The perfect component for audiophiles who love headphones and speakers equally

The SPL Phonitor X is a superb headphone amplifier, but it also works its magic on speakers.

Steve Guttenberg
Ex-movie theater projectionist Steve Guttenberg has also worked as a high-end audio salesman, and as a record producer. Steve currently reviews audio products for CNET and works as a freelance writer for Stereophile.
Steve Guttenberg
4 min read

The SPL Phonitor X headphone amplifier


SPL stands for Sound Performance Lab, and it's been making professional recording gear in Germany since the late 1970s, but to be honest I'd never heard of them. No matter -- when I spotted their slick-looking Phonitor X headphone amp at the Axpona audio show I just had to get it in for review. I admit I just have a thing for components with meters, even if they don't serve any rational purpose. Reviewed as tested, the Phonitor X's price is $3,299/£1,883, and that price includes the optional digital converter; it's $2,799/£1,577 without the converter.

Measuring 10.9 by 3.6 by 12.7 inches (278 by 100 by 335 mm), the Phonitor X is smaller than your average stereo preamp. My review sample had the snazzy red faceplate which looks cool, but red makes it difficult to read the labels under each of the controls. If I bought a Phonitor X I'd get it with the silver faceplate. It also comes in black.

Connectivity is straightforward -- there's XLR and 6.3mm headphone jacks, stereo XLR and RCA analog inputs and outputs, and if your Phonitor X has the onboard digital converter, you get optical, coax and USB digital inputs. SPL doesn't offer much info about the digital converter, other than to say it handles up to 192kHz 24-bit files.

The Phonitor X's matrix headphone processing promises soundstage expansion, and it works pretty well. Even so. I preferred listening with the sound processing turned off.

Phonitor X also features Voltair 120 volt rail technology, which SPL claims is "…four times as high as in standard audio designs. 120V Rail Technology is our reference technology developed and manufactured to run on an operating voltage of 120 volts, which corresponds to twice that of discrete operational amplifiers and four times that of semiconductor operational amplifiers." Whether the high voltage is chiefly responsible for the X's sound I can't say, but it does sound awfully nice.

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The SPL Phonitor X with Hifiman Susvara headphones

Steve Guttenberg/CNET

The Phonitor X doesn't come with a remote control, but it can function like one. You can teach it the codes of whatever remote you have. It may be from an extra Apple TV remote or a 1988 CD player remote you found in a drawer -- it can learn the codes and then control the volume level. I admit I never tried that function, so I can't say how well it works. Still, for an expensive component like the Phonitor SPL should have included a remote.

My review sample of the Phonitor X had the built-in digital converter, but I preferred the sound with my Arcam irDAC 2 converter. It was tonally richer and less "digital" sounding than the Phonitor X's internal one. Don't get me wrong -- the converter was transparent, I just prefer a little added warmth to the sound of my music. You of course might feel otherwise.

In any case, since digital converter technology is still advancing, it makes more sense to buy an external converter and upgrade it every four or five years to stay current.

The Phonitor X's sound is very tightly controlled, which is best exemplified by the sound of the bass on my favorite reggae albums, starting with Augustus Pablo's King Tubby Meets Rockers Uptown. Man, I've heard this music countless times, but here with the Phonitor X, Robby Shakespeare's bass is so much more present and alive. Every note is clean and deep; it's a very visceral presentation. Pablo's band is a monster rhythm machine -- the grooves are irresistible.

Switching over to my Pass Labs HPA-1 headphone amp-preamplifier, the sound loses some momentum and drive. Bass definition softens, the drums transients lose crispness, and the Phonitor X kicks harder. I came to feel the Phonitor X sound was neutral, which is what you might expect from a pro sound company. So if you crave lusty and sensuous sound, the Phonitor X won't keep you up late at night, it just tells it like it is.


The SPL Phonitor X rear panel


Then, switching to purely acoustic music from Rosa Passos and Ron Carter's Entre Amigos CD, I heard more detail and clarity as well as more "space" between the musicians over the Phonitor X. The PHA-1's sound was comparatively subdued as I spent time switching between my Abyss Diana and Audeze Fazor LCD-3 headphones. The Phonitor X's super-quiet noise floor lets you hear deep into the music.

It not only has lots of power, up to 3.7 watts per channel, it also has switchable gain levels, up to 24dB so it could easily drive my Hifiman Susvara and Abyss AB-1266 headphones. Those two have humbled most of the best amps, including the HPA-1.    

The Phonitor X was equally adept as a stereo preamp. Used with my First Watt F7 power amp and TAD ME-1 speakers the sound was brilliantly clear and concise -- the Phonitor X is certainly up to the job of serving as a preamp in a first-class audio system. You could also use the Phonitor X as a desktop preamp with a set of powered monitor speakers.  

The SPL Phonitor X is aimed at the serious headphone audiophile who probably already owns two or more high-end headphones and has a very decent two-channel audio system. For them, the Phonitor X would be a wise investment. 

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