Balancing is entirely about matched impedances on the hot and cold line to reject interference, and that really doesn’t apply to headphones or loudspeakers. Instead, ‘balanced headphones’ are really just headphones connected using four wires instead of three. Most headphones use the three‑wire format because it’s cheap and convenient, sharing a common return path for both earpieces. But since all wires have some resistance, the current flowing through one earpiece will set up a voltage across the shared return wire. This acts on the other earpiece, generating a small amount of crosstalk and distortion (particularly for very low‑impedance headphones). Grounding the two earpieces separately using the four‑wire configuration avoids this.
The four‑wire arrangement also allows the use of a bridged‑amplifier topology, in which two amps work together: one is connected to each side of the earpiece, pushing and pulling the signal between them in opposite polarities. The Pro iCAN uses this bridged‑amplifier configuration for its ‘balanced’ headphone outputs. The bridging approach can be helpful in mobile applications or where the amps’ power supply voltage is inherently restricted, as it allows twice the signal voltage to be generated across the earpiece, thus delivering more power than a single amp could. Of course, the same result can be achieved by doubling the power‑supply voltage, but bridging may be more cost‑effective in some situations. Either way, it’s really a ‘bridged amp’ format, not a ‘balanced’ one!
Pros
- Seriously high‑quality, and very powerful, headphone amplifier.
- Offers a multitude of three‑ and four‑wire connection options.
- Full differential and discrete component signal path.
- Useful bass boost and stereo width enhancing facilities.
- Selectable valve and solid‑state input stage options.
- Excellent technical performance.
Cons
- Non‑locking DC power connector.
- Can’t mute line out when headphones attached.
- Not an impulse purchase!
Summary
A very high‑quality headphone amplifier with huge output power, capable of driving the most challenging of headphones, and with every three‑ and four‑wire connection format covered, along with some useful sound‑tailoring options.
Information
£1999 including VAT.
$1999
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