Field Test: Focusrite ISA428 Pre Pack

Nov 1, 2003 12:00 PM, By Kevin Becka


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Recently, Focusrite has offered a product line aimed at the home studio. However, as the $1,995 ISA428 can attest to, the company has not forgotten its high-end roots. This “four-preamps-in-a-box” was a pleasure to use, and lives up to the expectations of classic Focusrite gear.

The front-panel controls on the ISA428's transformer-coupled preamps are placed far enough apart so that even the small ones — such as phantom power, phase and insert buttons — are easy to adjust. Below the large analog meters (with peak LEDs) is the knob to adjust gain in 10dB increments, a gain trim pot with a continuously variable ±20dB range, and a 16Hz to 420Hz sweep, -18dB/octave HP filter control. Each preamp section has push buttons to select the maximum attainable gain (+30/+60 dB); mic, line or ¼-inch instrument input source; variable- input impedance; and HP filter in/out. All buttons except the input and impedance controls are backlit.

The unit's right side handles the A/D converter functions, with an ADC Soft Limiter in/out toggle, clock-select button (44.1/48/88.2/96/176.4/192 kHz), 16/20/24-bit resolution switch, external word/ superclock select, digital lock light, and the dual-mode, six-segment LED meters. The meter's dual functionality is determined by the optional ADC card: If the card is not fitted, meters 5 through 8 are inactive and 1 through 4 read the output of each mic preamp, with the top LED representing 0 dBfs (+22 dBu). With the card installed, all meters are active and read the preconverter signal path after the soft limiter.

The back panel has the XLR I/Os for each mic preamp and four additional ADC inputs. Although there are only four mic preamps, installing the optional ADC card adds four additional digital line inputs; a nice add to the value of the ADC option, to say the least. In addition, each channel has three balanced TRS connectors, each carrying a line input, insert send and insert return.

The $695 ADC card has Lightpipe I/O, Word Clock I/O and two 9-pin connectors handling AES-only or combination AES and S/PDIF — eight channels of audio, a real plus. The AES-only connector can be configured as either single-wire or double-wire for backward-compatibility with older equipment. The other connector can be switched between AES or S/PDIF signals and needs only the right termination to correctly interface with its digital partner. One limitation of the card occurs when interfacing with Pro Tools|HD: With only four inputs above 96 kHz, you can't input the ADC's four additional line inputs into HD.


I used the 428 on a variety of instruments with several different mics. In a word, the 428 sounds fantastic. It's clean, clear, versatile and completely pro.

One of the most revealing tests for a mic preamp is using it with a ribbon mic; in this case, an AEA R84 on a number of sources. Here, the variable-impedance control became a valuable tone-shaping tool. I first used the mic on a Martin acoustic guitar and could control the sonic characteristics easily with the impedance controls. (For more on how the variable impedance control relates to ribbon mics, read the online extra at Ribbons tend to be low-output transducers, requiring a lot of input gain. I could get plenty of clean level out of the 428: a whopping 80 dB of gain. There was an expected bit of noise at the very top of the throw, but it was not a factor because I never needed that much boosting.

The optional digital section is especially sweet. I used it exclusively to get into Pro Tools|HD because it sounded so good. I used the 428 at 48 kHz and 96 kHz, recording acoustic instruments including dobro, upright bass, banjo, guitar and percussion. It was stellar in every application: I quickly appreciated how easily I could get a great sound. In one case, I recorded a Danelectro baritone guitar with great results. It was as simple as plugging it in and setting levels. The sound was crystalline, full-bodied and needed no EQ.

The 428's metering is perfect for digital recording. I found myself trusting it more and more with use. It's a confidence-builder that frees your mind for more creative use when you don't have to worry about checking three meters in your signal path.

The ISA428 is not simply four preamps in one box, but four preamps that sound so good. The box is pro inside and out with Lundahl 1538 input transformers, as originally spec'd by early Focusrite designs. The fit and finish are what you'd expect from Focusrite: Every knob, button, connector is top-notch. And it's a tweaker's delight, with extra touches such as variable-input impedances, dual-metering, HP filters and the optional digital back end (with added inputs).

All said, a couple of things could be better. The “low/ISA110/med/high” variable- impedance control settings are confusing. Competing boxes such as Groove Tube's VIPRE indicate values in ohms, which is easier to set in the heat of the session. However, the well-written ISA428 manual has a great tutorial on variable impedance to clear up any user questions. One minor point: On the rear panel, if inputs 1/2 were on top and 3/4 on the bottom, then hookups would be much more intuitive, especially for those blind gropes in the dark that are all too common in the working studio.

Aside from a few minor gripes, this preamp gets straight A's in all departments. If you're looking for a rock-solid, great-sounding, well-designed set of preamps — and who isn't? — then the ISA428 should be on your must-see list.

Focusrite, dist by Digidesign, 650/731-6300,

Click here for an in-depth look at what actually goes on with the variable impedance control in relation to ribbons, by Wes Dooley.

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