SPL Phonitor x Balanced Headphone Amp/Preamp

General Information

The Phonitor x is the ultimate headphone amplifier. It offers connections for headphones operated both balanced and unbalanced. With up to 3.7 W output power the Phonitor x delivers an impressive performance. The revolutionary Phonitor Matrix delivers the most realistic playback on headphones. As almost all music was mixed for speaker playback the Phonitor Matrix lets you experience music on headphones as being played back through speakers. The Phonitor x is not just a headphone amplifier, but also an excellent preamplifier that can also drive power amplifiers or active monitors. Up to five input sources can be connected to the Phonitor x. Two analog stereo inputs (XLR und RCA) and, if the optional DAC is installed, three more digital stereo inputs (USB, coaxial and optical).

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1000+ Head-Fier
[Hands on] SPL Phonitor X preamplifier / headphone amplifier (with a reference to the SPL Auditor)
Pros: Ample power reserves; capacity for voltage swings; dead-silent noise floor; neutral character; reference point for critical listening
Cons: ruthlessly revealing; may get you to sell your accompanying gear by showing it as lacking!

* Full disclosure, my Auditor is currently on sale, therefore one may understandably be led to think my reference to it is purely out of vested interest. However, I hope this review will offer an honest representation of my graduation experience from one generation to the other, while acknowledging the positive traits of an amplifier that has long remained under the shadow of its newer siblings.

** A version of this article is presented in Greek at Audiohub.gr

After my successful coexistence with the excellent Auditor from the German company SPL, I was given the opportunity to upgrade my office system with the newer Phonitor X, a preamplifier and headphone amplifier that has established itself in recent years as a reference point for many well-known hobbyists in the field. In fact, the upgrade from Auditor to Phonitor X is nothing less than an upgrade from the first generation of Phonitor to the second, as the Auditor was just a minimalist version of that amplifier without the proprietary crossfeed circuit (Phonitor Matrix) SPL is quite renowned for.

Too much has already been written over the various Phonitor models, so I won’t be repeating what’s already very extensively covered by others. The Auditor is a different case however; indeed, very little information is available online and you need to dig all the way to 2012 in order to get a first glimpse of a discussion. That being said, many people understandably graduated from the Auditor to the Phonitor X, keeping their faith to the many good traits SPL has consistently offered its ‘Pro-fi’ series over the years.

The differences between the Auditor and the Phonitor X have to do both with the evolution of the proprietary 120V rail op-amp circuit that SPL has developed for the analogue stage of its products, as well as the change of the output impedance of the headphone connectors: the Auditor was rated at 9Ω, therefore best suited for mid-to-high impedance headphones, while the Phonitor X is rated at 0.18Ω for the single-ended output / 0.36 for the balanced, widening therefore its base to cover for low impedance headphones such as those at the nowadays popular 32Ω category. Being a Phonitor means that is also features SPL’s Matrix crossfeed circuit, as well as two very catchy VU-meters that evoke a very Nagra-like 'professional' aesthetic.

Old and new: The Auditor strongly resembles other products that SPL has developed for the studio, while the Phonitor X stands as a regular consumer product with its own distinct aesthetic (namely, prosumer, or, in SPL’s terminology, “Pro-fi”).


VU-meters in mute mode: an extremely useful feature as many Phonitors are known to have blown their circuit because their owners plugged their headphones on a 'live' signal!


The Phonitor X does anything but lag behind other headphone amplifiers famously renowned for their power capacity such as the Schiit Mjolnir, the Burson Soloist / Conductor, or the Auralic Taurus. The following measurements are featured in the manual, without specifying differences between unbalanced and balanced output:

Max. Output Power (at +30 dBu @ 1 kHz)
1 W x 2 @ 600 Ohm impedance
2 W x 2 @ 300 Ohm impedance
3.7 W x 2 @ 120 Ohm impedance
2.9 W x 2 @ 47 Ohm impedance
2.7 W x 2 @ 32 Ohm impedance

On the contrary, SPL’s website features measurements that differ quite evidently from the aforementioned values, showing an emphasis on headphones with medium to high impedance:

Unbalanced Max. Output Power
2.7W x 2 @ 600 Ohm
5W x 2 @ 300 Ohm
1W x 2 @ 32 Ohm

Balanced Max. Output Power
8W x 2 @ 600 Ohm
3.5W x 2 @ 300 Ohm
0.7 x 2 @ 32 Ohm

In view of these differences, as well as the confusion that arises with some measurements mentioned in an older review of the Phonitor XE at The Headphoneer, I contacted SPL who clarified that the reason is due to a silent improvement they made to the circuit in order to add protection against short circuits. As the company states that they reserve their right to such updates without prior notice, along with the fact that very few people got in touch with them over the subject, they felt they should let both measurements roll without further clarification unless specifically asked by an interested party. That being said, it looks like Phonitors that were put in circulation over the last 3-4 years and henceforth output in accordance to the measurements specified on SPL’s website.

[Update: 21 Oct 2021] According to user @aleniola76 who contacted SPL on the same subject (see here), the company responded that
(...) both [measurements] are correct. The first one is the maximum output power when a +30dBu input 1k sine wave is send into the device. The second one is the output power when sending a 1k sine wave into the device causing a THD of 1%. The newer documents will show the later because it is better suited to get a feeling of how much power you will get out of the device until the sound get's less enjoyable. Keep in mind we are talking about a 1k sine signal. So even this value is not a real life value but that's the downside of all these specs – in the end they are just numbers to make devices comparable but do not say anything about the sound. I have never listened to headphones which could not be driven by a Phonitor before – so I assume it's enough power to drive them all.
To my understanding, the measurements on SPL's website represent their best case scenario —and the one most akin to real life circumstances.

Despite the ample power that covers for the majority of various headphone models, the Phonitor X has three stages of gain at the signal level. With the exception of notable beasts that are known to draw unnaturally large amounts of power to be driven properly, I honestly cannot imagine where it may be needed given the amount of power already available on tap:

DIP switch 1: ON = The headphone output is boosted to +22 dB.
DIP switch 2: ON = The headphone output is boosted to +12 dB.
DIP switch 1 and 2: ON = If both DIP switches 1 and 2 are ON, a boost of +24 dB is applied.

In comparison, the Auditor has much less power, but has more than enough stock when it comes to the high-impedance headphones that it is designed for (call me Beyerdynamic, Sennheiser, AKG, etc.):

Unbalanced Max. Output Power
1.7 W (+32.2 dBm) @ 1 kHz and 600 Ohm connection
360 mW (+25.6 dBm) @ 1 kHz and 30 Ohm connection

Both the Phonitor and the Auditor benefit from SPL's proprietary design of the main amplifier circuit (120 Voltair technology), which offers an incredible capacity for really large voltage peaks combined with an exemplary low noise floor. This is something that originally impressed me with the Auditor, as it gave the amplifier its capacity for fatigue-free listening even at high volumes, albeit in a very subtle and discreet manner. On the contrary, the remarkable nominal power of the Phonitor X gives it terrific analytical skills and lets it dissect the signal it receives into its most minute details.

Here’s where the similarities between the two models end. The Phonitor X clearly shows that it is the superior amplifier, taking the effortless neutral sound of the first generation and launching it into the stratosphere. The Auditor is very easy on the ear, and I would even venture to claim it’s rather forgiving, proposing thus a more relaxed version of SPL’s signature neutrality that might be more suited to headphones like the HD600, complementing its drawbacks rather than revealing them in their naked truth. In the end, the Auditor will take advantage of the 120V rail technology’s voltage headroom to create the impression of effortlessness. On the opposite side, the Phonitor X develops from the same trait to offer a very vocal silence: its dead quiet noise floor, combined with its vast power reserves, creates the impression of a void that’s hard not to acknowledge its presence. This is not your typical studio-grade neutral. Oddly but emphatically, the Phonitor X is present by removing itself out of the equation with admirable dexterity in an unusually refined manner. In my honest opinion, SPL has hit the jackpot with its proprietary op-amp design; certainly a treat to the seasoned ear that strays from seeking for an attention - grabbing signature.

Instead of getting more technical, I will just refer to the two videos SPL uses to explain its technology and substantiate its advantages.

In the current range of SPL, one can find a version of the Phonitor in many flavours and for equally many wallets:
  • around 1K € there’s the Phonitor SE (which is the cheapest option available in the line-up ) a stripped-down version that only features the amplifier stage and one single-ended output
  • at 1,4K € you can find the Phonitor E as an end-of-life product, featuring one single-ended and one balanced output (along with the advantages of the extended power capacity available through the latter)
  • Finally, at € 2-2.5K, you have Phonitor X and the Phonitor XE, the former having an additional pre-amplification circuit while the latter serves purely as a headphone amplifier offering as many outputs as possible for this purpose (1 x single-ended, 1 x 4pin balanced, 2 x 3pin balanced at the back)
For me, the choice of Phonitor X also brought an unexpected added value as an active preamplifier, driving my Fostex PM-04d desktop monitors with remarkable control and agility, at the same time revealing them for a capacity to scale that I couldn’t have imagined from such a middle of the line product. Admittedly I also didn’t imagine the advantages that active pre-amplification could bring to the table: the Auditor already offered a kind of pass-through signal output through 2xXLR, leaving the job of driving to the amplifier circuit of the monitors which I thought adequate, to say the least. However, the improvement I got from active driving was so great that I almost feel the need to complain about the poor standalone job the Fostex are doing in this regard!


Thus I close my impressions from this remarkable amplifier. As the days go by it becomes more and more clear that the Phonitor is not an amplifier that will mask the weaknesses of the gear you put behind it, probably putting me in a position to sell both the HD600 and the HiFiMan x Massdrop Model XX that I have in my roster. Therefore, while the first impressions are undoubtedly positive, the Phonitor's ability to mercilessly reveal mistakes is something that under certain conditions puts its owner in a rather uncomfortable position. In comparison, the Auditor is much friendlier, keeping most of the positive traits of the SPL warm-neutral house sound without offending the other components in the signal chain.

It is evident from the very first auditions that the Phonitor X can certainly keep its promise to act as a safe reference point for many critical auditions to come, guiding my future explorations with other components steadily and reliably. Judging from the experience I accumulated over the years through my ATCs (see signature), I also find it certain that at the end of this journey, once the mix is right, the Phonitor X may compensate for its revealing character with a performance that only other, more sophisticated implementations with special character can bring one to cross over (I’m thinking Susvara combined with Acoustic Masterpiece AM201-H or Trafomatic Primavera here). However, as a reference sound, I am already convinced that the Phonitor X sets a benchmark that can hardly be challenged at any degree...
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Thanks for the info, that's good to know on the DAC. I also like the XE for the rear HP jacks. Honestly, the only reason I haven't gotten any Phonitor yet is because of several reports I have read where the silkscreen printing on the faceplate wears off. But I hear they fixed that issue (fingers crossed!).
+1 👍 From what I read myself, this applied only to a small batch of Phonitors and SPL was quick to address the issue. So, unless you’re shopping second hand, it shouldn’t be anything to worry about.
Excellent review...I have wanted one of these babies for awhile! Thanks for this!
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Headphoneus Supremus
Pros: Most transparent & neutral, best "sounding", solid-state amplifier I've heard,
Excellent feature set, very cool VU meters.
Cons: DAC rate-switching issues under macOS and some audio-player software,
Need to pay attention when plugging/unplugging from the TRS jack.
SPL Phonitor x - Review


This will be a summary or TL;DR; version of my full review. The “full” review includes more detailed impressions on how the unit sounds, it’s features and how they work (in particular the “Matrix” feature), coverage of the optional DAC module and some thoughts on how it works with other gear.

The unit I am reviewing is on kind loan from “Headphone.com” for audition/review purposes.


The “SPL Phonitor x” is a premium, feature-rich, headphone amplifier and pre-amp, billed as having features and performance that lend it equal facility in professional/studio settings as well as in the role of an audiophile headphone system.

SPL Phonitor X with ZMF Eikon Teaser.jpg

The unit provides both balanced and single-ended source inputs and headphone outputs. A configurable cross-feed/speaker simulation “Matrix” feature, a granular balance/stereo/mono control, VU meters with configurable sensitivity and enough power to drive almost any headphone with power to spare.


In addition to “classic black”, the Phonitor x can also be had (along with the rest of the matching line of SPL components), in two additional colors … a classy looking silver and, perhaps my (guilty) favorite, a metallic red finish.

Three Colors (1024).png

An optional DAC module, the “DAC192” can be added to the unit (at time of purchase) for all-in-one operation. The unit I am reviewing is equipped with this module, details and impressions for which are contained in the full review.


The Phonitor x has a very solid feel to it; all of the switchgear is wonderfully tactile and engages firmly and positively with a satisfyingly solid “thunk”. The large, central, illuminated volume dial is buttery-smooth. All sockets mate solidly with both input and headphone connectors. Labels are clear and concise, with the functions they indicate being entirely unambiguous. The overall impression is that this is a very high-quality and entirely “premium” device.


The $2,499 question is, of course, “How does the SPL Phonitor x sound?”

In a word … fantastic!

For a start it is clearly both an entirely neutral and highly transparent performer. Using a variety of sources and headphones there’s no tonal shift beyond what those components impart by themselves.

How transparent? Sufficiently so that when paired with a Chord DAVE there was no noticeable loss in transparency or resolution vs. DAVE's native headphone output..

It covers up nothing, makes excuses for nothing, and lets the source show its true colors without omission or editorialization.

It is, for all intents and purposes, the proverbial “wire with gain”.

Lots of gain, if you want it …

There is an addictive sense of lurking power, absolutely effortless delivery and this is accompanied by an impression of “scale” to music that I’m not used to outside of either very-capable speaker systems or state-of-the-art tube-based headphone rigs.

Huge dynamic swings in the most powerful musical performances don’t even begin to phase this thing, while micro-dynamic nuances are fully resolved, even when they’re occurring together.

Transient response, perhaps mostly subtly exemplified by plucked strings and most vividly by rapid-fire electronic percussion is, to say the least, first class. Paired with Focal Utopia, HD800S or Abyss AB-1266 Phi, transients are lightning fast, and that remains the case with somewhat more laid back cans like the Audeze LCD-4.

Listening to one of my favorite instruments, the piano, both from commercial and my own recordings (of my own instrument), illustrates a pure, unwavering tonality. No emphasis, no bias, just a pure and honest reproduction of what the unit is being fed.

Treble is delightfully smooth, but without any loss of detail and maintains an excellent sense of air, space and, where called for, delivers any sparkle present in the source material - with no rough spots nor glare at all.

Bass is reproduced with excellent drive, slam and control and yet retains its texture. Tunes played in the lowest bass registers are ably communicated. Some of this is no doubt due to the significant available power, combined with larger than typical voltage drive.

Both upper and lower registers blend perfectly, seamlessly, into a fully detailed and present midrange. Once again I was struck by how transparent the performance of the Phonitor x was, even compared to the direct outputs of the DACs I’ve been feeding it with.

Detail and resolution are superlative; where brush strokes on cymbals or drum-skins are so well rendered that you can hear when the wire bundle is split or part of it clips the rim of the drum head. The inadvertent twisting of a bow as a violinist seems to shift the hold mid-note, minor utterances, odd, tiny, shifts in a vocalist’s tone, changes in the depth and pace of the artists breathing, environmental noises (chairs moving, pages turning in music, other sounds common to live recordings) are all clearly audible(fn).

Complex layering is easy to hear through and excellent separation make focusing on a given instrument, or voice, amazingly easy … either spatially (especially with the right headphones and the “Matrix” function in play) or by being able to isolate that one performer/instrument via its sound and how it is being played. If you want to pick a mix apart, or focus on part of an orchestra, the Phonitor x is an excellent tool.

Overall, music is portrayed with a distinct sense of “substance” and notes carry an interesting feeling of “weight”, despite the result never feeling anything other than realistic, natural and transparent.

This is set against a dead-silent, carbon-black, background. At no point, in normal operation, was the background anything other than completely silent. And it is, perhaps, in part due to the absolute void against which the music is delivered that results in the presentation being one of absolute clarity and vividity.


Simply put, the SPL Phonitor x is the best sounding solid-state headphone amplifier I’ve heard.

It maintains a neutral, accurate, extremely transparent rendering while providing ample drive to the most demanding headphones I own. It yields a huge sense of scale and power with effortless delivery, has excellent tonality AND tonal weight, transient response is superb and it plies it’s trade against a dead-silent, void-black, background.

The optional DAC module is a useful convenience feature, but I’d reserve it’s use for monitoring purposes - when listening for pleasure I would be looking elsewhere for a source.

If you’re looking at high-end headphone amplification, then the SPL Phonitor x really deserves to be on your audition list.

I am sufficiently enamored with the Phonitor x that I have decided to buy one; which is the highest recommendation I can give any component.

I contemplated rating this unit 4 stars instead of 5, due to the reported sensitivity of the the 1/4" TRS jack to shorting. However, I had no issues with this myself so I'm going to leave my rating based on it's audible performance and just note the precaution in the manual about turning down the volume/muting the unit when plugging/unplugging phones into that jack.


My name is grizzlybeast and I'm an audioholic.
Pros: Gorgeous tone and balance. Good performance
Cons: Could sound a little more controlled, Must read manual prior to use to avoid destroying the amp.




I was recommended the SPL Phonitor 2 when someone saw my posts in a forum regarding my preferences. When I decided to do some research I found that SPL released newer models and inquired where I could find a review. Sooner than later I was put in contact with a representative of Plurison.com who was not only happy to send review units but was enthused to let the units go on tour in the forums. 
Many thanks to Plurison for sending these units out and offering kind support along the way. 
Just to let you know, I have no reasons to fluff up or hide anything. I have no ties and here at earphiles we will not be posting disclaimers because there is no need. To follow are honest impressions of these units. 
SPL is not a brand that gets much coverage on the forums and more often than not I have been impressed by the less popular hands vs some of the more popular ones. I have been rewarded nicely by not being scared to try things. While this has bit me in the rear a few times I have discovered some cool gear in the process and the SPL's are of the latter. 


Phonitor E full specs click here
  1. 120 V Rail headphone amplifier
  2. Separate connections for headphones driven balanced and unbalanced 
  3. Suited for all headphones with impedances >10 ohms
  4. Balanced and unbalanced analog inputs (XLR and RCA)
  5. Optional digital inputs: USB, coaxial and optical
  6. Optional DAC: 192 kHz and 24 Bit, Win driver supplied, Apple Class compliant
  7. Phonitor Matrix with two presets for speaker-equivalent listening
  8. Volume remotely adjustable (learns any IR remote control)
  9. Maximum output power: 2 x 3.7 W (into 120 ohms)
  10. Frequency response: 10 Hz - 300 kHz
  11. THD+N: 0.00091 % 
  12. Dynamic range: 135.5 dB
  13. Standby/power on switch
  14. Linear power supply with toroidal transformer
  15. Front and Lid made from aluminum, housing made from sheet metal
  16. Made in Germany
Phonitor X full specs click here
  1. 120V rail headphone amplifier and preamplifier
  2. Separate connections and power amplifiers for headphone driven balanced and unbalanced 
  3. Suited for all headphones with impedances >10 ohms
  4. Balanced and unbalanced analog inputs (XLR and RCA)
  5. Optional digital inputs: USB, coaxial and optical
  6. Optional DAC: 192 kHz and 24 Bit, Win driver supplied, Apple Class compliant
  7. Balanced and unbalanced analog outputs (XLR and RCA)
  8. Innovative Phonitor Matrix: speaker-equivalent listening on headphones
  9. Laterality control: super-fine balance control
  10. Mono switch function
  11. Volume remotely adjustable (learns any IR remote control)
  12. Maximum output power: 2 x 3.7 W (into 120 ohms)
  13. Frequency response: 10 Hz - 300 kHz (-3 dB)
  14. THD+N: 0.00091 % (HP), 0.00085 % (Line)
  15. Dynamic range: 135.5 dB (HP), 136.3 dB (Line)
  16. AMP CTR connection with Performer power amplifier for coupled On/Off switching 
  17. Standby/power on switch
  18. Linear power supply with toroidal transformer
  19. Front and Lid made from aluminum, housing made from sheet metal
  20. Made in Germany


Upon receiving both units I went straight for the Phonitor X to unbox it. I wasn't expecting any fancy case or packaging. I really don't care about that stuff no matter how much it costs. Just double box it and don't ship me a 2.5k piece of equipment in a pizza box and I am fine. The packaging met my humble standards easily. Once I pulled the Phonitor X out I was slightly underwhelmed at the thin and hollow chassis but equally pleased that it didn't weigh as much as its size would lead me to believe. The unit from the front looked pretty nice to me. After I unpacked it and got it all hooked up on my desk it didn't take long for me to admire Vu Meters and aesthetics on the face-plate. Also the wonderful chrome feet that were secured under the unit gave it that high end look. What did take me long was to notice the gap between the face-plate and the chassis where you can see the lights of the meters shine through. No worries....Its all good. "So how does it sound?... I think it looks nice and even though it feels kind of cheap it doesn't look like it is" I thought. Well we will get into the sound later because there is some information in this section that is actually worth NOT skipping over this time. 
I enjoyed the Phonitor X's sound a lot so I unpacked the E unit to see how it would compare in sound quality. Well the E unit with the meter-less gray face-plate is obviously the less attractive but some of the lettering was kind of smeared. "Well this is a demo unit so It must have been the one the sent me because it could have been returned by an unhappy customer (as seen above)" I thought so ...No worries.... It's all good.
Well, as 'a first time for everything' would have it, I went to use the single ended jack of the Phonitor X and I heard pop, faint music playing, and the smell of burning metal emitting from the Unit. Ahhhh... man.... Well at least I got to thoroughly assess its sound quality. I only got to play with the Matrix / Cross-feed knobs a little bit though so the forthcoming section that describes the functionality of the X will be very limited.
I shipped the amp back and inquired about the problem. The rep told me that unfortunately users fail to read the manual and this problem has occurred before because you are supposed to mute the amp before plugging into the single ended jack. They didn't accuse me of misusing the product and were very polite and responsive. I can see how it does pay off to read the manual but it does not say that you need to mute it before turning the music on. It mentions that you must not plug in a mono jack (who in the heck has that for a headphone plug?)  into the single ended output. Apparently I may have failed to realize that if only one of the rings  of the stereo terminated plug makes  contact it can be considered mono for the split 10 milliseconds it takes to finish fully inserting the cable termination. I don't know... I am admittedly very shallow in my technical knowledge on how it all works but I can't rate the amp highly in this section due to my experience with it. The manufacturer is about the customers interest and uhhh...so am I. Please be careful with this unit and how you handle the single ended output jack. If I were to take this to an SBAF or Head-Fi meet I would tape the single ended jack so users wouldn't accidentally blow up my precious new toy.


Phonitor X

The Cross-feed of the X unit sounded very good with the HD6XX. The center image got pushed back and the midrange thinned out just a bit but the stereo image seemed more precise and easier to focus on. None of the fidelity seemed lost but the soundstage increased favorably depending on the setting. I preferred minimum and 1 on the crossfeed notch and found myself using the more acute angles (20 and 30) vs the larger ones. The effect was substantial but with less of the peakiness that the Pro iCan exhibited with its crossfeed. I did hear tonality change and the upper midrange and lower treble get a little more peaky but not as strongly as on the Pr
The Laterality is a welcomed feature that allows you to fine tune channel imbalanced with speakers and headphones.
Even though the face of the Phonitor has a lot of features on of them is hidden underneath the amp and is implemented in the form of Dip Switches. Dip Switches 1(headphone output +22 dB) and 2 (headphone output +12 dB) provide gain increases and were activated during use with no loss of fidelity during playback when boosting the signal.  Dip Switch 3 is for VU Meter Sensitivity. Dip Switch 4 and 5 make the signal paths direct and isolate the signal to either RCA or XLR output. It was very inconvenient to mess with these features under the amp though. I was always careful to not scratch it or the equipment around it while lifting it up to mess with the switches. 
As far as power goes, despite the X unit having much room on the dial the HE-6 exhibiting clipping when being brought slightly above normal listening volumes so that headphone is a no go with this unit in my humble opinion. 
The pre-amplifier I did not get to test as circumstances didn't allow me to have a go at it with my monitors.

Phonitor E

The Cross-feed presets of the E were far less effective but still proved useful. Hardly any of the tonality and sound quality was effected but the soundstage only expanded a little with the presets if any at all. It seemed less fatiguing listening with these presets which is what it is all about in the first place. The Matrix is not made to stretch the soundstage as much as it is made to reduce fatigue and provide a more natural soundstage where width far outweighs depth. That's what I heard and had no wows or complaints here for the E unit. 
There are two Dip Switches under the E unit as well that serve similar purpose to the first two under the X unit. However here is the other area that you see the E unit is not as souped up out as the X. They both have the same power ratings yet the way they reach that power and position of the volume knob differ quite a bit. I was trying to get the E unit to have as much headroom as the Phonitor X but it couldn't, even with both knobs activated. Let me take a step back to the X unit and cross my fingers in hopes that I don't confuse you. All of the knob of the knob of the X is not usable. You will either cause a hard to drive headphone to clip or you blow up your headphones before you get past 12 o'clock on the dial this is because the unit is also a preamplifier and the dial serves two purposes. Yet and still, even if you turn the E unit past 2 you won't get close to as loud as the X unit does before it clips.
  1. It is only boosting the RCA input signal with Dip Switch 2
  1. The soundstage depth decreases
  1. If you boost the output signal (Dip Switch 1) and boost the input signal (Dip Switch 2) then you will still not seem to have as much headroom as the X. Also If you boost both the input and output signal of the E unit the following happens
  2. The XLR output loosed clarity and becomes less refined 
  1. ONLY the RCA output becomes louder and and will sound better than the XLR output
I recommend only boosting the Output signal and you will have the same sound quality as the X unit without as much headroom. So a headphone like the HD650 sounded great on both amps. Also most planars don't need any more power than that anyway. Especially now. 
*Unit X does not have a selectable Input signal boost and does not need one. 
Unit E did not blow up when I plugged the single ended jack into the headphone output but it has the same warning as the X unit.

Internal DAC Option

It was a tough task to tough task to test the internal DAC with no other point of reference than my Pavane. They were light years apart in sound quality. In fact switching made me curious if others with a sub 1k DAC would appreciate the amps sound quality as much as I did (more to follow).  What I pulled away from it was that the DAC as well as the AMP were tuned neutral and non fatiguing with no detectable emphasis anywhere in the spectrum sans a hint of warmth. I would have loved to compare it to something of equal caliber but honestly you are just severely limiting the amps ability if you plan on using the internal DAC as your primary source. 




If an amp does poorly in this category it will be a deal breaker for me. The bass delivered by these amplifiers is not the best I have heard but it is most definitely not the worst. The amplifiers are not bass shy but sit pretty much at my targeted amount of what I believe is neutral in regards to quantity. My appetite for bass is a little more than your average enthusiast but I have come to like the amp itself to be neutral (true neutral, not bass shy) and my headphones to do the boosting. What I like the amp to do is make what ever bass is there slam. The Phonitor units deliver an average amount of slam so if you are looking for the most engaging experience these may not be for you. What I do hear though is  body, texture, and natural decay. 
It is neutral in the sense that it sounds unbiased in any direction and is neither emphasized, lacking, dry, or too wet, super controlled, or loose. ​
When it comes to bass control you will notice that while it's not necessarily loose, the natural decay gives the bass a more rounded presentation than a dry and technical. At first I thought they were a little rolled off in the sub bass because the organic sound can give that impression but listening to sub bass rumbles and tone sweeps show the sub bass is all there and deep even. The sub bass with EDM is rendered by the SPL units as bouncy instead of hard and fast with very linear sub bass rumbles that sound very well integrated into the music.
Personal preference in this area would be a smidgen tighter and more dense but as is still does the trick. Another listen would call that a nitpick. Why? because often times some solid states sound as if they do not let the bass resonate and the decay can often sound as if it does not have a realistic decline. I am I calling it wet? no… just slightly and tastefully bloomed with good extension and presence without sounding emphasized. 


First of all there is a markable lack of grit and grain. I have heard a blacker and more holographic background elsewhere but this amp is very refined and still has a nice black background with great clarity. Sure those are the technical aspects but... the midrange was laid across those traits with an almost perfect balance from the lower midrange into the upper midrange. It sounded round to me and slightly...minutely...boosted but that was only compared to my other amps. Spot on...When I first plugged my 650 into the Phonitor X I thought to myself "Well this sounds pretty good but nothing better than anything I have heard before". I should have known better than that because the first(short) moments of hearing the Utopia were a little similar. Comparison is an agent of revelation because it only took one swapping of amps to hear how natural and clean the midrange really was. I had to fight hard to find any digital facets while this amp was being fed by my Pavane and Rednet 3 and am still not convinced I did. The midrange only barely drew attention to itself but this is warranted since the midrange is the matter of music. But the bass is not left behind next to the pure midrange and neither is the treble. 
It could have been all mids and nothing else but the whole picture is well put together. You can say that the midrange is emphasized and I would disagree with you. If you said that the midrange was withdrawn, anyone who has heard anything would disagree with you. Vocals neither lack sweetness or sound overly lush. You get an honest window into the music all while knowing there is little flattery going on. Even compared to some tube amps the midrange is more realistic sounding but maintains good balance. The lower mids sound even. The midrange proper is full but neutral. The upper midrange has good presence without ever sounding honky. 
“Oh well Lee, that's because the 650 has a good midrange…duh” Nah…nope. The HD800 sounds a bit more natural but its thinness is still there. The Ether flows sound neutral and a little shouty albeit a tad less sterile than normal. The Ether Flow C’s still sound hollow (like on my other amps). The Hifiman Edition X sounds evenly balanced but still distant. Basically I am being bold in saying that most other solid state amps may be off in some area by comparison. First impressions led me to think there was emphasis here but that going back to other amps made them seem wrong and the phonitors correct. Realism is what this amplifier excels at. What does this amplifier emphasize? Reality. So the point is that the midrange will do maybe a little favor to your headphones but this amp is not to make headphone 'x' sound like headphone 'b'. 
A brief comparison to the Pro iCan (an amp that I was very impressed with) would affirm my sentiments here. The iCan had a sweeter, fuller lower midrange (that I find emphasized)  and even more so than  my Trafomatic Head 2 but the upper midrange was less present than the Phonitor E. Sure its blackground was possibly a tad blacker but the phonitor was not far behind and has better balance as well as harmonics and never sounds as weighed down. Also the phonitor X has a better soundstage display to help the midrange spread its wings.


I want to be short and sweet here. I am admittedly not a 'treble head' but I understand the role of treble in harmonics and at the same time do not like being distracted by harsh and metallic sounds. The Phonitors are not dark. They are not the most airy amplifier around but the air is present. The treble balance is neutral and I mean “true” neutral but it lacks the glare, grit, splashiness, and grain a lot of solid states are notorious for. Can you take an HD800  and hack away its 6-7KHz notch and turn it into an HD800S absolutely not but the treble of my modded HD800 was tolerable and much more refined than on my Cayin iHA6 with its more sparkly but offensive nature. Yet, tons of harmonics and overtones are rich and musical because of the treble that is there. Don’t get me wrong, I like my Cayin a lot but I have come to believe its a bit emphasized in the mid treble. Consequently the iha6 has good definition but relatively speaking definition(from 6-10kHz ) is not softened on the phonitors, it’s just not emphasized. The non-fatiguing aspects of the upper band is with a smoothness that therefore squelches a little bit of that snappiness and energy some look for so some may want more energy as well as body here. As for me, I am totally fine and in fact the distinct lack of plasticky sounding textures and digital like steeliness is very appealing to me. 
To sum it up and for the sake of simplicity I'm calling the treble smooth, present, realistic but not as snappy and energetic as some may prefer. Personally I'd pick this treble over 95 percent of the solid state amps I have heard...no I'm lying ... 100% of the solid state amps I have heard but I can totally understand if someone found it underwhelming as tastes vary. 



I have already covered this area briefly. The short story is that these amps do very well technically. If they are worth their asking prices based on technicalities alone, I would hesitate and say yes. Not a firm yes but a committed one. The features of the E unit are limited. With the X you are paying for more headroom, the full blown Matrix system, and a preamplifier that if it performs as good as the headphone amp is potentially a very good preamplifier. The E unit still performs admirably but this is what 1799 should sound like at minimum in regards to technicalities. For that price you can purchase the equally performing (in technical ties, relatively speaking) Pro ican and have features that compete with the X unit as well as even more power. I must make it clear though that merit by merit the features of the X outshine the PRO iCAN. I just rate the Pro higher in features because it costs less than he X unit by 700USD. However, the Pro iCan cannot touch this tonality even if it does possess a slightly blacker background and similar refinement. The iFi amplifier has a little more density and tonal weight, smaller soundstaging, snappier transients, a slightly blacker background, and more power. But as gear like the 650 proves balance and tonality go a long way especially when amps like the pro sound dark and the soundstage is narrow. That combination can be a turn off.  To find all around spot on tuning, along with the refinement, lack of grain and grit that the SPL units deliver is also pretty rare for solid state amps so that has to be considered as well. My Cayin iHA6 is equally detailed but less refined in the treble, less organic, less spacious, less dense, and less clean. The Cayin is 999USD but is also faster, has tighter bass, has more power, better control, and snappier transients but is the personification of what powerful neutral solid state amplifiers are usually considered to be and it doesn't possess nearly as much realism and tangibility. When I listened to the Pro iCAN or Cayin, I felt I was listening to equipment. The SPLs possess equal technical performance but more realism than any amp on my desk during the time of review and that aspect of performance was from the marriage of tonality and good technicalities.




There are those times when I ignore what I have read about a product and want to hear it for myself. The truth is that you can read so many reviews about something and once you hear it find that it is not for you. If you like an amplifier to play the music as it is and not add to it or take a way from it then you'd be at a loss to overlook the SPL units. Perhaps almost equally at a loss if you purchase one and overlook its warnings in the user manual. However, there is not one product launching with a 100% success rate in build quality, but these units come from a world where you would expect a more ruggedized build to take the abuse from a musical engineer. I will say though that if 'Pro-Fi' is a trend that SPL is trying to start, I'm with it. There ought to be more units built with that concept of tuning.
Can I fully recommend these products with a clean conscience? No. Only because at this point I have to conclude the review and the reasons for the amplifier blowing up remain to be known. But I will say that this is the best solid state amp I have heard the 650 with bar none and the sound quality is very rewarding to the discerning ear.
original review posted on earphiles.org
The explanation you were given for the x's failure is either bs, or if true is admission of a design fault, regardless of price. Should never happen, at any price. My 2 cents.
I agree. That's why it has 4 stars.  If not it would have had 5. On my website its laid out a little better because I can separate the aspects and give a better score. They sound great though. 



The amp blew up because you plugged in your headphones? It doesn't matter what the manual says, that speaks to very poor design engineering. I'm surprised the Germans would make such a thing. Maybe it's actually designed in China and just marketed by the Germans.

Point of reference.. I own a TEAC HA-501. If you turn it on, or change headphones, it mutes itself and indicates that with a glowing red LED. You have to turn the volume all the way down which brings the unit out of mute, and off you go. A well thought out and painless way of making sure you don't damage something (either the amp or your phones). Let's think about this feature and compare this to the SPL amp which spontaneously simply burns itself up. What a POS.