Sontronics Delta

Ribbon microphones were once very popular for live performance — there can’t be many people around who were playing in the ‘60s who don’t remember the ubiquitous Reslo model — although today we rely more on dynamic mics, with condenser models also becoming more commonplace. In fact, the ribbon mic is almost forgotten as a live tool, but Sontronics think it deserves a higher profile. Conceptually, the ribbon mic is a very simple device. A thin metallic ribbon is held under tension in a strong magnetic field so that when sound forces the ribbon to move, a small electrical current is generated within it. As the ribbon itself has a very low impedance, a transformer within the mic body is required to match the signal to the outside world.

Modern ribbon models are less fragile than their forebears, although they still need to be treated with respect and, unless they have active electronics, tend to require rather more preamp gain than their dynamic and condenser contemporaries. Sontronics’ answer to these concerns was to give their Delta ribbon mic on-board preamplification to ensure a healthy output level and to offer a lifetime warranty, which also covers the replacement of the ribbon should that ever be needed. Perhaps a more relevant question, though, is why go to all this bother when, on paper at least, the ribbon seems to have little to commend it?

As with all ribbon mics, the Delta has a figure-of-eight pickup pattern, rather than the cardioid and hypercardioid patterns that dominate the live marketplace, while its frequency response starts to roll off above 5kHz and can only manage a 20Hz to 15kHz overall response if you ignore the usual -3dB points convention and settle on something closer to 10dB or 12dB down at 15kHz. Surely this must be a recipe for acoustic feedback and a hopeless, dull sound?

These apparent shortcomings might be a consideration if you were using the Delta for live vocals, although a ribbon mic is still a great choice for recreating those creamy smooth pre-‘60s nightclub tones. However, Sontronics have built and voiced this mic primarily for use with electric guitar cabinets, which makes much more sense, as many studio engineers rely on ribbon mics in this application to deliver a strong low-end punch combined with a smoother high end, while not losing the essential bite of the guitar.

Additionally, it can be used to good effect on bowed strings and brass instruments to round out the sound and reduce the harshness associated with these instruments when close-miked. Closer examination of the Delta’s frequency curve shows it to be not dissimilar to that of the Sontronics Sigma studio ribbon mic, but with a subtle presence peak at around 2kHz to 4kHz, presumably added to flatter the ‘bite’ component of the electric guitar sound. It also features a flatter low end, whereas the Sigma has a bit of a bass ‘bump’.

Physically, the Delta has a distinctively retro rectangular shape with the same format casing as the Sigma studio ribbon model, but with different colouring on the side plates. It comes in its own aluminium flightcase, along with a very neatly engineered support cradle, which also offers a useful degree of vibration isolation. A screw-on locking ring secures the mount to the threaded XLR exit point of the mic, so there’s no risk of it falling out of the mount, while a plate on the mic grille informs the engineer that phantom power is required. This is a sensible inclusion, as most seasoned engineers will recognise the Delta as a ribbon mic from its shape, and if they didn’t know it was active, they’d make sure the phantom power was switched off, as passive ribbon mics can be damaged by the application of phantom power.

The noise figure of the mic is 14dB (EIN), which is very respectable, although when you’re going to stick a mic in front of a guitar amp, the mic’s noise performance is almost irrelevant and what matters more is its ability to handle high SPLs without clipping. A maximum SPL of 135dB is quoted (for 0.5 percent THD at 1kHz), which should be more than adequate for most situations. There are no pad or roll-off switches to worry about, so operation is simply a matter of connecting up and engaging the 48V phantom power source on your mixer or mic preamp. The fact that the mic is equally sensitive at the rear as at the front shouldn’t be a serious concern when you’re close-miking a guitar amp, although you can put an acoustic screen behind the mic in more demanding situations. Sensitivity is given as 11mV/Pa -45dB ±1dB (0dB = 1V/Pa 1kHz), which is ample when dealing with loud sound sources such as electric guitar cabinets and sufficient for use with less brash instruments such as strings, providing a decent mic preamp is used.

Our test was conducted at a live gig running the mic through a very sweet-sounding Fohhn PA system, and a little experimentation revealed that placing the mic towards the edge of the speaker cone gave an out-front sound that came very close to what was heard when standing in front of the amp, both for the cleaner sound and the more heavily overdriven. There was none of that gritty high end that often needs treating with EQ when using more conventional mics, while the throaty low end came across rather more convincingly. The sound also retained just the right amount of bite, so on the whole, the experience was very successful.

How important the tonal difference is compared to using a more obvious choice of dynamic mic is really down to taste, as I’ve always managed perfectly well with an SM57 until now, although I have to admit that I preferred the sound of the ribbon and little or no EQ was needed to get the sound I wanted. Even so, the cost difference is significant, so you’d need to be really picky about your guitar tone to invest in one of these mics, as you could buy a respectable guitar and amplifier for the same price. If you also do a lot of recording, then the decision might be easier, as the Delta makes a great studio mic for electric guitar and numerous other sound sources.

Ultimately then, the Delta has to be given the thumbs up for sonic attributes and for its lifetime warranty, but the fact that it is a studio-grade product at a studio-grade price means you may need to think hard about whether you can justify the cost of owning one purely for live performance. 0

Sontronics Delta

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