SPL are the initials usually associated with the term sound pressure level, but it is also short for Sound Performance Lab, a German firm that has been making professional recording gear since the late 1970s. Founded by Wolfgang Neumann, SPL grew out of the needs of his own professional studio, which was located near the Dutch border. After a few years Neumann sold the studio and began manufacturing pro gear full-time under the name SPL.
Since the early 80s SPL has been actively involved in building high-performance professional recording equipment under its own name as well as manufacturing OEM products for Sennheiser, Genelec, Terratek, and MB Quart. Among SPL’s own branded offerings are monitor controllers, interfaces, preamplifiers, compressors, power amplifiers, speaker simulators, and headphone amplifiers. We are going to look at one of its headphone amps, the Phonitor X.
The Phonitor X is part of SPL’s latest line of “pro-fi” gear, which bridges the gap between the professional and consumer markets. The Phonitor X is similar to SPL’s Phonitor II professional headphone amplifier, but with several features removed that were primarily of use to pros and with the addition of some controls that make it more user-friendly for consumers, including an optional DAC section.
The principal technical feature that separates the SPL Phonitor X from its competition is SPL’s 120-volt rail technology that reportedly reduces distortion and has an electric measurement the company claims is “four times as high as in standard audio designs,” which are typically around 30 volts. “THD measurements of the 120V op-amp show a difference of more than 3dB compared to the OPA134 at 36V—in sound pressure level, that corresponds to an improvement of more than 50%.” The first generation of SPL’s 120V amplifier circuit premiered in 1998 and was utilized until 2009. Since then SPL has gone through four more iterations, culminating in its latest balanced I/O driver first produced in 2013.
With balanced and unbalanced headphone outputs on the front panel and balanced and unbalanced line-level outputs on the back panel, the Phonitor X can serve as a preamplifier as well as a headphone amplifier. Maximum output is 3.7 watts into 120 ohms, but you can change the output settings via a series of dipswitches on the bottom of the unit. You can boost the factory default headphone output by either 12 or 22dB. You can also set up the Phonitor X so that a chosen input will go directly to the RCA or XLR outputs on the back without attenuation from the volume control.
On the back panel there is space for the optional DAC card. It was not yet in production when I received the Phonitor X, so I could not put it through its paces. That will have to wait for a follow-up. The card will utilize the AK4396 DAC chip and the current specification lists it as 192/24 capable. The chip can even support DSD, but as of now that is not included in its feature set, though it could be added via a firmware upgrade at a later time, depending on feedback from customers.
Ergonomics and Setup
Compared to some high-end audio gear that sports a “super-luxury finish” the Phonitor X cosmetics are more about function than bling. The front panel has a large, centrally located volume control flanked on the left by analog and digital source selector switches, an output selector switch, crossfeed angle control, crossfeed switch, and the matrix on/off switch. On the right side of the volume control is a pair of input level VU meters, balanced and single-ended headphone connections, and an on/off switch. The front panel itself is about ¼-inch thick and is available in silver, black, or red. My review sample was the red version, which looks lovely, though its mid-tone color makes reading the dark silver lettering exceedingly difficult for my well-worn eyes, especially in low light. I spent the first week of use with the owner’s manual on my desk, turned to the page with pictures of the front panel so I could see (and memorize) the control’s labels.
The back panel of the Phonitor X includes one pair of balanced and unbalanced analog outputs and one pair of balanced and unbalanced inputs. If your Phonitor has the optional digital interface it will also have a coaxial SPDIF, TosLink, and USB input. The back panel also has a pair of trigger controls to activate other SPL products, and an IR PGM that allows you to pair the Phonitor X with any remote control. Finally, the back panel contains an IEC AC connection and a power on/off switch.
The Phonitor X includes crossfeed and matrix circuitry. The Phonitor X is certainly not unique among SPL headphone amplifiers in this respect. The Phonitor X has fewer adjustable options than the Phonitor II, but it does have more choices than most other manufacturers’ headphone amplifiers, which usually have just on and off. The Phonitor X has four speaker angles 22°, 30°, 40°, and 55°, and five different crossfeed levels.
I used the Phonitor X as a headphone amplifier and as a preamplifier. Its primary input was from the Mytek Brooklyn’s balanced analog output. This allowed me to send the Mytek’s unbalanced output to another headphone amplifier so I could do matched-level A/B listening tests between them. I tried using the bypass setting on the Mytek’s volume controls to send an unattenuated line-level output signal to the Phonitor X, but it was slightly too high a level and clipped the Phonitor X’s VU meters. Fortunately, the Phonitor X has a switch that calibrates the meters so that 0VU is +12dB. I listened to both the analog and digital volume controls set at -9dB, and settled on digital volume attenuation as the most sonically transparent solution.
After the first ten days of use, I began to appreciate the Phonitor X’s ergonomic excellence and started using it primarily by feel. The large central volume control is easy to find, and from there, depending on what function you wish to adjust, you can find your way to every knob and switch without looking. SPL’s experience in making pro gear is probably the main reason the controls are so logical and easy to use.
On some devices VU meters are more for show than for practical use, but the meters on the Phonitor X have utilitarian value. First, whenever the Phonitor X is in mute mode they turn red, which makes it easy to tell if signal is really being passed through the Phonitor X to your headphones or power amplifiers. Secondly, since the VU meters measure the input levels, you can see if an input signal’s level is too low or high at a glance. Finally, the VU meters point up one potential problem with the Phonitor X: If the input levels are too high or low, you will need to alter them before they are routed to the Phonitor X because the unit itself has no way to attenuate input levels. The Phonitor has adjustable output levels, but it has no adjustments for input.
Unlike many high-gain or high-output headphone amplifiers, which have adjustable gain settings, the Phonitor X has no way to compensate for extremely high-sensitivity or low-sensitivity headphones. Given that the Phonitor not only has that 120-volt rail but also the option for an additional 12 or 22dB of gain, it’s hard to imagine that there are any “difficult to drive” headphones that the Phonitor X can’t power successfully. With my least efficient headphones, a pair of Beyerdynamic DT 990 600-ohm version, the Phonitor volume control barely edged past midway on my lower-output live concert and field recordings, without the need for any additional output boost from the dipswitches. With my most sensitive in-ear monitors, the Empire Ears Zeus (115dB sensitivity), there was noticeable hiss and some low-level hum and noise. So, if the vast majority of your listening is through sensitive in-ear monitors, the Phonitor X would not be your best option. That is not surprising given that in my experience very few headphone amplifiers have the ability to drive both sensitive in-ear monitors and inefficient large-diaphragm over-ears with equal efficacy.
Three headphones spent the most time tethered to the SPL Phonitor X: the new Focal Utopia, the MrSpeakers Ether C, and the Audio Technica ATH-W3000ANV. Both the Utopia and Ether C were attached using Moon Audio’s Silver Dragon cable with balanced terminations, while the ATH-W3000ANV was connected via its permanently attached, single-ended connection.
My first and last impression of the Phonitor X was one of unfettered power and control. Whether coupled to the new, lightning-fast Focal Utopia headphones or the venerable Grado RS-1 on-ears, the Phonitor X exerted a level of finesse that put it on par with the top echelon of headphone amplifiers, tube or solid-state, designed to handle difficult-to-drive headphones.
In the past I have not been impressed by the vast majority of headphone amplifiers’ implementations of “crossfeed.” This is usually a setting or collection of settings that adds some amount of right-channel information to the left, and left-channel information to the right. Even SPL’s Phonitor II, which had even more matrix and crossfeed setting options than the Phonitor X, did not generate a “better” soundstage implementation for me. But with the Phonitor X, I did find that with some material the matrix and crossfeed offered a wider, deeper, and more spatially precise soundstage. But the sonic changes were not all universally benign. The matrix and crossfeed circuits also introduced some shifts in the harmonic balance of all the headphones I used with them. With the crossfeed and matrix settings engaged, the lower midrange lost a bit of harmonic complexity and richness, while the upper midrange gained a bit of additional lucidity. But with some headphones that tend to be slightly warm-sounding with an overly rich lower midrange, such as the AudioQuest NightHawk or Audio Technica ATH-W3000ANV, I felt the harmonic changes were generally beneficial. Unlike other headphone amps where matrix and crossfeed stayed off after an initial audition, with the Phonitor X, I found that I often preferred listening with those settings engaged.
The Phonitor X has very little that could be called a prevailing or unique sonic character. Its overall harmonic balance is very much like what I hear from other high-quality solid-state headphone amplifiers such as the Audeze Deckard, except that, unlike headphone amplifiers with a 30-volt maximum output, the Phonitor X delivered unrestricted dynamic contrasts that pushed whatever headphones were attached to it to greater sonic heights. These greater dynamic swings were most obvious on my own live concert recordings. On quite a few I found that the Phonitor X expanded their dynamic range to the point where I needed to turn down my usual level settings to prevent the loudest passages from getting oppressively loud. Also unlike many headphone amplifiers whose sonic character changes during the such passages, the Phonitor X’s overall balance and control never shifted regardless of how near the VU meters approached 0dB. When I heard changes or additional hardness during dynamic peaks, it was coming from someplace other than the Phonitor X.
Bass extension and control through the Phonitor X were exemplary. Coupled to the new Focal Utopia headphones, “Dracula” by Bea Miller had more low-bass “oomph” than through other headphone amplifiers, such as the Moon Audio Inspire Dragon HPA-1, which demonstrated slightly less control of the bottom octaves. Listening to DJ Snake’s “Too Damn Low,” I was impressed by this combo’s ability to turn sub-bass into something melodious. For bouncy bass try Bastille’s “Good Grief” where the Carol Kaye-ish bass line came through loud and clear even during the thickly layered choruses.
When used as a preamplifier the Phonitor X proved quiet and capable of driving longer line-level connections with ease. I used the Phonitor X with a variety of amplifiers including the First Watt F7, the Bel Canto REF600M, and the NuPrime ST-10. In every case the Phonitor had an abundance of additional gain—I rarely turned the volume control past ¼ turn. Also the Phonitor X was dead quiet with all the amplifiers I connected it to. Its sonic character was clean, clear, and dynamic. While not quite as transparent and dimensional as using the Mytek Brooklyn connected directly to the power amplifiers, the Phonitor X used as a preamplifier added only the slightest amount of additional electronic haze to the aural picture.
With a $2800 budget you have a plethora of headphone amplifier/preamplifier options. Of course, I have not heard them all, but among those I have heard the Phonitor X offers a unique set of features coupled with outstanding performance. I still consider the Audeze Deckard headphone/preamplifier ($699) a superb value, but if you need a balanced line and headphone connection it isn’t going to work for you. When I compared the Deckard’s single-ended headphone output with the Phonitor X’s using the Focal Utopia headphones with their stock, single-ended cable, I was impressed by how similar the two headphone amps sounded, both in tonal balance and in soundstaging. But when I compared the Deckard’s single-ended output with the Phonitor X’s balanced output (using a balanced Moon Audio Silver Dragon cable), the balanced connection bettered the single-ended one with a slightly larger soundstage and better micro-dynamics.
The Moon Audio Inspire Dragon IHA-1 single-ended headphone/preamplifier ($1599) proved to be the Phonitor X’s sonic equal, but it has a different set of ergonomic strengths. Sonically the Moon has a more three-dimensional presentation and a larger soundstage, but it doesn’t have the Phonitor X’s rhythmic drive or low-bass control. And while the Moon has a balanced output for headphones, it lacks balanced input or output line-level connections, both of which the Phonitor X does have. Last point of difference—the Moon has only one single-ended output while the Phonitor X has two, one balanced and one unbalanced.
I returned the review sample of the NuPrime DAC 10-H DAC/preamplifier ($1795) before the Phonitor X arrived, so I did not have an opportunity to compare the two directly. I did find the DAC 10-H much harder to use via its front-panel controls. In fact, I relied heavily on its remote for all functions. Conversely, the Phonitor X front panel is easy to navigate by feel only. Also the NuPrime DAC 10-H’s deeply inset balanced XLR connection was not as easy to use as the flush-mounted connection on the Phonitor X. Lastly the Phonitor X has mechanical VU meters, which are, as we all know, really, really cool.
As I mentioned earlier, I can’t imagine a situation where the Phonitor X could run out of power and not be capable of optimally driving any pair of headphones. Sonically the Phonitor X offers a suave delivery with extremely good bass control and extension. When you add its well-laid-out controls and options, you have a product whose ergonomics are as good as its technical abilities. If you’re in the market for a headphone amplifier and preamplifier that can serve as a reference in either a dedicated headphone or nearfield audio system, the Phonitor X should be among your options. It is solid and well designed, and you can get it in red. What’s not to like?
Specs & Pricing
Type: Solid-state analog headphone amplifier with optional DAC card
Outputs: One pair balanced XLR, one pair unbalanced RCA
Output power: 2 x 3.7W (into 120 ohms)
Dynamic range: 135.5dB (HP), 136.3dB (Line)
Dimensions: 10.95″ x 3.94″ x 11.19″
Weight: 9.5 lbs.
Audio Plus Services (U.S. Distributor)
156 Lawrence Paquette Industrial Drive
Champlain, NY 12919