The ISA 428 MkII provides four of Focusrite’s prestigious transformer-based microphone preamps. It features the same classic circuitry and renowned audio quality found in the original at a new level of affordability. With selectable input impedance, direct instrument inputs and an optional eight channels of high-quality analogue to digital conversion, the ISA 428 MkII creates the perfect front end for the discerning recording professional.

First introduced in 1985, the ISA microphone preamp holds a reputation for outstanding transparency along with subtle warmth contributed by transformer core saturation. The addition of a variable impedance circuit allows ISA users to perfectly match the preamp with any microphone, or to use different settings creatively to shape the sound of the microphone. Unchanged for decades, the ISA microphone preamp topology offers incredible clarity and the signature Focusrite sound that makes it the top choice among many audio professionals today.

The optional class-leading eight channel A-D converter option used with the ISA 828 is also compatible with the ISA 428 MkII. Along with the four mic preamp inputs, four additional inputs allow you to route other line signals through the converter. High quality Burr-Brown Pro Audio Amplifiers and flagship PCM4220 A-D converter chips seated within Focusrite custom analogue circuitry deliver unparalleled performance. Specifications include a dynamic range of 122dB and jitter performance below 250 picoseconds. The card can be retrofitted at any time. Thanks to its convenient 25-pin D-Type connector, it integrates seamlessly with most digital workstations, including Pro Tools.

Four instrument inputs, instantly accessible on the front panel, allow quick and easy connection without the need for a separate DI box. Extra processing can be placed between preamp and conversion via the units dedicated insert points, featured on every channel. Finally, accurate six-segment LED metering is designed to catch even the fastest transients on every channel.

Over 25 years, Focusrite has earned a reputation for bringing superb audio quality and engineering excellence to an array of audio professionals. Whether you’re looking to preserve the sound of your classic microphones, or searching for the perfect front end for your digital studio, the ISA 428 MkII brings legendary tools to your studio at an exceptional new price.

The ISA Pre

The ISA microphone preamplifier was first introduced back in 1985. This transformer-based preamplifier formed the first half of the ISA110 mic pre and EQ module on Focusrite's critically acclaimed Forté console. This console, and the later Studio console were hailed by many as the finest sounding consoles ever built.

The ISA microphone preamplifier went on to form the cornerstone of all ISA and RED Focusrite products. The topology has never changed, except for the addition of a variable impedance circuit, allowing ISA users to either perfectly match the preamp with any microphone, thus maximizing level, or to use different settings creatively to shape the sound of the microphone being used. The original ISA 110 setting was supplemented by three further impedance settings.

The Focusrite preamp is renowned for its transparency, but there's also a subtle warmth that transformer core saturation contributes. This seeming contradiction of warmth plus beautifully open, unrestricted high frequencies, is a classic hallmark of the mid 80's Focusrite designs.

With processors whose bandwidth is strictly limited to the audible (20Hz to 20kHz) bandwidth alone, significant roll-off can still occur, affecting the higher audible frequencies of the signal. Therefore, in order to capture every subtle nuance, exactly as it occurs whilst avoiding any roll-off, the preamp must operate over a far greater bandwidth. The extremely broad frequency response of Focusrite preamps - close to 200kHz at the top end - guarantees accurate phase response across the much narrower range of human hearing, the roll-off point being moved entirely outside of the audible hearing range.

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