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Dual mono mic preamp continues, but updates, the ISA tradition

$1,124.99 MSRP, $899.99 street



By Craig Anderton



The ISA Two occupies a single rack space.


With today’s DAWs capable of recording hundreds of tracks and running at least dozens of plug-ins, attention is returning to the fundamentals: acoustics, monitors, mics, and mic preamps. Over a quarter-century after the inception of the first Focusrite ISA mic preamp (fashioned by Rupert Neve back in 1985 on commission from George Martin), Focusrite’s preamps have become a part of recording history; now the Focusrite ISA Two dual-mono preamp brings Focusrite technology into a new decade, yet remains based on the original ISA 110 preamp.





The front-panel, high-impedance  instrument inputs use 1/4", unbalanced jacks.


Both preamp channels have identical I/O. The front panel has two 1/4” instrument input jacks—convenient, as you don’t have to reach around the back to plug in. (The input impedance exceeds 2Megohms—high enough to prevent loading down passive pickups, but low enough to avoid excessive noise pickup.



The rear panel I/O is identical for both channels.


The rear panel has XLR in, XLR out, 1/4” TRS line in, and 1/4” TRS insert send and receive jacks. A front panel insert in/out switch routes the return to the output; signal always feeds the send jack, which provides a parallel preamp out if needed. AC power comes from a standard IEC cable, not a wall wart.



With the global power supply, all you need is an IEC cord with the appropriate plug for a country's electrical standard.



Mic preamp design is science, but it’s also art. I feel much of what gives a “warm” sound is the input transformer; the ISA Two uses Lundahl LL1538 input transformers, which employ an unusual winding technique to extend high-frequency response—a quality often lacking in lower-cost units. They also provide 20dB of gain, which helps boost the signal-to-noise ratio as the transformer contributes no hiss.

The response for the mic and instrument inputs is down less than -1dB at 100kHz, even with 60dB of gain (the line level input tops out a little lower, around 80kHz). Sure, you can’t hear that high; but the extended range means it can handle standard audio frequencies effortlessly. Just as adding “air” above 20kHz with EQ has an effect in the audio range, so does extended high-frequency response.




Controls for the two input channels are identical. The buttons illuminate when active.


The two channels’ controls are identical. One button steps through the three inputs, while a second button steps through four different mic input impedances. Especially with dynamic mics, this isn’t just about matching, but being able to change the mic’s character. Depending on the mic, the difference can range from somewhat subtle to almost having four different mics.

A “master” gain range button selects either a 0-30dB or 30-60dB range for the Gain control, which has four steps. Each step represents 10dB of change (e.g., -20, -10, 0, or +10dB for the line in and 0-30, 10-40, 20-50, or 30-60dB for the mic in). A secondary, variable trim control can add up to +20dB of additional gain for the mic and line ins, or serve as an input level control for the instrument input. Given the continuing comeback of ribbon mics, a preamp with 60dB of gain just isn’t enough anymore; the ISA Two’s 80dB maximum gain is welcome.

Each preamp also has a three-pole high pass filter for “mud” reduction (16-420Hz, 18dB/octave slope) with in/out button, as well as a button for phase (polarity) flip and +48V phantom power.



The LED meters can be calibrated for particular signal levels or applications.


Two eight-stage LED meters round out the front panel, but these are unusual in that you can calibrate them to particular applications using two rear-panel trim controls.



Focusrite traditionally aims for an open, transparent, solid-state sound as opposed to the “thick” or colored character often associated with tube gear. However, the input transformer does add a subtle, pleasing quality—although it’s tough to describe, “warmth” comes close—and as a rule of thumb, a better transformer means a more pleasing effect. (I know one very well-known composer who didn’t like the sound of her multitrack digital tape recorder, and simply added high-quality transformers at the inputs—it made a huge improvement.)

The variable impedance is a great touch. Guitarists know how different impedances affect the sound; the same principle applies here. Raising the impedance gives a brighter sound with more level, while lower impedances tend to emphasize lows. With some vocalists, changing the impedance can actually be more effective than changing mics.

Finally, the noise seems very low—and kudos to Focusrite for publishing the output noise spec at unity gain, which gives a more realistic idea of what to expect compared to the equivalent input noise spec, which is also included. Channel crosstalk is excellent, as is the common mode rejection ratio for the the mic ins.

Overall, Focusrite has managed to produce a high-quality, open-sounding pair of mic pres, but kept the price reasonable by including only those “bells and whistles” essential to premium preamplification. For smaller studios seeking better preamps, I’d say the top features are the transformer inputs, sound quality, instrument ins, gain suitable for any mic type including ribbons, and the option to choose different impedances and therefore, expand the range of tones available from a limited number of mics. I should also mention that the included, printed documentation is clear and helpful—something that's not always a given with gear these days. It’s been a long time since the ISA One got a makeover, but the ISA Two is a worthy addition to the ISA range.


CraigGuitarVertical.jpgCraig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.

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