SPL Phonitor 3

Headphone Amplifier
By Phil Ward

With its clever Phonitor Matrix, this high‑end headphone amp aims to deliver a more speaker‑like listening experience.

You perhaps don’t need me to point out that there’s something of a disconnect between the way most commercial music is mixed (on loudspeakers) and the way it’s increasingly consumed (via headphones). One result of this is that mixing on headphones is becoming much more common. Whereas, a decade or two ago, headphones in studios were primarily present for tracking and overdub duties, these days they also have an important mix role. This is especially the case for Dolby Atmos music mixes (other immersive systems are available), where the most often consumed end product is probably an Apple Spatial binaural headphone downmix.

A further consequence of the expanded studio role of headphones is that headphone amplifiers have become more relevant. Previously, we all just plugged our headphones into an interface or mixing desk headphone socket, or maybe into a headphone distribution amp, and perhaps didn’t think too hard about how that affected the headphone sound. Yet, mixing on headphones means we’ve become more sensitive to headphone sound quality. The subject of this review, SPL’s Phonitor 3, reflects the increasing significance of headphone amplification. But, more than that, it offers some intriguing headphone output configuration options. Christened by SPL the Phonitor Matrix, the configuration options enable some significant manipulation of the headphone listening experience, primarily with the aim of making it more speaker‑like.

It’s probably worth me mentioning that while I’m looking at the standard version here, SPL also offer a slightly more expensive option, the Phonitor 3 DAC — this covers much the same ground, but it also features a built‑in 32‑bit, DSD‑capable D‑A converter.

Ins, Outs & Basics

While I’ve introduced the Phonitor 3 as a headphone amplifier, and that function does generally cover its defining set of features, it’s also a monitoring preamplifier that offers three balanced stereo XLR input pairs and one balanced XLR stereo output pair, for the connection of active monitors. Input source selection for both monitor preamp and headphone amplifier functions is achieved by a simple three‑position rotary switch on the front panel, and output volume is adjusted by a large and satisfyingly tactile machined‑aluminium volume knob.

Having just deployed the term ‘tactile’, it strikes me that it’s a suitable one for the Phonitor 3 more generally, because the traditionally constructed and black‑painted all‑metal enclosure feels really substantial and no‑nonsense. It looks and feels like it means business. Also apparently meaning business is the Phonitor 3’s headphone amplifier itself. It’s powered, say SPL, from ±60V rails to provide significantly greater output power with very low noise and distortion, and its very low output impedance means there’s negligible change in frequency response with variable headphone impedance.

I’ve mentioned the volume control and input selection switch on the Phonitor 3’s front panel, but there’s a lot more besides. Firstly, dominating the right‑hand‑side of this panel are two retro‑looking VU input level meters that, say SPL, display BBC‑style meter ballistic characteristics. At this point I will recommend Hugh Robjohns’ fascinating history and explanation of the VU meter in SOS May 2024, called ‘VU Meters: Virtually Useless or Very Useful?’.

Second up, beneath the VU meters and alongside the 6.3mm headphone output socket, are six slide switches that engage or disengage the Phonitor Matrix options, and provide left/right channel swap, left/right channel polarity, left/right channel solo, VU range, and headphone or XLR output. On the left side of the front panel are five rotary controls and a further slide switch that configure and adjust the Phonitor Matrix and an option called Laterality.

The Phonitor 3 can switch between three sources, and can deliver a clean output for speakers, or a Matrix‑processed signal for other headphone amps. [The dual rear legending, with one being upside down for convenient viewing 'over the top', is a nice touch others would do well to adopt - Ed.]

Enter The Matrix

To begin with, let’s consider the Phonitor Matrix options. The first is Crossfeed and, with the Phonitor Matrix enabled, turning this knob feeds an increasing amount of left‑channel signal into the right headphone channel, and right‑channel signal into the left headphone channel. The idea is to simulate the psychoacoustics of listening on loudspeakers where, it should perhaps go without saying, both ears hear both channels to some degree. Crossfeed, though, also adds some EQ to compensate for the fact that more interaural crossfeed from a pair of speakers is likely also to be accompanied by slightly emphasised high‑frequency balance. Adding crossfeed, say SPL, corrects to some extent the ‘false’ stereo image presentation of headphone listening that results from its absence.

The second Phonitor Matrix option, Angle, is related to Crossfeed, in that it compensates for the interaural crossfeed time delay phenomenon (it takes fractionally longer for sound from each speaker to reach one ear than the other) of the speaker listening experience that’s absent on headphones. Again, the intention is to make headphone listening more speaker‑like. The angle referred to in the parameter is the one that would be created by the stereo spacing of the imagined loudspeakers. The wider the spacing of the loudspeakers, the greater the interaural crossfeed time difference between them. As with Crossfeed, the Angle adjustment also comes with EQ to reflect the variation in head‑related acoustic absorption at different imagined speaker angles.

The third Phonitor Matrix option, Centre, enables adjustment of the relative level of the centre signal to compensate for the over‑emphasis that will potentially result from adjustment of the Crossfeed and Angle parameters.

The final front‑panel knob, Laterality, controls a function that’s related to a traditional balance control. However, it simultaneously reduces the level of one channel while the other increases, and also offers extremely fine adjustment (just ±2.25dB across the Laterality control’s full range). The intention is to provide a balance control that can compensate for reduced hearing sensitivity in one ear.

One more function to mention is the DIP switch array on the rear panel. As well as offering a +12dB headphone output option, this allows the headphone Phonitor Matrix options to be routed to the rear‑panel XLR outputs, with or without the volume control operational. This enables, for example, a second headphone amplifier to be fed with a signal that’s been processed by the Phonitor Matrix.

I have a pretty wide variety of headphones available... and each one sang with an impressive and seductive sense of clarity and impact.

Sound Opinion

But what, I’m sure you’re wondering, does all this actually sound like? Well, to get the basics out of the way first, the fundamental headphone sound quality of the Phonitor 3 is, to my ears, excellent. I have a pretty wide variety of headphones available, with significantly differing sensitivities, impedance characteristics and tonal qualities, and each one sang with an impressive and seductive sense of clarity and impact when driven by the Phonitor 3. When considering its Phonitor Matrix functions, I have to admit that to begin with I was somewhat underwhelmed, because I found their effects decidedly subtle. But as I began to listen more and tune into their characteristics and behaviour, my opinion changed: I found the Phonitor Matrix functions increasingly interesting and useful, particularly the Angle and Centre functions. In fact, after getting used to the Phonitor Matrix processed headphone sound for a while, switching back to unprocessed headphones was a genuine disappointment.

There’s no getting away from the fact that it’s a niche product, and when it comes to my opening point about the disconnect between people mixing on loudspeakers but listening on headphones, processing headphones to sound more like speakers probably asks more questions than it answers. But the Phonitor 3 is a likeable and strong product that’s impressively constructed and technically interesting. The headphone amp itself is good, and I could see the Phonitor 3 becoming indispensable in the right setting. It does a good job of emulating the speaker listening experience on headphones, and I can certainly see its potential in mastering studios or in mix environments that are extensively headphone rather than speaker based.

Alternatives

The professional audio world isn’t short of high‑performance headphone amplifiers: the Benchmark HPA4, DACS Purity, Violectric HPA V550 and iFi Pro iCAN Signature, for example. But if the Phonitor Matrix functions of the Phonitor 3 particularly appeal, then it’s one of a kind.

Pros

  • Very high‑performance headphone amplification.
  • Fascinating and versatile headphone processing.
  • Very high build quality.

Cons

  • Perhaps a solution looking for a problem?

Summary

The Phonitor 3 is an interesting and very well‑engineered product that does extremely competently exactly what it sets out to do.

Information

Phonitor 3 £1899. Phonitor 3 DAC £2599. Prices include VAT.

SCV Distribution +44 (0)3301 222 500.

sales@scvdistribution.co.uk

www.scvdistribution.co.uk

spl.audio

Phonitor 3 $1899. Phonitor 3 DAC $2599.

spl.audio

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Published September 2024

From the same manufacturer