Today, discerning music enjoyment often takes place via high-sounding headphones. And as with a high-quality hi-fi system, it is by no means only the “loudspeaker” that produces the sound, but also the amplifier – it is no different with headphones. In everyday life, this detail is often overlooked: In Smartphones, inexpensive and miniaturised operational amplifiers are at work, and even in more expensive audio interfaces, the obligatory headphone amplifier is one of many features rather than a dedicated selling point. However, if you spend several hundred Euros on a pair of high-quality headphones, it makes sense to look around for an adequate “amp” as well.
SPL from Niederkrüchten in Germany has taken on this task with several devices for home and studio use. The Phonitor se marks SPL’s entry into the audiophile camp, the Professional Fidelity series emphatically focuses on high-quality technical solutions which are also used in SPL’s professional products.
The unit, which weighs just under 3 kg, already looks a size bigger than the last Phonitor One we tested. It has a first-class finish and is housed in an elegant, flat metal case with an internal power supply. At the time of purchase, you can choose between three decorative colours for the brushed front of the device: Black, silver or red. You can also choose between a version with and without an integrated D/A converter.
The Phonitor se offers an asymmetrical headphone output (6.3 mm jack) and a large, low-friction level control made of milled aluminium. In addition to the power switch and the configuration of the Phonitor matrix (see below), there are two switches on the front panel for selecting the input. You can choose between an analogue Cinch input and the optional, but not retrofittable D/A converter DAC768xs (with AKM AK4490 equipment), which was installed in the test unit. This allows sampling frequencies of up to 768 kHz and 32 bits as well as DSD up to 11.2 MHz (DSD256). The second switch selects between the available digital interfaces USB, S/PDIF coaxial and S/PDIF optical, which are located on the back of the unit, as are the solid, gold-plated RCA connectors.
The Phonitor se also uses SPL’s own Voltair technology. In order to achieve a better signal-to-noise ratio and increased dynamics, SPL uses specially developed operational amplifiers with a supply voltage of ±60 volts (a YouTube video by SPL can be found here). Conventional components/operational amplifiers only work with ±15 volts operating voltage (for the transformed DC voltage), which is used for signal amplification. This indeed results (on the measurement sheet) in a dynamic range of more than 140 dB and a signal-to-noise ratio that surpasses the built-in converter with 114 dB. The overload reserve also increases, so that the amplifier hardly ever has to operate at its limit, relative to the reference level.
The Phonitor se impressed us with its straightforward operation. Selection of the sound source is self-explanatory. In addition to volume control and source selection, the manufacturer’s own Phonitor matrix is also used, which can be activated here in two gradations. This purely analogue circuit aims to give headphones the characteristics of a loudspeaker reproduction. A little context: Sound recordings are almost always mixed via loudspeakers. If you use headphones instead (when working on the mix, but also when just listening to music), the listening impression inevitably differs with regard to the level components, the stereo panorama and the depth gradation. This is due to both the in-the-head localisation and the perfect separation of left and right channels, which does not exist in real life. In fact, this “crosstalk of the channels” goes hand in hand with physiognomic filtering. SPL provide an easy to understand explanation.
To summarise, the sound experience under a pair of headphones is often spectacular, but not necessarily more realistic when it comes to mixing. The Phonitor Matrix addresses these disadvantages with a circuit that takes into account the crosstalk between the stereo channels including filtering, the placement angle of the (non-existent) speakers and a level compensation of the phantom centre. With the Phonitor se, the crossfeed parameter can only be adjusted in two steps. Up to 30 per cent of the signal from the opposite side is mixed in, taking into account the corresponding filtering, which has an increasing effect above 500 Hz. The placement angle of the loudspeaker simulation is preset to 30 degrees corresponding to 250 µs propagation delay. For this purpose, the centre signal is lowered by 1 dB in order to embed the stereo centre correctly again after using the crossfeed parameter. Illustrative listening examples can be found at this link, which you should listen to with headphones.
Depending on the impedance, the output power per channel of the Phonitor se ranges from 1 watt (32 ohms), 2.7 watts (600 ohms) and 5 watts (250 ohms). With this power, even demanding headphones can be driven. If that is not enough, the output level can be increased by a further 12 dB with a dip switch on the underside of the unit.
In contrast to the larger models and the now discontinued Phonitor e, I felt the absence of a connection option for balanced headphones or simply a parallel second headphone output. It would have been nice to have the possibility of a remote level control – it is only found in the Phonitor x and xe models and represents a deliberate compromise in order to be able to ensure the other device quality in this price range. Finally, the red status LED on the red version could have been changed to a more striking colour – I actually forgot to switch off the device several times.
SPL describes the Phonitor se as an entry-level Voltair model. With a retail price of around 1,000 Euros or 1,400 Euros (with transducer), there is no doubt that there are high expectations for the device. And indeed the test unit met these expectations in full. We tested it with the Sennheiser models HD 660 S (for review), HD 800 S and HD 820. For our listening test, I used the USB interface in combination with Tidal on a Windows computer. The requisite driver allows a quick start-up and could be used for sound output without any problems. Using macOS and iOS, the Phonitor se even worked compliantly via USB.
In general, the better the headphones, the more clearly noticeable the performance gains in the amplifier range. Compared to the standard output of my Focusrite audio interface Clarett 4Pre, the cheaper Phonitor One was already audibly superior. The Phonitor se again performs in the next highest quality class. It behaves as an audiophile amplifier should: tonally balanced and neutral, high-resolution, noise-free, with superior dynamics and, of course, reserves that deliver sufficient levels even with quieter tuned designs.
The Phonitor Matrix offers two sound variants in which the typical super-stereo effects are toned down. In fact, the spatiality as well as the spectral tuning is changed. Two coherent variants are offered, which can be of great help especially in sound evaluations. You should spend a few minutes listening to the altered sound characteristics. Otherwise, let your taste decide and choose between the emphatically wide headphone effect and two variants that are closer to the listening impression with a loudspeaker. In fact, the circuit reduces the localisation in the head, which is quite remarkable. However, it must also be noted that the sound result still does not take place in front of the head as with a loudspeaker.
With the Phonitor se, SPL undoubtedly offers a high-quality and convincing-sounding headphone amplifier that is aimed at audiophile music consumers. Superior workmanship and technology as well as a coherent and finely drawn sound image with the best dynamics and sufficient power reserves should satisfy almost all requirements for music enjoyment with conventional, high-quality headphones, which ultimately justifies the price. In the version with integrated converter, which makes more sense in my opinion, the Phonitor se also turns out to be a convincing interface for output with modern streaming media and Hi-Res files from a computer. Given the audiophile demands and the price, however, it could have been improved by being a balanced interface.
- Ear couplingAmplifier
- Weight without cable2,800 g
What's in the box
- Power cord
- All technical data can be found on SPL's product page.