We’ve covered the various technical accolades of the Clarett+ preamp elsewhere, but in this piece we’ll explore its exceptional mic preamp, which makes Clarett+ interfaces — and anyone who records with them — stand out from the crowd. Here we’ll uncover how decades of Focusrite’s design experience have helped craft an input stage with very high headroom, low distortion and ultra-low noise, so you can capture exceptionally pure recordings and achieve a professional sound, whether miking guitars, recording vocals or tracking drums.

What makes a good preamp?

The ideal mic preamp adds nothing and takes nothing away from the microphone’s signal — just amplifies it to a level that can be captured by the interface’s analogue to digital (A-D) converter, which is the next stage in the signal chain after the preamp. A good preamp will have an extremely flat frequency response, to ensure that every sound recorded is captured as accurately as possible. An excellent preamp, like that found in Clarett+ interfaces, maintains that flat response at all gain levels, so no matter how loud or quiet your sound, or what kind of microphone you’re using — whether it’s an old ribbon mic or a state of the art condenser — your recordings stay pristine.

Another key preamp specification is Equivalent Input Noise. This tells you how much unwanted noise (heard as hiss) is being added to the signal in the amplification process. A good preamp is one with a low EIN figure. In a remarkably clear preamp, like in Clarett+, noise remains low at all gain levels. The ultimate recording preamp also caters for all the scenarios you’re likely to encounter in the studio or on the road. At one end of the scale, that means offering enough gain for quiet spoken-word recordings. At the other, it means providing enough headroom for very loud signals. Close-miked drums can generate huge transient spikes, and not every preamp design can swallow these without clipping or other distortion.

The extra mile: a fully differential signal path

When designing Clarett+, our engineers weren’t content with simply ensuring the main pillars of good preamp design were taken care of. It’s one thing to design a mic preamp that tests well in isolation, quite another to design a complete system that maintains stellar performance from input to output. If you’re familiar with studio equipment, you’ll have heard connectors and cables described as ‘balanced’. An unbalanced connection has only a single signal wire, and it’s vulnerable to noise pickup, especially where there are mains power supplies and other sources of electromagnetic radiation (mic preamps in an audio interface are packed into a small box with a lot of other electronics). To combat this, we balance the connection by running an additional wire alongside the signal wire. This picks up the same noise, and is connected in reverse polarity, so that the noise is cancelled out. Once this extra wire is in place we can go further and create a ‘differential’ connection, where the second wire also carries the wanted signal in reverse polarity. This effectively doubles the peak-to-peak voltage that can be accommodated, giving us twice as much headroom as well as cancelling out noise pickup. Clarett+ uses a fully differential signal path throughout, maintaining internal headroom and ensuring nothing can compromise the quality of its preamps.

All-analogue Air

Whenever you need pure, uncoloured sound, Clarett+ won’t let you down. But sometimes we do want to add some colouration to our recordings. One reason why older consoles and preamps are valued is because, in some circumstances, they do colour the sound. Certain aspects of that colouration can be emulated using software plug-ins, such as the gritty saturation that comes from overdriving an input transformer. What can’t be added after the fact, though, is the way in which some preamps and microphones interact.

This interaction results from the impedance relationship between mic and preamp, and it’s especially significant with passive dynamic and ribbon mics. By the time your signal has been converted to digital and recorded in your DAW, it’s too late to recreate this effect, which is why the Clarett+ preamp has Focusrite’s unique Air option with impedance switching and relay control. When engaged, Air’s all-analogue circuitry switches the impedance to 2.2kΩ and adds two cumulative high shelves, totalling a 4dB boost in the high frequencies. Closely modelled on the classic Focusrite ISA preamp designs that are now so sought-after, this adds more presence to high frequencies and ‘loads’ a mic in exactly the same way as a vintage design.

A nod to where it all started

When the late Rupert Neve founded Focusrite in the ’80s with the goal of creating the best-sounding, best-performing audio equipment possible, he wouldn’t have known that his technical insight and designs would be influencing recording technology bearing the same name nearly 40 years later. Those original concepts still lie at the heart of today’s Focusrite products, and so does the no-compromise philosophy. Clarett+ preamps embody the spirit of the very first Focusrite modules, and provide artists, engineers and producers with equipment built around the same ethos of ultimate clarity. With Clarett+ — like the original Focusrite ISA modules — when you need perfect clarity, extremely low noise and masses of headroom, Clarett+ has you covered. And when you want rock and roll excitement, all you have to do is adjust your gain, add some all-analogue Air, and hit record.

Words: Sam Pryor