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Focusrite ISA Two

Microphone Preamplifier
Published July 2012
By Matt Houghton

Making professional‑quality preamps available at project-studio prices has been Focusrite's forté for many years, and this design doesn't disappoint.

Focusrite ISA Two

Focusrite's blue-and-yellow liveried ISA range of mic preamps and channel strips has proved popular, so I've not been surprised to see the same technology emerge in different form factors. The ISA One, for example, which we reviewed back in SOS October 2008 (/sos/oct08/articles/focusriteisaone.htm), took the preamp out of more expensive channel strips or racks of multiple preamps to bring a single, high‑quality preamp with digital output within the reach of most serious recordists, and in a portable format, too. The latest addition to the stable is the ISA Two.

As the name implies, the objective appears to have been to make two high‑quality, versatile preamps available at a sensible price. Although the basic design is essentially the same as that of other preamps in the range, there's one notable omission: there's no digital output, and no provision to add one. Instead, you'll need to connect the analogue outputs to your audio interface or stand-alone A‑D converters. Presumably, this decision has been made, in part, to help meet the price point, but it's no great loss in my book: firstly, many people would never bother with the digital outs, so why should they be asked to pay for them? Secondly, Focusrite already offer plenty of ISA mic preamps that do have this feature. Nonetheless, some competitors' products, such as the Audient Mico, do offer a digital output as standard, so it's worth considering whether this is a feature you require.

The Sound Of ISA

Usefully, the ISA Two features send and return jacks which allow you to insert EQs or other processors into the signal path.Usefully, the ISA Two features send and return jacks which allow you to insert EQs or other processors into the signal path.

Assuming that you don't need digital connectivity, then, what exactly do you get for your money? Like all others in the ISA range, the Two employs a Lundahl LL1538 input transformer on each channel. These are among the cleaner-sounding transformers used in pro‑audio gear. In fact, when I asked Per Lundahl about the recent trend for using transformers to provide coloration for creative use, he explained that Lundahl never aim for colour, but rather strive to create the cleanest‑sounding transformers that provide true galvanic isolation. This transformer is designed to provide an extended flat frequency response, the idea being that most of the high‑frequency drop‑off (which occurs in all transformer-based mic preamp designs) is placed well outside the threshold of human hearing. That, presumably, helps to explain why the Focusrite marketing bods can describe the ISA preamp as being warm and transparent at the same time — terms which, at first sight, might seem to conflict!

Whether or not it's attributable to the transformers, that description is fair, as there's a definite, albeit subtle, sense of colour being imparted by this preamp. It's nothing over the top, by any means — just a hint of pleasant thickening. This 'warmth' side of the equation is similar in character to classic Neve preamps such as the 1073, though slightly less obvious‑sounding, to my ears.

In common with other ISA preamps the Two offers a 60dB gain range, and this is shiftable by up to 20dB using a trim control, giving you an impressive total gain range of 0‑80dB when using the two controls in tandem. This should cover most eventualities I can think of. I couldn't discern any problems with noise that could be attributable to the preamp (rather than the mic), even when applying significant amounts of gain.

I didn't take technical measurements, but it's worth me saying that the sound of the two channels seemed extremely well matched, and I'd be happy to use them for stereo applications. There's no ganged stereo operation, but the steps on the main gain control make it easy to match the gain of the two channels, while the continuously variable 20dB trim control allows you to make fine balance adjustments.

The ISA Two's front panel features several useful controls, not least that which allows you to select from different input impedances.The ISA Two's front panel features several useful controls, not least that which allows you to select from different input impedances.Another feature will be of particular interest to anyone who regularly uses dynamic mics, including passive ribbons: the input impedance is switchable via a control on the front panel, with Low (600Ω), ISA 110 (1.4kHz), Medium (2.4kHz) and High (6.8kHz) settings available. While the impedance tends to make little or no difference to the sound of phantom‑powered condensers, active ribbons, and valve mics that use their own power supply, it does usually affect the sound of passive dynamic mics — including ribbons, of course. I tested this feature using a few dynamics, including a Shure SM57, a Heil Sound PR40 and a Beyerdynamic M201, and in all cases there was a clearly audible difference in sound between the different settings. Usually, I found that I preferred the High setting, but these tests were necessarily limited in scope, and there's no guarantee that everyone's taste would agree with mine. I'd certainly be keen to try out different impedance settings on different material, not to mention each time I had a new dynamic mic to try out.

The ISA preamp was initially designed as a console preamp (other than the variable impedance option, the design is pretty much unchanged since it was first employed in the Focusrite Forte console), so I'd expected it to be versatile enough to be used in a range of genres and on a range of sources. To confirm this, I recorded several instruments, including my own vocals, drum overheads, and both acoustic and electric guitar (the last, through my Fender Twin amp, provided the main test for the variable impedance options discussed above).


Mic choice and placement, of course, usually makes a much greater contribution to an end result than the preamp does, and while people (including myself) will always lust after 'that' sound delivered by a particular combination of preamp and mic, the ISA design is remarkably versatile — to the extent that I'd be more than happy to use the ISA Two with pretty much any of the mics in my collection, and on pretty much any source. It is this 'Swiss Army' flexibility, combined with the gentle sonic enhancement, that makes this, for me, a classic design in its own right.

Given the price per channel of around £350$450 (street), it has to be said that the ISA Two is up against some strong competition from the likes of the DAV BG1 and the Audient MiCo, both of which are more affordable. But while the DAV is hard to beat on value for a nice, clean‑sounding preamp, it doesn't offer many of the features of the ISA Two, with neither as much gain available nor variable impedance options. The Mico is something of a bargain, offering both digital outputs and an interesting variphase feature... but, again, there's less gain available, and fixed input impedance

So the ISA Two offers something a little different. When you throw in the other useful features that are available on each channel but which I've not discussed above (polarity inversion, insert effects send and return jacks, a high‑pass filter, eight‑segment LED meter, and both front‑panel instrument and rear‑panel line input), and the usual high quality of construction from Focusrite, what you have here is an awful lot of preamp for a very reasonable price. It's a product that should prove a useful workhorse in the studio for many years to come.  

Published July 2012

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