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Sontronics Mercury

Multi-pattern Valve Microphone By Jack Ruston
Published December 2017

Sontronics Mercury

Sontronics have had great success building mics for specific applications — but their new flagship is designed to take almost anything you can throw at it.

Back in November 2015, I reviewed Sontronics’ large-diaphragm valve cardioid mic, the Aria. And I liked it — in fact it’s fair to say that it was a glowing review, an opinion which I stand firmly behind, having had the opportunity to use the microphone on a number of subsequent occasions. So when I heard tales of a new Sontronics product, the Mercury, I was keen to get my hands on it and find out more. The question is, what exactly does my hot little hand now hold? And the answer is that it holds another large-diaphragm valve condenser. What does it not hold? It does not hold an Aria MkII. Friends, gather round...

The Mercury is a dual-diaphragm valve microphone with a continuously variable polar pattern. It’s a robust, bottle-type design, built with premium parts — in a move by designer Trevor Coley towards the high end of the market, this design incorporates the finest electrical components. Coley told me: “To be honest, a microphone is quite a simple thing — it’s a transducer and an amplifier, but there’s some magic in the middle. You design a circuit, and that design dictates your component values. But I was experimenting with some of these things, with the tolerances, the quality and consistency. I wanted to find out if the best really made a difference, and in what way. Was there an audible improvement that would justify the extra cost to the customer?”

Some would say, without hesitation, that of course the better components would yield a better result, and even express surprise that Coley would even ask himself the question. But it’s worth remembering that, historically, not only have some of the finest-sounding and most highly prized professional audio products incorporated components that could, on paper, be considered less-than-premium, but also that Coley himself had managed to deliver one of them in the form of the Aria, without resorting to the nth degree of component sourcing. As it happens, in the final analysis, he did identify significant performance gains through these experiments, and the concept of the Mercury was born.

Liquid Metal

The microphone is predominantly made here in the UK — while some of the metalwork is manufactured by Sontronics’ partners in China, the electronics are all domestic, and the product is assembled here, at the company’s facilities in Dorset. Referring back to premium electronics for a moment, Coley tells me, “There are three capacitors that are absolutely critical to the audio path: a polystyrene capacitor, and two silver mica capacitors. All have one percent tolerance. They’re as good as you can get.” While he remains understandably tight-lipped about exactly who supplies them, he will say that they’re also of UK manufacture.

The machined brass body features the familiar bold, screened logo, making it clear which side of the mic is which. The microphone weighs in at a reassuring but not outlandish 2317g and measures 250 x 90 x 80mm. It comes in a velvet-lined wooden box, which sits in a foam-lined aluminium road case, the various sections of which snugly enclose the power supply unit, shockmount, eight-pin audio cable and the power cable. This selection of accessories, robust and functional if not especially beautiful, will be familiar to any Aria devotee, with the exception of the larger shockmount and the addition of the continuously variable rotary polar-pattern selector on the front panel of the PSU. Also on that panel are a -10dB pad switch, and a 75Hz high-pass filter switch. Further technical specifications are as follows: frequency response is 20Hz-20kHz; sensitivity is 18mV/Pa, or -33dB ±1.5dB (0dB = 1V/Pa at 1kHz); impedance is ≤200Ω; equivalent noise level is <12dB (A-weighted); and maximum SPL (for 0.5 percent THD at 1kHz) is 125dB (more on headroom later).

As mentioned above, this is not simply a premium reinvention of the Aria design, with the addition of a few bells and whistles. Sontronics often voice their products in an application-specific way — the Delta for guitar amps, or Aria for vocals, for example — but the Mercury is aimed at more general use out on the studio floor. And a studio mic this certainly is — it’s not really ‘one for the road’ as such. The continuously variable pattern, and lack of any deliberate tailoring in the frequency response, offer the mic to a broad range of applications and techniques. It has a great deal of headroom, on paper, yes, but perhaps even more so in practical use. It’s designed to be a ‘go to’ mic, the one you put up by default out in the studio — maybe the one you don’t really take down. It’s designed to be the overhead, the room mic, the piano mic, the acoustic guitar, the amp... or perhaps the main vocal. It’s supposed to take what you throw at it, to keep your options open, not to box you into a corner sonically. Its development was characterised by three years of extensive listening tests, and it’s designed to sound superb at all times. So... does it?

Out Of This World?

If I had to pick two words that best describe the sound of the Mercury microphone, they would be ‘present’ and ‘transparent’. There’s a clarity here, a definition and coherence all the way from the bottom to the top of the frequency response. It sounds modern, open, solid and defined.

The design choices, both electrical and mechanical, contribute to this — the relative separation of the headbasket from the body yields an increase in presence, and the tight tolerances in those capacitors yield advantages in terms of the phase between the dual diaphragms. Where two back-to-back diaphragms are combined to achieve variable patterns in this way, they would, in an ideal world, be identical. In practice they never can be, but the quality and stability of the circuit to which each is connected affects how close they can get to that ideal. There’s a distinct lack of that veiled smearing that affects some lesser products, and no part of the frequency spectrum that feels indistinct or cloudy, so it’s easy to imagine why Coley felt that there was some benefit to this additional production cost, even without the ability to make the comparisons that he himself made on the test bench.

I made a number of drum recordings at The Old Chapel Studios in Nutbourne, which showcase these qualities. Drums can tell us a lot about a microphone. They exhibit a wide range of frequencies, and in a relatively ambient space like this, they reveal off-axis coloration. Any loss of definition can have an obvious negative impact, and a lack of headroom quickly flags itself up as a ‘thwocky’, constrained character on louder transients. Both drummer James Ivey and I found none of those disadvantages — the clarity, presence and open nature of the sound was impressive. Transients were crisp and clear, but the low-end depth and definition indicate that this isn’t simply a question of being bright. Yes, the microphone is bright, but it’s a quality borne out of coherence and transparency, rather than artificial boost or deliberate resonance. Moving between omni, cardioid and figure-8 patterns, and between spaced and coincident positions, the flexibility of the mic reveals itself quickly. I found myself able to dial the room sound up and down in the transition between omni and cardioid, and exclude certain elements of the kit using the deep nulls of the figure-of-eight pattern. The room blended beautifully with the direct sound of the kit, allowing for a lively, natural portrayal.

At this point, it’s worth coming back to the subject of headroom. This is a mic with more apparent headroom than the specifications would suggest. Coley confirms this: the numbers are, he says, conservative, with several more decibels in hand. And so, as a drum overhead, this is a microphone that remains crisp and clear on the transients even without the use of the -10dB pad. This is a considerable advantage for a mic of this type; so often I find myself ultimately swapping a condenser overhead out because it just can’t cope with the louder sections of a track. I’m forced to go for a slightly different character as a result, but this microphone represents a legitimate option in this respect.

On acoustic and electric guitars, that same definition and coherence yielded some beautiful recordings. Again the continuously variable pattern behaved almost like a tone control, moving the listener closer to the source as the omni became cardioid, closing out the room and increasing the proximity effect.

A grand piano is an instrument with a complicated, harmonic high end and upper mid-range. If a microphone is peaky, a close position can often result in an uneven, confused presentation. Typically, you then need to pull back outside the instrument, away from the soundboard in order to minimise this ugliness. But in the context of a pop or rock recording, that might not be appropriate — often you might prefer to be ‘up close and personal’, perhaps with the lid down to the ‘short stick’, with heavy blankets or covers to increase isolation from other instruments in the room. Placing a pair of Mercurys in cardioid, as close as possible to the soundboard, I was able to achieve clarity and presence, without distracting, unworkable resonances. This is a testament to the quality on offer here, and it’s a trait that I noticed throughout my tests of the microphone.

On the right voice it’s capable of stunning results — pulling the details out of darker-sounding singers, moving them to the front and centre of the music. But this isn’t a microphone tailored towards vocal use in the way that the Aria is. And neither can it be — once we accept the benefits of that extended high-frequency response, we must also accept that if, on a brighter voice, we go close in the way that modern genres often require, our recording is going to risk revealing an unnatural amount of ‘esses’ and fricative content.

This is characteristic of almost all of what one might term ‘posh, modern’ microphones. It’s one of the reasons why old U67s, for example, are so desirable on vocals — they control the top end, by their nature, as does the Aria. And one of the things about old U67s, again as with the Aria, is that they could sometimes benefit from a greater degree of presence and clarity in other applications. As ever, it just depends on your source. I was able to achieve some beautiful vocal recordings during the review period — a degree of detail on a dark, delicate, almost mumbled vocal that other options, Aria included, were unable to compete with — but Sontronics have designed this mic to spend its time pointing primarily at instruments out in the studio, and it’s worth keeping this in mind if you’re buying blind.

So that’s the limitation. It’s not really a criticism, more the illustration of an inconvenient universal truth in audio recording — the microphone is irrelevant without the source. In other words, if you need to record a variety of different sources, the chances are you’re going to need a variety of different microphones with which to do so.

But I do have a criticism. The continuously variable polar-pattern control has markings screened on the casing, showing the pattern at three positions: hard left (at seven o’clock) for omni, straight up (12 o’clock) for cardioid and hard right (five o’clock) for figure-8. Considering the significance of stereo applications with a product like this, and that much is made by Sontronics of the near-identical nature of two examples of the Mercury, it seems to me that more in the way of a visual means of matching patterns between two mics could be important here. Sure, it’s fine if you’re going omni, cardioid or figure-8 — you can’t go far wrong — but in the intermediate positions it’d be nice to have a bit more of a chance at precisely aligning the two controls. I don’t really want to guess where 10:45 is in a dimly lit live room. Going a step further, a little dab of fluorescent paint in the groove indicating which direction the control is pointing would be a nice touch too. This design is not the worst offender at any budget in this respect. It’s something that a number of manufacturers could possibly consider, especially since with a continuously variable pattern control they’re not cloning the classic German designs of the 1940s and ‘50s.

Mercury Rising

This is another extremely strong product from Sontronics. It’s a fresh design with a nod to classic form, rather than allowing itself to suffer the restrictive inhibitions of a clone. It also represents extraordinary value: as with previous Sontronics products, it doesn’t burn its budget on excessive cosmetic gloss, but preserves it instead for the components that affect how it will sound. You could buy a pair for the same price as a single mic of similar sonic quality. Of course the devaluation of Sterling plays a part in the way professional audio products now stack up on the Google ‘Shopping’ tab, but that’s not the only contributing factor. We’re coming to expect Sontronics to punch above the price range, and in this case, again, they do.

If, just for a moment, we buck the trend for romanticising vintage equipment and consider investment from the standpoint of a professional with a job to do, a pair of Mercurys, an Aria, a handful of Solo dynamics and a couple of Orpheus condensers or Sigma ribbons and you’d have the basis of a mic collection that would stand tall in any typical studio session — and all for less financial outlay than a single eye-watering foray onto eBay. I’m not the only one to feel that way — Gary Barlow was the company’s first customer for a Mercury, and the latest Ed Sheeran record relies on an Aria as well as an assortment of other products from the Sontronics stable. This is, again, a product that puts its money where its mouth is. I might just do the same.  


There are a number of possible alternatives in terms of switchable- or variable-pattern large-diaphragm condensers. In this price range, products from the likes of Blue, Peluso and Telefunken all suggest themselves. I would however suggest that even if your budget extends further, putting more expensive options from Brauner, Neumann, or Microtech Gefell within reach, it would still be worth auditioning Mercury before making a final decision.

Planetary Alignment

As this microphone is so suited for use in the context of a stereo pair, is there a matched stereo option? Well, the nature of the tight component tolerance dictates that two models should be extremely close in sound and performance, if not identical. The wild-card here is the valve (the mic uses the same JJ valves as in the Aria).

Plotting Course

Sontronics MercurySontronics MercurySontronics MercuryThe frequency response plots exhibit a fairly typical sort of shape for a modern, large-diaphragm microphone of this type. Broadly speaking they show a relatively flat response, with a gentle high-frequency lift.

In my experience, you can’t really draw any conclusions about the sound from these sorts of plots when taken in isolation. Sometimes you can see evidence on a plot for a characteristic you can hear when you test a microphone, but in general I’d caution against attaching too much importance to them. I’ve included them here for the sake of completeness, and if I was asked to summarise how the plots relate to the results on offer, I’d say they present no surprises.

Hearing Is Believing...

I’ve provided a series of audio examples to illustrate the capabilities of this mic, including files from the drum recordings with James Ivey at The Old Chapel, an electric guitar recorded here in my own studio, as well as a nylon guitar also recorded here in my control room, and taken from the Oktoba single ‘Chance’. You can hear them at:

Download | 108 MB


  • Superb sonic performance regardless of cost.
  • Affordable.
  • Presence and transparency.


  • Precise position of pattern control dial could be more obvious.


In the Mercury, Sontronics have achieved new heights with yet another star that doesn’t cost the earth.