Repost from sister site

By Michael Liang and Kevin Veneble

Yep, pretty much rocket science...

At Audio360 we often use the term "audio geeks". Michael Mercer has been known to state that he's been "geeking out" on a product at least once a week. It seems even some manufacturers are in on the joke! Case in point: Light Harmonic's GEEK OUT and Geek Pulse DACs; the former starting to ship this month.

But our inner geeks lay deeper than that.

In some cases the audio geek is preceded by your standard-issue geek. The geekiness is strong with us, as identified by the college physics books carried around in the third grade, the ability to identify every dinosaur, and the preternatural ability to simultaneously impress mothers and repel girls.

In the mid-80s it was every geek's dream to attend Space Camp.

Space Camp is at Marshall Field in Huntsville, Alabama. As a child growing up in Alabama I was able to visit Marshall Field and learn the history of American space travel. My parents even bought me the Space Shuttle manual. I spent hours staring at the fold out diagrams, marveling over the number of knobs and switches.

Knobs. And switches.

My fondness for circuitry never got me to Space Camp however, and my interests gradually shifted in a musical direction. But I never lost my infatuation with knobs and switches, so my inner geek remained intact.

I also never forgot that it was a group of German engineers and scientists that made the United States's journeys into space possible. I remain in awe of innovative German engineering to this day, including that of Sound Performance Lab.

See? Rocket science. Get it?

Build and Design

Sound Performance Lab, or SPL, is a German manufacturer of products for audio playback and production. They produce consoles and signal processors for use at recording and mastering studios, including the studio of legendary mastering engineer Bob Ludwig: Gateway Mastering. Their products are designed primarily for professional use, though the SPL Phonitor 2 is designed for both home music playback and in the studio. When I removed the SPL from the box, it's sheer size and heft along with the grace of it's design left me a bit breathless.

The Phonitor 2 reminded me of staring at the flight deck in the Space Shuttle simulators. It's the same sense of awe I get when looking at a Neve or SSL recording console. The unit is beautifully designed and impeccably engineered. Everything is laid out for ease of use, and the design is visually stunning. The build quality is exquisite. The knobs and switches feel substantial. The volume knob is especially smooth in operation, allowing for easy, small changes in gain. The RCA and XLR plugs on the back of the unit are first class as well. The 1/4-inch headphone jack on the front seemed a little loose to me and Michael, but gave neither of us any actual problems.

While the outside is solid and classy the true innovation in the design of most SPL products lay in the 120V audio rail system. Most audio equipment runs with ±15V or ±18V power rails, while high end SPL equipment runs at ±60V: including the Phonitor 2. This required that new discrete analog op-amps be designed to run at this high voltage. The main benefit to this design approach is far more headroom. In fact the the op-amps claim a signal-to-noise ratio of 116dB with an additional headroom of 34dB, giving a dynamic range of 150dB. The dynamic range at the headphone output is said to measure at 134dB.


Headphone amplifiers are usually pretty simple devices. One or more inputs for audio devices to a headphone output with a simple input selection and volume control configuration. Just looking at the faceplate of the Phonitor 2 lets you know there's much more going on in there. This is where the excellently written 32 page manual came in handy.

There is an input selector switch on the left hand side for selection between 3 inputs: two XLR and one RCA. The XLR inputs can be used as balanced or unbalanced inputs depending on the wiring of the connecting cable. Below the input selector is a switch that selects between headphone output and the XLR outs on the back of the unit. The XLR outs can be used as balanced or unbalanced outs and to drive balanced headphones. I was unable to test the latter as I didn't have the right kind of balanced cable. The output jacks are male XLR. Most headphone cables in dual XLR mode are also male.

Above and to the right of the input selector is what SPL calls the matrix. This is the crossfeed, simulated speaker angle, and center volume reduction selector knobs. In the middle of the matrix is the switch to engage crossfeed and angle or all three effects. A large portion if the manual is devoted to this section of the amplifier and I won't go into specifics of how it works here. Basically this is used to emulate the sound of near field monitors for more accurate mixing and mastering in the studio. It can also be used to make the sound more natural by adding a bit of the right side of a stereo mix into the left ear and vice versa.

To the right and below the matrix are the solo and phase reversal switches. These allow you to hear each side of a stereo mix individually or check for phasing issues in a track. The large volume knob commands the most attention, positioned at the center of the faceplate. The volume has a motorized potentiometer that allows for the unit's volume to be controlled by remote. Instead of including a remote SPL put a handy remote control learning button on the back of the unit. I tried this out with the remote control that came with my Rogue Audio Cronus and it worked wonderfully.

To the right of the volume knob is the mono-stereo-laterality switch. While mono and stereo are pretty self explanatory, laterality may not be. The laterality switch position and corresponding knob are used to control balance of left to right to compensate for hearing loss in one ear. Above the laterality knob are the yellow backlit meters which come in handy for watching your input levels. The VU calibration switch may seem strange until you realize that underneath the unit are dip switches for different gain levels. The dip switches allow for normal, +6, and +12 db increases in gain as well as setting the RCA input between professional and commercial input levels. Finally you have the 1/4-inch headphone jack rounding out the crowded but highly functional faceplate.

It's all about the sound!

Kevin Venable:

The beautiful build quality and engineering innovation would be pointless if the SPL Phonitor 2 didn't sound good. The Phonitor doesn't sound good. It sounds amazing! My current reference amplifier, the Woo Audio WA7, is so quiet that you hear no noise. The SPL is another beast altogether. At times it seems the music comes wafting out of a black hole. I thought I knew what the black background reviewer cliche meant. I was wrong.

It isn't just the noise floor however, the music has great timing with the Phonitor 2. Music is just passed on as received. Sonic changes from source components are immediately apparent. Everything I used sounded extremely clean and musically fulfilling.

The SPL Phonitor 2 plays with the big boys in headphone amplification, as it should for it's price. It drove all the headphones I threw at it easily with near perfection: from the 32ohm KEF M500, to the 600ohm Beyerdynamic T1; all without breaking a sweat in the lowest gain setting. In fact none of my headphones needed extra gain from the amp. I tried +6 with the T1 to see if it sounded better. It didn't sound better, it just gave me less volume to play with. I couldn't go above 9 o'clock comfortably. I also engaged the +12 db gain boost in order to listen for noise, but it remained dead quiet.

I tried the amplifier with various sources but settled on the following configurations for my listening impressions...

For digital playback I used my Macbook Pro running Amarra HiFi to the Miniwatt N4 (as USB-to-SPDIF converter) to the MHDT Labs Stockholm V2 DAC, which is in for review as well. I wired this into XLR1 in unbalanced mode with some Hosa RCA to XLR cables. Cable like this can be found at any pro audio store and are nice to have around, especially for amplifiers like this.

For analog playback I ran my VPI Traveler with a Denon DL-103 into a Parks Audio SUT (step-up transformer) and Parks Audio 6922 tube phono stage. This went into the RCA input on the SPL Phonitor 2. I tested line-stage functionality by running the XLR out into the power amp input of my vintage NAD 3130 via unbalanced cables. Speakers were NHT Mini monitors.

Listening to music through the SPL Phonitor 2 was one of the most enjoyable listening experiences of my life. At times it was almost transcendent.

One of those moments was just after I received a prototype cable from WyWires for my Sennheiser HD700. I was listening to Pat Benatar's In the Heat of the Night album remaster from Mobile Fidelity on my analog rig. On the B side of the record is a song called "Don't Let It Show". It begins with Pat and a guitar, then builds from there into a nice driving rock tune. As the track built-up, each instrument fell into place beautifully and I was whisked away by the emotional palpability of the music. It was one of those moments that showcases why this hobby is so amazing, and with this amplifier those moments came frequently.

The bass performance of the SPL is quite good too: very well extended and controlled, sounding great with electronic dance music and acoustic bass lines. The six string bass histrionics of Thundercat test the power, precision, and delicacy of the low end of any component. The Phonitor 2 played back "Oh Sheit it's X" from his Apocalypse album with all the power, funk and humor the bassline exudes, all with superb control through the Beyer T1.

For midrange I picked up the AKG K701 and gave Ted Greene's Solo Guitar album a listen. The guitar sounded sublime, rich in timbre and harmonics. I sat transfixed until the end of the album, barely able to move. Ella Fitzgerald's Here Come Charlie was fascinating: her phrasing exquisitely rendered. When I listened to Gemini Syndrome's Lux through the T1 I was actually stunned, as chills went up my spine. I love Gemini Syndrome but that isn't why I was so stunned. I know the singer Aaron Nordstrom very well and I have heard him sing in person without amplification as well as on stage many, many times. What I heard from my digital playback system with the SPL Phonitor 2 was as close to sitting with Aaron in a Hollywood apartment with an acoustic guitar at 3:00AM as I've ever heard.

I often come back to Steven Wilson's "Luminol" from the Raven that Refuses to Sing for evaluating higher frequencies. If you haven't heard it I recommend you give it a listen and pay particular attention to the insane cymbal work. The SPL played that cymbal work back with all of it's intricacy superbly reproduced. I decided it might be time to branch out a bit, so I dropped side 4 of the Acoustic Sounds Blue Note reissue of Wayne Shorter's Night Dreamer on the VPI Traveler. Elvin Jones ride cymbal work and McCoy Tyner's piano intertwined like beautiful serpents in the higher frequencies, floating above the rest of the music.

The London Philharmonic recording of Holst's The Planets showed the SPL to be balanced in frequency response and extremely capable of reproducing fine nuances. A beautiful recording that ends with a Women's Chorus that is a haunting aural treat.

The Phonitor 2 is stunning as a standard headphone amplifier, and well worth the money without the matrix circuitry engaged. However, I found that I often used a portion of the Matrix. The crossfeed and speaker angle settings added a touch of naturalness to the sound that I loved. I enjoyed the ability to reduce the center volume on certain cans especially the AKG K701. The Matrix is designed to emulate the sound of near field monitors for mixing, and I think it does a good job.

For pure listening enjoyment your mileage may vary though. Switching from straight headphone out to the matrix reduces bass impact and overall definition. For the headphone enthusiast this may be problematic, but this is not a design flaw. It is eerily similar to what happens when you switch from headphones to small near field monitors in the studio.

In simulating a studio environment, allowing an engineer to work late into the night without a drastic change in the sonic environment, the Phonitor 2 and it's Matrix circuitry hits the ball far, far out of the park. For the rest of the music loving population the SPL is a crystal clear and musical performer in both the headphone and line-stage departments.

Michael Liang:

When Warren Chi initially approached Kevin and I about reviewing SPL's new Phonitor 2 I was a bit concerned (hesitant maybe the right word). Maybe even a little scared. Why me? What did Warren know that I didn't?

I haven't had much experience with the original Phonitor. Outside of watching Jude's informative overview video on Head-Fi TV (link), my only real-life encounter with the original Phonitor was at a local headphone meet over a year ago. However, because of my modest headphone collection (I stopped counting after the first 200) Warren felt that I would at least be able to put the Phonitor 2 through its paces in standard headphone mode.

From an enthusiast's perspective, one can't ignore the substance of the Phonitor 2. It's packed with features not commonly found in traditional headphone amplifiers. The imposing front panel is full of knobs and dials and switches, as well as more knobs and dials and switches; all surrounded by additional knobs and dials and switches. It's rather intimidating at first glance. It also boasts a rear panel that will suit even the most complex system configuration. But despite all that, getting the Phonitor 2 up and running was a piece of proverbial cake.

For a clutter-free workspace, I opted for a DAC with a small footprint. The new $499 Wyred4Sound µDAC-HD fit neatly behind the Phonitor 2. A short run of Nordost Heimdall 2 RCA cables connected the µDAC-HD to the SPL's solo unbalanced input. On the opposite end of the µDAC-HD is a single USB cable (bus-powered) connected to my MacBook Pro with Retina display. Sonic Studio's Amarra Symphony app did the heavy lifting as the sound engine over iTunes. In fact, the toughest part of getting the Phonitor 2 singing for me was choosing which headphones to use from my collection!

Naturally, I wanted to grab a studio monitor like a Beyerdynamic DT-770 or the new Audio Technica M50x, since the Phonitor 2 is derived from the pro audio world. Not so fast there speed racer: I'm also interested in the Phonitor 2's performance with low-impedance IEMs (in-ear monitors) - specifically with regards to the noise floor. Moving like a factory robot in repetitive motion, I switched from IEMs with dynamic drivers to balanced armature designs to hybrids of the two designs while a zero bit (total silence) track played through the system. The Phonitor 2 was absolutely silent, regardless of the volume knob's position. Daddy likes.

A fellow member (Nomax) suggested that I try the new AKG $1499 reference headphones (K812) with the Phonitor 2. It just so happens that I have this headphone here for review. I've been listening to the K812 on my beloved Lehmann Audio Linear headphones amplifier.
Editor's Note: For those of you who don't know Michael as well as we do, you should at least know that he's absolutely in love with his Lehmann Audio Linear. It's his favorite headphone amplifier, and he never misses a chance to let us know what a beast it is. Seriously, if the Lehmann Linear didn't have electricity running through it, he'd fuck it. #rolleyes

The Lehmann is a fabulous amp, and has long been the king of my headphone amplifier collection. You can read our full review on the Linear USB (with DAC version) here (link). AKG also thinks Lehmann Audio amplifiers pair well with their new reference headphone. They used pro versions of the Linear as the official amplifier for their K812 launch.

The AKG K812 is a ridiculously transparent headphone. Righteously so, being a reference studio model. If your system is not up to snuff, it'll let you know by jabbing the flaws of your system straight into your ears. Fortunately, you don't have to suffer with the Phonitor 2 at the helm.

I am a big fan of Sarah McLachlan. On the last track, Last Dance, from her "Surfacing" album, the Phonitor 2 was able to extract more presence and weight from the cello being played beside her piano than I've heard before. Reproducing the tonal accuracy of a piano can be challenging for audio playback systems, but the Phonitor 2 had no trouble at all. Sarah's airy voice in Angel sounded real, like being in the live room with her. Crediting the Phonitor 2's ultra-low noise floor, I noticed improved decay in her voice and in the instruments as well.

But the AKG K812 is still a relatively new headphone in my collection so I turned to an old friend the Sennheiser HD800 for further evaluation. I queued up one of my favorite soundtrack albums: "Pleasantville". The first track, Fiona Apple's version of Across The Universe (originally by The Beatles) sounded like the headphone got a kick in the rear and was delivering its best. Fiona's voice was imaged ahead of the instruments, giving the track some depth. The bass was noticeably tightened up.

Moving to Roberta Flack's Killing Me Softly (Remastered): the kick drum on this track - which is primarily in the right channel, came through with more speed and energy than I've ever heard through the HD800. Oh yeah, the synergy between the Phonitor 2 and HD800 was out of this world. I wish the SPL supplied a XLR adaptor for use of balanced headphones on the Phonitor 2. From my experience with Sennheiser's own flagship headphones amplifier (HDVD800), running the HD800 in balanced configuration is significantly better than unbalanced.

Still, you don't need high-priced reference level headphones to appreciate the Phonitor 2's sonic performance. Even the $299 Mad Dog headphones by Mr. Speakers performed stunningly well with this amp. I felt like I was getting every last drop of what this headphone can do.

The Phonitor 2 is so musically enjoyable there were days I was excessively late to my day job because I didn't want to stop listening. Owning a headphones amplifier of this caliber makes having a large headphones collection more fun. The Phonitor 2 will reward you with the full capabilities of what each headphone can do.

As I packed up the Phonitor 2 to be shipped to Kevin, I began to feel some separation anxiety. This is not a feeling I've had with any other headphone amplifier to date - not even my Lehman Linear. The Phonitor 2 left a mark in my life.

It was like falling in love for the first time all over again. I look forward to spending more time with the Phonitor 2, and maybe even it's features! I will be adding it to my reference/testing rig soon. It's going to be my new reference headphone amplifier.


Kevin Venable:

The SPL Phonitor 2 is an exquisite amplifier in both concept and execution and I found nothing wrong with it's presentation of music. There are however a few things that a very high end tube amplifier does that I missed. Namely the tonal color and dimensionality that tubes seem to bring to the music. This is personal preference at this point, and that tonal color to some is not a true reproduction of sound. I just happen to miss that enjoyment here.

Michael Liang:

The Phonitor 2 is a tool for audio professionals so it has to be as neutral/accurate in audio reproduction as possible which is what I love most about this product. It would be nice to have a second independent 1/4-inch headphones output on the front panel. This would allow for two users to enjoy the Phonitor 2 simultaneously, or direct comparison of two headphones. As mentioned in the review; the inclusion of a Y XLR adaptor for use with balanced headphones would also be beneficial.


It is obvious that both of us had a wonderful time with the SPL Phonitor 2. It has an ability to make music that is pure beauty, along with a superb feature set. Michael has decided to purchase one as he can not bear the thought of being without it. Kevin wants to buy one badly as well and only finances and his love of tubes are making him wait a bit before making the final decision.

Whether you work in music production or are a confessed music addict (and/or headphone enthusiast), the SPL Phonitor 2 should definitely be on your short list of headphone amplifiers. Its feature set puts it in a league of it's own.

Highly, highly recommended.