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Sontronics Sigma Phantom-Powered Ribbon Microphone

Although limited in sonic scope, the Sigma is recommended for its solid performance, affordability, build quality, and striking good looks.

Another phantom-powered ribbon mic has come to our attentions. Is this one of those “really cheap” ones or one of the “really cheap, but good” ones or one of the “not quite cheap, but really good” ones?

Actually, it’s something completely different. It is the Sontronics Sigma, the “British-designed, artsylooking” one, the one that the Queens of the Stone Age guy uses.

Sure, I may joke about the crowded ribbon mic market we find ourselves in today, but all in all, it’s a good thing for engineers. Digital recording and super-aggressive mixing/mastering techniques make smooth-sounding ribbons like the Sigma a very useful tool for modern production, especially with active electronics (requiring 48V phantom power, resulting in hotter output and than typical ribbons) that open up some additional applications.

Full disclosure, the Sigma has been around for nearly three years now, offers its US distributor FDW Worldwide; at the time, it was only one of two phantom-powered ribbons on the market. But for many of us, it’s still a fresh and alluring option in professional ribbon microphones.


The Sigma comes in a sturdy aluminum case—combination-lockable and velvet lined with cutouts for mic and shockmount. That shockmount deserves mention not so much for its function as its form; with its large, arced arms supporting the engraved and vaguely Art Deco body of the mic, every single performer at the studio commented positively about the Sigma—hopefully upping their game from the inspiration!

The Sigma lists frequency response at 20 Hz to 15 kHz (with the high-end roll-off beginning at about 5 kHz), impedance at less than 150 ohms, max SPL of 135 dB (at 0.5% THD at 1 kHz), a symmetrical figure of 8 pattern, self-noise at 14 dB (A-weighted).

In Use

The Sigma arrived just prior to a drum-tracking date, so I first tried it out for drum room ambience with a loud, powerful player. About 10 feet behind the drums and six feet off the ground, the Sigma picked up the entire kit nicely, but with pronounced distortion in the low mids. I wish it could have handled the high SPL, but after a lo-mid scoop at the most distorted frequencies, a rolloff of the lows with a shelving filter, a slight high-end boost and some compression, the room sound was nicely gritty and added some rock attitude to the mix.

As expected, the Sigma was ideal on tambourine, with pleasant transients, a solid middle, and that rolled off top that makes ribbons so nice on such bright, transient sources. These qualities also nicely reproduced some flute overdubs (especially when paired with a condenser) with much desired warmth in the low mids and a pleasantly understated top end (that de-emphasized valve clicks and noises). Even with the Sigma’s active electronics, a lot of gain was required, but self-noise was not an issue.

On solo acoustic guitar I used a spaced pair of AKG C451s for detail and mounted the Sigma further back for the middle of the image and some air — bull’s eye! The Sigma provided all the bottom I needed (and could ever hope for), a little ambience and smooth articulation to the finger picking. After time alignment, a 3 dB scoop at 200 Hz and a little top boost, I had thick and round bass notes with great stereo imaging and plenty of open top-end detail — sweet.

I tried the Sigma on a baritone vocalist and got results that were just too tubby and lacking in highs for this singer. In fact, I never did find a perfect match for the Sigma on vocals during the review period, although I’ll bet it would sound good on thinner voices and aggressive stuff, as most ribbons do. I did try multiple impedance settings with my Manley TNT preamp, but (predictably) found no appreciable differences, unlike non-active ribbons. During these vocal tests I found that the rear lobe of the figure 8 pattern has a noticeable low-mid bump in its response, not quite symmetrical, but typical for ribbon mics.

The Sigma will do the job on electric guitar with some limitations. Side by side with my AEA R92 ribbon, both did a great job of picking up thick, clean, jazzy tones. But for some hardrocking overdubs on “11” (with a Marshall and a Mesa Boogie) the R92 held up to the SPL but the Sigma noticeably distorted. I had the Sigma at a 45-degree angle to the speaker cone, but had to back off to about 24 inches or so to avoid clipping and get a roomier tone.


Considering its smooth, classic ribbon response, inspiring looks, quality accessories, and active electronics, I’m going to recommend the Sigma. Sure, its versatility is limited but it does what ribbons are expected to do: smooth out transients, pickup real bottom end and round off the top end. Maybe you don’t have a high-gain preamp, you need your first ribbon, or you’re looking to expand your palette of ribbons. Either way, you’re good to go with the Sigma.

Rob Tavaglione owns and operates Catalyst Recording in Charlotte NC, you can reach him at

Sontronics Helios

by Rob Tavaglione

As I reviewed the Sigma, I was also able to try out the Sontronics Helios, a large-diaphragm (1.07-inch capsule), multi-pattern tube microphone that came in an aluminum case with power supply, stand mount, and a lined wooden box for the Helios itself. The large, round capsule housing/windscreen, engraving and yoke-mount make for an inviting look to vocalists that just begs to be sung into.

In figure of 8, I had the pleasure of singing a two-part harmony with an alto vocalist, aiming for an extremely intimate, blended, and breathy sound. I found the rear lobe response to be much thicker in the lows and low-mids, so I put the alto on that side and my baritone on the thinner, front lobe. A healthy squeeze from the Chandler Germanium compressor and I got that sweet, up-close and personal blend that can be so elusive with overdubbing and multiple mics.

In cardioid however, the Helios was a bit too strident, with a strong and very present top end that I found to be too harsh on many singers. I did find good use for it on two songs, both slower, more legato-type songs that didn’t have aggressive consonants, but more sustained vowels. The Helios offered lots of definition and sibilance, maybe too much as I had to employ some heavy de-essing and a high shelving rolloff at 10k.

In omni, I had the most fun of all with the Helios, gathering ’round the boys for three backup vocal sessions. Some were singing, others were shouting, but all got picked up with realism and a sense of space via the Helios. I used the built-in HPF and more of that Chandler compression, but here the healthy top end and sibilance were my friend, providing a defined presence and a taste of the room that was much needed for salsa, punk, and blues group vocals.

I also tried the Helios on acoustic guitar, where its placement was very sensitive and its tubey top-end signature was not always a good fit, not unlike an AKG C12 in that app. I did enjoy the Helios on an old 1960s Magnus organ, where the key clicks and reedy whine it captured was interesting and helped define the track from a virtual instrument.

I’m sure it’s versatile, but I can’t help but think of the Helios simply as a vocal mic. It’s the sexy looks, it’s the multi-pattern versatility, and it’s the top-end. Essentially, it is a cool vocal mic.